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  • Polymer and Materials Science  (15)
  • 1
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: The application of radiotracer technique for the determination of small corrosion rates of tantalum, a tantalum-niobium-alloy and zirconium in azeotropic nitric acidThe radiotracer technique following neutron activation is a suitable means to measure hitherto hardly detectable, very low corrosion rates. In azeotropic nitric acid, tantalum and the tantalum-40niobium alloy show at 20 to 120°C approximately the same corrosion rates between 0.2 · 10-6 and 8 · 10-6 mm/a; the apparent activation energies are 30 to 40 kJ/mol.In the temperature region from 20 up to 81°C the corrosion rates of zirconium are between 7 · 10-6 and 5 · 10-4 mm/a; the apparent activation energy is 47 kJ/mol.In the case of zirconium, check measurements (analysis of the corrosive medium with AAS and ICP) with non-activated sheet-metal sections resulted in similar corrosion rates.
    Notes: Die Radiotracer-Methode nach Neutronenaktivierung ist geeignet, bisher kaum erfaßbare, sehr geringe Abtragungsraten zu bestimmen. Tantal und die Tantal-40Niob-Lergierung zeigen in azeotroper Salpetersäure bei 22 bis 120°C annähernd gleiche Abtragungsraten von 0,2 · 10-6 bis 8 · 10-6 mm/a; die scheinbaren Aktivierungsenergien betragen 30 bis 40 kJ/mol.Die Abtragungsraten von Zirconium liegen im Temperaturbereich von 20 bis 81°C zwischen 7 · 10-6 und 5 · 10-4 mm/a; die scheinbare Aktivierungsenergie ergibt sich zu 47 kJ/mol.Im Falle des Zirconiums führten Kontrollmessungen (Analyse des Angriffsmittels mit AAS und ICP) an nicht aktivierten Blechabschnitten zu vergleichbaren Abtragungsraten.
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  • 2
    ISSN: 1057-9257
    Keywords: II-VI compound ; SrS : Ce ; Photoluminescence ; Concentration quenching ; Phosphorescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: The luminescence efficiency of SrS: Ce powders in the doping range from 0.01 to 1.0 at.% was investigated by photoluminescence decay studies. The radiative decay time of Ce3+ in SrS was determined to be 27 ns. The onset of concentration quenching at concentrations higher than about 0.7 at.% has been obtained. The photoluminescence spectrum of Ce3+ exhibits two emission bands as a consequence of the ground state splitting. The Huang-Rhys factor of the 5d-4f transition was estimated to be about 6. The inhomogeneous broadening of the emission band of samples with higher doping level has been investigated by site-selective and time-resolved spectroscopy.
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  • 3
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acidZirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10-6 to 5 · 10-4 mm/y, for tantalum: 10-8 to 4 · 10-6 mm/y, and for the Ta-40Nb alloy: 2 · 10-7 to 8 · 10-6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities.The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F- and at a temperature of 108°C, corrosion rates between 5.3 · 10-3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced.The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10-3 mm/y at 50°C/280 ppm F- and 1.4 · 10-2 mm/y at 110°C/320 ppm F-. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude.The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing.
    Notes: Wegen ihrer hohen Korrosionsbeständigkeit gegenüber zahlreichen Angriffsmitteln sind Zirconium und Tantal sowie die Legierung Tantal-40Niob von großer technischer Bedeutung. Die bisher in azeotroper Salpetersäure p.a. zwischen 20 und 121°C gemessenen Abtragungsraten liegen für Zirconium zwischen 7 · 10-6 und 5 · 10-4 mm/a, für Tantal zwischen 10-8 und 4 · 10-6 mm/a und für die Legierung Ta-40Nb zwischen 2 · 10-7 und 8 · 10-6 mm/a [1]. Diese Abtragungsraten werden durch geringe Fluoridzustände oder -verunreinigungen wesentlich erhöht.Mit der Radiotracermethode nach Neutronenaktivierung wurden die Abtragungsraten in azeotroper, fluoridhaltiger Salpetersäure bestimmt. Zirconium ist schon gegen kleinste Fluoridspuren sehr empfindlich. Im untersuchten Bereich von 0.15 bis 10 ppm F- liegen bei 108°C die Abtragungsraten zwischen 5.3 · 10-3 und 3.1 mm/a. Eine Grenzkonzentration, unterhalb der das Fluorid die Korrosionsgeschwindigkeit nicht mehr beeinflußt, kann für Zirconium nicht angegeben werden.Bei Tantal und der Legierung Ta-40Nb nimmt oberhalb einer Grenzkonzentration von 10 ppm F- die Korrosionsgeschwindigkeit stark zu. Die höchsten Abtragungsraten liegen zwischen 8.4 · 10-3 mm/a bei 50°C/280 ppm F- und 1.4 · 10-2 mm/a bei 110°C/320 ppm F-. Dabei ist Tantal über den gesamten erfaßten Bereich um etwa das Zehnfache beständiger als die Legierung Ta-40Nb.Sowohl bei Tantal als auch bei Zirconium stellt sich die Abtragungsrate unabhängig von Vorbehandlungen ein.
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  • 4
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A model system was developed to study the influence of the rubber formulation and/or the aging conditions on the adhesion between brass and rubber. The bonding compounds were vulcanized on thin, homogeneous brass layers that had been prepared by sputtering onto special polymeric substrates; some of these compounds were steam-aged under controlled conditions subsequently. After the separation of the polymeric film, combined analytical electron microscopy (transmission electron microscopy/energy dispersive spectroscopy; TEM/EDS) and sputter neutral mass spectrometry (SNMS) analyses were performed. While the TEM/EDS studies offer a detailed insight into the morphological structure of the interphase, the SNMS depth profiles allow a rapid and reliable differentiation between various rubber formulations. With these model samples the beneficial effect of boric acid esters on the adhesion of cobalt-containing bonding compounds, which is observed in a typical short-term adhesion test after steam-aging, can be explained: boric acid esters act with cobalt salts as corrosion inhibitors for brass, preventing the growth of a thick intermediate ZnO/Zn (OH)2 layer that is the starting point for delaminations.
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  • 5
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The extinction coefficients of the CH3 deformation vibrations of short chain branchings in saturated polymeric hydrocarbons was determined in dependence on the length of side chains in model substances. The number of CH2 groups arranged between the main chain and methyl group of alkyl branchings affects essentially the intensity of the absorption at 1378 cm-1. The results were applied in the quantitative evaluation of CH3 vibrations for the calculation of the number of branchings in high pressure polyethylene.
    Notes: Die Extinktionskoeffizienten der CH3-Deformationsschwingung von kurzen Kettenverzweigungen in gesättigten polymeren Kohlenwasserstoffen wurden in Abhängigkeit von der Seitenkettenlänge an Modellsubstanzen ermittelt. Die Zahl der CH2-Gruppen, die sich zwischen Hauptkette und Methylgruppe der Alkylverzweigung befinden, beeinflußt wesentlich die Intensität der Absorption bei 1378 cm-1. Die Ergebnisse werden auf die quantitative Auswertung der CH3-Schwingung zur Berechnung von Verzweigungszahlen im Hochdruckpolyethylen angewendet.
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  • 6
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The short chain branching in low density polyethylene obtained under various conditions were determined by γ-irradiation followed by gaschromatography of the gaseous scission products. The pressure and temperature of polymerization were found to affect the kind and number of branchings. The branching structure and reaction parameters are related and discussed on a kinetic concept.
    Notes: Die Kurzkettenverzweigung von unter verschiedenen Bedingungen synthetisierten Hochdruckpolyethylenen wurde mit Hilfe der γ-Bestrahlung und nachfolgender gaschromatographischer Analyse der Spaltgase bestimmt. Es wurde experimentell belegt, daß Reaktionsdruck und Polymerisationstemperatur Art und Anzahl der Seitenzweige beeinflussen. Verzweigungsstruktur und Reaktionsparameter werden zueinander in Beziehung gesetzt und auf der Grundlage kinetischer Überlegungen diskutiert.
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  • 7
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The effect of propylene and vinyl acetate used as comonomers in the synthesis of high pressure ethylene copolymers on the hydrogen transfer is discussed. The structural changes caused by the comonomers in the chain segments and possibly enabling transfer reactions did really not result in measurable differences of the number of short chain branchings by intramolecular transfer. The differences in the potential and rotational energy in these structures and that of the unsubstituted CH2 chain is suggested to be small with respect to kT, thus the hindrance of rotation being unimportant. The number and kind of short chain branchings depend decisively, as in the homopolymerization of polyethylene, on the reaction parameters pressure and temperature.
    Notes: Der Einfluß der Comonomere Propylen und Vinylacetat auf die intramolekulare Wasserstoffübertragung bei der Hochdrucksynthese der Ethylen-Copolymere wird diskutiert. Es wird gezeigt, daß die durch den Einbau der Comonomere bedingten strukturellen Unterschiede in den zur Übertragung befähigten Kettensegmenten keine meßbaren Änderungen der Zahl der durch intramolekulare Übertragung gebildeten Kurzkettenverzweigungen hervorrufen. Es wird angenommen, daß die Differenz zwischen dem Rotationsenergiepotential dieser Strukturen und dem der unsubstituierten CH2-Kette klein bezüglich kT sein muß, so daß das Rotationsbehinderungspotential nur eine gering fügige Änderung erfährt. Entscheidend für die Zahl und Art der Kurzkettenverzweigungen sind wie bei der Homopolymerisation des Ethylens die Reaktionsparameter Druck und Temperatur.
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  • 8
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The Ti5Ta alloy shows interesting corrosion behaviour and is becoming technologically important, e.g. for chemical plant construction. Welding and further mechanical tests gave good mechanical properties. Therefore, the corrosion of this alloy was studied in comparison with the corrosion of unalloyed Ti and Ta. The samples were corroded for up to 24 days in hot 67.5% nitric acid.The resulting surface layers were investigated with SEM, transmission electron microscopy (TEM), energy dispersive x-ray microanalyses (EDX), AES and sputtered neutral mass spectrometry (SNMS). Under these conditions, the oxide growth seems to be dependent on the orientation of the crystallites at the surface, which was not observed under milder attack. When Ti5Ta samples were immersed for 5 days in boiling HNO3, the oxide layer was ∼300 nm thick and a particular crack pattern developed on some grains during drying in air at room temperature. This was observed only for oxide layers thicker than 300 nm.After corroding Ti5Ta in boiling HNO3 we observed a TaTi atomic ratio of up to 1:1 using ESCA and up to 5 μm thick Ta oxide-rich scales. The selected area diffraction pattern in the TEM indicates that the oxide film may contain mixed Ti/Ta oxides. The extraordinary Ta oxide enrichment, which is due to the selective dissolution process of Ti, is believed to cause the good corrosion resistance of the alloy. It was not observed after heat treatment in air up to 800 °C or after corrosion tests in HNO3 at room temperature.
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  • 9
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The wave number at maximum intensity, half width and integral absorption of model polyethylenes were determined. The line shape profiles of the δs(CH3)-vibration are statistically evaluated by momentum analysis. The measured and calculated spectral parameters are correlated with the kind of branching. The consequences for the analysis of the distribution of side chains having different length in high pressure polyethylene are discussed.
    Notes: Von methyl-, ethyl-, butyl- und hexylverzweigten Modellpolyethylenen werden die Wellenzahlen am Intensitäts-maximum, die Halbwertsbreiten und die integralen Absorptionen gemessen. Die Linienformprofile der δs(CH3)-Schwingung werden auf der Grundlage einer Momentanalyse einer statistischen Auswertung unterzogen. Der Verlauf der gemessenen und berechneten spektralen Parameter wird mit der entsprechenden Verzweigungsart korreliert. Die Konsequenzen für eine Analyse der Verteilung der im Hochdruckpolyethylen enthaltenen unterschiedlich langen Seitenketten werden diskutiert.
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  • 10
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The results obtained in investigating the long chain branching of high pressure polyethylene (LDPE) and emulsion polybutadiene (PB-E) are provided. Besides 13C NMR data measured in the low and high field region (with hydrated PB-E) comparative values of molecule contraction in solution are considered. The change of the molecular weight distribution and the relationships between molecular weight and intrinsic viscosity in dependence on conversion in the emulsion polymerization of butadiene was investigated. The data required for determining the contraction factor were obtained by combining gel permeation chromatography and solution viscosity measurements. The differences of the results are discussed with respect to their causes.
    Notes: Es wird über Ergebnisse von Langkettenverzweigungsanalysen am Hochdruckpolyethylen (PE-LD) und Emulsionspolybutadien (PB-E) berichtet. Die Ergebnisse aus der 13C-NMR-Spektroskopie im niederen und hohen Feldbereich (am hydrierten PB-E) werden mit Informationen aus den Untersuchungen zur Molekülkontraktion in Lösung verglichen. Die änderungen der Molmassenverteilung sowie die Zusammenhänge zwischen Molmasse und Grenzviskosität als Funktion des Umsatzes bei der Emulsionspolymerisation des Butadiens wurden untersucht. Die Daten zur Bestimmung des Kontraktionsfaktors g′GPC wurden aus der Kombination von Gelpermeationschromatographie und Viskositätsmessungen erhalten. Die Ursachen für die unterschiedlichen Resultate werden diskutiert.
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