Slip casting of silicon nitride for pressureless sintering

Properties of aqueous slips of silicon nitride/spinel mixtures were studied. Vanisperse CB was used as deflocculant. It was shown that mixtures previously milled in water form stable slips, while those milled in isopropanol form jelly-like aqueous suspensions unsuitable for casting. A single-stage slip may be prepared by milling and mixing Si₃ N₄ powder with spinel and water without a deflocculant. Viscosity, pH and density of the slips were studied and a set of crucibles was cast and fired in nitrogen at 1650° C for 1 h to bulk density 3.1 g cm^–3.