Investigation of the oxidation of skutterudite by thermal analysis

Abstract

The interaction of the mineral skutterudite (Co, Fe, Ni)As 3- x with oxygen was studied using differential thermal analysis. Thermogravimetry and X-ray diffraction were used as supplementary techniques. The oxidation was found to be a complex process which included the simultaneous dissociation of the mineral to lower arsenates and arsenic, and the oxidation of the products to arsenates and arsenic oxide vapour. The resulting mixture was composed of two arsenates (2CoO · As 2O 5 and 3CoO · As 2O 5). The relative amounts of each arsenate were dependent on the partial pressure of oxygen. There was no evidence of the formation of any cobalt oxide species. The thermal dissociation behaviour of skutterudite in an inert atmosphere was also examined by thermal analysis. There was a two-step release of arsenic vapour accompanied by the formation of the di- and monoarsenides. Synthetic CoAs 3 was also examined and the results were compared with those of the mineral.