The phase separation in melt-casting of ceramic materials by high-gravity combustion synthesis has been investigated based on experimental results. It is proposed that the extent of phase separation depends on the high-gravity factor, the viscosity of matrix melt, the size of Ni droplets or bubbles, and the lifetime of matrix melt. A greater high-gravity factor, lower viscosity of matrix melt, larger size of Ni droplets or bubbles, and longer lifetime of matrix melts facilitates phase separation. Pure and dense ceramics can be prepared from optimization of processing parameters, which includes enhancement of the high-gravity field by increasing rotation frequency and radius, elevation of reaction temperature by choosing more exothermic reactants or by preheating, and application of an extra pressure to promote the removal of bubbles as well as shrinkage cavities. (C) 2012 Elsevier B.V. All rights reserved.