Measurement Conditions and Procedures for Isothermal Thermogravimetric Studies

As follows from the consideration of the third-law method (Chapter 4), its use for determining the reaction enthalpy requires estimation of the equivalent pressure Peqp of the gaseous product under the conditions of free-surface vaporization of the reactant. This, in turn, involves determination of the absolute rate of decomposition J (kg m?2 s?1) and, hence, of the effective surface area of the decomposing sample. This problem, as applied to crystals, powders, and melts, is discussed below.