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  • 1
    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: There are indications that the chemical reaction involved in bound rubber formation proceeds via a free-radical mechanism for compounds filled with reinforcing hydrated fine-particle silica, as well as in the case of carbon black as filler. The high potential of silica as a rubber reinforcer is indicated by its bound rubber formation. This potential was realized by the extent of filler-polymer interaction developed in silica-filled vulcanizates cured by peroxide and by high-energy radiation, respectively. Both these relatively simple curing systems are postulated to effect crosslink formation via a free-radical mechanism. The value, after cure, of the ratio of the crosslink density of the filled compound to the crosslink density of the respective unfilled compound, η/η0, was taken to be a logical measure of the ability to reinforce. In natural rubber compounds filled with silica (30 vol.), the values of η/η0 obtained were 1.6-1.9 for peroxide-cured material, and 3.6 for radiation-cured material. Comparisons are made with similarly cured HAF black-filled stocks. Sulfur-cured natural rubber stocks filled with HAF black (30 vol.) generally exhibit η/η0 values in the range of 1.5 to 2.0. Comparative effects of antioxidants are described.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 594 (1991), S. 167-178 
    ISSN: 0044-2313
    Keywords: Nickel titanate, NiTiO3 ; high temperature phase transition ; electrical conductivity ; X-ray ; DTA ; i.r. ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contributions to the Properties of Titanates with Ilmenite Structure. I. Aspects of a High Temperature Phase Transition in NiTiO3NiTiO3 (Ilmenite structure) shows an anomalous increase of the electrical conductivity in the temperature range between 1 250°C and 1 290°C. The temperature dependence of the Seebeck coefficient is also found to be anomalous in this region. DTA experiments are consistent with a phase transition; the transition enthalpy was estimated to ΔuHm = 17 ± 3 kJmol-1.NiTiO3 powders and single crystals were quenched from 1 350°C and 1 200°C to room temperature; in principle no differences of the lattice parameters or atomic positions could be detected. The determination of the distribution of cations using x-ray powder methods failt because of strong texture effects. Structure refinements with single crystal methods suggest an ordered Ilmenite structure independent of the quenching temperature.The results are in agreement with a reversible order-disorder transition of higher order. It seems to be impossible to quench the high temperature phase by conventional methods.
    Notes: Nickeltitanat (NiTiO3, Ilmenit-Typ) zeigt im Temperaturbereich zwischen 1 250°C und 1 290°C einen anormalen Anstieg der elektrischen Leitfähigkeit bei gleichzeitiger deutlicher Abnahme der Aktivierungsenergie. Auch die Temperaturabhängigkeit des Seebeck-Koeffizienten verläuft im genannten Temperaturbereich anormal. DTA-Untersuchungen deuten auf einen Phasenübergang hin; die Umwandlungsenthalpie ΔuHm beträgt 17 ± 3 kJ mol-1.Von Temperaturen unterhalb und oberhalb des Anomaliebereiches abgeschreckte Proben (Pulver und Einkristalle) weisen keine signifikanten Unterschiede in den Gitterkonstanten oder Atomlagen auf. Die Bestimmung der Kationenverteilung mit Hilfe röntgenographischer Pulvermethoden scheiterte am Auftreten starker Textureffekte. Einkristalluntersuchungen zeigen unabhängig von der Abschrecktemperatur eine geordnete Ilmenitstruktur an.Aus den erhaltenen Daten wird auf einen enantiotropen Ordnungs-Unordnungsübergang höherer Ordnung geschlossen, wobei die Hochtemperaturphase als mit den verwendeten Methoden nicht abschreckbar zu betrachten ist.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0044-2313
    Keywords: Nickel titanate ; high temperature phase transition ; electrical conductivity ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Beiträge zu den Eigenschaften von Titanaten mit Ilmenitstruktur. IV. Der Einfluß eines Ordnungs-Unordnungs-Übergangs auf die elektrische Leitfähigkeit von NiTiO3 bei hohen TemperaturenNiTiO3 zeigt einen Ordnungs-Unordnungs-Übergang von der geordneten Ilmenitstruktur in die Korundstruktur mit statistischer Besetzung der Kationenpositionen. Diese Phasenumwandlung wird von einem sprunghaften Anstieg der spezifischen elektrischen Leitfähigkeit begleitet, die als Funktion der Temperatur und der Sauerstoffaktivität untersucht wurde. Mit Hilfe eines Ordnungsparameters läßt sich die Leitfähigkeitsänderung im Bereich des Phasenübergangs beschreiben. Ein Defektmodell für NiTiO3 wird vorgestellt.
    Notes: NiTiO3 shows an order-disorder transition from an ordered ilmenite structure to a corundum structure at high temperatures. The transition is followed by a strong increase of the specific electrical conductivity. The conductivity was investigated as a function of temperature and oxygen activity. An order parameter according to common phase transition theories can be used to describe the behaviour of the conductivity in the transition region and vice versa. A model for the defect structure of NiTiO3 is presented.
    Additional Material: 8 Ill.
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  • 4
    Publication Date: 1975-11-01
    Print ISSN: 0022-460X
    Electronic ISSN: 1095-8568
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Elsevier
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