Effects of Li<SUB>2</SUB>O on Densification, Microstructure and Thermal Property of Spark Plasma Sintered AlN Ceramics

Abstract

A newly developed rapid densify technique, spark plasma sintering (SPS), is used to prepare full-densified aluminum nitride (AlN) ceramics which are poorly sinterable. Some sintering aids are also used to promote the AlN ceramics' densification and improve its thermal conductivity. In this work, effects of sintering aid Li2O on densifica- tion, microstructure and thermal property of SPS sintered AlN ceramics were investigated. Results suggest that the ini- tial sintering temperature of AlN samples reduce from 1550℃ to lower than 1200℃ with 1.0wt% Li2O and 1.5wt% Sm2O3 (or Y2O3) adding as sintering aids . With Li2O addition, AlN compacts can be fully densified at 1650℃. The microstructure of AlN compacts indicates that Li2O is beneficial to generate aluminate liquid phase with better wet- tability and promote the densification of AlN ceramics, but it is unable to obtain higher relative density of AlN com- pacts because the escapement of gas phase though out liquid phase is very difficult in a rapid sintering process. Meanwhile, Li2O addition affects the growth of AlN grains, and the better wettability of aluminate with AlN grain in- duces the homogeneous distribution of grain boundary phase. The deterioration of thermal conductivity of AlN ceram- ics is caused by the fact that the scattering of phonon is enhanced by small grain size and the secondary phase spreading adequately along the AlN grain boundaries. The thermal conductivity of AlN samples with 1.0wt% Li2O and 1.5wt%Sm2O3 as sintering aids is lower than that of sample only with Sm2O3 as sintering aids.