A microwave susceptor bed useful for sintering ceramics, ceramic composites and metal powders is described. The susceptor bed includes granules of a major amount of a microwave susceptor material, and a minor amount of a refractory parting agent, either dispersed in the susceptor material, or as a coating on the susceptor material. Alumina is the preferred susceptor material. Carbon is the most preferred parting agent. Also described is a sintering process using the bed and to novel silicon nitride products produced thereby.