Search

The development of instrumentation has allowed thermal analysis to become a widely used method not only in calorimetry but also in the field of non-isothermal kinetics that, however, provides a simplified philosophy of measurements. From the beginning, a methodology is used describing the course of reaction in a simplified temperature regime measured in an inert sample. In a most common case of DTA, the degree of reaction is subtracted from the partial areas of the as-cast peak in the unified mode of the peak linear background. Usually, the effect of thermal inertia, resulting from the reality of heat transfer and changing the peak background to a non-linear s-shaped form, is not incorporated. Therefore, the question of whether or not to include this effect of thermal inertia has become a current underlying problem of thermo-analytical kinetics. The analysis of the rectangular input heat pulses and their DTA responding fundamentally point to the need to include it thus becoming essential and not negligible. In the case of parallel evaluations, the effect of inertia can be partially compensated for each other such as in the Kissinger evaluation method. The study presents a broad overview of the thermo-analytical methodology used and points to the often-neglected literature. However, standard mainstream kinetics procedures need be fixed, and an improved solution found to account for the effect of heat transfer and dissipation, which is becoming the focus of thermal analysis methods of future and also the intention of this review.

In the field of thermoanalytical kinetics, which is widely used, basic questions arise regarding a possible description of the effect of heat transfer and subsequent thermal inertia. Current practice still uses a simplified interpretation of directly measured data for an inert sample at a constant temperature rise to describe the studied reaction, which leads to a simplified reaction conversion ratio, which is further used for various mathematical processing. The analysis of the introduced rectangular heat pulses and their indication by DTA clearly shows that the effect of thermal inertia is fundamental and not negligible. This is, after all, known from calorimetry, where the integral constant of inertia has historically been used to calibrate the descending temperature, but it cannot generally be applied to the whole temperature process due to its nonlinearity. In the case of parallel processing, for example by gradually increasing the heating rate, the effect of thermal inertia can be partially compensated for each other which have yet to be confirmed. However, for the kinetic analysis of a single peak, it is necessary to adapt to the effect of the thermal delay due to thermal inertia, which, similarly to the measured enthalpy, is tied to the sample size. Of course, it will be up to the researcher to find a solution that also includes the effect of heat transfer and dissipation, which should become the main principle of thermoanalytical methods of the future, as shown by current examples combining thermal processes with their specific kinetics. [ABSTRACT FROM AUTHOR]

This paper critically analyzes the traditional method of kinetic determination of activation energy by sectioning the recorded differential thermal analysis peak area. This procedure is incorrect because it misses the impact of thermal inertia, which changes the shape of the peak's base line from straight to s‐shape. This effect has been known since the Newton cooling law, but the resulting errors persist to be interwoven into all the kinetic methods based on nonisothermal thermoanalytical measurements. Relating to calorimetry, it is necessary here because heat inertia has become a standard part of heat determination via using the Tian historical equation. The role and impact of heat inertia is discussed and analyzed in detail. [ABSTRACT FROM AUTHOR]

Although the Newton cooling law has been known for three centuries, the nonisothermal kineticists are still ignoring its consequent heat inertia effect when calculating widely cited activation energies. The kinetic background is revised. The features and significances of heat transfer are analyzed and shown in its historical occurrence. DTA equation is revised as well as the Tian calorimetric relation showing the necessity of heat inertia inclusion. The authority of traditional practice of kinetic analysis is revealed and discussed in more detail including the problems and perspectives of nontraditional ideas regarding the mainstream. [ABSTRACT FROM AUTHOR]

Instead a classical obituary the rich scientific results of Pavel Holba are survived emphasizing his contribution to the underpinning and determination of hyperfree energy and associated definition of novel terms of phtochability and plutability as well as the characterization of equilibrium background of processes and its impact on the kinetic data evaluation. Not less important are his findings on the resolution and impact of heat inertia as an often forgotten effect influential in DTA kinetics which is known since the 1701 Newton cooling law. His attempts to improve the interrelation between thermodynamics and kinetics are underlined. [ABSTRACT FROM AUTHOR]

The equilibrium (thermodynamic) temperature of a body is defined by zeroth law of thermodynamics as a quantity obtained by thermometer as a result of thermal equilibrium between the body and the thermometer. However, the term temperature is also used for description of any instantaneous thermal state during processes where no thermal equilibrium is reached. The proposal of Tykodi to divide thermal science into three branches has been modified to express the dependence of temperature on time and position inside a system. The three branches have been called thermostatics (equilibrium thermodynamics), thermostatics (thermodynamics of steady = stationary states) and thermokinetics (thermal science dealing with unsteady-non-stationary states). Equilibrium temperature is used only at thermostatics. For other branches of thermal science where the Newton cooling law and/or any of both Fourier laws are applied, no equilibrium temperature with respect to zeroth law is expected. Thermal analysis studying unsteady states (temperature is a function of time t as well as of space coordinates x) should be subject of thermokinetics, and the appropriate kinetic models should include the local temperature changes evoked by self-cooling or self-heating due to process running inside sample. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The famous Kissinger's kinetic evaluation method (Anal. Chem. 1957) is examined with respect to: a) the relation between the DTA signal θ ( t) and the reaction rate r( t) ≡ dα/d t; b) the requirements on reaction mechanism model f(α); and c) the relation of starting kinetic equation to the equilibrium behavior of sample under study. Distorting effect of heat inertia and difference between the temperature T of extreme DTA deviation and the temperature T at which the reaction rate is maximal are revealed. The kinetic equations respecting the influence of equilibrium temperature T, especially fusion temperature T, are tested as bases for a modified Kissinger-like evaluation of kinetics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]