AbstractA method is described for preparing silicon nitride bodies of almost theoretical density. Silicon nitride powder is hot pressed with a small proportion of catalyst, preferably magnesium oxide or nitride, at 1850°C. The bodies have very high flexural strength up to high temperatures, and preliminary measurements of creep rate and thermal shock-resistance indicate that dense silicon nitride should be a suitable material from which to make components required to operate under high stress at temperatures up to∼1200°C.