Flash Sintering Process And Mechanism Research Of La_1-xCa_xCrO₃ Ceramics

Lanthanum chromite（LaCrO₃）has a wide range of applications in many aspects due to its excellent electrochemical performance and high temperature stability.However,LaCrO₃ has the higher sintering temperature,and the volatilization of chromium occurs above 1000℃during the sintering process.This is why lanthanum chromate ceramics is difficult to densify and fabricate.In recent years,a technique called"flash sintering"has been proposed and applied to materials in various fields.Flash sintering has a series of characteristics:fast sintering rate,low sintering temperature,and short holding time etc.In this thesis,LaCrO₃ ceramics were prepared by flash sintering,and the mechanism of flash sintering behavior was investigated.In addition,interrelationship of parameters during flash sintering was explored by data analysis.Lanthanum chromate powder was prepared by the solid-phase method and the sol-gel method respectively.Experiments were conducted by self made flash-sintered device to investigate the flash sintering behavior under different electric field strengths.By changing the current density or the holding time at the constant electric field strength,the effect on flash-sintered samples was analyzed to obtain better quality lanthanum chromate ceramics.The sintering experiment was performed by means of constant voltage and increasing current,and the performance of the obtained material was compared with that of the traditional sintered material.The results show that as the electric field strength was increased from 15 V/cm to 35V/cm,the flash onset temperature of the sample decreased from 316℃ to 141℃.Especially,under the condition of electric field strength of 25 V/cm,increasing the current density from100 A/cm²to 140 A/cm²at constant holding time,or increasing the holding time of the flashing stage from 10 s to 300 s at constant current density,the densification of the lanthanum chromate material was increased,and the grain size was obviously increased.LaCrO₃ ceramics made by flash sintering method are not only superior to LaCrO₃ ceramics prepared by traditional sintering in terms of electrical conductivity,hardness and relative density,but also can avoid the volatilization of Cr element.Due to the high temperature during the flash sintering process,it is difficult to accurately measure it with the instrument.In this paper,the black body radiation theoretical model was used to estimate the sample temperature.The power generated by the current density under high electric field strength is high,and the estimated temperature is relatively high.It can be said that during flash sintering event,The rapid temperature rise inside the material is accomplished by the Joule heating effect.By calculating the heating rate in the flashing stage,it is concluded that the heating rate of the sample under different electric field strengths is 10²-10⁴℃/min.The rapid heating rate suppresses the growth of the grains and increases the driving force for densification.This is why flash sintering technology can be realized in a short time.Based on the study of flash sintering behavior,by changing the initial conditions and the electric field strength,this paper explore the inducement of flashing sintering.LaCrO₃ splines with different Ca doping amounts were prepared to change the initial electric conductivity,after that flash sintering experiments were performed under different electric field strengths to obtain the flash onset temperature at the corresponding case.At last,the regularity of the effect of the initial electric conductivity and the electric field strength on the flash point was analyzed.