Thermal decomposition and dehydration of magnesium perchlorate hexahydrate

Abstract

The dehydration and thermal decomposition kinetics of magnesium perchlorate hexahydrate have been studied using thermograviinetric analysis, differential scanning calorimetry and x-ray diffraction techniques in conjunction with isothermal gas evolution vs. time measurements. For Mg(ClO 4) 2-6H 2O dehydration occurs in a complex manner in three distinct temperature regions between 148–197, 248–278 and 344–395°C. Each region is associated with the removal of 2H 2O. For Mg(ClO 4) 2 between 369 and 429°C the fractional decomposition, α, vs. time curves are sigmoidal and consist of an induction period, an acceleratory period followed by a short decay stage up to α $ ̃ 0.5 and a slow decay stage from α ~ 0.5 to completion. Above 417°C this long decay stage is replaced by an acceleratory stage. Activation energies for the induction, acceleratory, first and second decay stages are 78.6 ± 2.0, 65.3 ± 5.6, 48.9 ± 6.4 and 58.0 ± 11.1 kcal mol −1, respectively. The results suggest that decomposition proceeds via the formation of an intermediate, (MgO-MgClO 4), which dissociates at low temperatures and decomposes rapidly to MgO above 417°C. The principal effects of exposure to 60Co gamma rays prior to thermal decomposition is to reduce the induction period and increase the rate of the acceleratory period. These results have been interpreted as the introduction of additional nucleation sites by the irradiation and are consistent with previously reported data on irradiation effects on thermally decomposed inorganic solids.