Flash Sintering Of PZT And KNN Ceramics

PZT ceramics are one of the most widely used piezoelectric ceramic materials.The preparation of PZT ceramics by conventional solid phase sintering requires high temperature conditions and long-term heat preservation.During this process,Pb volatilization is severe,which causes the stoichiometric ratio of PZT ceramics to deviate,and seriously pollutes the environment and production equipment.In order to solve the problem of Pb volatilization,an effective and feasible method is to reduce the sintering temperature and sintering time of PZT ceramics.In addition,KNN ceramics is a lead-free piezoelectric ceramic material developed in recent years.Due to the volatilization of alkali metals K and Na at high temperatures,it is difficult to prepare dense KNN ceramics by conventional solid phase sintering methods.Therefore,a new sintering method has been developed to prepare KNN ceramics.In this research,a new type of electric field assisted sintering technology-flash sintering technology was used to prepare PZT and KNN ceramics.The flash sintering technology can greatly reduce the sintering temperature and sintering time,suppress the volatilization of Pb,K and Na elements effectively,thus preparing dense and pure phase PZT and KNN ceramics.The main research contents and results are as follows:?1?Pure phase PZT ceramic powder was prepared by sol-gel method,and then PZT green body was obtained by dry pressing,and then a DC electric field of 300-600 V/cm was applied to the green body under the action of electric field.The sintering behavior was studied in detail.The results show that the sample flashes when the electric field strength and the furnace temperature reach a certain value,that is,the conductivity of the sample increases sharply,accompanied with rapid sintering densification;the initial temperature of the flash burns reduced with the increase of the electric field strength.The dense PZT ceramics were successfully prepared by sintering at 538°C for 30 s under the action of an electric field of 600V/cm.The average grain size decreased with the increase of field strength.After the flash sintering,the current density has important effect on the sample density and grain size;the luminescence of the sample can be observed during the flash sintering;the actual temperature of the sample is estimated by the blackbody radiation model,and it is found that Joule heating does not fully explain the rapid densification of PZT ceramics during flash sintering.We believe that in addition to Joule heat,the large amount of defects promotes the sintering densification process.?2?NaNbO₃ and KNbO₃ ceramic powders with good dispersibility were prepared by molten salt method at 800°C,and then NaNbO₃ and KNbO₃ ceramic green bodies were obtained by dry pressing.The sintered densification process was carried out under the electric field of 400-700 V/cm.It is found that NaNbO₃ and KNbO₃ flash when the electric field strength and furnace temperature reach a certain value;the flash sintering technology can effectively inhibit the volatilization of Na₂O and K₂O at high temperature,and can produce dense and pure phase NaNbO₃ and KNbO₃ ceramics.Flash sintreing technology can play a unique role in the sintering preparation of ceramic materials containing volatile components.?3?Using NaNbO₃ and KNbO₃ ceramic powder as the starting material,the Na/K molar ratio is 1:1 and uniformly mixed and dry-pressed to obtain the NaNbO₃-KNbO₃ green body,and then a 400-700 V/cm DC electric field is applied for sintering.The results show that the NaNbO₃-KNbO₃ green body flashes at 950°C,921°C,897°C,810°C,and the pure phase and dense KNN ceramics are obtained in 30 s;as the increase of electric field strength,the temperature at which the sample flashes decreases;during the flash sintering process,the solid phase reaction and sintering occur simultaneously.