Initial Sinterability of α-Silicon Nitride with Addition of Beryllium Oxide

Abstract

It is meaningful to understand the relation between the activity of powder evaluated by physicochemical methods and its initial sinterability. In the present work, the influences of powder properties on moldability, initial sintering behavior and microstructual development of sintered body were investigated. The initial sintering of three kinds of silicon nitride powder, LC 10 (code L), H1 (code H) and A-100 (code T), added with 3wt% BeO was performed under nitrogen atmosphere without pressure. The results obtained are as follows:
(1) The moldability of the angular shaped powder (T) consisting of aggregated particles was low. Between the two fine powders (L, H) consisting of primary particles of irregular shape, the powder (L) having more ultra-fine particles was slightly behind in moldability.
(2) If the tendency of densification depend qualitatively on two parameters, i.e., the moldability and the activity for sintering which each powder is possessing, a sequence of the activity per unit particle for sintering was as follows: L>H>T. The sequence agreed with that of specific surface area of powders. However, the densification rate in the initial stage was concluded as follows: H>L>T.
(3) The bulk density of sintered body was highest at ca. 1660°C for all Si₃N₄. The addition of BeO promoted the α→β phase transformation and the order of transformation rate accorded with that of initial sinterability.
(4) The bulk density of green body increased linearly with an increase of compaction pressure within the range of 3ton/cm², and the compaction pressure had no connection with the α→β transformation.