Porosity and shrinkage behaviour of silicon nitride compacts

Partially sintered compacts of Si-Al-Y-O-N batches with 12 wt% inorganic additives as sintering aids were studied by mercury porosimetry in dependence on its thermal pretreatment. Data interpretation was complicated by strong hysteresis phenomena, caused by so-called ''ink-bottle'' pores, which remain occupied by mercury, when the applied pressure is released. One has to consider also different chemical reactions occuring between the batch components at heating-up. The influence of nitrogen overpressure on the shrinkage behaviour was studied for 3 different batches. In opposite to low-additive silicon nitride material studied by other authors, here the actual porosity of the samples at the point of pressurization - up to 5 MPa - does not influence its weight loss and final density. (orig.)