Technical Studies Of In-situ Formed Dense Aluminium Titanate Ceramics

Aluminum titanate is one of materials with high temperature resistance and low expansion.It has many excellent properties,such as low coefficient of expansion,low thermal conductivity,corrosion resistance,high melting point and good thermal shock resistance.But for its low mechanical strength and decomposition at specific temperature,It should been used in high-temperature refractory materials more widely.In order to solved the intrinsic defects of aluminum titanate,reasearcher focused mainly on two aspects:one is to suppress the decomposition at intermediate temperature of aluminum titanate by adding additives,and the other is to increase the strength by adding the second phase components.Although adding additives can improving the thermal stability,the improvement to strength of the material is less;although the development of composite ceramics can increased the strength,generally the coefficient of thermal expansion of the material will increase.In terms of the preparation process,the partial synthesis method and the partial decomposition method are generally used.These two methods are twice synthesis methods,which have many technological processes and high production costs.The in-situ formation process can well solve these deficiencies.In this paper,a dense aluminum titanate ceramics was prepared by solid-phase in-situ formation method.The feasibility of in-situ formation of Al₂TiO₅ ceramics was explored,and with in-situ formation,the effects of different additives on the phase composition,microstructure and thermal stability were investigated.The phase transition mechanism in the sintering process and thermal decomposition process and the microscopic mechanism of the densification of aluminum titanate ceramics were elucidated.In the process of in-situ formed aluminum titanate ceramics,the optimum process parameters for the material preparation were determined by particle size,bulk density,and DSC/TG analysis;and studied the effect of MgO additive on the structure and properties of aluminum titanate ceramic with in-situ formation by determined the phase composition,lattice constant,microstructure,relative density,thermal expansion,and bending strength,etc..In the study of the thermal stability of in-situ formed aluminum titanate ceramics,with analyzing the changes of phases composition and lattice constants before and after the thermal stability test,the effect on the thermal stability of different additives such as MgO,SiO₂ and MgO+SiO₂ were discussed.By the SEM of the sample after thermal decomposition,the reason of the thermal decomposition of the aluminum titanate ceramic was analyzed.It was believed that TiO₂precipitated on the grain boundary during the decomposition process,causing segregation and decomposition of Al₂TiO₅ components.The resulting product is a mixture of Al₂O₃ and MgAl₂O₄.Based on the formula of better thermal stability,the ceramic with adding talc were preparated.The analysis of phase composition,lattice constant,microstructure,density,pore distribution,thermal expansion,and bending strength shows that the talc Mg²⁺will form a solid solution with Al₂TiO₅.A proper amount of talc can be added into the formula to preparete dense-density aluminum titanate ceramics with high bending strength and low thermal expansion coefficient.In this paper,the in-situ formed aluminum titanate ceramics was first proposed.By synergistic effects of adding various additives,aluminum titanate ceramics with low coefficient of expansion,good thermal stability,high density and high strength were prepared.Then its application in a variety of industries should been realized.