A series of additives releasing ammonia after thermal decomposition were examined to evaluate their effect on the carbothermal reduction and nitridation of fly ash in the preparation of SiAlON (silicon aluminum oxynitride) powders. The reactions were studied at 1400 degrees C and times of 1-4 h. The addition of certain decomposable additives can accelerate the nitridation. Therefore, a reduction of the nitridation temperature and/or a shorter nitridation time can be achieved. CaSiAlON whiskers were observed in the reaction products by scanning electron microscope, X-ray diffractometer, and energy-dispersive X-ray spectrometer measurements. The nitrogen content in the final product was measured by nitrogen/oxygen analyzer as an index of the extent of the nitridation reaction. Fly ash powders from the Huntley and Hatfield power plants were investigated in this work.