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  • Chemistry  (24)
  • crystal structure  (2)
  • 42.75
  • 1990-1994  (24)
  • 1994  (24)
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  • 1990-1994  (24)
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  • 1
    ISSN: 0933-5137
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Beschreibung / Inhaltsverzeichnis: High temperature behaviour of materials for gas turbine blades manufactured in new technologyOn gas turbine blades for the middle and last stages of stationary gas turbines, the service-relevant material properties were examined. The specimens were taken from forged blades of alloys Nimonic 101 and Udimet 720 and from two fine grain versions of cast blades of alloy IN-792. In the range of service relevant temperatures long-term creep rupture tests, annealing tests, relaxations tests as well as low and high cycle fatigue tests were carried out.
    Notizen: An in neuer Technologie gefertigten Schaufeln für die mittleren bis hinteren Laufreihen von stationären Gasturbinen wurden betriebsrelevante Werkstoffeigenschaften bestimmt. Die Untersuchungen erfolgten an den Schmiedelegierungen Nimonic 101 and Udimet 720 und an zwei Feinkornvarianten der Gußlegierung IN-792. Im Bereich der Anwendungstemperaturen wurden Langzeitstandversuche, Glühversuche, Relaxationsversuche sowie nieder- und hochfrequente zyklische Versuche durchgeführt.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 95-97 
    ISSN: 0935-6304
    Schlagwort(e): Chemical warfare agents ; Microcolumn liquid chromatography ; Enantiomeric separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An improved interface for the on-line coupling of microcolumn liquid chromatography (micro-LC) with thermionic detection (TID) is described. Modifications have been made to enable separate adjustment of the eluent introduction and the detector flame temperature in order to improve the sensitivity and ease of use of the system.The micro-LC-TID was used for the chiral separation of the nerve agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX). Baseline separation for the enantiomers of VX was obtained on Chiralcel OD using 1% isopropanol in hexane as the eluent. The detection limit of VX using 60 nl injections is ca. 5 μg/ml (ppm range). However, when using large-volume injections (10 μl) the detection limit is ca. 25 ng/ml (ppb range).
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    ISSN: 0947-5117
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Beschreibung / Inhaltsverzeichnis: Microbial deterioration of materials - simulation, case histories, and countermeasures for inorganic nonmetallic materials: Biodeterioration processes on inorganic materials and means of countermeasuresBiodeterioration processes on inorganic materials such as natural stone, concrete, or glass can be subdivided into biogeochemical and biogeophysiological mechanisms according to their damage characteristics. In connection with the partial acidification and dissolving of components, biocorrosion as a result of biogenic release of inorganic and organic acids, as well as the biogenic oxidation of mineral forming cations, a certain weakening in the structure of the respective material can occur. The formation of biofilms on the surfaces of the inorganic materials impairs not only the aesthetical appearance of an object but also causes alterations in its humidity and temperature behaviour. In addition, due to the shrinking and swelling effects of biofilms, mechanical pressure to the mineral unit can occur (bioerosion, bioabrasion). Location and environmental factors which could lead to specific, biogenically determined weathering phenomena on these materials will be presented and elucidated. For controlling biodeterioration processes, the development and selection of environmentally-friendly, yet effective, inorganic and organic biocidal additives for stoneprotection agents as well as the use of gas (e.g. ethylene oxide) in their far-reaching significance for future material research will be presented here.
    Notizen: Biodeteriorationsprozesse an anorganischen Werkstoffen wie Naturstein, Beton oder Glas können in ihren Schädigungsweisen nach biogeochemischen und biogeophysikalischen Mechanismen unterteilt werden. Im Zusammenhang mit der partiellen Ätzung und Lösung von Bestandteilen, hervorgerufen durch die biogene Freisetzung anorganischer bzw. organischer Säuren (Biokorrosion) sowie der biogenen Oxidation mineralbildender Kationen (Biooxidation), kommt es zur Schwächung, des Gefüges im jeweiligen Werkstoff. Durch den Aufwuchs von Biofilmen auf den Oberflächen anorganischer Materialien kommt es neben ästhetischen Beeinträchtigungen auch zu Veränderungen im Feuchte- und Temperaturverhalten des Werkstoffes sowie aufgrund von Schrumpfungs- und Quellungsprozessen von Biofilmen zu mechanischer Druckbelastung auf den Mineralverband (Bioerosion, Bioabrasion). Standort- und Umweltfaktoren, die zu entsprechend biogenen Verwitterungsphänomenen an anorganischen Werkstoffen führen, werden vorgestellt und erläutert. für die Bekämpfung der Biodeteriorationsprozesse werden die Entwicklung und Auswahl umweltgerechter, aber dennoch wirksamer anorganischer bzw. organischer biozider Zuschlagstoffe für Gesteinsschutzstoffe sowie Begasungen (z. B. Ethylenoxid) in ihrer weitreichenden Bedeutung für die zukünftige Materialforschung vorgestellt.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 51 (1994), S. 407-413 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Isothermal DSC investigations on pure as well as glass, carbon, and aramid fibre-reinforced poly(phenylene sulfide) (PPS) were carried out in order to obtain informations on the crystallization kinetics, that is, the Avrami exponent, constant, half-time of crystallization, and (final) degree of crystallinity. PPS is a typical representative of semicrystalline polymers with a maximum degree of crystallinity of about 60%. The Avrami exponent reaches values from n = 2.1-2.7 depending on fibre type but independent of crystallization temperature. The system aramid fibre/PPS has a much shorter half-time of crystallization than the other three systems that could be attributed to the high nucleation effect of the aramid fibre surface to PPS. As a consequence of the high nuclei density a transcrystalline zone is built up around the aramid fibre. The relatively low value of the Avrami constant was discussed and a computer simulation attempt was made to understand the measured value quantitatively. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 1011-1023 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The formation of nodular structures in the top layer of ultrafiltration membranes is considered. A critical review of mechanisms described in the literature is given. Flat-sheet poly(ether sulfone) membranes and hollow-fiber poly(ether sulfone)/polyvinylpyrrolidone membranes were made by coagulation of a polymer solution in a nonsolvent medium under different circumstances. From these experiments, a number of empirical rules are found to describe the resulting morphology of the top layer. A new mechanism for the formation of a nodular structure is proposed. It is based on the small diffusion coefficient of the polymer molecules compared to the diffusion coefficient of solvent and nonsolvent combined with a high degree of entanglement of the polymer network. For unstable compositions, phase separation will proceed by growth in amplitude of concentration fluctuations. The rapid diffusional exchange of solvent for nonsolvent in the top layer leads to vitrification of the maxima of the concentration fluctuations that form the nodules. Complete disentanglement of the polymer chains between the nodules is not reached, which explains the small pores and the low porosity of ultrafiltration membranes. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 1497-1512 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The mechanism of foaming a glassy polymer using sorbed carbon dioxide is studied in detail. A glassy polymer supersaturated with nitrogen forms a microcellular foam, if the polymer is quickly heated above its glass transition temperature. A glassy polymer supersaturated with CO2 forms this foam-like structure at much lower temperatures which indicates the Tg-depressing effect of CO2. Having this interpretation in mind, the overall sample morphology, i.e., a porous foam enclosed by dense outer skins, can be completely explained. The dense skins, however, are not homogeneous but show a nodular structure when analyzed by SEM and AFM. Foaming experiments with samples having a different thermal history suggest that the nucleation mechanism underlying the foaming process is heterogeneous in nature. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    ISSN: 1052-9306
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A method is described for the determination of the antitumour drug cyclophosphamide and six stable metabolites in plasma of cancer patients, namely dechloroethyl-cyclophosphamide, 4-keto-cyclophosphamide, carboxy-phosphamide, alcophosphamide, nor-nitrogen mustard and the N-chloroethyl-1,3-oxazolidine-2-one, as methyl and/or trifluoroacetyl derivatives by single ion monitoring gas chromatography/mass spectrometry, mostly in the electron capture chemical ionization mode. The isolation of most metabolites was performed by solid-phase C-18 extraction in weakly acidic medium. The phosphoramide mustard isolated under these conditions decomposes readily to the nor-nitrogen mustard during derivatization. The original nor-nitrogen mustard and the chloroethyl-1,3-oxazolidine-2-one were isolated by liquid extraction with ethyl acetate in alkaline medium. Recoveries of 75-99% were measured using spiked blank plasma samples. Quantitation of metabolites in patient plasma samples was performed using two sets of calibration curves for the concentration ranges of 1-100 ng and 0.1-10 μg of metabolite per millilitre of original plasma.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 6 (1994), S. 55-62 
    ISSN: 1040-7685
    Schlagwort(e): supercritical fluid chromatography ; packed capillary columns ; thermionic detection ; organophosphorus pesticides ; vegetable extracts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Packed capillary supercritical fluid chromatography coupled with thermionic detection was used for the selective determination of nineteen organophosphorus pesticides in vegetable extracts. The chromatographic behavior of some pesticides was studied using seven different stationary phases. Addition of an organic modifier to carbon dioxide was needed to improve peak shape and reduce retention. Quantitation of organophosphorus pesticides in vegetable extracts showed good linearity. Extraction was performed in a one-step extraction procedure using a water-miscible solvent (acetone) and an organic solvent with limited water capacity (dichloromethane). Under these conditions a wide range of both polar and apolar pesticides can be recovered from vegetable extracts down to the 3-25 μg kg-1 level. The recoveries found ranged from 35 to 95% depending on the polarity of the pesticides.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    ISSN: 1040-7685
    Schlagwort(e): capillary GC ; reversed-phase LC ; on-line coupling ; solvent vapor exit ; pressure-balanced carrier gas system ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A large-volume introduction system for capillary gas chromatography (GC) is described which can be coupled on-line with reversed-phase liquid chromatography (LC) using 2 mm i.d. LC columns. An on-column interface with a special retention gap, coated with a very thin film (0.02 μm) of Carbowax was used. Insertion of a solvent vapor exit before the analytical gas chromatography column allowed the solvent evaporation rate for an azeotropic acetonitrile/water mixture (84:16, v/v) to increase from 20 to 175 μL min-1 at 91°C and 150 kPa inlet pressure. A volume of 200 μL of this mixture containing phenanthrene and the potential basic drug eltoprazine, could be injected into the retention gap at introduction rates up to 200 μL min-1, under partially concurrent solvent evaporation conditions. Repeatability (CV = 2.4%) and linearity (at least 10-1000 ng mL-1) were satisfactory. The Carbowax-coated retention gap has a relatively large retention power for the polar solute. This means that the solvent can be completely evaporated through the vapor exit without loss of analyte. With apolar solutes, losses will occur if evaporation is unduly prolonged. In order to allow the use of a nitrogen-phosphorus detector, a special pressure-balanced carrier gas circuit was designed and tested for total solvent-free performance of the detector. With this set-up, 150 μL injections of eltoprazine in the acetonitrile/water azeotrope were made at an introduction rate of 200 μL min-1. No traces of acetonitrile were detected, while analyte detectability was 20-fold higher than with the FID.Finally, the practicability of reversed-phase LC-GC was demonstrated by on-line heart-cutting of the phenanthrene-containing fraction from a 2 mm i.d. LC column using acetonitrile/water (84:16, v/v) as eluent, and analyzing it by capillary GC-FID.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 51 (1994), S. 399-406 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A computer simulation model was developed to investigate spherulitic growth in polymers of infinite and plate-limited volume as well as in fibre-reinforced polymer composite systems. Parameters like thermal nucleation rate and athermal nucleation density, plate distance, and fibre content were varied. The simulation crystallization process was evaluated following Avrami's method in the case of infinite volume and by stepwise approximation by Avrami functions in the case of limited volume. In addition, the simulation method allows the visualization of the growing entities at any phase of crystallization. Therefore the geometry of growing entities can be easily compared with the corresponding crystallization exponent. A good agreement between the crystallization exponent and the growth geometry was found.Depending on nucleation mode, “infinite” systems yield Avrami exponents of 3 and 4. In plate-limited volume, a transcrystallization effect was observed in case of high athermal nucleation density on plate surface and large plate distances. This particular skin effect decreases the three-dimensional growth to a one-dimensional needle-shaped one. Small plate distance changes the spherical to a disk-like growth, resulting in crystallization exponents of 2 or 3, depending on nucleation mode. The crystallization behaviour of fibrereinforced composite systems is more complex. Low fibre content or large fibre distance and high athermal nucleation density on the fibre surface induce the formation of transcrystalline zones. The three-dimensional growth of the spheres at the beginning is restricted by their neighbours, so that their geometry changes to a pyramidical one. They grow with a front normal to the fibre surface and the crystallization exponent is shifted in between 2.0 and 2.6 depending on nucleation density. High fibre content leads to a growth along the triangular channels between three adjacent fibres; the corresponding exponent amounts to 1.6. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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