Hydrogen reduction of industrial nickel oxides

Thermal gravimetric analysis (TGA) was used to investigate the reduction behaviour of three industrial nickel oxides. Both isothermal and non-isothermal reduction experiments were carried out. Due to the low BET surface area and relative dense structure of the Goro NiO, it was reduced at a slower rate than both Tokyo NiO and Sinter 75 which were the two other nickel oxides investigated. In the temperature range from 400 to 600 degrees C, the rate of reduction increased with increasing temperature and increasing hydrogen pressure. Microscopic analysis showed that in this temperature range, the reaction followed the topochemical model. When the temperature was increased to 700 and 800 degrees C, the reduction rate decreased noticeably. Microscopy showed inner bands of metallization inside the outer metallic rim seen at lower temperatures indicating partial blockage of the interface between the reacted and unreacted NiO core.