Electrolytic Synthesis Of Zirconium Silicide,Zirconium Carbide And Their Composites In Molten Salt

With the rapid development of Chinese zirconium industry,the utilization of zirconium ore through a high efficient,cost-effective and environment friendly way and the development of the new process to produce zirconium,zirconium-beraing alloys and other zirconium-based top products are significant to the adjustment of zirconium industry structure and the sustainable development of zirconium material in the long term.At present,varieties and quantities of high-end products in China are too few,which mainly rely on import.Therefore,it is necessary to find an economical,green,efficient method to produce top products in the zirconium metallurgy industry and realize the high efficient utilization of zirconium resource.In this study,the electrochemical reduction was carried out for preparation of Zr-Si intermetallics,ZrC,ZrC/ZrSi nanocomposites and ZrC/FeSi composites directly from low-cost ZrSiO4 and ZrO2 in molten salt.In addition,the process parameters and the possible reaction pathway were also investigated in detail.The objective was to release zirconium from the silicate type zirconium ore efficiently and prepare Zr-beraing materials in a simple,environment friendly process.The main results are summarized as following:Zr-Si intermetallics with grain size in the range of several hundred nanometers are controllably prepared by the electrochemical reduction of ZrSiO4 and ZrSiO4/SiO2 mixed pellets at 3.1 V and 800 ? for 15 h in molten CaCl2-NaCl.The final product composition can be controlled by adjusting the molar ratio of Si to Zr containing in the starting material,and ZrSi,ZrSi2 and their mixture are obtained by the process.The reduction pathway of ZrSiO4 and SiO2 to Zr-Si intermetallics undergoes several calcium-containing intermediate phases,such as CaSiO3,Ca2SiO4,and calcia-stabilized zirconia(CSZ).Ultrafine ZrC powders with the diameter of 50 nm are synthesized by the electrochemical reduction from ZrO2 and carbon at 3.1 V under 800 ? for 20 h in molten CaCl2-NaCl.The reduction pathway of ZrO2 and carbon to ZrC undergoes several intermediate phases,such as CaZrO3 and ZrCxO1-x.Carbides are obtained by the synergetic process of electrochemical reduction and carbonization.ZrC/ZrSi nanocomposite powders are in-situ synthesized from ZrSiO4 and carbon through a one-pot electrolytic process at 2.8-3.1 V and 850 ? for 20 h in molten CaCl2-NaCl.The reduction pathway of ZrSiO4 and carbon to ZrC/ZrSi composite powders involves the decomposition of ZrSiO4 by CaO,the oxygen removal and in-situ carbiding.During the electrochemical reduction process,ZrSi is preferentially formed,then ZrC is in-situ generated and ZrC/ZrSi composites are obtained.The ratio of carbide phases to metallic phases in the final product can be controlled by adjusting the amount of carbon in the staring materials.The morphology and structure of ZrC/ZrSi composites can be controlled by changing the electrolytic parameters.The sample fabricated at 3.1 V consists of composite nanoparticles,involving the ZrSi matrix reinforced with the nano-sized ZrC particles.While the sample formed by electrolysis at 2.8 V is composed of nano fibers,which is featured by the ZrSi single crystal core and ZrC polycrystalline outer coat.ZrC/FeSi composite powders are in-situ synthesized from ZrSiO4,Fe2O3 and carbon by the electrochemical reduction at 3.1 V and 850 ? for 20 h in molten CaC12-NaCl.ZrSiO4 was decomposed into calcium-containing intermediate compounds(CaSiO3,CSZ and CaZrO3)by combination with calcium oxide during the electrochemical reduction.Then,the calcium-containing intermediate compounds are reduced into Zr and Si.Finally,Zr combines with C and form ZrC,while Si alloys with Fe to form FeSi.