Research On Preparation Of Nanocrystalline Zrc Powers

Taking ZrO₂,carbon black,Mg powers as the reactants,Firstly,the parameters of the ball milling-sintering process,inculuding ball to powder ratio milling time, singtering temperature,singtering time etc,was studied.Second,ZrC powders were produced by sintering directly and the combined ball milling-reaction sintering process respectively.Finally,the powders of ZrC were prepared by ball-milling and high temperature sintering,and were fourter milled,change of the small powder was studide during the ball milling process.The composition and morphology of the powder were observed by XRD and SEM.The results showed that:the efficiency of ball milling was good when ball to powder ratio was 40:1 and milling time was 72h.The raw powder was decreased continuously during the planetary ball milling process,which was helpful for inter-diffusion,but there was no generation of new phase,and ZrC was generated during sintering process.The powder after ball milling sintered at 1373K for 4h insulation product is more pure ZrC powder.The pure ZrC powders weren't obtained for a long time when the layed powder was sintered at 1373K.The unbleached powders of ZrC were prepared by ball milling and high-temperature sintering and were further milled.Found that the larger decline of ZrC peak strong was trend.After 48h ball milling,the ZrC peak strong wasn't change,at this time,the grain size of ZrC(111) was 13.3nm and the FWHM was increased by about 50%,the particle size has no significant change during ball milling process.During ball milling process,the raw powders had been deformated and welded and smashed,the high density defects were formatted in powder,the refined powder produced a large number of nano-grain boundary,these factors enable the system free energy to increase,the C and ZrO₂ could be to form solid solution so that reduced the distance of diffusion significantly and provided the power for diffusion.The phase of MgO was created simultaneously with ZrC phase during the sintering process when ZrO₂ was taken as the zirconium source.As a co-exited phase,MgO can not only prevent the reuniting of ZrC powder,but also restrain the crystal growing effectively, the impurity phases of MgO,Mg and ZrO₂ can be eliminated easily in acid washing process;active Zr element would be formed in the replacement reaction of Mg and ZrO₂,and the replacement reaction could release a few of heat,which make the ZrC phase can be formed in a lower temperature.