Aluminothermic reduction of zinc sulfide induced ball milling-Effect of ZnS:Al molar ratio on the raw mixture

Mixtures of zinc sulfide and aluminum (ZnS-Al) with different stoichiometric molar ratios were prepared. Then the mixtures were milled in a planetary ball mill with different times. The results indicated that aluminothermic reduction of zinc sulfide progress gradually during ball milling and the reaction does not complete after 10 hours milling. The traces of mechanically induced self - sustaining reaction (MSR) did not observe in the zinc sulfide-aluminum mixtures induced ball milling. The 3 hours milled mixtures of ZnS-Al were heated isothermally under flow of argon atmosphere for one hour. The XRD analysis of the isothermal heated samples indicated that hexagonal zinc aluminum sulfide, (ZnAl2S4), is the major product. The spinel phase (ZnAl2S4) was well crystallized after isothermal heating of 3 hours milled sample in the zinc sulfide-aluminum mixtures with molar ratio of 4:2. However, no traces of aluminum sulfide phase observed in the XRD patterns of milled mixture ZnS-Al with molar ratio of 3:2. The possibility formation of product phases was explained using HSC software of thermodynamic assessments and phase diagram of ZnS-Al2S3 system. The results showed that addition of aluminum more than of stoichiometric ratio has negative effect on the crystallization of ZnAl2S4 spinel phase. Finally, the results of isothermal heated samples showed that Al/Zn ratio and molar ratio of zinc sulfide-aluminum in the initial mixtures have significant effect on the formation of zinc aluminum sulfide (ZnAl2S4) phase.