Preparation of silicon nitride powder from silica and ammonia

Silicon nitride powders were obtained in a reaction of SiO2 powders with NH3. The influence of the following parameters on the quality of Si3N4 was determined: silica particle size, temperature and furnace heating programme, sample heating time, ammonia flow rate and application of the selected mineralising agents. The powders of silica were characterised by: optical microscopy, SEM, X-ray phase analysis and thermal analysis. The products of the syntheses were tested by: optical microscopy, SEM, X-ray phase analysis, IR spectroscopy and classic quantitative analysis. The investigations resulted in elaboration of a method of preparation of crystalline silicon nitride powders containing more than 96% Si3N4. The discussion on the influence of magnesium nitride additive on the Si3N4 synthesis process has also been carried out.