Effect of metal oxide catalysts on thermal decomposition of potassium bromate

Abstract

Kinetic studies on the effect of metal oxide catalysts, (25 ~o w/w) such as CrzO3, CuO, MnO2, AI~O3 and TiO~, on the thermal decomposition of KBrO3 have been carried out. The kinetic parameters of the catalysed and uncatalysed decompositions were calculated by the Freeman--Carroll, Coats--Redfern and Horowitz--Metzger methods. It has been found that A1203 is almost as good a catalyst as any other oxide used unlike in the thermal decomposition of KC103. In the case of TiO, there was an increase in the activation energy of decomposition. Of the other oxides Cr203 underwent reaction and was converted to dichromate and so the parameters of the reaction were not calculated. The effect of varying amotints of A1203 on the thermal decomposition was also studied.The oxysalts of halogens such as KC103, KC104 etc., are widely used in explosives and pyrotechnics. As such, studies on the thermal decomposition and high temperature properties of oxyhalogen salts are important and a review on this has recently been published [1 ]. The effect of metal oxide catalysts on the thermal decomposition of KC103 was investigated by Rudolff and Freeman by TG and DTA [2], but the extent of catalysis was not interpreted in terms of kinetic parameters of the reaction. Bancroft and Gesser [3] studied thermal decomposition of several bromates by thermobarogravimetry. So far there seems to be no report on the effect of metal oxides on the thermal decomposition of KBrO3, and this prompted us to investigate the work detailed below. In this paper the kinetics of the catalysed and uncatalysed thermal decomposition of KBrO 3 have been studied by thermogravimetry. The oxides used as catalysts are Cr203, CuO, MnO2, AlzO3 and TiO2. Of these Cr203 underwent reaction and so the kinetics was not followed. The kinetic parameters were calculated by three well known methods viz., the differential method of Freeman and Carroll [4], the integral method of Coats and Redfern [5] and the approximation method of Horowitz and Metzger [6]. All the oxides except TiO2 behaved similarly with respect to the decrease in energy of activation. The effect of A1203 was rather unexpected as it was unlike the case of KC103.

Effects of admixtures of potassium bromide on the thermal decomposition of potassium bromate

“…It is evident that the change is associated with complete melting, for at a higher temperature a lower concentration of bromide ions is sufficient to produce melting than that required at a lower temperature [4]. The TG and DTA show that the melting point of potassium bromate is lowered from 703 K to 673 K [5,6], where it also starts to decompose.…”