Study On Preparation Of AlN Ceramics By Aqueous Tape Casting And Spark Plasma Sintering

In this paper, the suppressing hydrolysis ability of AlN powder was highly promoted by surface modification, AlN green tape was successfully prepared by aqueous tape casting, AlN ceramics with high thermal conductivity was made by spark plasma sintering（SPS）, in the mean time, the influence of various factors on viscosity of aqueous suspension was studied. Homogeneous and dense AlN green tape was achieved by the optimization of the paste preparing process, different influences on properties of AlN ceramics were researched. The mechanism of densification in SPS sintering process and influences brought by variation of categories or composition on properties of AlN ceramics were revealed. Microstructures of interfaces between different kinds of metals and AlN ceramics were studied, well combined interfaces were constructed when AlN ceramics co-fired with W.The results showed that AlN powder treated with phosphate can be better protected from hydrolysis, p H of suspension stayed the same in the first 12 hours when AlN powder was modified with 4wt% aluminum dihydrogen phosphate acid.Upon the addition of 1wt% ammonium citrate tribasic, the zeta potentials indicating good stability of the suspensions. The viscosities of slurries were affected by the factors such as content of the binder, the value of R（binder/ plasticizer）. Furthermore, the viscosities showed a typical shear thinning behavior, which was appropriate for tape casting.The addition of multiple sintering additive not only accelerated grain growing, but also helped the crystallization of second phases. Density of AlN ceramics was maximized with 2wt% Li₂CO₃-CaCO₃-Dy₂O₃ when the sintering temperature was 1800°C and kept for 10 minutes in SPS. The multiple sintering additive was able to react with Al₂O₃ to remove oxygen impurity, when the thermal conductivity and dielectric property of AlN ceramics were improved. When the content of Li₂CO₃-CaCO₃-Dy₂O₃ was 4wt%, the AlN ceramics showed excellent performance in dielectric properties and thermal conductivity reached to 89 W /（m·K）.Various metals including Ag, Cu, Au and W were co-fired with AlN ceramics. SEM and EDS results of microstructures showed that well-constructed interfaces were prepared between W and AlN ceramics after co-fire process, and no obvious diffusion at the interfaces was detected.