Study On Gelcasting Forming Process Of AlN Ceramics

Aluminum nitride ceramics is widely used in electronic packaging materials, piezoelectric devices, protective coating and transparent ceramics due to its high thermal conductivity, excellent insulation and dielectric properties, strong corrosion resistance and thermal expansion coefficient matched with silicon, etc.In this dissertation, gelcasting technology was applied to prepare AlN ceramics, and four aspects were investigated: the gelation behaviors of ethanol solution of Trimethylolpropane triglycidyl ether(TMPGE) were characterized; the preparation of AlN slurry with high solid loading and low viscosity; gelcasting processes for preparation of AlN ceramics; effect of solid loading on property of AlN sintering body. The main results obtained are as follows:(1) The polymerization reaction kinetics was studied. The results showed that with the increase of the temperature and TMPGE concentrations, the reaction rate of gelation increased, and the gelation reaction activation energy about 40~50 kJ/mol hardly changed.(2) The effect of dispersants, solid loading in volume and ball milling time on the viscosity of AlN slurry were investigated. The 45 vol% AlN slurry with the minimum viscosity of 22 mPa·s was obtained by adding 0.6 wt% dispersant and ball milling 24 h. The viscosity of AlN slurry raised with the solid loading increased, and the viscosity of 54 vol% AlN slurry was 244 mPa·s.(3) AlN green body with no defect was prepared by using n-caprylic alcohol and physical degassing method and drying under high alcohol humidity.(4) The fine AlN green bodies with 54 vol% solid loading in volume, 65.8% relative density, about 2.5% linear shrinkage and the maximum bending strength of 10.31 MPa were prepared. The effect of solid loading in volume and epoxy resin concentrations on the property of green body was studied. The results showed that with the solid loading increased, the density of AlN green body raised, and the linear shrinkage and flexure strength decreased, and the microstructure gradually consolidated.(5) The binder of AlN green body was removed by slow warming at the rate of 1 ?/min and heat preservation at 580 ? for 1 h. Sintering was carried out at 1800? for 6h in nitrogen atmosphere. The nearly full densed AlN ceramics with 99.67% relative density was prepared.The XRD analyses, density, microstructure and mechanical property of AlN ceramics were characterized. The results showed that with the solid loading increased, the densty of AlN sintering body increased, and the flexural strength increased first and then decreased. The maximum flexural strength is 305 MPa.