The Investigation of the Oxidation Kinetics of Phosphotungsten Suboxide

Abstract

Dark blue colored phosphotungsten suboxide, which has the characteristics of phosphate tungsten oxide bronze, is formed during the thermal decomposition of ammonium phosphotungstate hydrate (APTH) in inert gas atmosphere. The aim of this study is to investigate the oxidation kinetics of phosphotungsten suboxide at isothermal conditions. Pellets prepared from phosphotungsten suboxide powder that were preheated at 1173 K temperature in inert gas atmosphere were used in the oxidation experiments. The sensitive measurement of weight increases was determined by the microelectronic microbalance. The oxidation reaction was carried out in the temperature range of 690 and 778 K and oxygen partial pressure range of 0.04 and 0.21 bar. The effects of gas flow rate, temperature, and oxygen partial pressure on the reaction rate were determined. The rate equation was derived by applying the ''Nucleation and Growth Kinetics'' model. The reaction rate was found to be of 0.94 order with respect to oxygen partial pressure, and the activation energy was 159 kJ mol )1 .

Complex Leaching Process of Scheelite in Hydrochloric and Phosphoric Solutions

“…Previous work suggested that the leaching process could be controlled by interfacial chemical reaction (Rodriguez et al, 20 Zhao et al, 21 Cem et al, 22 and Kalpakli et al 23 ). In this case, the kinetics equation of the liquid-solid reaction may be written as follows:…”