Preparation And Properties Of Lanthanum Zirconate Based Ceramic Powder

Lanthanum zirconate(La2Zr2O7,LZO)with calcite structure is a binary oxide with high melting point(2300?),good high temperature stability,high catalytic activity,excellention conductivity,low sintering rate and thermal conductivity.It is considered to be one of the most potential coating materials in the 21st century.However,the thermal expansion coefficient is lower than that of YSZ,which limits it to be used as coating material.Therefore,it is of great value to improve the thermal expansion coefficient of lanthanum zirconate.In this paper,lanthanum zirconate based ceramic powder with calcite structure was prepared by chemical coprecipitation and solid phase sintering.The effects of Ce,Sm and Mg elements on the thermal expansion coefficient of ceramic powder were investigated,and the effects of pH value and holding time of cationic concentration(c),reaction temperature(T),solution on the preparation process of co-precipitation were investigated.The parameters of coprecipitation are as follows:c?1mol/L,T=60?,t=30 min,pH?10.The effects of Ce,Sm and Mg elements on the crystal structure and thermal expansion coefficient of calcined lanthanum zirconate based ceramic powder were studied by means of(XRD),scanning electron microscope(SEM),Raman spectrum(Raman),infrared spectrum(FTIR)and other means of X-ray diffraction analysis.The main research contents are as follows:The optimum conditions for the preparation of La2-2xCexMg0.3Zr2O7(x=0,0.1,0.2,0.3,0.4)ceramic powder by coprecipitation-solid-phase sintering were determined:T=1200?,x=0.3.XRD analysis of the powder shows that the ceramic powder obtained from the La2-2xCexMgxZr2O7 precursor kept at 1200? for 3h has a pyrochlore structure and contains free-state Mg elements in the form of oxides.Powder raman,ftir data showed that:1200?ceramic powder changed from disordered fluorite structure to pyrochlore structure.At 1200?,The thermal expansion coefficient of La1.4Ce0.3Mg0.3Zr2O7 is the largest,which is 9.86×10-6/K,compared with La2Zr2O7,the thermal expansion coefficient is increased by 3%.The optimum conditions for the preparation of La2-2xCexMg0.3(Zr0.7Ce0.3)2O7(x=0.0.1,0.2,0.3,0.4)ceramic powder by coprecipitation-solid-phase sintering were determined:T=1200?,x=0.3.Powder raman,ftir data show that:when x?0.4,ceramic powder begins to change from pyrochlore structure to fluorite structure,and pyrochlore has a higher coefficient of thermal expansion than fluorite structure;At 1200?,La1.4Ce0.3Mg0.3(Zr0.7Ce0.3)2O7 has the largest coefficient of thermal expansion,which is 10.39×10-6/K,compared with La2Zr2O7,the thermal expansiol coefficient is increased by 8%.The optimum conditions for the preparation of La2-xSmx(Zr0.7Ce0.3)2O7(x=0,0.1,0.2,0.3,0.4)ceramic powder by coprecipitation and solid phase sintering were determined as follows:T=1200?,x=0.3.The XRD analysis of the powder shows that the La2-xSmx(Zr0.7Ce0.3)2O7 ceramic powder obtained at 1200? for 3h has the structure of calcite and contains free Sm and Mg elements in the form of oxide.The powder Raman,FTIR data show that the ceramic powder changes from disordered fluorite structure to calcite structure at 1200?.At 1200?,The thermal expansion coefficient of La1.7Sm0.3(Zr0.7Ce0.3)2O7 is 10.08×10-6/K,compared with La2Zr2O7,the thermal expansion coefficient is increased by 5%.