The effect of AlN powder properties on thermal conductivity was studied by evaluation of powder properties, analysis of sintering behavior and measurement of thermal conductivity. Six commercially available AlN powders were used in as-received form. The as-received powders were mainly evaluated for particle size distribution, SEM observation and chemical analysis. Degree of aggregation of the powders was characterized by comparison of aggregation from SEM micrographs and the change of particle size distribution by ultrasonication. Each powder was processed by adding 5 wt% of Y2O3 as a sintering aid, then green bodies were formed by CIP after uniaxial press and sintered at 1900-degrees-C for 3 h in 0.203 MPa N2 gas. The sintering behavior was studied at 1500-degrees, 1700-degrees, 1800-degrees and 1900-degrees-C. It was found that the powders containing hard aggregates densified slowly and their sintered bodies had low thermal conductivity in spite of low oxygen content. The mechanism of slow densification and decrease of thermal conductivity is explained by a mechanistic model. This model includes aggregate structure, condition of liquid phase formation and oxygen trapping.
