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 alpha-phase Si3N4 powders was studied, and the results were compared with a commercial powder. The alpha-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 degrees C for up to 2 h. After sintering, the density and the amount of beta-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 degrees 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. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.