Study on phase evolution during reaction synthesis of ultrafine (Ti, W, Mo, V)(CN)–Ni composite powders

Ultrafine (Ti, W, Mo, V)(CN)–Ni composite powders were synthesized from oxides by carbothermal reduction–nitridation at 1300 °C for 4 h. The phase evolution of the reaction products and the formation mechanism of (Ti, W, Mo, V)(CN) and Ni solid solution phases were investigated systemically at 600–1300 °C. The present study shows that the formation of NiWO4 and NiMoO4 has an important effect on the reduction of WO3, MoO3 and NiO phases. At higher synthesizing temperatures from 1000 to 1300 °C, the phase transformation of TiO2 complies with the following evolution sequence: TiO2 → Ti3O5 → TiCN. In addition, the differences in the intensity change between the (1 1 1) and (2 0 0) diffraction peaks of (Ti, W, Mo, V)(CN) can be used to characterize the phase evolution of (Ti, W, Mo, V)(CN) solid solution. Especially, it was first found that the dissolution and precipitation of W, Mo and V in Ni phase during powder synthesis are related intimately to the formation mechanism of (Ti, W, Mo, V)(CN) solid solution phase.