A method and apparatus are provided for producing a product comprising a nitride compound, such as for example silicon nitride. A reactor is provided which has a chamber defined therein which is divided into a combustion zone and a reaction zone. A combustible mixture is injected into the combustion zone and accordingly combusted to form hot combustion products. At least one reactant (i.e. silane) is injected at the boundary between the zones so as to be carried into the reaction zone by the combustion products and react to form raw product comprising the nitride compound. The raw product can be purified by subsequent processing to remove oxygen and convert by-products to the desired nitride compound. The product of the invention has a low level of impurities and is made up of primarily submicron, highly uniform particles. This makes the product particularly useful for fabrication of sintered ceramic parts.