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  • 1990-1994  (1)
  • 1985-1989  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Composition-microstructure-property relationships in ceramic monofilaments resulting from the pyrolysis of a polycarbosilane precursor at 800 to 400 °C (1991)
    Springer
    Journal of materials science 26 (1991), S. 1517-1530 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A 15 μm monofilament was extruded from a Yajima's type molten polycarbosilane, stabilized by addition of oxygen and heat-treated at 800 to 1400 °C under an argon atmosphere. Two important phenomena occur during pyrolysis. At 500 to 750 °C, an organic-inorganic state transition takes place with a first weight loss. It yields an amorphous material stable up to about 1100 °C. At this temperature, its composition is close to Si4C5O2. It can be described as a continuum of SiC4 and/or SiC4−x Ox tetrahedral species (and possibly contains free carbon), with a homogeneity domain size less than 1 nm. The amorphous filament exhibits a high strength and semi-conducting properties. Above 1200 °C, a thermal decomposition of the amorphous material takes place with an evolution of gaseous species thought to be mainly SiO and CO, an important cross-section shrinkage and the formation of 7 to 20 nm SiC crystals which are surrounded with a poorly organized turbostratic carbon. The amorphous-crystalline state transition results in a drop in the tensile failure strength and an increase, by four orders of magnitude, in the electrical conductivity which becomes temperature independent. The former effect is due to the crystallization of the filament and the latter to a percolation phenomenon related to the intergranular carbon. The low stiffness is also due to the presence of carbon. It is anticipated that this transition is mainly related to the decomposition of the silicon oxycarbide species. Finally, a 40 to 50 nm layer of turbostratic carbon is formed at the filament surface at 1200 to 1400 °C whose origin remains uncertain. It is thought to be mainly responsible for the formation of the carbon interphase in the high-temperature processing of ceramic matrix composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00544661
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Residue analysis of triazine herbicides in soil: Comparison of a capillary gas chromatographic and a high-performance liquid chromatographic method (1986)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 325 (1986), S. 377-380 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary Two methods for the determination of triazines in soil were developed and compared. After extraction of the residues with methanol and clean-up by gel permeation chromatography, the samples evaporated were analysed for triazines by splitless capillary gas-chromatography with NP-detector (GC-NPD) and microbore high performance liquid chromatography with UV detector (HPLC-UV) at 222 nm. Both methods gave similar results. The microbore HPLC method was suitable for the analysis of a number of triazines at 10 ppb whereas capillary GC method was used for the analysis of triazines at 5 ppb. Satisfactory average recoveries for the two methods were obtained at 80 ppb and 20 ppb, respectively.
    Notes: Zusammenfassung Zwei Methoden zur Bestimmung von Triazinen im Boden wurden entwickelt und miteinander verglichen. Nach der Extraktion der Rückstände mit Methanol und clean-up durch Gelpermeations-Chromatographie wurden die Proben eingeengt und auf Triazin-Rückstände hin untersucht. Zur Detektion wurden die splitlose Capillar-Gas-Chromatographie mit NP-Detektor (GC-NPD) und die Microbore-Hochdruckflüssig-Chromatographie mit UV-Detektor (HPLC-UV) bei 222 nm verwendet. Beide Methoden ergaben vergleichbare Ergebnisse bei einem Minimum an Zeit- und Materialaufwand und der Möglichkeit der Automatisation der Rückstandsanalytik. Die Microbore-HPLC-Methode erreichte nach einfachem GPC clean-up eine Nachweisgrenze von 10 ppb im Vergleich zu 5 ppb bei der Capillar-GC-Methode. Zufriedenstellende Wiederfindungsraten wurden für beide Methoden bei 80 ppb und 20 ppb ermittelt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00505463
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Release routes of incorporated desmetryn from EVA-films. An example for the behavior of low volatility additives in polymers under outdoor conditions (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 34 (1987), S. 2069-2077 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: Release of desmetryn into the gas phase from films of ethylene-vinyl acetate copolymer, in which the herbicide was incorporated for special agricultural applications, was investigated for comparison with release into water and under outdoor conditions. It could be shown that the rate of release of the active chemical into the gas phase was negligible compared with that into water and only slightly dependent on temperature in the range 0-75°C.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1987.070340602
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    Paper (German National Licenses)
    Fulltext
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