Sintering of silicon nitride using Be additive

An as-sintered polycrystalline silicon nitride product of complex shape of a preformed compact of particulate material, said as-sintered product having a density ranging from at least about 80% to about 100% of the theoretical density of silicon nitride, said as-sintered product consisting essentially of silicon nitride and beryllium, said silicon nitride ranging from the .beta.-form to at least about 80% by weight .beta.-form-20% by weight .alpha.-form based on the total amount of said silicon nitride, said beryllium ranging in amount from less than about 0.1% by weight to less than about 2.0% by weight of said silicon nitride, said as-sintered product according to X-ray diffraction analysis ranging from a single phase body to one comprised of a primary phase and a secondary phase.