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  • 11
    Digitale Medien
    Digitale Medien
    Leuconostoc mesenteroides growth kinetics with application to bacterial profile modification (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 865-873 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Leuconostoc mesenteroides ; dextran ; kinetics ; bacterial profile modification ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Bacterial profile modification (BPM) is being developed as an oil recovery technique that uses bacteria to selectively plug oil depleted zones within a reservoir to divert displacing fluids (typically water) into oil-rich zones. Leuconostoc mesenteroides, which produces dextran when supplied with sucrose, is a bacterium that is technically feasible for use in profile modification. However, the technique requires controlled bacterial growth to produce selective plugging.A kinetic model for the production of cells and polysaccharides has been developed for L. mesenteroides bacteria. This model, based on data from batch growth experiments, predicts saccharide utilization, cell generation, and dextran production. The underlying mechanism is the extracellular breakdown of sucrose into glucose and fructose and the subsequent production of polysaccharide (dextran). The monosaccharides are then available for growth. Accompanying sucrose consumption is the utilization of yeast extract. The cell requires a complex media that is provided by yeast extract as a source of vitamins and amino acids. Varying the concentration ratio of yeast extract to sucrose in the growth media provides a means of controlling the amount of polymer produced per cell. Consequently, in situ bacteria growth can be controlled by the manipulation of nutrient media composition, thereby providing the ability to create an overall strategy for the use of L. mesenteroides bacteria for profile modification.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260430905
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  • 12
    Digitale Medien
    Digitale Medien
    Foamed gel barriers in porous media: Breakdown and permeability evolution (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2487-2498 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Foamed del has begun to play an important role in permeability modification applications because of the reduced chemical requirements. Foamed gels create impermeable barriers in porous media; however, once a critical pressure differential is exceeded, the permeability increases with increasing pressure. A two-dimensional network model was developed to estimate foamed gel barrier performance in terms of the maximum pressure a barrier can withstand and the evolution of the foamed gel barrier's permeability. The formation of conductive pathways and the accopanying permeability increase were estimated from a model of the pressure-induced deformation and repture of individual lenses. The evolution of conductive pathways changed from invasion percolation (high elastic modulus, rigid gel) to a lens rupture chain reaction initiated by teh rupture of a single lens (low elstic modulus gel) as the elastic modulus of the gel was decreased. The apparent fractal dimension of the first conductive channel ranged from 1.89 to 1.06 for high and low wlastic modulus gels, respectively. This dependency of breakthrough and breakdown is unique and produces a large range of breakdown behavior for any degree of microscopic heterogeneity.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690411114
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  • 13
    Digitale Medien
    Digitale Medien
    Model for the reaction-rate-limited dissolution of solids with Etch-rate heterogeneities (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 2654-2660 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The coalescence of isotropic etch pits observed in the dissolution of semiconductor substrates is studied using a discrete model for the evolution of the surface under reaction-rate-limited conditions. The model discretizes the solid into cubic elements and repetitively applies dissolution rules to the individual elements. The rate of mass removal is based on the number and arrangement of the element's exposed faces and the specified reaction-rate parameters. Detailed knowledge of the surface normal is not required. The model shows that even at moderate etch pit densities, the effects of the coalescence do not significantly alter the trends observed for noncoalescing etch pits.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690420926
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  • 14
    Digitale Medien
    Digitale Medien
    Reaction kinetics of photoactive defects in semiconductor dissolution (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 2279-2287 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Uniformity and predictability are the principal qualities sought for all wet chemical etches. The establishment of these qualities, however, is hindered by a number of factors, such as nonuniformities in the starting material and random fluctuations in the local temperature and reactant concentration, which can lead to variations in etch rate across the surface of a wafer. The effects of variations in the local etch rate on the morphological development of an etching surface and on the overall etch rate of the semiconductor are discussed. The system studied was an Al0.4Ga0.6As/GaAs heterostructure photodissolved in nitric acid using 730-nm laser light. Defects in the AlGaAs layer, which etched faster than the surrounding material, were responsible for variations in the etch rate. The defects also exhibited a degree of photosensitivity that has not been previously observed. It was also found that not all of the defects spanned the AlGaAs epilayer. A model for the overall etch rate was based on a system of noninteracting cylindrical defects with a distribution in depths.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690420816
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  • 15
    Digitale Medien
    Digitale Medien
    Kinetics of silica particle formation in nonionic W/O microemulsions from TEOS (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 3153-3163 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The kinetics of silica particle formation by the ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) in water-in-oil (W/O) microemulsions containing a nonionic surfactant was investigated using Fourier-transform infrared spectroscopy, transmission electron microscopy, and light-scattering techniques. The results show that TEOS hydrolysis and silica-particle growth occur at the same rate, indicating the growth of silica particles is rate-controlled by the hydrolysis of TEOS. The rate of TEOS hydrolysis in microemulsions is first order with respect to the concentration of aqueous ammonia (29 wt. % NH3), but depends weakly on the concentration of water. Based on the fact that TEOS hydrolysis follows a nucleophilic (SN2) substitution of the TEOS's ethoxy group with hydroxyl ion, the kinetic data suggest that both water and ammonia remain predominately in W/O microemulsion droplets. The rate of TEOS hydrolysis also depends on the surfactant concentration that controls the molecular contact between hydroxyl ions and TEOS in the solution. Due to the reaction-controlled growth mechanism, the silica-particle size distribution retains virtually the same shape over the growth period. The final average size of silica particles can be varied from 26 to 43 nm by adjusting concentrations of water and surfactant. Increasing the water concentration decreases the average size and uniformity of silica particles. For a given water concentration, the smallest and most uniform silica particles are produced at intermediate water-to-surfactant molar ratios (about 1.9). The results are discussed in terms of the effect of water concentration on the stability of the hydrolyzed silica reacting species during the nucleation of particles and of the water-to-surfactant molar ratio on the compartmentalization of silica species in microemulsions.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690421115
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  • 16
    Digitale Medien
    Digitale Medien
    Colloidally induced smectitic fines migration: Existence of microquakes (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 565-576 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The phenomenon of colloidally induced fines migration is a challenge of both scientific and industrial importance. Its occurrence impacts permeability reduction and alteration of flow pathways in porous media, particulate contaminant migration in groundwater flow, and filtration. The release of smectitic fines is a threshold type of process resulting from discontinuous jumps, called microquakes in the interlayer spacing. There is a critical salt concentration at which these microquakes occur and produce fines migration in the porous media. The changes in the microstructure with decreasing salt concentration were analyzed using X-ray diffraction. The transition between crystalline and osmotic swelling regime is also shown to depend on the type of cation. A mathematical model developed using colloidal principles predicts the swelling behavior of smectites in aqueous solutions. The model can predict the transition of swelling from crystalline to osmotic regimes and explain the effect of different cations on the transition.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690430302
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  • 17
    Digitale Medien
    Digitale Medien
    Fundamental study of the dissolution of calcium phosphonates from porous media (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 2883-2896 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Phosphonate-scale inhibitors are commonly used to prevent scale formation in many industrial processes involving high-salinity brine solutions. To effectively prevent scale formation in these industrial processes, one must have a fundamental understanding of how phosphonates are released into high-salinity brines. Because phosphonates can precipitate with divalent cations such as calcium, their release into aqueous media is often governed by many dissolution mechanisms. This study focuses on the release of calcium-phosphonate precipitates from porous media (as related to oil-field applications) and a mathematical model describing these release mechanisms based on mechanistic studies of pore-level phenomena. The phosphonate used was 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). The release of two distinct calcium-HEDP precipitates from porous media was studied: soluble, fibrous 1:1; insoluble, spherical 2:1. Visual studies using etched-glass micromodels showed that five distinct regimes govern the release of 1:1 calcium-HEDP precipitate from porous media. Conversely, the release of 2:1 calcium-HEDP precipitate was dominated by two distinct regimes. A continuum model developed describes the release of both precipitates from porous media by mathematically describing each of the distinct release regimes and defining conditions under which the transition between release regimes occurred. Experimental data agreed excellently with model simulations for both precipitates.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690421017
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  • 18
    Digitale Medien
    Digitale Medien
    Modeling flow in disordered packed beds from pore-scale fluid mechanics (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1377-1389 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Network models are an effective means of incorporating pore-scale heterogeneity into flow models of porous materials. The drawback to these models used to be the inability to obtain quantitative macroscopic parameters representing larger (experimental-scale) media. However, recently developed modeling techniques, combined with more widely available computational resources, make the simulation of macroscopic parameters from a network approach viable. A network model for the slow flow of an incompressible fluid in disordered packed beds is presented. Fundamental fluid mechanics equations are solved at the pore scale and then translated to macroscopic behaviour using a network approach. The results reproduce experimental permeabilities and show excellent quantitative fits to residence time distributions for mechanical dispersion in real beds. Simulations of the RTD are of special interest, because they are definitive links between pore-scale flow behavior and macroscopic responses.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690430602
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  • 19
    Digitale Medien
    Digitale Medien
    Determination of flow profiles in porous media using shifts in gamma spectra (1990)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 36 (1990), S. 827-836 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A new technique was developed to determine the tracer location and fluid velocity in porous media nonintrusively. This technique exploits the competitive effects between the photoelectric interaction and the Compton scattering phenomenon to determine the distance between a radioactive tracer in a porous medium and an externally positioned detector. The photon energy distribution shifts toward lower photon energies as the tracer moves away from the detector. The shift in the energy distribution can be quantified by the ratio of the scattered photon intensity to the full energy photon intensity. A convective-dispersion model was used to determine the spatial distribution of the radioactive tracer. An analog Monte Carlo method was developed to simulate photon transport in porous media. Comparison between experimental data and the model shows that in-situ tracer velocities can be accurately predicted.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690360604
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  • 20
    Digitale Medien
    Digitale Medien
    Effect of the resonance parameter on a chemical reaction subjected to ultrasonic waves (1967)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 13 (1967), S. 453-456 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Experimental results are presented which indicate that the application of a fixed intensity of ultrasonic waves to a water-tetrachloride solution containing dissolved air provides yields of chlorine varying from zero to maximum simply as a function of the liquid height in the capillary above the transducer. The difference in heights of the liquid between zero and maximum yields is found to be equal to one-quarter the wavelength of the ultrasonic wave in the liquid. A mathematical model to explain this phenomenon is presented.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690130313
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