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  • Electronic Resource  (691)
  • 1990-1994  (691)
  • 1980-1984
  • 1993  (691)
  • Chemical Engineering  (638)
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  • Electronic Resource  (691)
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  • 1990-1994  (691)
  • 1980-1984
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  • 1
    ISSN: 1432-2285
    Keywords: Abies alba ; Abscisic acid ; Damage ; Gas chromatography ; Needles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The amount of abscisic acid (ABA) in needles of silver fir from a natural location was investigated with regard to position in the crown, damage, seasonal variation, and needle age. Because of problems of quantification of ABA in coniferous needles, which contain numerous secondary plant products, a method for reliable determination of both isomers cis-trans-ABA (c-ABA) and transtrans-ABA (t-ABA) was developed. By means of gas chromatography (GC) using an electron capture detector (BCD) and a programmed temperature vaporizer (PTV) injector complete separation of both compounds was achieved. Two different pairs of fir were investigated — in each case a damaged and a healthy tree. Needles from both trees from the first and the second pair collected in September contained 500–1100 ng c-ABA/g fresh weight (FW), and the concentrations of t-ABA varied from 400 to 700 ng/g FW. Investigations from the second pair show highest amounts of 2900 ng/g Fw c-ABA and 1800 ng/g FW of t-ABA in May and June. For the first pair a higher c-ABA content was found in needles from the top of the crown than in those from the middle and the base. This difference could not be confirmed in the analysis of the second pair. Because of the strong natural deviation no statistically significant difference between the healthy and the damaged tree was found. The first pair of firs examined showed a higher t-ABA concentration than the second one. In this case the highest amount was found in the top of the crown. Methodical mistakes during the clean-up procedure and in quantification by gas chromatography could be excluded. The presence of c- and t-ABA in the purified extract was corroborated by mass spectrometry. With regard to the seasonal variation both isomers of ABA show an unequivocal trend. The maximum concentration is achieved in May to June, whereas the content is minimal in August/September. In any case the level of t-ABA is lower than that of c-ABA. No correlation between the amount of ABA and the needle age could be established.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    International archives of occupational and environmental health 64 (1993), S. 503-507 
    ISSN: 1432-1246
    Keywords: Biological monitoring ; Carbon disulphide ; Dithiocarbamate ; Gas chromatography ; Mass spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Blood carbon disulphide (CS2), both free and total, was determined by gas chromatography-mass spectrometry in 112 “normal” subjects and in 20 subjects employed in a dithiocarbamate factory, comprising ten blue-collar workers involved in dithiocarbamate production and ten white-collar office staff. The ten production workers were examined over two workshifts, the first at the beginning of the week (Monday) and the second after an intervening period of at least 1 day. Three blood samples were taken for each shift studied, one prior to starting work, one at the end of the shift and the third 16 h after the end of the shift (on the following morning). The mean CS2 blood levels measured in the 112 normal subjects was 663 ng/l for the free fraction and 3178 ng/l for the total. In 16 blood samples taken from the ten dithiocarbamate factory office workers, the mean free and total CS2 blood levels were 846 and 4140 ng/l, respectively, i.e. not significantly different from those observed in the normal subjects. At the end of the first 8-h shift, the ten dithiocarbamate factory production workers had free and total CS2 values of 1070 and 8471 ng/l, respectively, which were significantly higher than those observed prior to starting work (240 and 4738 ng/l). All the total CS2 levels measured in the shop-floor workers, with the sole exception of the values recorded prior to the start of the Monday shift (4738 ng/l), ranged from 7047 to 8471 ng/l and were significantly higher than those measured in the white-collar staff (4140 ng/l).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1246
    Keywords: Acrylonitrile ; Adducts ; Biological monitoring ; Gas chromatography ; Hemoglobin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A new, simple and fast procedure of measuring acrylonitrile (ACN) in ACN derived mercapturic acids such as S-(2-cyanoethyl)-L-cysteine(CyEC), and in hemoglobin (Hb) and plasma protein adducts and urinary metabolites in rats and humans exposed to ACN was developed. ACN in mercapturic acids or proteins was analyzed by capillary gas chromatography (GC) by liberating ACN at a high-temperature in the injector port of GC with or without oxidizing sulfur atoms of the ACN-bound cysteines into sulfoxide form by hydrogen peroxide in vitro. At 350 °C, more than 90% of ACN in authentic CyEC was recovered by this method. Increasing a single ip dose of ACN from 5 to 50 mg/kg produced proportional increases in ACN bound to Hb 24 hr after the treatment. The alkylation of plasma protein with ACN was about 1/10 as low as that of Hb. After repeated daily ip doses of 1–10 mg/kg, ACN in Hb decreased with a half-life of about 9 days. ACN was also detected in the blood of workers exposed to ACN for 1 to 10 years at a Siberian synthetic rubber factory.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0738
    Keywords: Pigment Yellow 17 ; 3,3′-Dichlorobenzidine ; Biotransformation ; Gas chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rats were exposed by inhalation to the technically highest administrable concentration of 230 mg Pigment Yellow 17/m3 air for 4 h. Inhalability of the dust was guaranteed by a mass-median aerodynamic diameter of 1.0–1.1 μm. For 14 days after exposure, urine and serum samples were analysed for 3,3′-dichlorobenzidine, the parent carcinogenic amine of the test compound. No 3,3′-dichlorobenzidine could be detected either in urine or blood, the detection limit being 5 ng/ml for both media. Based on the results of this study there is no evidence for metabolic cleavage of Pigment Yellow 17 to 3,3′-dichlorobenzidine in the rat.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 649-652 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Triglycerides in cheese ; Programme temperature (PTV) injection ; Silica capillary columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid gas chromatographic method for the analysis of triglycerides in cheese on a capillary column with a programmed temperature vaporizer has been developed. Fat were extracted with hexane to dryness. The reproducibility of the method was assessed and the coefficient of variation for the total triglycerides was 2.50%. Recovery of individual triglycerides ranged between 87 to 105%.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Curie-point pyrolysis ; Multivariate analysis ; Sodium dodecylbenzene sulfonate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Multivariate analysis can be applied to quantitative analysis of sodium dodecylbenzene sulfonate (DBS) by pyrolysis gas chromatography. The pyrograms obtained from mixtures of DBS and polyoxyethylene lauryl ether (PEG) were normalized for the peak heights and areas of several internal standards which appeared in every pyrogram, against the characteristics peaks for DBS and PEG. This normalization method gave smaller experimental errors than when using one internal standard. The normalization values were used for cluster analysis unchanged. The values were calculated correlation coefficients and principal component analysis was performed using 11 data base and a set of sample data simultaneously. One calibration curve was calculated from the principal component scores. The DBS content of a sample was obtained from the calibration curve. Calculated values were in fair agreement with theoretical values.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 36 (1993), S. 187-190 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Solid-phase extraction disks ; Pesticides ; Soil analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A systematic study comparing the methodology and analytical results obtained in an investigation of seven pesticide residues (Molinate, Atrazine, Carbofuran, Pirimicarb, Prometryn, Malathion and Tetrachlorvinphos) in soil samples is reported. Solid-phase extraction (SPE) using glass columns and 47 mm disks of octyl and octadecyl-bonded silica was used in the pesticide analysis. The best extraction efficiency and clearest extracts are obtained with C8 disks. The analyses were carried out by capillary gas chromatography with nitrogen and phosphorus detection. Recovery experiments were performed at ppb levels in spiked soil samples. The average recoveries of the compounds were 53–77%. Detection limits are between 5 and 30 ng g−1 based on 5 g moist soil sample. The method was validated by comparing it with conventional liquid-liquid extraction.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Fatty acid methyl esters ; Diesel fuel substitute ; Glycerol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A GC method for the determination of free glycerol in vegetable oil methyl esters used as diesel fuel is described. The sample preparation includes dissolving in dimethylformamide, silylation with bistrimethylsilyltrifluoroacetamide (BSTFA) and separation on a methyl silicone capillary column using either FID or MS detection. The recovery was tested using standard samples containing known amounts of glycerol. The results of the analysis of different samples were compared with those obtained by enzymatic determination. The method described offers a far more sensitive and quick determination of free glycerol compared to other methods.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Electron capture detection ; Trichothecenes ; Cereal grain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Various analytical methods developed for trichothecene determination, including TLC, HPLC, GC, supercritical fluid chromatography (SFC) and enzyme immuno assay (EIA) are reviewed. In addition a new method is described for the simultaneous determination of the trichothecene mycotoxins deoxynivalenol (DON), nivalenol (NIV), 3-acetyldeoxynivalenol (3-ADON), diacetoxyscirpenol (DAS), T-2 toxin (T-2), HT-2 toxin (HT-2) and T-2 triol (TRIOL), in Austrian wheat and corn samples by GC-ECD. A clean-up procedure has been developed using a combination of liquid-liquid and liquid-solid extraction. Trichothecenes were detected as their heptafluorobuturyl esters or alternatively as trimethylsilyl ethers (only sensitive for deoxynivalenol and nivalenol) using nandrolone or chloramphenicol as internal standard. Four derivatization techniques using HFBI, HFBA+DMAP on polystyrene, TMSI and TMSI+BSA+TMCS have been studied and the advantages and disadvantages of each are discussed. Quantification of trichothecenes from 10 to 1000 ppb in cereals could be accomplished routinely.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 37 (1993), S. 215-217 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Unified retention indices ; Dimethylsiloxane stationary phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic, unified retention-indices of 56 alkylbenzenes up to C15 on dimethylsiloxane OV-101 and SE-30 stationary phases are given. These values agree well with the corresponding experimental values used in the statistical treatment of the experimental data.
    Type of Medium: Electronic Resource
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 37 (1993), S. 259-263 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Quantitative analysis ; Ethylene oligomer by-products ; n-Alkanes, n-alkenes and 2-alkyl-1-alkenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method using temperature-programmed poly-dimethylsiloxane OV-101 and poly(pheny ether) (5 rings) capillary columns was developed to separate and quantify the reaction by-products in ethylene oligomers. It was found that the content of 2-alkyl-1-alkenes, 2-alkenes and n-alkanes in the C8−C18 α-olefin fractions amounts to 29, 10 and 2.6% respectively.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 37 (1993), S. 211-214 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organic solvents ; Routine analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method for the analysis of organic solvents in chemical products is described. The analysis is performed by the use of a polar column, Supelcowax 10, and a non-polar column CP-Sil-5CB. Samples containing a non-volatile matrix or water were analysed by headspace analysis. The identification of the solvents in a sample, based on GC retention times on one column, is confirmed by GC of the sample on the second column. The method has been found to be suitable for the routine analysis of solvent mixtures.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 37 (1993), S. 264-270 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Temperature programmed ; Peak widths ; Polynomial interpolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Isothermal chromatographic measurements lead directly to ΔH v o and A (entropy term) of solutes, and three constants of an empirical relationship between peak width and column temperature. From the thermodynamic parameters ΔH v o and A retention temperatures have been computed by means of a theoretical model including temperature dependence of carrier gas viscosity, and subsequently retention times; programmed retention indices have been determined by linear and polynomial interpolations. By substituting the value of the calculated retention temperature in the above-mentioned relationship, peak width at half-height for a linear temperature may be estimated. Predicted retentions correlate with observed data, with a P-value ≤0.01; simulation accuracy is generally 6–10% for peak widths. Retention indices of some organochlorine species, separated on an OV-101 capillary column, may differ by as much as 26 units depending on the method of calculation. Polynomial-calculated indices are more consistent with the retention index scheme, and have smaller standard deviations and better constancy at different heating rates.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Inverse gas chromatography ; Poly(ethylene glycol) 20M ; Retention mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The properties of poly(ethylene glycol) 20M (PEG 20M) coated on the hydroxylated surface of Chromaton N AW were investigated by inverse gas chromatography. It was found that the solid form of PEG 20M exhibits partition as the retention mechanism even below its melting range. The contribution of adsorption to the specific retention volume was also determined. It was demonstrated that inverse gas chromatography establishes the existence of a polymer surface layer but precise determination of its thickness is difficult. The limitation of the applicability of inverse gas chromatography results from the structure of the investigated surface layer which is thin and not coherent so that solute molecules can penetrate it.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 33-37 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Crown ether polysiloxane phases ; Selectivity mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The phase recognition mechanism of nine groups of position isomers on four crown ether polysiloxanes, OV-1701 and PEG 20M has been investigsated by measuring various thermodynamic parameters. The high selectivity of crown ether polysiloxane phases is due to hydrogen bonding and the extent of fitting between the analytes and the crown ethe cavity. The effects on selectivity of cavity size, heteroatoms and substituent groups on the crown ether are discussed.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Equilibrium headspace sampling ; Partition coefficient determination ; Theory of chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The new phase ratio variation method is described which represents a convenient way for the determination of gas-liquid partition coefficients for practical purposes, utilizing equilibrium headspace-gas chromatography (EHS-GC). This method is based on the relationship between reciprocal peak area and the phase ratio in the vial containing the sample solution; it involves regression analysis of the EHS-GC measurements of a number of sample vials containing the same sample solution but with a wide variation of phase ratios. Examples are given for both aqueous systems and systems consisting of a stationary (liquid) phase used as the solvent; comparison of the measured values with results obtained by other methods shows satisfactory agreement. A critical discussion of the conditions influencing the accuracy of the analytical results is given.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 109-110 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Unified retention index ; Correlation of data ; Hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic unified retention indices for 43 hydrocarbons (alkanes and cycloalkanes) are given for squalane and OV-101. Comparison of these values and unified retention index increments are presented as linear regression equations with high correlation coefficients and acceptable standard deviations.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 160-166 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Neural networks ; Classification ; Pattern recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Artificial Neural Networks are proposed for the classification of vegetable oils submitted to gas chromatography analysis through their FAME profiles. Three important neural networks are evaluated here: the Hopfield model as a content-addressable memory (CAM), the Hamming model and the multi-layer perceptron. A brief description of these nets is first presented and further implemented for the classification of known vegetable oils. After the learning step, unknown samples are presented to the nets and the identification step performed. The performances of these nets are compared for the recognition of popular vegetable oils, including several edible oils.
    Type of Medium: Electronic Resource
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  • 19
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Mass spectrometry ; Atomic emission spectroscopy ; Pulp mill effluents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Three chlorinated dimethyl sulfones and five chlorinated thiophenes have been identified in the alkaline extraction liquor from a bleach plant by gas chromatography with atomic emission detection (GC-AED) and with mass spectrometry (GC-MS). The information on elemental content obtained by GC-AED enabled a rapid screening of the sulfur compounds and provided important structural information complementary to the mass spectral data. Quantitation was accomplished by GC-AED based on universal calibration.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 209-215 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Gas chromatography-mass spectrometry ; Tagetes ; Plant volatiles ; Extractions ; Natural insecticides ; Mosquitos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Volatiles from three species of the genustagetes, commonly called marigold have been isolated and characterized. Simultaneous steam distillation extractions (SSDE) produced consistently extracts of higher insecticidal activity than Soxhlet extractions. Methylene chloride was the best solvent. Volatiles isolated from theminutae species showed higher activity than those frompatula anderecta. Comparison of extracts from the flower, foliage and roots of the plant showed that most of the activity is located in the flower. The volatiles are highly effective toward both larvae and adult mosquitoes.
    Type of Medium: Electronic Resource
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  • 21
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 237-240 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Enantioselectivity ; Polysaccharide chiral stationary phase ; Amylose tris(n-butylcarbamate) ; Grob test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Seven aromatic and alkyl amylose and cellulose carbamates have been tested as chiral stationary phases in gas chromatography. One of them, amylose tris(n-butylcarbamate) can be used for enantiomer separation.
    Type of Medium: Electronic Resource
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  • 22
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 290-294 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Solid phase extraction ; Organochloride pesticides ; Water analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatography of chlorinated pesticides in water is carried out after adsorption of a 50 mL sample using a cartridge containing 100 mg CN-bonded porous silica and extraction with 500 μL pentane. The average recovery for eight organochloride pesticides at 1 ppb was 〉95%. The procedure described is simple, selective and reproducible.
    Type of Medium: Electronic Resource
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  • 23
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 339-343 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Preconcentration techniques ; Trace gas analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The blanks in preconcentration methods for determining trace amounts of impurities in ultra-pure gases, which include the preconcentration volume of sample gases, carrier gas impurities and atmospheric contamination are discussed and three concentration methods for eliminating blank errors are proposed. These are, the differential volume method by concentrating at the same flow-rate but different times (DVMSF), the differential time method by concentrating the same volumes at different flow-rates (DTMSV) and the differential volume method by concentrating for the same times but different flow-rates (DVMST). DVMST is proposed as the best method for its ability to eliminate all blank errors described. The methods are used to determine trace amounts of Ar+O2 and N2 in ultra-pure hydrogen. Calculations demonstrate that the methods can effectively improve analytical accuracy.
    Type of Medium: Electronic Resource
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  • 24
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Micropacked columns ; Retention behavior ; LC silica packing materials ; Silanol groups
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Gas chromatographic retention of cyclohexane and benzene on microcolumns packed with silica-based materials for liquid chromatography has been investigated to elucidate the relationship with the surface properties of the packing materials. Differences in capacity factors (Δk′) for these two hydrocarbons were related to the surface area of the packing materials. For untreated silica gels, the Δk′ value increased with increasing total surface area of the column employed and measurement of Δk′ for chemically-bonded stationary phases allowed estimation of accessible residual silanol groups.
    Type of Medium: Electronic Resource
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  • 25
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Pesticides in groundwater ; Solvent extraction ; Multiresidue analysis ; Selective detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple multi-residue procedure has been developed and applied to the analysis of pesticides in groundwater samples from the Comunidad Valenciana, a predominantly agricultural area on the Mediterranean coast of Spain. The procedure includes a liquid-liquid extraction, after addition of NaCl on the samples, and a subsequent analysis by capillary gas chromatography using a dual detection system with electron capture and nitrogen-phosphorous detectors. This allows the determination of more than 30 compounds (organophosphorous, organochlorine and pyrethroid pesticides) at the low ppb (μg l−1) levels. Detection limits obtained varied between 0.01 μg l−1 (lindane, fonofos) and 0.5 μg l−1 (cypermethrin). An additional injection of the sample extracts into a gas chromatograph equipped with a column of different polarity and electron capture detector is used for the confirmation of chromatographic peaks. The recommended procedure has been applied to 66 ground water samples. Pesticides, including organophosphorus and organochlorine compounds were detected in 31 of them, in levels ranging from 0.02 to 0.7 μg l−1.
    Type of Medium: Electronic Resource
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  • 26
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace sampling ; PTV-System ; Ethephon in drinking water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An indirect GC method is described for the determination of Ethephon in drinking water on the basis of the headspace analysis of the ethylene formed from Ethephon. In order to reach the necessary detection limit, the entire volume of the static headspace distribution is transferred into a cold injection system (CIS). There, the ethylene is adsorbed on Carbosieve SIII at 10°C and, subsequently, desorbed at 300 °C. The water vapour included in the headspace is completely eliminated through the splitting system. By means of this technique, a detection limit of 0.05 μg/l water was reached.
    Type of Medium: Electronic Resource
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  • 27
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 37 (1993), S. 399-401 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Viscosity ; Carrier gases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Equations are derived for viscosities of H2, He, N2 and Ar for use at chromatographic temperatures which are accurate to within 0.3% for H2, and 0.1% for the other gases. The effect of pressure is usually negligible but may increase the viscosity of N2 or Ar by as much as 0.5% at 25°C or lower and 5 atm or higher.
    Type of Medium: Electronic Resource
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  • 28
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 393-399 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The univariant element, Q1 P0, and the multivariant elements, Q1+P0 and R2+ P0, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q1 P0 element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q1+ P0 and R2+ P0, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 29
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 377-382 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The viscoelastic responses of some molten polymers, and particularly of low density polyethylene (LDPE), are known to vary with processing history. Reasons for the variations include the effects of shear history on morphological states of the polymer, or on its molecular weight parameters. A typical low density polyethylene has been used to test the shear-history dependence concept following a variety of processing steps. The polymer was sheared in single-screw and twin-screw extruders, and in a high speed melter / mixer (Gelimat). Samples also were precipitated from very dilute solutions in trichlorobenzene and in p-xylene. GPC analyses showed that, in general, these procedures did not affect the various moments of molecular weight. An exception was the Gelimat-mixed sample, for which mild reductions in Mn and Mw were noted. In contrast, melt viscosity and elasticity readings, the former from low shear evaluations and the latter from extrudate swelling, were affected by the various procedures. A drop in melt viscosity and in elasticity was observed, being most pronounced for precipitated and twin-screw extruded versions of the LDPE. Reductions also were observed in the specimen sheared in the Gelimat instrument. Following conditioning at the test extrusion temperature (170°C), viscous and elastic responses tended to revert to those of the unsheared control sample, the exception again being the sample sheared in the Gelimat melter / mixer. Of the various mechanisms proposed in the literature to account for transient property changes such as those reported, temporary changes in the degree of chain entanglement appear the most satisfactory explanation. Irreversible alterations in viscoelastic properties may be associated with changes in molecular weights due to processing at high shear.
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  • 30
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 400-409 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A model for the filling stage of injection molding of viscoelastic thermoplastics in cavities of complex shape is presented. The model considers two-dimensional melt flow, with converging and diverging flow patterns induced by complex boundary shape and by the presence of an obstacle. The model is non-isothermal (with the melt loosing heat to the mold walls as it travels into the cavity) and handles a viscoelastic (following the White-Metzner model) material with properties that vary with temperature, shear rate, and pressure. The numerical method is based on finite differences, with boundary fitted curvilinear coordinates used in the mapping of the flow field (which has an arbitrary shape that evolves with time) into a time invariant rectangle. The numerical results reveal geometry-induced asymmetries in the flow and thermal fields as well as the effect of various process parameters on the pressure and temperature profiles in the cavity. The model admits variable cavity thickness, thus allowing for a treatment of the cavity thickness as a process parameter in the simulations.
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  • 31
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 497-500 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO2, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.
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  • 32
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 33
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 513-521 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The overall isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP)-dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Half-time was determined via differential scanning calorimetry as a function of the experimentally controlled variables dilution, crystallization temperature, and the addition of nucleating agent. The influence of these variables on crystallization mechanism and spherulitic structure, as implied by the Avrami analysis, was determined. The influence of these variables on fold surface energy was examined by the Lauritzen and Hoffman analysis.
    Additional Material: 6 Ill.
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  • 34
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The overall non-isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP) in dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Crystallization peak temperature was determined via differential scanning calorimetry as a function of the experimentally controlled variables iPP concentration, cooling rate, and nucleating agent concentration. The influence of these variables on crystallization mechanism and spherulitic structure as implied by the Ozawa and Ziabicki analyses was determined. The non-isothermal crystallization kinetics presented here are the first for iPP-diluent systems with and without nucleating agent.
    Additional Material: 8 Ill.
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  • 35
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 543-548 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The static shear strength and static friction of three thermoplastics have been investigated for the case of contact between a bulk plastic sample and a very smooth metallic plate. The minimum tangential force required to shear the interfacial adhesion bonds between the two surfaces was measured and defined as the adhesion component of friction Fa. Experimental results showed that Fa is large when the surface energy is high or the interfacial energy is small and that a correlation may exist between this force and the work of adhesion evaluated from Dupré equation. The real area of contact Ar was also measured using an optical device designed to handle samples and experimental conditions similar to the static friction tests. It was found that Ar is proportional to Pa0.9 where Pa is the apparent pressure of contact and an increase of Fa with Pr was observed. The static shear strength τ has been evaluated as the ratio Fa/Ar, and its relationships with the real contact pressure P approximated by linear functions. It was concluded that τ increases at high P, although it has not been verified for ultra-high-molecular-weight polyethylene. An attempt has been made to explain the observed break in the data. The results indicated that (τ/τb) = κ′(τa/Pa) where b refers to bulk, a to apparent values, and κ′ is a proportionality constant that depends on the plastic material.
    Additional Material: 10 Ill.
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  • 36
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    Polymer Engineering and Science 33 (1993), S. 549-558 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A variety of different styrene monomers [styrene (S), p-fluorostyrene (p-FS), pentafluorostyrene (PFS), p-chlorostyrene (p-ClS), p-bromostyrene (p-BrS), p-methylstyrene (p-MS), p-tert-butylstyrene (p-tBS), p-methoxystyrene (p-MOS), p-ethoxystyrene (p-EOS), and p-propoxystyrene (p-POS)] have been polymerized by radical and cationic mechanisms. Copolymers of S/PFS, S/p-ClS, S/2-vinyl-naphthalene (2-VN), and S/p-phenylstyrene (p-PhS) were prepared by radical polymerization. All polymers were fully amorphous and transparent and exhibited only one glass transition temperature in the temperature range 77 to 141°C. Thin films of the polymers were subjected to external electrical partial discharges (PD). Typically, 20 PD experiments were conducted for each polymer and the data for the time to breakdown were adapted to the two-parameter Weibull distribution function. The resistance towards PD of the various polymers was found to depend strongly on the monomeric structure. Complementary PD experiments on a series of narrow molecular mass polystyrenes confirmed that the minor variation in molecular mass between the different styrene polymers is of no importance for the PD resistance. The PD resistance of the homopolymers decreased in the following order: PS ≍ P(p-MS) 〉 P(p-tBS) ≍ P(p-BrS) 〉 P(p-POS) 〉 P(p-ClS) ≍ P(p-MOS) 〉 P(p-EOS) ≍ P(p-FS) 〉 P(PFS). The time to breakdown for copolymers of S and PFS decreased monotonously with increasing PFS content. Styrene copolymers with low molar contents of 2- VN and p-PhS exhibited a higher resistance towards PD than PS. The results are discussed with reference to various properties of the studied polymers, such as segmental mobility, ionization potential, resonance stabilization, and reactivity of the radicals formed.
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  • 37
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 38
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    Polymer Engineering and Science 33 (1993), S. 614-621 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The glass transition temperatures in bismaleimide-based resins were investigated using different stoichiometric ratios of 1, 1′-(methylenedi-4, 1-phenylene)bismaleimide (BMI) and 4, 4′-methylenedianiline (MDA). The resin cure involves a low temperature primary amine addition to the maleimide double bonds and a high temperature homopolymerization of the maleimide double bonds. The network topology and the glass transition temperature changes with resin composition and curing conditions were determined using differential scanning calorimetry (DSC). An empirical model was used to relate the glass transition temperature to the extents of the amine addition and the homopolymerization reactions in 1:1 and 2:1 BMI:MDA resins. The changes in thermal properties with resin post-cure were also examined.
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  • 39
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    Polymer Engineering and Science 33 (1993), S. 640-644 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dynamic mechanical properties, tensile properties, and scanning electron microscopy of blends of poly(methyl methacrylate) and polycarbonate were investigated after phase separation above their cloud point temperature by annealing in a hot press. The dynamic mechanical properties show that phase separation proceeds more distinctly for the blends annealed at higher temperature and for longer time. The scanning electron micrographs show that the morphology of phase separated blends varies with the conditions of heat treatment. The tensile properties of phase separated blends deteriorate on account of the coarsening of the brittle dispersed phase over the optimum size and the occurrence of voiding during the heat treatment.
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  • 40
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    Polymer Engineering and Science 33 (1993), S. 665-674 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The packing stage starts at the end of mold filling. During this stage, additional material is forced into the mold to compensate for the shrinkage during subse-quent cooling. Underpacking results in molded parts with dimensional variation. Overpacking causes flash at the parting lines, stick during ejection, and excess residual stresses resulting in warpage. The packing stage is thus extremely important in the determination of the final quality of the product. Despite its importance, analysis of the packing stage has been relatively ignored, particularly the viscoelastic effect. In this work, the analysis of the isothermal packing stage is presented for a Maxwell fluid. A set of governing equations is derived for a two-dimensional mold and solved using the Galerkin finite element method. In addition to the distribution of velocity and pressure, the model predicts the stresses in the planar direction, which could be used for subsequent calculation of the residual stresses.
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  • 41
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    Polymer Engineering and Science 33 (1993), S. 675-685 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The objective this work was to determine the effects of selected polyester catalysts on the reaction of a polyester with epoxy functional polymers. Polyesters containing various catalyst metals were melt blended with either an ethylene-co-glycidyl methacrylate or a styrene-co-glycidyl methacrylate copolymer. The viscosities of the blends were monitored as a function of mixing time using torque rheometry. In addition, the molecular weight distributions of selected samples were analyzed using gel permeation chromatography. Both the torque rheometry and the gel permeation chromatography results indicate that the polyester reacts with epoxy functional polymers. This reaction occurs under conditions and at processing times which are readily obtainable in conventional melt processing equipment. Furthermore, the reaction kinetics of polyesters with glycidyl methacrylate copolymers are dramatically affected by the nature of the catalyst system used to prepare the polyester. Under the conditions used, antimony catalysts are particularly effective at promoting the reaction between polyesters and the epoxy functionality and the activity of the catalysts studied appears to decrease in the following order: antimony 〉 gallium 〉 tin ≃ titanium 〉 germanium. Manipulation of the polyester catalyst system may offer a method to control the extent of reaction obtained in reactive processing of polyesters with epoxy functional compounds.
    Additional Material: 16 Ill.
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  • 42
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    Polymer Engineering and Science 33 (1993), S. 709-715 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The flow kinematics of power-law fluids in fishtail dies is studied. A general isothermal three-dimensional finite element code developed by the authors is used for the flow analysis purpose. The basic geometry of the fishtail die is defined by simple super-elliptical curves, which allows a smooth transition from a circle to a slit. The three-dimensional path line and the residence time distribution (RTD) are calculated from the velocity field obtained from the finite element solution of the conservation equations. The effects of the rheological properties and the die geometry on the path line pattern and the residence time distribution are investigated. The results indicate that as both the length of the transition zone and the fishtail angle increases, the residence time distribution becomes more uniform. However, the power-law index does not affect the residence time distribution significantly.
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  • 43
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    Polymer Engineering and Science 33 (1993), S. 736-741 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The polymers of the aromatic nitrogen compounds N-methyl-pyrrole (P-N-Me-PPY), carbazole (PCarb), and aniline (PANI) have been investigated with electro-optical and surface analytical methods. The in-situ reflection spectra indicate the formation of polarons or bipolarons during electrochemical oxidation, depending on polymer type. The absorption bands can be attributed to changes in the electronic structure with regard to the applied potential. Photocurrent spectra of P-N-Me-PPY and PCarb show a p-type semiconducting behaviour for the polymers in the reduced state. The transition to the oxidized state with quasi-metallic properties is indicated by a significant shift in the Fermi level energy and can be followed with XPS and UPS measurements.
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  • 44
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    Polymer Engineering and Science 33 (1993), S. 838-844 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Extruded films of liquid crystalline polymer (LCP)/fluoropolymer blends were melt drawn to develop uniaxial orientation of a microfibrillar dispersed LCP phase. The anisotropy of the films increased with increasing draw and LCP content in the blend. Laminated composite plates were prepared using the extruded sheets as prepreg. The mechanical properties and coefficient of thermal expansion (CTE) of the prepreg and laminates agreed well with predictions from composite lamination theories. The potential for replacing glass fiber reinforced fluoropolymers with LCP/fluoropolymer blends in applications such as microwave circuit boards is discussed.
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  • 45
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 46
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 865-876 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This review presents a general picture of suspension, dispersion, and interfacial polycondensation processes employed for the preparation of beaded resins, dry powders, and high solid dispersions. The polymer systems covered include polyamides, polyesters, polycarbonates, polyurethanes, and phenol-formaldehyde and urea-formaldehyde resins. Basic features of heterogeneous polycondensation processes are outlined, and different mechanisms of particle formation in suspension, dispersion, and interfacial polycondensation are discussed. Effects of manufacturing parameters such as feed ratio, droplet/particle stabilizer, and stirrer speed on product characteristics are also briefly covered.
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  • 47
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    Polymer Engineering and Science 33 (1993), S. 781-788 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The extrudate swell and the dynamic rheological properties of poly(butylene terephthalate) (PBT) and polyamide 6 (PA6) binary blends were investigated at 240°C. The extrudate swell of the blend varies with the viscosity ratio and composition of constituents, and it is several times larger than that of homopolymers when the viscosity ratio of constituents is around unity. The dynamic oscillatory data could be interpreted by Oldroyd's emulsion model proposed by Graebling, et al. These results suggest that the extrudate swell is caused by the shape recovery of the dispersed particles. A semi-empirical method to estimate the terminal relaxation time with experimental data was introduced, and a clear correlation between the extrudate swell and the terminal relaxation time was obtained.
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  • 48
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    Polymer Engineering and Science 33 (1993), S. 819-826 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Much work in recent years had focused on the improvements of the impact properties of engineering thermoplastics by the addition of a low modulus modifier that contains polar moieties as a result of polymerization or that has been modified to contain polar moieties as a result of various grafting techniques. Styrenic block copolymers (styrene-ethylene/butylene-styrene) functionalized with maleic anhydride have proved useful as impact modifiers and compatibilizers in blends with engineering thermoplastics. This paper focuses on the use of these functionalized elastomers to modify nylon 6. In such compositions, a nylon material with unique mechanical performance may be achieved using the functionalized elastomer either alone or in combination with an unfunctionalized styrenic block copolymer. The optimization of performance in these rubber toughened polyamide blends using various types of styrenic block copolymers is discussed. The morphology as it pertains to performance is also reviewed. The information contained herein may prove useful in obtaining a better understanding of the mechanisms of compatibilization and modification of nylon 6 systems.
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  • 49
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    Polymer Engineering and Science 33 (1993), S. 827-837 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Oriented blends of poly(ethylene terephthalate) (PET) and high density polyethylene (HDPE) with and without compatibilizing agent have been studied with regard to orientation temperature, stretch rate, extension ratio, mode of orientation, and blend composition. These oriented blends have been characterized using infrared spectroscopy and differential scanning calorimetry. The tensile and tensile impact properties were also investigated. The results show that blends with compatibilizer show strain hardening upon orientation, whereas the blend without compatibilizer does not strain harden upon orientation. The blends with less PET content have been difficult to orient. The morphology of these blends show fibril structure, highly oriented in the direction of stretch. Infrared measurements show that PET within the blend has undergone strain induced crystallization upon orientation. It has also been observed that the mechanical properties, such as the modulus and ultimate stress, show improvement upon orientation. Simultaneously stretched blends show better physical properties than sequentially oriented blends.
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  • 50
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    Polymer Engineering and Science 33 (1993), S. 895-900 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper illustrates the factors that control brittle failure under fatigue loading for test specimens cut from medium-density polyethylene pipes for gas distribution. A square bar specimen cut from a pipe with a notch was made and a fatigue test was conducted to cause a brittle failure. To obtain the correlation among stress range, frequency, temperature, and cycles to failure in this fatigue test, Coffin-Manson's frequency-modified fatigue life equation was adopted and the material constants were determined. By gradually lowering the frequency, the resistance to creep can be estimated because cycles to failure - indicating the fatigue damage - decreased, and the actual loading time - indicating the creep damage - increased.
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  • 51
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    Polymer Engineering and Science 33 (1993), S. 923-930 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The interfacial tension, phase morphology, and phase growth was determined for four polymer blend systems: polyethylene/polystyrene, polyethylene/polyamide-6, polystyrene/polyamide-6, and polystyrene/poly(ethylene terephthalate). Generally, high interfacial tension correlates with coarse phase morphology and rapid phase coalescence. The addition of various potential compatibilizing agents to these binary blend systems results in lowered interfacial tension, finer and stabilized phase morphologies. The characteristics of different compatibilizing agents were compared for several of the blend systems. We also look at the influences of compatibilizing agents on mechanical properties of the blend systems. Some compatibilizing agents are able to produce substantial improvements in ultimate properties.
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  • 52
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    Polymer Engineering and Science 33 (1993), S. 937-943 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Unidirectional sheets were extruded of an in-situ composite of thermotropic liquid crystalline Vectra B950 in a matrix of polyphenylene-ether and polystyrene. Three important processing parameters were systematically varied: draw-ratio, slit opening and extruder throughput. Morphology and mechanical properties of these films were determined, and qualitatively related to the processing conditions.
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  • 53
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    Polymer Engineering and Science 33 (1993), S. 959-970 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: It is of great importance to accurately measure or predict the Residence Time Distribution (RTD) in designing extruders and/or in setting up a proper operating condition, because chemical reactions depend significantly on the RTD and temperature when chemical reactions take place during the extrusion process. A previous method to predict the RTD can analytically determine RTD, Residence Time Distribution Function f(t) and Cumulative Residence Time Distribution Function F(t), based on a simplified two-dimensional velocity field in an extruder. However, this previous method cannot accurately take into account the three-dimensional circulatory flow inside the extruder. The present paper suggests a new method to accurately determine the RTD taking into account the three-dimensional circulatory flow and presents a new formula derived to calculate f(t). In order to demonstrate the applicability of the new method including the circulatory flow effect, RTD, f(t) and F(t) were calculated based on a three-dimensional velocity field obtained via a quasi-three-dimensional finite element analysis. It was found that the previous method has a tendency to underestimate the RTD, owing to the neglect of the three-dimensional circulatory flow in comparison with the new method.
    Additional Material: 13 Ill.
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  • 54
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    Polymer Engineering and Science 33 (1993), S. 980-988 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Experimental data confirm the utility of the following simple equation in predicting the spin coating behavior of polyimide precursor solutions: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm h} = {\rm c\beta }_{\rm 0} {\rm k}^{{\rm \beta }_{\rm 1} } {\rm \omega }^{{\rm \beta }_{\rm 2} } {\rm t}^{{\rm \beta }_{\rm 3} } \quad\quad\quad\quad{\rm (1)} $$\end{document} in which \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {c = {\rm polymer\, solution\, solid\, weight\, fraction;}} \\ {\beta _i = {\rm fitted\, coefficient\, (Greek\, letter\, beta)};} \\ \quad{h = {\rm film\, thickness\, after\, cure\, or\, solvent\, removal};} \\ \quad{k = {\rm polymer\, solution\, kinematic\, viscosity, centistokes};} \\ {t = {\rm time},{\rm and;}} \\ \quad{\omega = {\rm wafer\, spin\, speed, rpm (Greek\, letter\, omega)}.} \\ \end{array} $$\end{document}.
    Additional Material: 8 Ill.
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  • 55
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ternary systems consisting of polypropylene (PP), ethylene-propylene-dieneterpolymer (EPDM) and different types of inorganic fillers (kaolin, BaSO4) have been investigated with respect to their mechanical behavior. On the basis of an Interphase model, it was possible using the modified van der Poel equation to describe the temperature dependence of the storage modulus G′(T) and the loss modulus G″(T). The interphase properties G′(T) and G″(T) could be calculated.
    Additional Material: 11 Ill.
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  • 56
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    Polymer Engineering and Science 33 (1993), S. 1251-1260 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Signal deterioration of optical discs depends strongly on the substrate surface roughness. Characteristics of surface roughness of the molded substrate have been studied in order to clarify the transcription mechanism of smooth surfaces in injection molding of polycarbonate resin. When the melt temperature, mold temperature, and injecting rate are low, microscopic flow marks more than 5 nm deep are observed on the surface. These flow marks are formed when the melted resin near the mold wall is cooled to the no-flow temperature of resin before it comes into contact with the mold wall. Molding transcription improves by optimizing the molding conditions for preventing these flow marks. As a result, the surface roughness of the molded substrate obtained is 3.2 nm in maximum height Rmax, which is nearly equal to that of the mold stamper at 2.7 nm in Rmax.
    Additional Material: 17 Ill.
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  • 57
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    Polymer Engineering and Science 33 (1993), S. 1279-1287 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A finite element numerical analysis of preform inflation associated with the injection blow molding process has been developed using a neo-Hookean constitutive model. The analysis is capable of predicting final wall thickness distributions for axisymmetric mold geometries. Experimental studies were conducted on a Uniloy injection blow molding machine (Model 189-3 and Model 122). A twelve ounce (355 mL) cylindrical bottle mold was instrumented with contact sensors, thermocouples, and pressure transducers. Visualization studies of the inflation process were performed using specialized tooling and high-speed video cameras. The experimental studies provide justification for analyzing the deformation by means of a static elastic approach. The predicted wall thickness distribution is in reasonable agreement with the experimental data. Nonuniformities in the temperature distribution in the preform were found to have the most significant impact on the inflation behavior and the resulting wall thickness.
    Additional Material: 13 Ill.
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  • 58
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    Polymer Engineering and Science 33 (1993), S. 1301-1307 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dielectric α-relaxation of a bisphenol-A type epoxide oligomer has been investigated in the vicinity of the glass transition temperature (Tg) by the direct current (DC) transient method. The logarithm of the DC transient current for the oligomer was well approximated by the third order function of the logarithm of time. The complex dielectric constant was calculated through the Fourier transformation of that approximation function according to Simpson's integration rule in a frequency range of 10-5 - 1 Hz. At the temperature around the Tg (45°C), the dielectric α-relaxation process of the oligomer was found to be governed by the Havriliak-Negami equation. The relationship between the DC conductivity (σ) and the dielectric relaxation time (τ), σ·τm = const, is valid near and above the Tg of the oligomer. The DC transient current method combined with the DC conduction and the dielectric bridge measurements is considered to be a practical tool for analyzing the dielectric α-relaxation process of the epoxide oligomer over a wide frequency and temperature range.
    Additional Material: 9 Ill.
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  • 59
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    Polymer Engineering and Science 33 (1993), S. 1329-1335 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this study, styrene-(ethylene-co-butylene)-styrene (SEBS) triblock copolymer (Kraton G-1652) was modified with maleic anhydride (MA). The maleated SEBS was used as compatibilizer for the blends of Nylon 6 (PA6) and SEBS. The morphology and impact strength of the blends were measured as functions of concentration and MA graft ratio of maleated SEBS. The compatibility and fracture mechanism of the blends were evaluated from the SEM micrographs of the xylene-etched surfaces and of fractured surfaces. Some of the blends exhibited an impact strength up to about 30 fold greater than neat PA6. The fracture involved both both cavitation and shear yielding. The mechanism of compatibilization of maleated SEBS in the ternary components blends was proposed.
    Additional Material: 5 Ill.
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  • 60
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    Polymer Engineering and Science 33 (1993), S. 1341-1351 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper reports on the theoretical and experimental studies of structure formation and strengthening (stiffening) of flexible-chain polymers. Two techniques of strengthening relying on the melt extrusion, i.e., orientational crystallization (crystallization initiated by melt extension) and drawing (uniaxial stretching of a crystallized polymer) are analysed by theory. The experiments involved preparation and study of melt extruded films and film fibers of linear polyethylene formed by the two techniques mentioned above. The effect of the degree of orientation and other parameters of the formation processes on the mechanical characteristics and the factors limiting the ultimate values of these characteristics are discussed. It is shown that multistage drawing succeeds in achieving a higher tensile strength and elastic modulus (1.2 and 35 GPa, respectively) than the orientational crystallization, which gives 0.8 and 15 GPa. The strengthening by drawing is accompanied by microcrack formation. In contrast, no discontinuities are observed in orientationally crystallized samples up to their ultimate extension.
    Additional Material: 13 Ill.
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  • 61
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    Polymer Engineering and Science 33 (1993), S. 1370-1371 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 1 Ill.
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  • 62
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    Polymer Engineering and Science 33 (1993), S. 1381-1389 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Because of the inability of existing automotive bumpers to absorb energy during impacts over the supports, energy absorbers have to be used to make bumpers effective in barrier impacts. A parametric analysis of a novel double-beam bumper concept has shown that its performance, in terms of energy absorption and impact forces, is insensitive to the location of the point of impact. Physical realizations of this concept, which may not require more material than existing designs, and which are particularly suited to thermoplastic materials, have been developed.
    Additional Material: 16 Ill.
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  • 63
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    Polymer Engineering and Science 33 (1993), S. 1270-1278 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Flow in a three-dimensional channel with a sinusoidally-wavy, vertical wall is examined for the case of applied down- and cross-channel velocity components. An important parameter for the analysis of the nature of laminar mixing in the flow field occurs when the changes in the downstream direction can be decoupled from the changes in the cross-channel direction, thereby allowing for a two-dimensional solution of the system of equations. This paper shows the effect on the nature of laminar mixing when the decoupling of the momentum equations from a fully three-dimensional case to one where a two-dimensional solution can be performed. Experiments are performed on a channel with sinusoidally varying vertical walls that cover the range of decoupling criteria. Silicone pigmented either white or black was run in the apparatus, cured, and cross-sectioned. The cross sections embody a local, detailed history of the state of mixing as it proceeds down the mixer. The amount of mixing is presented as a function of position at each cross section for the different channel configurations. The nature of mixing changes from a linear growth rate in the amount of interfacial area to an exponential rate as the amplitude of the wave is increased. Results demonstrate the existence of chaos, islands, and the factors affecting the mixing behavior.
    Additional Material: 8 Ill.
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  • 64
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    Chromatographia 35 (1993), S. 503-505 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Silanol terminated Chirasil-Val ; Cross-linking with polyfunctional silanes ; Enantiomer separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A method for the immobilization of Chirasil-Val has been studied based on the cross-linking which takes place between terminal silanols of Chirasil-Val and polyfunctional silanes. A leached, dehydrated and tetramethoxysilane-treated glass capillary coated with silanol terminated Chirasil-Val containing 5% tetraacetoxysilane as a cross-linking agent showed a maximum extractability of 15% without any loss of chirality.
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  • 65
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    Chromatographia 37 (1993), S. 51-56 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Halogenated hydrocarbons ; Headspace sampling ; ECD detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Simple sampling and preconcentration technique for the analysis of volatile halogenated hydrocarbons in water is described. For the separation a selective capillary column is used in combination with an ECD. Quantitative data are given.
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  • 66
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Fused silica open tubular columns ; Serial coupled columns ; Phase ratio optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary There are a number of parameters which have to be chosen depending on the analysis being done in gas chromatography. While the choice of stationary phase material is based on the solutes to be separated, the thickness is dependent on the concentration and the volatility of the components to be analyzed. This study undertakes a coupled column phase ratio optimization by connecting a short piece of a particular column prior to a normal length of an analytical column. Various columns of different dimensions (phase ratio), but of the same stationary phase material (methyl silicone), are coupled together by a deactivated glass press-fit connector, and the efficiency and capacity are measured. The coupling of fused silica open tubular columns is optimized in efficiency by matching or decreasing the phase ratio of successive columns. Capacity optimization is accomplished by increasing the phase ratio of consecutive columns. Capacity and efficiency optimization are opposing each other; therefore, if some efficiency can be sacrificed a substantial increase in capacity is possible.
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  • 67
    ISSN: 1612-1112
    Keywords: Supercritical fluid chromatography ; Gas chromatography ; High speed analysis ; Thermal desorption ; Two dimensional analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A two-dimensional supercritical fluid-gas chromatography system was constructed and evaluated. A 50-μm i.d. capillary column coated with a 50 % cyanopropyl polysilixane stationary phase was used as the firstdimensional column. Group-type separations of polycyclic aromatic hydrocarbons, based on the number of aromatic rings, were achieved using this column under SFC conditions. A 25-μm i.d. liquid crystal column was used as the second-dimensional column under GC conditions. The effluent from the first column (SFC) was received continuously by the second column (GC) through a thermal desorption modulator. The thermal desorption modulator (prepared at the head of the second column) generated a series of concentration pulses from the first column effluent. These concentration pulses served as injections to the second column, and were developed into a corresponding series of high-speed chromatograms. Grouptype sample bands from the first column were separated into individual components on the second column. All sample substances passed through both columns to generate two sets of retention data, which could be used for more accurate compound identification.
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  • 68
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Capillary column sampling ; Additivity of variance in GC ; Aqueous samples ; PAHs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The possibility of using capillary columns for both sampling and gas chromatographic analysis of aqueous micropollutants has been studied. Factors influencing gas chromatographic band dispersion of the solute were investigated and a mathematical relationship developed correlating the properties (ID, df) of the capillary columns to the degree of dispersion of adsorbed substances has been derived. The experimental results obtained with aqueous samples are in good agreement with the theoretically forecast data. The method developed allows gas chromatographic dosing of traces of organic substances, reducing inconvenience deriving from excessive sample handling to a minimum. Non-refocusing of the analyte does not, in any significant way, compromise column efficiency for substances that are not very soluble in water.
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  • 69
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace analysis ; Steam distillation ; Phenols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-temperature headspace analysis performed under static conditions above 100°C increases the sensitivity of gas chromatographic determination of volatile phenols in aqueous solutions 20–100 fold and reduces the detection threshold, to 10 μg×1−1. To improve the sensitivity and reduce the threshold still further, preliminary concentration by high-temperature microdistillation at elevated pressure is proposed. A theoretical model of this process has been developed. The possibility of concentrating volatiles by high-temperature microdistillation has been experimentally confirmed.
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  • 70
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    Chromatographia 36 (1993), S. 215-217 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Polar columns ; Vegetable oils ; Sterols ; Unsaponifiable matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The analysis of both the total unsaponifiable matter and the sterol fractions in vegetable oils has been performed with a new polar column (TAP, Chrompack). The use of a polar column, which is characterized by high thermal stability, has led to the identification of a greater number of constituents than the use of a nonpolar column (i.e. SE 52, SE 54). The polar column enhances the separation of the main classes of unsaponifiable matter (sterols, 4-methyl sterols and 4,4′-dimethyl sterols). When used for the unsaponifiable and sterol fraction analyses, it offers a powerful tool for characterizing the lipid source.
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  • 71
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid chromatography ; Mass spectrometry ; β-agonists
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Different chromatography — mass spectrometry techniques for the analysis of β-agonists have been compared. Gas chromatography — mass spectrometry (electron impact) has been used, as also has liquid chromatography coupled to the mass spectrometer by either thermospray or electrospray interfaces. The results obtained by the three method were compared in terms of sensitivity, selectivity, and richness of information provided by the analysis. It was found that using electrospray ionization, very powerful analysis could be achieved with high sensitivity, thus providing significant potential for the analysis of β-agonists.
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  • 72
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Crown ether polysiloxane phases ; Capillary columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two crown ethers, di(tert-butylbenzo)-propyl-15-crown-5 polysiloxane (PSO-DTB-15C5) and dibenzo-propyl-15-crown-5 polysiloxane (PSO-DB-15C5) have been synthesized and coated onto fused-silica capillary columns. The chromatographic characteristics, including column efficiency, polarity, phase transition temperature, operating temperature range and selectivity, were studied. Excellent selectivity was obtained for the separation of polar position isomers, especially phenol and dinitrotoluene isomers. The separation mechanism is discussed.
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  • 73
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention indices ; Adsorption effects ; n-Tetradecenes ; n-Tetradecynes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The correction of the reproducibility of retention indices on polar capillary columns with different film thickness, using more polar reference standards instead ofn-alkanes, was investigated. It was found that the replacement ofn-alkanes by 1-alkenes, 3-alkynes and n-alkylbenzenes as standards significantly improves the reproducibility of retention indices and diminishes their temperature increments forn-alkanes,n-alkynes and arenes on PEG 20M columns.
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  • 74
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    Chromatographia 35 (1993), S. 539-542 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid crystals ; Diffusion coefficients ; Xylenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The molecular diffusion coefficients of xylene isomers have been determined at different temperatures in the three phases (smectic, nematic and isotropic) of 4,4′-bis(heptyloxy)azoxybenzene (BHOAB) by gas chromatography. The results obtained are discussed in terms of molar volume, polarity and length-to-breadth ratio of several isomers. The activation energy of diffusion processes of solutes in the three phases of the liquid crystal has been calculated.
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  • 75
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    Chromatographia 36 (1993), S. 225-233 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Selective ionization detectors ; Organic fuelled flames ; Lead, tin, phosphorus, halogens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The selectivities of two flame-based ionization detectors identified as a Remote FID (RFID) and a Flame Thermionic Ionization Detector (FTID) have been improved by introducing methane as a fuel for the flame. Both the RFID and FTID feature a detector struture in which the ionization polarizer and collector are located several centimeters downstream of an oxygen-rich flame, rather than immediately adjacent to the flame as in a flame ionization detector. The RFID detects long-lived negative ions produced in the flame by the combustion of lead, tin, phosphorus, or silicon compounds. The FTID re-ionizes and detects neutral electronegative products generated by combustion of nitrogen, halogen, or phosphorus compounds. An organic-fuelled RFID can detect 1 pg Pb (Sn, P)/sec with a selectivity of the order of 106 versus hydrocarbons. An organic fuelled FTID is applicable to detection of compounds at nanogram and higher levels. FTID selectivity for PCB compounds in a transformer oil matrix is of the order of 105∶1. The improved selectivity achieved by using an organic-fuelled flame is also applicable to the detection of phospholipid and other non-volatile N, P, or Cl compounds using an FID/FTID detector accessory for a TLC/FID analyser.
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  • 76
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    Chromatographia 37 (1993), S. 105-106 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Occupational hygiene analysis ; Epichlorohydrin in air ; Trace analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method has been developed for the determination of trace amounts of epichlorohydrin in workplace atmospheres. Collection is peroormed in two bubblers in series both containing dichloromethane. Optimum conditions for sampling and analysis have been established. The lower limit of determination is 0.05 μg/mL with an RSD of ±5%.
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  • 77
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    Chromatographia 37 (1993), S. 277-280 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Hydrogenation of 1,5,9-cyclododecatriene ; Retention index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of the products obtained by the hydrogenation of 1,5,9-cyclododecatriene stereoisomers on fused-silica capillary columns coated with dimethylsilicone and cyanopropylmethylsilicone stationary phases was investigated. Retention indices of cyclododecatrienes, cyclododecadienes, cyclododecenes and cyclododecane were determined at three temperatures. The respective standard deviations were 0.3 and 0.6 i.u. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic hydrocarbones is discussed.
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  • 78
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    Chromatographia 37 (1993), S. 250-258 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention data ; Stationary phases ; Phase constants ; Linear free energy relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Specific retention volumes and retention indices for selected compounds can be predicted from different sets of stationary phase constants by multiple regression. Errors in the corresponding calculated retention times are between 5 and 15%. Intercept (A) and slope (B) values are given for 72 McReynolds stationary phases. The A value can be predicted from the retention index of benzene with a standard deviation of 9%.
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  • 79
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    Chromatographia 37 (1993), S. 546-548 
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace sampling ; Methyl methacrylate monomer ; Contact lens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A modified gas chromatographic method is described for the determination of free monomer in contact lenses, irrespective of the method of production. It thus becomes possible to assess very quickly the conformity of such lenses with hygiene regulations. This method allows direct supervision of production or determination of the quality of a product of unknown origin in only 15 min. Production tests of new polymerization initiators, reactors for polymerization, etc. can also be carried out.
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  • 80
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    AIChE Journal 39 (1993), S. 422-433 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The memory integral based on convolution of the unit step response to loading a clean pellet with concentration history at the pellet surface is proposed for computations of mass transfer in adsorption process simulation. Although rate laws are widely used to describe diffusion and sorption in pellets for slow (Glueckauf, 1955) and moderate (Kim, 1989) rates of mass transfer, these models fail to describe mass transfer at short contact times because the concentration history experienced by the pellet is not accounted for. To facilitate memory integral computations, approximations to the unit step response to loading a clean pellet are derived based on a single moving finite element and by asymptotic matching in time. Numerical evaluation of the memory integral is demonstrated on simple cycles which show the merits of this approach.
    Additional Material: 6 Ill.
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  • 81
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    AIChE Journal 39 (1993), S. 397-412 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The problem of bulk, transition and Knudsen regime diffusion in structures of freely overlapping fibers of various orientation distributions was numerically investigated, and the interrelation of the resulting effective diffusivities was examined. Fibers were randomly positioned and oriented in d = 1, 2, or 3 directions. A Monte Carlo simulation scheme was employed to determine the effective diffusivities from the mean-square displacement of random walkers traveling in the interior of the porous structure. The effective diffusivity was found to depend strongly on the orientational distribution of the fibers, porosity of the fibrous structures, and Knudsen number. The tortuosity factor decreased in general with increasing porosity, approaching at the limit of dilute beds the lower bound derived for each direction of diffusion from variational principles. The simulation results agreed well with experimental values of the bulk tortuosity of fibrous beds from the literature. It was also found that the reciprocal additivity or harmonic average effective diffusivity expression (Bosanquet formula), commonly used to estimate transition regime diffusivities from the values at the ordinary and Knudsen diffusion limits, provides an excellent approximation for the effective diffusivity of fibrous beds, except for that parallel to the fibers of a unidirectional structure.
    Additional Material: 17 Ill.
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  • 82
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    AIChE Journal 39 (1993), S. 461-470 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The asymptotic behavior of fixed-point methods in the complex domain is studied. Both direct substitution and Newton's method exhibit stable periodic and aperiodic behavior from real- or complex-valued starting points. Moreover, multiple stable periodic orbits can exist for direct substitution. Traditional trust region (or dogleg) methods, on the other hand, often terminate at singular points, which correspond to nonzero-valued saddlepoints in the least-squares function that can be arbitrarily far from a solution. Furthermore, the basins of attraction of these singular points are usually dispersed throughout the basin boundaries in the complex domain, clearly illustrating that singular points (via the dogleg strategy) also attract either real- or complex-valued starting points.In light of this, an extension of the dogleg strategy to the complex domain, based on a simple norm-reducing, singular point perturbation, is proposed. This extended trust region method removes all forms of nonconvergent behavior and always terminates at a fixed point, even from critical point (worst-case) initial values. Many numerical results and geometric illustrations using chemical process simulation examples are presented.
    Additional Material: 9 Ill.
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  • 83
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    AIChE Journal 39 (1993), S. 446-460 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most of the advanced nonlinear control algorithms require a model of the system to be controlled. Unfortunately, most of the processes in the chemical industry are nonlinear, and fundamental models describing them are lacking. Thus there is a need for the identification and control of nonlinear systems through available inputoutput data. In this article, we briefly introduce the input-output model used (polynomial ARMA models), and analyze its stability and invertibility. This paves the way to the development of a nonlinear-model-predictive controller. Implementation issues such as modeling of disturbance, state and parameter estimation are discussed. The theory presented is illustrated through examples.
    Additional Material: 6 Ill.
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  • 84
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    AIChE Journal 39 (1993), S. 471-492 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The separation of a binary mixture, using a third component having intermediate adsorptivity as desorbent, in a four section countercurrent adsorption separation unit is considered. A procedure for the optimal and robust design of the unit is developed in the frame of Equilibrium Theory, using a model where the adsorption equilibria are described through the constant selectivity stoichiometric model, while mass-transfer resistances and axial mixing are neglected.By requiring that the unit achieves complete separation, it is possible to identify a set of implicit constraints on the operating parameters, that is, the flow rate ratios in the four sections of the unit. From these constraints explicit bounds on the operating parameters are obtained, thus yielding a region in the operating parameters space, which can be drawn a priori in terms of the adsorption equilibrium constants and the feed composition.This result provides a very convenient tool to determine both optimal and robust operating conditions. The latter issue is addressed by first analyzing the various possible sources of disturbances, as well as their effect on the separation performance. Next, the criteria for the robust design of the unit are discussed. Finally, these theoretical findings are compared with a set of experimental results obtained in a six port simulated moving bed adsorption separation unit operated in the vapor phase.
    Additional Material: 18 Ill.
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  • 85
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    AIChE Journal 39 (1993), S. 505-509 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 86
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    AIChE Journal 39 (1993), S. 513-517 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 6 Ill.
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  • 87
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    AIChE Journal 39 (1993), S. 518-520 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Tab.
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  • 88
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    AIChE Journal 39 (1993), S. 510-512 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
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  • 89
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    AIChE Journal 39 (1993), S. 1716-1720 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Chabazite zeolites are used at Oak Ridge National Laboratory to decontaminate wastewaters containing 90Sr and 137Cs. Treatability studies show that chabazite can remove trace amounts of these nuclides from wastewaters containing much higher concentrations of calcium and magnesium. The design of ion-exchange columns for multicomponent systems requires a method for predicting multicomponent equilibria from binary, ternary and quaternary experiments, since the number of experiments required for an empirical equilibrium model is not generally feasible. Binary interaction parameters for the Wilson equation are used to predict solid-phase activity coefficients for the five-component system. The sum of squares of deviations between experimental and predicted solution concentrations for the data points available is calculated. The average deviation per data point for the five-component system is lower than for some of the ternary-and four-component data sets containing calcium or magnesium.
    Additional Material: 3 Ill.
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  • 90
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    AIChE Journal 39 (1993), S. 1708-1715 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The limiting current technique was used to measure area-averaged mass-transfer coefficients for surfaces containing many small reactive areas arranged in various patterns. Partially masked platinum electrodes were fabricated using photolithography, and mass-transfer measurements were performed with a rotating disk apparatus. The average mass-transfer coefficient was sensitive to the fraction of the electrode area exposed (ε), declining from values near that for a fully exposed surface for ε = 0.5 to less than 1% of the fully exposed value for ε = 0.001. For any given ε, the mass-transfer coefficient declined with increased spacing between reactive sites. The results were relatively insensitive to details of the site distribution, such as whether the sites were arranged in regular arrays (square or hexagonal lattices) or distributed randomly over the surface. For all conditions studied, the mass-transfer coefficient greatly exceeded that predicted by conventional models which apply the stagnant film approximation to the fluid surrounding a representative active site. This finding is qualitatively consistent with recent computational results, which suggest that convective transport enhances mass transfer at partially active surfaces to an extent not accounted for by adjustments in the effective film thickness.
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  • 91
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    AIChE Journal 39 (1993), S. 1720-1720 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 92
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    AIChE Journal 39 (1993), S. 1272-1280 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An instability analysis has been carried out to elucidate the unsteady flow conditions encountered in the typical circulating fluidized bed units in light of the conveyor-solids feeder interaction. The results successfully predict the critical velocity and the maximum solids circulation rates reported in the literature and explain the origin of such unstable conditions. Furthermore, the simulation, for the first time, reveals the importance of unit structure in improving the performance of circulating fluidized bed systems. Finally, the concept of a high-density circulating fluidized bed is proposed.
    Additional Material: 12 Ill.
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  • 93
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    AIChE Journal 39 (1993), S. 1303-1321 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The product compositions in single-feed distillation columns can be specified only in certain regions of the composition space, which depend only on the pressure, feed, and vapor-liquid equilibrium for the mixture. In nonideal mixtures, even without azeotropes, the regions may allow unusual product distributions. For example, the distillate in a “direct split” is composed primarily of the lightest component. Intuition and experience with relatively ideal mixtures suggest that the next most plentiful component is the intermediate boiler. In nonideal mixtures, however, with or without azeotropes, the next most plentiful component may be the highestboiling species with only trace amounts of the intermediate boiler. For azeotropic mixtures, distillation boundaries may give rise to additional restrictions on the product compositions. We describe how simple distillation boundaries deform into continuous distillation boundaries and, in a limited number of cases, how the simple distillation boundaries can be crossed in continuous columns for certain ranges of the design variables. Unfortunately, such designs may be quite sensitive to model uncertainties or to disturbances in the parameters.
    Additional Material: 24 Ill.
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  • 94
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    AIChE Journal 39 (1993), S. 1377-1388 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Deposition of wax on the wall of oil pipelines is often regarded as a problem since the tube diameter is reduced. Consequently, more power is needed to force the same amount of oil through the system. A mathematical model for quantitative prediction of wax deposition for each hydrocarbon component has been developed. Each component is characterized by weight fraction, heat of fusion, and melting point temperature. A model explains how a phase transition in the flow from liquid oil to waxy crystals may create a local density gradient and mass flux, which depends on the local temperature gradient. The model predicts that wax deposition can be considerably reduced even when the wall temperature is below the wax appearance point, provided the liquid/solid phase transition, expressed by the change in moles of liquid with temperature, is small at the wall temperature. Deposition as function of time has been obtained as a solution of differential equations derived from the principles of mass and energy conservation and the laws of diffusion.
    Additional Material: 9 Ill.
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  • 95
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    AIChE Journal 39 (1993), S. 1411-1414 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 7 Ill.
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  • 96
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    AIChE Journal 39 (1993), S. 1415-1419 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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  • 97
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    AIChE Journal 39 (1993), S. 1389-1397 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rigorous and approximate methods are compared for the simulation of CO2 absorption into aqueous alkanolamine mixtures of methyldiethanolamine and diethanolamine. In addition, data for the mixtures containing monoethanolamine and the simultaneous absorption of CO2 and H2S are presented. For the rigorous approach, the simplified eddy diffusivity theory is used to simulate the liquid-phase hydrodynamic characteristics. The approximation methods examined are the pseudo-first-order approximation, the interpolation approximation of Wellek et al. (1978), the algebraic combined flux (ACFLUX) approximation and the modified combined flux (MCFLUX) approximation. The latter approximation utilizes the reaction zone concept to determine the kinetic preference of the absorbing gas at the gas-liquid interface. Under the range of conditions studied, the MCFLUX approximation predicts very accurately the CO2 and H2S flux rates in mixed amine systems, as compared with the rigorous solution of the differential equations.
    Additional Material: 7 Ill.
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  • 98
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    AIChE Journal 39 (1993), S. 1406-1410 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 9 Ill.
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  • 99
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    AIChE Journal 39 (1993), S. 1420-1420 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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    AIChE Journal 39 (1993) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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