Study on the preparation of molybdenum silicides by the silicothermic reduction of MoS₂

In this paper, a novel process about the silicothermic reduction of molybdenum disulfide was proposed to prepare molybdenum silicides. This new method has a short process, which is beneficial for energy saving, environmental protection and cost reduction relative to the traditional methods by using pure molybdenum and silicon as the raw materials. It was found that the phase compositions and microstructures of products were greatly influenced by the molar ratio of Si to MoS₂ and temperature. From the experimental results, it was concluded that MoSi₂, Mo₅Si₃ and Mo₃Si can be prepared when the temperature was above 1100 °C, 1300 °C and 1500 °C, and the Si/MoS₂ molar ratio was 4, 2.6 and 7/3, respectively. When the Si/MoS₂ molar ratio was less than 4 and the temperature was below 1100 °C, only one Mo-Si compound (MoSi₂) was generated; while above 1200 °C, the excessive MoS₂ could react with MoSi₂ to generate Mo₅Si₃, but Mo₅Si₃ can't react with excessive MoS₂ below 1300 °C; until above 1400 °C, Mo₅Si₃ and MoS₂ can react to generate Mo₃Si. However, even at 1600 °C, excessive MoS₂ couldn't react with Mo₃Si but can be decomposed. Besides molybdenum silicides, other products SiS or SiS₂ can also be generated. SiS could escape from sample at 1100 °C in the form of gas while SiS₂ couldn't. Both the increases of temperature and molar ratio of Si to MoSi₂ were beneficial for the decrease of the residual sulfur content in the final products. From the experimental results, it was found that as increasing the temperature or the molar ratio of Si to MoS₂ from 7/3 to 4, the grain size of products increased and the sintering phenomenon among grains was more and more obvious. - Highlights: • MoSi₂, Mo₅Si₃ and Mo₃Si were prepared by silicothermic reduction of MoSi₂. • SiS as a gas by-product can be separated from molybdenum disulfide above 1100 °C. • Increases in temperature and Si/MoS₂ ratio were beneficial for removing sulfur. • Sintering phenomenon became more obvious as increasing Si/MoS₂ molar ratio.