Controllable syntheses of Mo5Si3 and Mo3Si by silicothermic reduction of MoS2 in the presence of lime

Abstract

Molybdenum silicides (Mo–Si) have attracted great interest owing to their good electrical conductivity, ultra-high melting point and well oxidation resistance. In this work, the controllable syntheses of Mo5Si3 and Mo3Si powders by silicothermic reduction of MoS2 in the presence of lime are studied for the first time. The internal mixture composed of MoS2 and Si is wrapped by sufficient CaO. After the reaction is finished, the synthesized molybdenum silicides can be easily separated from the desulfurization layer by peeling off the desulfurization product. The results show that Mo3Si and Mo5Si3 can be prepared at 1500 °C for the samples with the MoS2:Si molar ratio of 1:1.7 and 1:2.33, respectively. In addition, the results show that both SiS2 and SiS can be formed during the heating process. The thermodynamic analysis about the disproportionation reaction of SiS indicates that the existence of SiS2 depends on the partial pressure of SiS (PSiS) and temperature. Moreover, it is demonstrated that SiS2 is preferentially formed under low temperature conditions. As the temperature rises, it is much easier for SiS2 to react with Si to form SiS. Additionally, this work experimentally proves for the first time that SiS gas can directly reduce MoS2 to form MoSi2 and SiS2. Subsequently, the recovery of S in the desulfurization product was studied. S in MoS2 was first captured by CaO in the form of CaS (accompanied by Ca2SiO4 and Si). In order to solve this CaS containing desulfurization product which is detrimental to the environment, CaS in the desulfurization product is react with Fe2O3 and C to form FeS. This work provides new insights into the closed-loop capture and recovery of S in the process of extracting metals or metal compounds from sulfide ores.