Mechanical properties of sintered Si₃N₄ from powder produced by fluidized-bed direct silicon nitridation

Si₃N₄ powder, produced by the fluidized-bed direct nitridation of silicon, was blended with water, compacted by pressure slip casting, and sintered under a pressurized nitrogen atmosphere. Compacts made from the powder showed roughly the same sinterability as those made from commercially available imide-process powder, yielding a hardness of H _v 1570, a fracture toughness of 7.2 MPa√m, and a three-point bending strength of 1062 MPa, highest values attainable with Si ₃N₄. The powder produced by the fluidized-bed direct nitridation may replace the Si₃N₄ powder from the other process, when water is used for preparing slips. A processing rout is proposed, which may realize a substantial reduction of total cost for producing sintered Si₃N₄ parts.