A study of the mechanism of isothermal decomposition of moist polycrystalline CaO2 . 2H2O2 samples by EPR and Raman spectroscopy

Upon the isothermal decomposition of crystalline samples of CaO 2 . 2H 2 O 2 with an admixture of an aqueous solution of hydrogen peroxide, dioxygen is evolved, the phase of calcium peroxide is formed, and an EPR signal ofthe O - . 2 radical anion with g x = g y = 2.00260 and g z = 2.00745 appears. The kinetics of the signal accumulation is close to the S-shaped kinetics of oxygen accumulation. The fact of self-acceleration of the reaction is supported by the time dependence of the ratio of the intensities of the v(O-O) bands caused by CaO 2 and CaO 2 . 2H 2 O 2 in the Raman spectrum. The kinetics of accumulation of stabilized radical anions O - . 2 reflects the process of accumulation of the CaO 2 phase with the radical anions incorporated into defects of its crystal structure. The half-conversion times derived from the EPR spectra and from the oxygen evolution are close to each other, and their temperature dependences obey the Arrhenius law with E = (65 ′ 5) kJ/mol. The decomposition is accelerated in the presence of a large water excess, and the accumulation of both the EPR signal and oxygen is described by a first-order kinetic curve rather than by an S-shaped curve. The data obtained support the previously suggested model of the two-stage autocatalytic decomposition of CaO 2 . 2H 2 O 2 with participation of water.