Sintering of Beryllia—Part II: Hot Pressing of Beryllia Powders of Different Origins and Thermal Treatments

Abstract

Beryllia of high density and controlled microstructure is necessary for application as moderator in various reactor systems. Normally, high density beryllia is prepared by hot pressing at temperatures beyond 1700°C. The sintering behaviour, either in cold pressing and sintering or in hot pressing is influenced by the powder characteristics of the raw material. In this investigation, the sintering behaviour during hot pressing of beryllia powders of divergent characteristics (i.e. prepared from different compounds and subjected to different calcination treatments) has been studied. It was found that powders derived from the sulphate by calcination at 750°C, attained a densification of over 99% theoretical density (2.99 gm/cc; theoretical density 3.01 gm/cc) at a temperature of 1400°C. Attainment of densification at lower temperatures results in little grain development and thus offers the chance to obtain samples sintered to a high density and controlled microstructure. Attempts are made to relate the densification behaviour and microstructure development to the characteristics of the raw powders.