The Preparation Of MgTiO₃ And Y₃Al₅O₁₂ Ceramic Nanopowders And The Study Of Electric Field-assisted Sintering

Magnesium titanate（MgTiO₃）and yttrium aluminum garnet（Y3Al5O12,YAG）are important functional ceramic materials,which are widely used in the electrical,laser,radar and other high-tech fields.However,the sintering of MgTiO₃ and YAG ceramics requires high temperature（1600 ℃）for a long time,which not only wastes energy consumption,but also deteriorates its physicochemical properties.Therefore,it is important to prepare MgTiO₃ and YAG ceramics at a relatively low temperature.In order to realize the low temperature sintering of MgTiO₃ and YAG ceramics,the MgTiO₃ and YAG powders were prepared by polyacrylamide gel method,and then the sintering behavior under the aid of electric field was discussed.MgTiO₃ nanopowders were prepared via polyacrylamide gel method by using Ti（SO4）2,Mg（NO3）2,acrylamide,N,N’-methylenebisacrylamide and ammonium persulfate as raw materials.The effects of water content,acrylamide content,Mg/Ti molar ratio and calcination temperature on the phase transition process of MgTiO₃ were studied.The powders were analyzed and characterized by XRD,SEM and TG-DSC.The experimental results show that the particle size of the powder decreases with the increase of acrylamide content.When the molar ratio of Mg/Ti > 1 and c（AM）> 2 mol/L in the precursor solution,the dry gel is homogeneous and has no pore structure,and its surface is precipitated without salt particles.When the calcination temperature reaches 800 ℃,the MgTiO₃ powder with good crystallinity and pure phase can be obtained,and the average particle size is 61 nm.When the electric field intensity applied to the specimen does not change,the current density suddenly increases at a certain temperature as the sintering temperature gradually increases,and the specimen shrinks sharply.When the electric field intensity is 500 V/cm,600 V/cm,700 V/cm and 800 V/cm respectively,the sintering temperature corresponding to the current mutation is 1241 ℃,1228 ℃,1154 ℃ and 1128 ℃.That is,with the electric field strength increases,the sintering temperature corresponding to the current mutation gradually decreases.The study also found that with the increase of the electric field intensity,the power dissipated on the specimen increases,and the estimated temperature of the specimen is also increased according to Joule heat.In contrast,the sintering temperature and sintering time are gradually reduced.YAG nanopowders were prepared via polyacrylamide gel method by using Y（NO3）3·6H2O,Al（NO3）3·9H2O,acrylamide,N,N’-methylenebisacrylamide and ammonium persulfate as raw materials.The decomposition process,YAG phase transition process and powder were analyzed and characterized by thermogravimetric-differential scanning calorimetry（TG-DSC）,X-ray diffraction（XRD）and transmission electron microscopy（TEM）respectively.The results show that the organic matter in the gel is completely decomposed at 632 ℃.The YAG phase is formed when the calcination temperature is 885 ℃,and YAG pure phase can be obtained when the calcination temperature is 900 ℃.At the same time,it is found that the increase of acrylamide content will affect the phase transition of YAG and decrease the phase transition temperature of YAG.According to the TEM analysis,when the molar ratio of AM/Al is 120:1 and the specimens are calcined at 900 ℃,1000 ℃ and 1200 ℃ for 2 h respectively,the average particle size of the obtained powders is 35 nm,63 nm,113 nm.YAG billet in the electric field assisted sintering process,to keep the specimen electric field strength unchanged,with the sintering temperature gradually increased,the current density will also increase dramatically.When the electric field intensity is 500 V/cm,600 V/cm,700 V/cm and 800 V/cm,the sintering temperature corresponding to the current mutation is 1356 ℃,1334 ℃,1293 ℃ and 1242 ℃.That is,with the increase of electric field intensity,the sintering temperature corresponding to the current mutation gradually decreases.In addition,as the electric field intensity increases,the dissipated electric power（Joule heat）increases,and the actual temperature of the specimen is also increased.