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Spark plasma sintering (SPS) method was applied to prepare aluminum nitride/boron nitride (AlN-BN) composites using Sm 2 O 3 –CaF 2 as sintering additives. Effects of sintering additive and BN content on microstructure, thermal conductivity and dielectric properties of AlN-BN composites were investigated. The results reveal that dense AlN-BN composites with uniform microstructure can be successfully fabricated by SPS method. Suitable sintering additive not only promotes sintering densification process but also improves thermal and dielectric properties of AlN-BN composites through liquid phase sintering. AlN-BN composites containing 8 wt.% sintering additives exhibit higher thermal conductivity and lower dielectric loss. BN content, sintering additive, impurity elements, secondary phases, dislocation, and pores have influence on dielectric loss of AlN-BN composites. The main polarization mechanism of AlN-BN composites might be the space charge polarization. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) ceramics were sintered with spark plasma sintering (SPS) technique using Y 2 O 3 (Sm 2 O 3 )–CaF 2 as the sintering additives. The purification effect of sintering additives, dielectric properties, microstructure and polarization mechanism of AlN ceramics were investigated. The densification process curves indicate that both sintering additive and special SPS sintering mechanism are conductive to reducing the sintering beginning temperature. The results of lattice parameters of AlN ceramics suggest that suitable sintering additives have prominent purification effect on the crystal lattice of AlN ceramics. Dielectric constant increases with Y 2 O 3 (Sm 2 O 3 ) content increasing, and the AlN ceramic containing 2 wt.% Sm 2 O 3 -1 wt.% CaF 2 exhibits the lowest dielectric loss. Oxygen impurities, dislocation and amorphous layer in the crystal structure of AlN ceramics increase dielectric loss of AlN ceramics. The space charge polarization caused by secondary phases and other defects might be the main polarization mechanism of AlN ceramics. [ABSTRACT FROM AUTHOR]

Abstract: Dense aluminum nitride ceramics were prepared by Spark Plasma Sintering at a lower sintering temperature of 1700°C with Sm2O3 as sintering additives. The effect of Sm2O3 content on the density, phase composition, microstructure and thermal conductivity of AlN ceramics was investigated. The results showed that Spark Plasma Sintering could fabricate dense AlN ceramics with superior thermal properties in a very short time. Sm2O3 not only facilitated the densification via the liquid-phase sintering mechanism but also improved thermal conductivity by decreasing oxygen impurity. Thermal conductivity decreased with increasing amount of Sm2O3 and the highest thermal conductivity was obtained for the AlN ceramics with 2wt.% Sm2O3 content. During Spark Plasma Sintering process, only 2–3wt.% sintering additives was enough to fabricate dense AlN ceramics, and the microstructures played a key role in controlling the thermal conductivity of AlN ceramics. [Copyright &y& Elsevier]