Preparation Of Low-shrinkage Alumina Ceramics Via Incorporation Of Pre-sintered Alumina Powder Based On Isobam Gelcasting

Owing to the excellent properties including robust mechanical strength,excellent hardness,good chemical stability and desirable wear resistance,ceramics have been used as good structural materials.However,a densification process with an inherent linear shrinkage inevitably occurs during sintering as a consequence of pore elimination in ceramic body.Uneven shrinkage would result in dimensional deviation,deformation and cracks,which hampers their further applications in large size,complex shape parts.Only minor size changes occur during the preparation process of low shrinkage ceramics,which not only improves product yield,bur also lowers the production cost,and has a good application prospect in the industrial field with strict requirements on size.Therefore,increasing scholars have been attracted by the research of low shrinkage ceramics which has become a significant direction for the development of ceramics.Low shrinkage and high-performance alumina ceramics have been prepared via incorporation of pre-sintered alumina powder based on Isobam gelcasting for the first time.Firstly,the Isobam based gelcasting process with alumina has been optimized.Carboxylic acids were selected to assist the dispersion because Isobam alone could not achieve the ideal effect when the solid loading of suspension was high.Suitable additives to effectively decrease viscosity and have minimal impact on gelation strength were uncovered from various carboxylic acids through investigation on zeta potential,viscosity of suspensions and yield stress,modulus of elasticity of wet green bodies.The results showed that alumina ceramics were produced from 54 vol% suspensions with 0.5 wt% Iaobam assisted by 0.04 wt% phthalic acid and 0.03 wt% oxalic acid,and its flexural strength and Weibull modulus were 448±44 MPa and 12.1,respectively.Secondly,the preparation and properties of pre-sintered alumina powder were studied.It is of great significance to optimize the preparation process of pre-sintered alumina powder due to its extremely important role in the preparation of low shrinkage alumina ceramics.The optimum process for preparing pre-sintered alumina powder was determined by studying the shrinkage rate,milling time and micromorphology.The results showed that the effective sintering holding time and milling time were 0.5 h and 48 h,respectively.Finally,the preparation and properties of low shrinkage alumina ceramics were studied.The optimum addition amount and pre-sintering temperature were determined via systematically investigating the influence of pre-sintered alumina powder and powder’s pre-sintering temperature on the viscosity of suspension and mechanical properties,microstructure of sintered bodies.The results showed that low shrinkage alumina ceramics with flexural strength of 294.5±33.0 MPa,linear shrinkage of 7.79 % and relative density of 91.5 % can be obtained from 58 vol% suspension with the addition of 60 wt% alumina powder pre-sintered at 1600?C.In summary,the results of this thesis broadened the application range of Isobam in suspension with high solid loading.They laid a foundation and provided a new idea for the deep research and application of low shrinkage ceramics,and also provided a new way for the industrialization of ceramics with large size and complex shapes.