Kinetics differential thermal analysis

Kissinger H E 1957 Reaction kinetics in differential thermal analysis Ana/. Chem. 29 1702... 

Crystallization kinetics have been studied by differential thermal analysis (92,94,95). The heat of fusion of the crystalline phase is approximately 96 kj/kg (23 kcal/mol), and the activation energy for crystallization is 104 kj/mol (25 kcal/mol). The extent of crystallinity may be calculated from the density of amorphous polymer (d = 1.23), and the crystalline density (d = 1.35). Using this method, polymer prepared at —40° C melts at 73°C and is 38% crystalline. Polymer made at +40° C melts at 45°C and is about 12% crystalline. 

Differential thermal analysis (DTA) Onset temperature of exotherms, heat of reaction, Cp, approximate kinetics... 

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

Kissinger, H. E., "Reaction Kinetics in Differential Thermal Analysis," Anal. Chem., 29,1702 (1957). 

Katz, J. R. and Van Itallie, T. B. (1930). Abhandlugen zur physikalischen chemie der starke und der brotbereitung. Zeitschrift fur physikalische chemie. Abteilung A. A150,90-99. Kissinger, H. E. (1957). Reaction kinetics in differential thermal analysis. Analytical Chemistry. 

The temperature of maximum transformation rate is easily determined using either of two similar techniques called differential scanning calorimetry (DSC) or differential thermal analysis (DTA). These techniques are extremely useful in the kinetic study of both isothermal and nonisothermal phase transformations. 

The common methods of investigating the kinetics of explosive reactions are differential thermal analysis, thermogravimetric analysis and differential scanning calorimetry. 

Any compd or mixt whose heat of formation is smaller by 500 J/g (or more) than the sum of the heats of formation of its reaction products must be regarded with suspicion and handled with more than usual care. The hazards involved in working with a potentially expl system are directly proportional to the amount and to the rate of energy release. Because the reaction kinetics cannot be predicted, the propensity of a new system for expl reaction must be determined. The sensitivity of the system can be evaluated by means of impact, friction, shock and electrostatic discharge. Appropriate methods are reviewed in the Experimental and Hazard Assessment section of this article. Sensitivity to heat or elevated temp may be evaluated by use of differential thermal analysis (DTA)... 

TATB has excellent thermal stability. Exothermal decompn can be observed at about 330° in a differential thermal analysis (DTA) run at a heating rate of 10°/min, Arrhenius expression kinetic constants for the most observable condensed-phase decompn reaction are E=59.9kcal/mole and (the pre-exponential) Z= 3.18 x 1019sec I (Ref 34)... 

In a more recent study (Ref 16), Merzhanov s school used high dilution with inert materials to study the kinetics of exothermic reactions over a wider temp range than was previously feasible. Dilution prevents self-ignition of the studied sample and also minimizes temp gradients. The method used is an adaptation of DTA (differential thermal analysis) in which temp... 

Differential Thermal Analysis and Reaction Kinetics for nth Order Reactions , AnalChem 49 (1977), 998 51) K. Kishore, Thermal De-... 

Several methods have been developed over the years for the thermochemical characterisation of compounds and reactions, and the assessment of thermal safety, e.g. differential scanning calorimetry (DSC) and differential thermal analysis (DTA), as well as reaction calorimetry. Of these, reaction calorimetry is the most directly applicable to reaction characterisation and, as the heat-flow rate during a chemical reaction is proportional to the rate of conversion, it represents a differential kinetic analysis technique. Consequently, calorimetry is uniquely able to provide kinetics as well as thermodynamics information to be exploited in mechanism studies as well as process development and optimisation [21]. 

Borchardt, H.). and Daniels, F. (1975) The application of differential thermal analysis to the study of reaction kinetics, Journal of American Chemical Society, 79, 41-6. 

H. Kissinger, Reaction kinetics in differential thermal analysis, Analytical Chem. 29 (1957) 1702-1706. 

Blumberg, A. A. Differential Thermal Analysis and Heterogenous Kinetics The Reaction of Vitreous Silica with Hydrofluoric Acid. J. Phys. Chem. 63, 1129 (1959). 

Thermal decomposition kinetics of complexes have been studied by thermogravimetry and differential thermal analysis in order to understand the thermal stability and the mechanism... 

The microanalytical methods of differential thermal analysis, differential scanning calorimetry, accelerating rate calorimetry, and thermomechanical analysis provide important information about chemical kinetics and thermodynamics but do not provide information about large-scale effects. Although a number of techniques are available for kinetics and heat-of-reaction analysis, a major advantage to heat flow calorimetry is that it better simulates the effects of real process conditions, such as degree of mixing or heat transfer coefficients. 

The fact that flame retardants and salts alter the kinetics, as well as the products, of the pyrolysis reactions is confirmed by the investigations of Tang and Neil involving thermogravimetric and differential thermal analysis methods (see Section 11,6 p. 446). These investi-... 

Besides the isothermal kinetic methods mentioned above, by which activation parameters are determined by measuring the rate of dioxetane disappearance at several constant temperatures, a number of nonisothermal techniques have been developed. These include the temperature jump method, in which the kinetic run is initiated at a particular constant initial temperature (r,-), the temperature is suddenly raised or dropped by about 15°C, and is then held constant at the final temperature (7y), under conditions at which dioxetane consumption is negligible. Of course, for such nonisothermal kinetics only the chemiluminescence techniques are sufficiently sensitive to determine the rates. Since the intensities /, at 7 ,- and If at Tf correspond to the instantaneous rates at constant dioxetane concentration, the rate constants A ,- and kf are known directly. From the temperature dependence (Eq. 32), the activation energies are readily calculated. This convenient method has been modified to allow a step-function analysis at various temperatures and a continuous temperature variation.Finally, differential thermal analysis has been employed to assess the activation parameters in contrast to the above nonisothermal kinetic methods, in the latter the dioxetane is completely consumed and, thus, instead of initial rates, one measures total rates. 

Analytical pyrolysis is considered somehow apart from the other thermoanalytical techniques such as thermometry, calorimetry, thermogravimetry, differential thermal analysis, etc. In contrast to analytical pyrolysis, thermoanalytical techniques are not usually concerned with the chemical nature of the reaction products during heating. Certainly, some overlap exists between analytical pyrolysis and other thermoanalytical techniques. The study of the kinetics of the pyrolysis process, for example, was found to provide useful information about the samples and it is part of a series of pyrolytic studies (e.g. [6-8]). Also, during thermoanalytical measurements, analysis of the decomposition products can be done. This does not transform that particular thermoanalysis into analytical pyrolysis (e.g. [9]). A typical example is the analysis of the gases evolved during a chemical reaction as a function of temperature, known as EGA (evolved gas analysis). 

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