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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]

The famous Kissinger's kinetic evaluation method (Anal. Chem. 1957) is examined with respect to the feasible impact of the individual quantities and assumptions involved, namely the model of reaction mechanism, f(a) (with the iso- and nonisothermal degrees of conversion, α and λ) the rate constant, k(T) (and associated activation energy, E), heating/cooling rate, P (supplementing additional thermodynamic term for the melt undercooling, ΔT) and above all, the association of the characteristic temperature, Tm , with the DTA peak apex. It is shown that the Kissinger's equation, in contrary to the results of Void (A nal. Chem. 1949), is omitting the term of heat inertia arising from the true balance of heat fluxes. The absence of this term skews the evaluated values of activation energies. [ABSTRACT FROM AUTHOR]

The equations for heat capacity measured under isodynamical conditions (fixed activity of a single component) are derived for partly open systems exchanging one component with the surroundings while keeping the contents of all other components constant. Compared to conventional isobaric (and isoplethal) heat capacity of a strictly stoichiometric phase, the isodynamical heat capacity of a nonstoichiometric phase is found to involve two additional terms-the saturation contribution due to incorporation (or release) of the free component and the contribution due to deviation from stoichiometry reflecting a different number of the involved phonon modes (due to different free component content) and in some cases a variation of free component incorporation mechanism. [ABSTRACT FROM AUTHOR]

The re-calcination of commercial metakaolin was carried out and structural changes were observed in relation to pozzolanic activity and specific surface area in temperature range 500–1000 °C. The re-calcined metakaolins were characterized by XRD, SAXS, SEM, TEM in relation to structure state and reactivity variation based on Chapelle test. The re-calcination led to ∼40% rise of reactivity in the range of 650–800 °C. Considering the structural changes the mullite phase crystallization and partial sintering of the particles caused rapid decreasing of reactivity. SAXS spectrum revealed the formation of new phase already at annealing temperature 800 °C. [ABSTRACT FROM AUTHOR]