TG and DTA studies on the thermal decomposition of KClO 4-α-Fe 2O 3 mixtures

Abstract

The catalytic effect of α-Fe 2O 3 on the thermal decomposition of KClO 4 was studied by TG and DTA methods. The ferric oxide was prepared from FeC 2O 4· 2H 2O by its thermal decomposition in air. DTA and TG curves showed that the addition of α-Fe 2O 3 led to an acceleration effect on the solid-state decomposition of KClO 4. The acceleration effect increased with a decrease in the preparation temperature and an increase in the mixing ratio of α-Fe 2O 3. From TG curves, the rate constant, k, was estimated by assuming a first-order rate law. An Arrhenius plot of yk showed a straight line, which had a sharp bend at the temperature, T B, characteristic of the respective α-Fe 2O 3 sample. It was suggested that the solid-state decomposition proceeded below T B and the liquid-state decomposition above T B. The fraction of KClO 4 decomposed in the solid state, α B, was estimated to be 0.03 for pure KClO 4. The α B value for the sample mixed with αFe 2O 3 prepared at 1000, 750 and 500°C was 0.065, 0.07 and 0.39, respectively. The increase in mixing ratio resulted in an increase in α B: α B = 0.06 for 1% α-Fe 2O 3, 0.16 for 10%, 0.26 for 30% and 0.39 for 50%. The activation energy of the solid-state decomposition, E s, of pure KClO 4 was 78.4 kcal mol −1 and those of KClO 4 + α-Fe 2O 3 mixtures were 53.6, 60.2 and 60.8 kcal mol −1 for the oxide prepared at 500, 750 and 1000°C, respectively. The change in mixing ratio of the oxide did not show any effect on E s. The activation energy of the liquid-state decomposition, E 1, for pure KClO 4 was 151.4 kcal mol −1 and those of KClO 4 + α-Fe 2O 3 mixtures were in the range 147.8–155.4 kcal mol −1 . Changes in the preparation temperature and the mixing ratio of α-Fe 2O 3 did not give a systematic influence on E 1.