Study On Technology And Properties Of Lanthanum Chromate Ceramics Bonded By Zirconium Boride Composite Interlayer

Chromic acid lanthanum ceramic is a kind of composite oxide of ABO₃perovskite type system,corrosion resistance,high temperature has good chemical and physical stability,is a new type of electric heating material,but because of the brittleness of chromic acid lanthanum ceramic itself and not easy workability,making large and complex ceramic production difficulties,limits its application scope,and the actual application,Some large and complex lanthanum chromate products are partially damaged and cannot be reused.Large and complex lanthanum chromate ceramics can be prepared by using the connection technology,and part of the damaged products can be repaired,which opens up a new idea for solving the problem of the molding and repair of lanthanum chromate ceramics.Zirconium diboride matrix composites have high melting point,high strength,high hardness and high conductivity,good chemical stability,and the properties of lanthanum chromate ceramics as electric heating element are similar.In this paper,zirconium diboride matrix composite material is used as an intermediate layer for the connection of lanthanum chromate ceramics,which can not only take advantage of the excellent properties of zirconium diboride,but also does not affect the properties of lanthanum chromate ceramics itself,which is helpful for the connector to obtain similar properties to the base metal.In addition,the Plasma generated by the pulse current and the pressure in the sintering process in the Spark Plasma Singering（SPS）technology can reduce the sintering temperature of the powder,and the characteristics of low voltage and high current can make the powder sintering compact.It is of great significance to connect lanthanum chromate ceramics with zirconium diboride matrix composites as the interlayer by means of discharge plasma technology.ZrB₂-Al composite and ZrB₂-SiC composite ceramics were prepared by SPS sintering technology.The experimental results show that when ZrB₂:Al=1:1（mol）powder mixture,sintering temperature is 1500℃,rising and cooling rate is 100℃/min,axial pressure is 30MPa,holding time is 5 min,the interlayer block with density of 99.29%is sintered.The thermal expansion coefficient is also 9.56×10^-6·K^-1,the resistivity is 0.04 mΩ·cm^-3,the thermal expansion coefficient and resistivity are more matched with lanthanum chromate ceramics.When ZrB₂in the addition of 10vol%SiC,after 1500℃sintering,the preparation of the density of 88.37%of the composite ceramic block thermal expansion performance of 7.50×10^-6·K^-1,the resistivity of 0.02 mΩ·cm^-3,and lanthanum chromate ceramics is more matched.Two kinds of ZrB₂composites were used as the interlayer,and the bonding experiments of lanthanum chromate ceramics were carried out by means of spark plasma sintering technology.The bending strength and bonding interface of lanthanum chromate ceramics were investigated under different raw material ratio and sintering temperature,and the bonding mechanism was analyzed.In this experiment,the mixed powder with molar ratio of ZrB₂:Al=1:1（mol）was used as the interlayer connection temperature of 1500℃,and the connector with the highest bending strength of 23.79 MPa was obtained.With 90vol%ZrB₂+10vol%SiC mixed powder as the interlayer and sintering temperature at 1450℃,the joint with the highest bending strength of 29.7 MPa was obtained.When lanthanum chromate ceramics are connected with ZrB₂composite as the interlayer,the main method of high strength bonding is diffusion bonding,and the secondary method is reaction bonding.