Synthesis And Study On Structure Of Nano-hafnium Carbide Ceramic Powders

Hafnium carbide?HfC?is a refractory and non-stoichiometric transition metal carbide that has the highest melting point of known single compounds?3890^oC?.Hafmiun carbide has many wide application fields,such as high temperature refractory materials,composite materials,hard alloy,areospace field and field emission cathode materials due to its high strength,high hardness,low surface work function and high thermal and electeical conductivities.Therefore,how to prepare nano hafnium carbide is crucial for the preparation and application of hafnium carbide ceramics.In this paper,the nano hafnium carbide powders were synthesized by sol-gel combining high temperature process in vacuum furnace using citric acid and hafnium tetrachloride as raw materials.Through the control of the sol-gel process and the ratio of raw materials,the homogeneously mixed gel was obtained.Then,the pyrolysis products?HfO₂-C?were prepared by low temperature pyrolysis in tube furnace?Argon atmosphere?.The pyrolysis products were treated by ball milling,and HfO₂-C powders with good uniformity and small particle size were obtained.Finally,the nano hafnium carbide powders were quickly synthesized in the vacuum furnace.This paper studied the effects of different sol-gel processing methods and different carbon-to-hafnium ratio on pyrolysis process and HfC powder synthesis process,and the influence of pyrolysis process and ball milling treatment process of pyrolysis products on phase composition and microstructure of pyrolysis products.And the effect of high temperature heat treatment process on the synthesis of HfC powders.The results show that when the ratio of carbon and hafnium is 6,the pyrolysis temperature is 800 ^oC,the pyrolysis time is 60 min and the ball milling time is 4 h,the good homogeneous pyrolysis product?HfO₂-C?can be obtained.When the high temperature heat treatment temperature is 1700 ^oC and the holding time is 3 min,the pure phase HfC powders with good grain growth and average grain size of about500 nm can be prepared.The HfC particles have uniform size distribution,good dispersion and crystallization degree,and low oxygen content?0.692wt%?.Compared with the traditional synthesis method,the sol-gel combined with rapid heat treatment process has greatly reduced the temperature of high temperature heat treatment.By controlling the crystallization state and nucleation process of the prolysis products,HfO₂-C composite powders with high activity can be obtained.Uniform and pure HfC powders with fine particles can be synthesized at lower temperature.While spark plasma sintering?SPS?technology has a rapid heating and cooling process in a few minutes,it is difficult to achieve batch production.The effective discharge between particles produces local high temperature,which leads that the structure of HfC powders is not uniform and the oxygen content of HfC powders is relatively high.The method of synthesizing hafnium carbide powders in this paper is sample and can be used for the preparation of nano hafnium carbide powders on a large scale.