Jaroslav Šesták

Study of the kinetics of the mechanism of solid-state reactions at increasing temperatures

Abstract Possible reasons for the misinterpretation of non-isothermal kinetics are discussed. The importance of the correct selection for the assessment of the progress of the reaction and the acquisition of representative experimental data, as well as the effect of non-isothermal conditions and possible change of the equilibrium on the kinetic equation are stressed. Detailed attention is given to the probable mechanisms of individual cases of solid-state reactions as expressed in integral and/or differential forms of kinetic equations. Reactions controlled by the movement of phase boundaries, by simple nucleation. by nucleation followed by nuclei growth and by diffusion are discussed; a combined form of differential equation suggested for the preliminary. appraisal of possible mechanisms is

Rationale and fallacy of thermoanalytical kinetic patterns

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.

Heat inertia and temperature gradient in the treatment of DTA peaks

Historical development of methods and theoretical basis of differential thermal analysis (DTA) are outlined. DTA is a procedure in which the heat transfer toward the sample plays an important function and the associated process in the sample is manifested by deviation of temperature difference from its background. This difference ΔT is not directly proportional to the rate of the process (dα/dt) but includes also the effect of heat inertia proportional to the slope dΔT/dt as it was derived and incorporated into DTA equation by Vold (Anal Chem 21:683–688, 1949), Borchardt and Daniels (J Am Chem Soc 79:41–46, 1957), and suggested to be corrected in the authors’ previous papers (1976). However, the correction with respect to heat inertia has so far been omitted (particularly after the boom of non-isothermal kinetics started by paper of Kissinger (Anal Chem 29:1702–1706, 1957)). DTA experiments with rectangular pulses realized by micro-heater inside the sample show that the correction of DTA signal employing calculated heat inertia term of the DTA equation is reliable but not yet fully sufficient. It was a reason to derive a more complete DTA equation including a term expressing the changes in the temperature field inside the sample during process. Possibilities for improving of DTA (and DSC) data processing are discussed. Itemized 150 references with titles.

Diagnostic limits of phenomenological models of heterogeneous reactions and thermal analysis kinetics

Abstract Kinetic models of solid-state reactions are often based on a formal description of geometrically well defined bodies treated under strictly isothermal conditions; for real processes these prepositions are evidently incorrect. It can be equally useful to find an empirical function containing the smallest possible number of constants. In such a case the models of heterogeneous kinetics can be assumed as a distorted (fractal) case of the simpler homogeneous kinetics and mathematically treated by multiplying by an “accomodation” function. In addition, the conventional thermoanalytical (TA) studies apply intentionally the experimental conditions with constant heating and/or cooling where the models validity must again be investigated. The general method of kinetic data evaluation is proposed to include two-step evaluation: first, determining the activation energy, E , from a set of TA curves at different heating rates, and second, using the pre-established E to search for the reaction mechanism by analyzing the entire course of the single TA curve. In this respect the possibility of a simultaneous determination of all kinetic data is discussed. The computer method is recommended to be based on the evaluation of two specific functions available for a direct derivation from experimental data.

Kinetics with Regard to the Equilibrium of Processes Studied by Non-Isothermal Techniques

The non-isothermal degree of conversion and the equilibrium advancement for the process Aeq are denned by the relationship = ?.eq, where is the isothermal degree of conversion. The precise meaning of non-isothermal kinetics in relation to basic types of processes studied under dynamic conditions is discussed. For an invariant type of process the correct form of the kinetic equation is investigated. For the universal non-isothermal kinetic equation, a modified rate for the process is given by

Chapter 12 – THERMOMETRY AND CALORIMETRY

This chapter provides a brief methodical classification of thermometry and calorimetry. The method in which the heat is transferred through a thermocouple system is often called Tian–Calvet calorimetry. A specific group consists of isoperibolic calorimeters, which essentially operate adiabatically with an isothermal jacket. There are other versions such as the throw-in calorimeter, where the sample is preheated to high temperatures and then dropped into a calorimetric block, and combustion calorimeter, where the sample is burned in the calorimetric block. A separate field forms enthalpiometric analysis, which includes liquid flow-through calorimeters and thermometric titrations lying beyond this brief introduction. A thermometric procedure, which is quite similar to the convenient relaxation calorimetric method for measuring heat capacities, is the pulse-heating technique. The popular technique of differential thermal analysis (DTA) belongs among the indirect dynamic thermal techniques in which the change of the sample state is indicated by the temperature difference between the sample and geometrically similar inert reference held under identical experimental conditions. The advantage of this widely used method is a relatively easy verification of differences in the thermal regimes of both specimens, and the determination of zero traces during the test measurements, currently replaced by inbuilt computer programming.

Applicability of DTA and kinetic data reliability of non-isothermal crystallization of glasses

Abstract This article presents a survey of recent points of view on the principles of correct analysis of DTA measurements, and discusses the relationship between isothermal and non-isothermal kinetics and the applicability of individual methods of kinetic data evaluation. The thermophysics of the glassy state is also considered with regard to possible kinds of relaxation processes. The practical use and reliability of DTA in studying crystallization processes in glasses is discussed in detail.

Heat inertia and its role in thermal analysis

The history of the term inertia is mentioned, and the effect of the heat inertia phenomenon is found in equations derived by Newton and Tian as well as in works of Vold and Borchard and Daniels. The mathematical correction of heat inertia consequences can be portrayed using the both differential and/or integral forms. It has been confirmed by the effective rectification applied to DTA (and heat-flux DSC) responses reflecting well the need of heat inertia corrections as to attain the original shape of inserted rectangular heat pulse.

Is the original Kissinger equation obsolete today: not obsolete the entire non-isothermal kinetics?

Physical meaning of activation energy is analyzed from the viewpoint of non-isothermal kinetic evaluation. The term of heat inertia, meaning the degree of slowness with which the temperature of a body approaches that of its surroundings, is examined, and its impact on activation energy determination is discussed, which is particularly functional for a DTA peak kinetic appraisal. Impact of a process equilibrium background on kinetics is recollected as specifically important for Kissinger kinetic evaluation distinguishing competent case of glass cold crystallization on heating but unsuitable for melt crystallization on cooling without introducing additional thermodynamic terms. Parallel to non-Arrhenian kind of kinetics, an analogous model-free description is advocated accentuating a generalized approach by logistic functions.

Thermal analysis of Micro, Nano- and Non-Crystalline Materials

Thermal Analysis of Micro-, Nanoand Non-Crystalline Materials: Transformation, Crystallization, Kinetics and Thermodynamics complements and adds to volume 8 Glassy, Amorphous and Nano-Crystalline Materials by providing a coherent and authoritative overview of cutting-edge themes in the field of crystalline materials. In particular, the book focuses on reaction thermodynamics and kinetics applied to solid-state chemistry and thermal physics of various states of materials. In this volume the fundamental and historical aspects of phenomenological kinetics and the equilibrium background of processes are detailed. Crystal defects, nonstoichiometry and nano-crystallinity, reduced glass-transition temperatures and glass-forming coefficients are covered. The determination of the glass transition by DSC, the role of heat transfer and phase transition in DTA experiments, and the explanation of DTA/DSC methods used for the estimation of crystal nucleation are reviewed. Structural relaxation and viscosity behaviour in glass and associated relaxation kinetics are also examined, together with the influence of preliminary nucleation and coupled phenomenological kinetics nucleation on both the strongly curved surfaces and nano-particles. The book investigates crystallization of glassy and amorphous materials including oxides, chalcogenides and metals, non-parametric and fractal description of kinetics, disorder and dimensionality in nano-crystalline diamond. Moreover, it analyzes thermal analysis of waste glass batches, amorphous inorganic polysialates and bioactivity of hydroxyl groups as well as reaction kinetics and unconventional glass formability of oxide superconductors. Written by an international array of distinguished academics, Thermal Analysis of Micro-, Nanoand Non-Crystalline Materials: Transformation, Crystallization, Kinetics and Thermodynamics is a valuable resource to advanced undergraduates, postgraduates, and researches working in the fields of applied material thermodynamics, thermal analysis, thermophysical measurements and calorimetry.