Masako Kataoka

Influence of Nitride on Sinterability of the Composite of Lithium Aluminum Silicate and Silicon Carbide

Ceramics with zero thermal expansion coefficients at room temperature (293K) were investigated. We found the thermal expansion coefficient was controlled by a compounding ratio of lithium aluminum silicate (LAS) and silicon carbide (SiC), which have negative and positive thermal expansion coefficients respectively. Although it was difficult to densify the composite of the LAS and SiC (LAS/SiC) in the sintering process, an addition of nitride improved the sinterability of the LAS/SiC. In order to examine the effect of the nitride additive, at first, the melting point of the LAS with silicon nitride (Si3N4) or aluminum nitride was measured by TG-DTA. The melting point of the LAS decreased with existence of nitride. It is believed that the densification of the LAS/SiC was promoted by the nitride, because the nitride causes the LAS/SiC to form a liquid phase, thereby decreasing the melting point. Next, the lattice constant of the LAS with Si3N4 was measured by XRD and it was verified that the a-axis was longer and the c-axis was shorter than those of the LAS without additive. It is supposed that this phenomenon is due to the substitution of nitrogen for oxygen in the LAS lattice, and the decrease of the melting point of the LAS with nitride seems to be influenced by this substitution of nitrogen.

The Effect of Ag and PbO on Sintering Behavior of PbSr(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3

The effect of Ag and PbO on the sintering behavior and the piezoelectric properties of PbSr(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 system has been studied. A small addition of Ag enhances the value of er. and Kr. In the specimen with Ag addition, the grain growth was observed by use of SEM. The shrinkage vs temperature curves showed that the shrinkage of the specimen with Ag addition abruptly increases from 900°C and the value of shrinkage at 1100°C is as twice as the additive-free specimen. The shrinkage vs time plots revealed that the grain boundary diffusion is dominant on the sintering of PMN-PZT with Ag and Pb addition.