Dehydration of solids in different modes as a proof of their primary congruent dissociative vaporization

Abstract

The main purpose of this paper is to prove the applicability of the mechanism of congruent dissociative vaporization (CDV) to the solid-state decomposition kinetics through the comparison of the fundamental theoretical relationship Ei/Ee=(a+b)/a resulted from this mechanism with experiment. It has been shown that the ratios of Ei and Ee parameters of the Arrhenius equation measured in the isobaric and equimolar modes (in the presence and absence of H2O vapour) for 22 reactants with the general formula aSalt⋅bH2O or aOxide⋅bH2O are in agreement with the values of (a+b)/a. The relative standard deviation is only 17% and the correlation coefficient is close to 0.99. A probability of accidental correlation for all set of the E parameters taken from the literature is lower than 4⋅10–16 . This strongly supports the validity of the CDV mechanism. The problem of stability of polyatomic molecules of inorganic salts in the gaseous state, which are the primary decomposition products of crystalline hydrates, was also discussed on the basis of recent mass spectroscopy studies. It was concluded that any doubts in the applicability of the CDV mechanism as a general mechanism of solid-state decomposition reactions are unsound.