Sintering behaviour of silicon nitride powders produced by carbothermal reduction and nitridation

In this study, the sintering behaviour of silicon nitride (Si3N4) powders (having in situ form sintering aids/self-sintering additives) produced directly by the carbothermal reduction and nitridation (CRN) process is reported. The sintering of as-synthesised α-phase Si3N4 powders was studied, and the results were compared with a commercial powder. The α-Si3N4 powders, as-received contains magnesium, yttrium or lithium–yttrium-based oxides that were shaped with cold isostatic pressing and tape casting techniques. The compacts and tape casted samples are then pressureless-sintered at 1650–1750 °C for up to 2 h. After sintering, the density and the amount of β-phase formation were examined in relation to the sintering temperature and time. The highest density value of 3.20 g cm−3 was obtained after only 30 min of pressureless sintering (at 1700 °C) of Si3N4 powders produced by CRN from silica initially containing 5 wt.% Y2O3. Silicon nitride powders produced by the CRN process performed similarly or even better than results from the pressureless sintering process compared with the commercial one.