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  • Author or Editor: Eva Černošková x
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Abstract  

There are two different opinions in the literature on the combustion mechanism of the Si-Pb3O4 system. Differential thermal analysis, X-ray diffraction and infra-red spectroscopy have been used to examine the thermal behaviour of the mixture to characterize its combustion products and judge the validity of both proposed reaction paths. It was concluded from the results that the Si-Pb3O4 system exhibits rather complicated reaction mechanism including both gas-solid and solid-solid (proceeding below oxidant decomposition temperature) reactions whose importance depends on the fuel content of the mixture.

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Abstract

Single crystals of cycloocta-Se, unambiguously characterized by XRD were prepared and used in a study of its allotropic transformation to polycatena-Se by DSC supported by Raman spectroscopy and optical microscopy. It was found that the transformation of a Se8 single crystal to polycrystalline Sen proceeds progressively within the volume of the monoclinic single crystal without shape change. All the results of DSC, Raman spectroscopy, and optical microscopy indicate that previous proposals on cycloocta-Se melting during transformation are not realistic.

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Journal of Thermal Analysis and Calorimetry
Authors: Marek Liška, Zdenek Černošek, Mária Chromčíková, Jana Holubová, Eva Černošková, and Libor Vozár

Abstract  

The results of StepScan DSC obtained for various oxides, chalcogenides, and organic glasses are discussed in connection with the commonly accepted theory of the glass transition. The new experimental features supporting the apparent idea of a reversible equilibrium being a part of the glass transition that is commonly interpreted as purely kinetic-relaxation phenomenon are discussed. Two alternative methods of the description of the reversible part of StepScan DSC record are compared:the empirical one using the exponential-power function [1 − exp(T/T g)n], and the second one based on the van’t Hoff’s equation describing the temperature dependence of equilibrium constant in terms of reaction enthalpy, ΔH. The adequacy of the empirical description is rationalized in the framework of the Tool–Narayanaswamy–Moynihan’s relaxation theory.

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