Preparation And Investigation Of Al₂O₃ Ceramic Substrate

The wet forming technology is usually used to prepare Al2O3 ceramic substrate, such as tape casting, rolling casting, slip casting, gel casting and so on. The gel casting has pay close attention as it has the excellence of simple equipment, homogeneous microstructure, low distortion and extensive application. In the work, The gelcasting technology was used to prepare 96 Al2O3 ceramic substrate using highly-pure Al2O3 as raw material, and the sintered steatite, calcium carbonate and kaolin clay as sintering aid.In this casting for shaping of alumina ceramic, an essential requirement and key problem is to prepare the well-characterized suspension with high solid content and stability. The effects of pH value, dispersant content and milling time on the suspended property and stability of suspension, which includes the measurement for zeta potential of Al2O3 powder, the experiment for sedimentation of suspension and for viscosity measurements of suspension. The result of measurement for zeta potential indicates that the dispersant can greatly affect the zeta potential of powder and it can change the isoelectric point (IEP) from 8.2 to about 5. When pH value of the suspension with dispersant is 8~9, the absolute value of zeta potential of powder is the maximum. The sedimentation experiment indicates that the sedimentation is lower and the stability is better in the range of alkalescence and there exists an optimum dispersant content of 0.4%. The viscosity experiment indicates that when pH value is about 8, dispersant content is 0.4% and milling time is 24 hours, the viscosity value is the minimum in each condition and the suspension possesses good flow property.The obtained 45vol%(Al2O3 solid loading) Al2O3 matrix suspension was cast, then gelated and dried. The obtained green bodies sintered at 1530℃have a density of 3.7g/cm3, a microhardness of 1.49GPa and the bending strength of 300.78MPa.The densification of materials was investigated.The microstructure and thermal, electrical and optical properties of the sintered bodies were studied by using SEM, thermal expansion instrument and so on. The results of microstructure of the samples show that the grains arrange uniformly and orderly, and the pore ratio is low. The average coefficient of thermal expansion of sintered samples is 8.34×10-6K-1 and the thermal diffusivity is 0.0668～0.0154cm2/s from 20℃to 1000℃, and reduces with increasing the temperature. The electrical insulating performance is excellent, and volume resistivity is 6×1015～2×1010Ω·cm from 22℃to 500℃. The electrical resistivity decreases with the increment of temperature. In the range of the testing frequencies, the dielectric constant is 9.3~9.4 and the dielectric loss angle tangent is 2.2×10-3～5.4×10-3. The dielectric constant firstly decreases and then keeps constant as the frequency increases. The dielectric loss angle tangent reduces firstly, and then increases.