Thermal decomposition and dehydration of sodium perchlorate monohydrate

Abstract

The dehydration of sodium perchlorate monohydrate proceeds in two stages corresponding to the removal of 0.2H 2O and 0.8H 2O per mol at 60 °C and 150 °C, respectively. The thermal decomposition at 490 °C is preceded by a phase transformation at 309 °C (orthorhombic → cubic) and melting at 472 °C. Between 490 °C and 520 °C the fractional decomposition (α) vs. time ( t) curves for molten NaClO 4 in vacuum are sigmoidal indicating an autocatalytic process. The α, t isothermal data are best fitted by a first order autocatalytic equation ln[(α + k 2/ k 1)/(1 − α)] = ( k 1 + k 2) t + ln( k 2/ k 1) over the temperature range 490–520 ° C, where k 1 is the autocatalytic rate constant and k 2 a first order rate constant. The activation energies for the two simultaneous occurring processes are 289.3 ∓ 5.4 and 208.9 ∓ 3.8 kJ mol , respectively. Gamma irradiation up to doses of 7.5 · 10 7 rad produced no observable effect on the subsequent thermal decomposition. The final solid product of the decomposition is sodium chloride in all cases.