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  • Author or Editor: J. Šesták x
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Abstract  

Besides a short introduction to historical data on inorganic and polymeric glasses, some aspects of the glassy-state are analyzed: particularly, induced entropy changes, characteristics of the glass transformation and a novel anharmonicity vibrational approach. The horizons and scientific prospects for the nano- and non-crystalline states are discussed.

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Abstract

Modeling tradition is reviewed within its historical maturity from Plato do Penrose. Metaphors in nonisothermal kinetics achieved a wide application mostly employing models derived by means of undemanding isothermal descriptions. Geometrical basis of such modeling is revised and discussed in terms of symmetrical and asymmetrical (pentagonal) schemes. The properties of interface (reaction separating line) are found decisive in all cases of heterogeneous kinetics. Application of fractal geometry is accredited, and associated formal kinetic models based on nonintegral power exponents are acknowledged. Typical erroneous beliefs are dealt with showing common kinetic misinterpretation of measured data and associated mathematical manipulability of kinetic equations. The correction of a measured DTA peak is mentioned assuming the effects of heat inertia and temperature gradients.

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The most debatable and discrepant viewpoints of non-isothermal kinetics are discussed in the form of twelve questions and answers. The reputation of non-isothermal kinetics when carried out by thermoanalysts; the consequences of simplified concepts transferred from the kinetics of homogeneous reactions; the physical meaning of basic kinetic parameters in solid-state processes; the kinetic compensative effect and interdependence of kinetic parameters using the Arrhenius rate constant; the mutual usefulness of differential and integral methods of kinetic data evaluation; their accuracy and correctness; the reliability of DTA measurements; non-isothermal versus isothermal investigations; equilibrium and kinetic data and their mutual effect; the extended discussion initiated by MacCallum and Tanner; non-isothermal data publication policy; and finally the use of computers.

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The importance of the thermal behaviour of glasses is illustrated. Some procedural characteristics for glass preparation upon quenching are discussed to distinguish the positive effects of increasing cooling rate. The basic thermodynamic quantities, kinetic data and procedural parameters are listed. The glass-transformation interval is treated in detail to demonstrate the temperature-dependences of heat capacity, enthalpy an Gibbs energy for as-quenched and annealed glasses, exemplifying processes of thermally stimulated reordering. Particular attention is paid to DTA measurements, which are of use for the determination of characteristic temperatures and to for the distinction of possible types of processes which occur upon reheating. Most common cases are illustrated by a series of hypothetical ΔH vs. T and ΔT dta vs. T plots. Different glass formation coefficients based on the onset temperatures are discussed to confirm the general knowledge that their maxima match with concentration regions close to that of invariant melting of the system.

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Abstract  

The notion of heat is thoroughly analyzed and historical links are discussed particularly with accentuation on its interdependence to contemporary thermal physics. Thermodynamics is discussed in relation to both the traditional development of equilibrium and the modern description of disequilibrium (related to real-open systems) as well as to the affiliated aspects of information. Dissipation is shown to provide a new kind of self-organized structure. Impact of mathematics is also displayed (fractal structures, bifurcations, vibration, topology, etc.). Exploitation of fire as an analytical tool and manufacturing power is analyzed. Generalized engines are shown in the sense of information transducers. The text gives a congruous view to various historical and modern concepts and gradual development of ideas that emerged during the continual understanding of order and disorder.

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