EFFECT OF ADDITIVES ON THE THERMAL NITRIDATION OF SOL-GEL DERIVED SILICA-GEL

Silica gels derived by the sol-gel technique with and without additives such as hexamethylene tetramine, carbon fibre, glucose, etc., were nitrided at different temperatures employing a mixture of nitrogen gas and liquid ammonia. The gels and the nitrided products are characterized by infrared, X-ray diffraction, differential scanning calorimetry, thermogravimetry and surface area studies to investigate the extent of nitrogen incorporation and the effect caused by the nitrogen introduction on the physico-chemical properties of the gel. The gel sintered in air is also investigated for comparison purposes It is shown that gels synthesized with additives incorporate more nitrogen compared to the gels without additives. It is also shown that nitrided products are thermally stable, tend to have a crystalline structure depending upon the processing conditions, and that the surface area of the gels decreases upon nitridation, the extent of which is influenced by the nitrogen content and nitridation temperature.