Aqueous injection moulding of silicon nitride

The fabrication of pressureless sintered silicon nitride parts by low press ure injection moulding of aqueous slurries is described. A basic requiremen t for this process is the preparation of a stable suspension with high soli ds content and appropriate rheological properties. The temperature has also a determining role in the stability conditions of the slip. In this work t he effect of temperature on the rheological behaviour of silicon nitride aq ueous slips was studied taking into account slip parameters such as the typ e and concentration of deflocculant, pH, ageing, etc. Once the stability co nditions were determined, the effect of a gelling agent (agarose) on the sl ip rheology was also studied in order to optimize the injection conditions. The rheological behaviour of slips containing 1 wt.% agarose was studied a s a function of temperature as well as the influence of sintering aids. Inj ection moulding was performed at temperatures of 60-65 degreesC and a press ure of 0.4 MPa. Final densities of about 90% theoretical are obtained after sintering at 1750 degreesC in N-2 flow. (C) 2000 Elsevier Science Ltd. All rights reserved.