the conversion in thermodynamic result of the experimental signals provided by DTA and Company devices is not a "formula". In particular, the effect in the sample was modified by the samples thermal parameters, the flow of inert gas and the heat transfer from the furnace. The results are "particular" for each sample / device / varaible parameters. The study was clearly interesting and difficult. In the older days as 1950 the Calvet calorimeter working in isoterm furnsih deformed signals and the search of true dissipation was a partially solved problem using deconvolution in varaible systems. The effects of temperature programming induces more intrinsic difficulties. The method of "pushbutton" was not completely useful.
Pls. find below a brief discussion on TGA, DTA and Broido’s method to calculate thermodynamic parameters.
{A}TGA = Thermogravimetric Analysis; sometimes performed simultaneously with DTA/DSC, and sometimes separately.It measures accurately the sample mass versus T with high accuracy (typically AT LEAST 10 µg with 0.1 µg resolution) to see if the sample changes mass (loosing humidity of powders, decomposition of carbonates e.g. CaCO3 --> CaO + CO2, oxidation of metals e.g. 3 Fe + 2 O2 --> Fe3O4).Such data are used very often for phase diagram determination, kinetic of reactions, purity analysis, and much more.
{B}DTA = Differential Thermal Analysis: You heat a sample in a crucible and a reference in another (but identical) crucible simultaneously. The DTA signal is the temperature difference between sample and reference, typically plotted versus temperature T. If a 1st order phase transformation (also melting is such phase transformation!) occurs, the DTA signal makes a peak to the endothermic direction (= sample colder than reference). The "onset" of this peak is the transformation (melting) at T.
{C}Thermodynamic Parameters: Although the following three methods can be used to calculate the various thermodynamic parameters but Broido method is easy to apply
[i[Freeman–Carroll method
[ii]Sharp–Wentworth method
[iii] Broido’s method
Broido’s method is used to calculate thermodynamic parameters (kJ/mole) of compounds.
From TGA curves which are the plots of ln [l n (1/y)] versus 1000/T where [y] is the fraction of undecomposed complex at the temperature [T]. Then:
Eact= -2.303.R . slope of the curve.
∆ H= Eact- RTd.
∆ S=∆H/T-4.576 log T/K^/ -47.22.
∆G=∆ H-T. ∆ S.
R (gas constant), K^/= - ln [l n (1/y)];Td (temperature of decomosition).
Higer the value of Eact, the more is the thermal stability of the complex.
Entropy: A concept that is not a physical quantity
https://www.researchgate.net/publication/230554936_Entropy_A_concept_that_is_not_a_physical_quantity
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