Development of Water Based Processing of Silicon Nitride Materials

To strengthen the position of Si 3 N 4 as a competitive material in structural applications, cheap raw materials as well as efficient and environmentally friendly processing routes are required. In this work, water-based processing of a medium-cost commercial Si 3 N 4 powder (SICONIDE P95, Permascand AB, Sweden) was developed. This was done by planetary milling to improve the sintering performance and by freeze granulation to ensure high granule quality. Re-dispersing of a milled and freeze granulated/freeze-dried powder resulted in significantly improved rheological properties, enabling high solids-loaded suspensions (< 57 vol%). Adding sintering aids (6 wt% Y 2 O 3 and 2 wt% Al 2 O 3 ) prior to milling and pressing aids (PVA/PEG or latex/PEG) prior to freeze granulation gave excellent pressing performance and CIPed components, which sintered to nearly full density using GPS (Gas Pressure Sintering). The microstructures were characterized by a bimodal grain size distribution and negligible porosity. Mechanical data, flexure strength of 600-900 MPa, indicated possibilities of approaching material properties obtained with more expensive powders and processing routes. PVA/PEG was shown to be the more favorable pressing aid system compared to latex/PEG that gave lower strength.