The aim of this investigation was to synthesize Si3N4 through the reaction of nitrogen with SiF4(g) produced during the thermal decomposition of sodium hexafluorosilicate (Na2SiF6) and based on an experiment design, optimize the processing conditions. The quantitative effect and the contribution of the processing parameters on the arnount of Si3N4 formed was determined using analysis of variance (ANOVA). Results show that particles, whiskers/fibers and coatings of alpha and beta-Si3N4 can be produced in the same reaction chamber where the silicon precursor (SiF4) is generated. The optimum conditions for maximum amount of Si3N4 formed are: 60 min, 1300 degrees C, N-2-NH3, 17 mbar, a preform of 85 SiC: 15 Si (wt.%) with 50% porosity, and a compact of Na2SiF6 of 25 g. The versatility for synthesizing Si3N4 with a variety of morphologies through an in situ process suggests the potential of the proposed route for the economic production of Si3N4O (c) 2005 Elsevier B.V All rights reserved.