Self-propagating high temperature synthesis of SiAlON

Abstract In this work, a new method of SHS process has been investigated for the synthesis of SiAlON under low nitrogen pressure. A gel mixture of silica and sodium oxide (sodium silicate) as a reactant and catalyst was produced by alkali melting of silica, solving the results in water and heating in auto clave. Al powder was also used as reactants. Urea and aluminum nitrate hydrate was used as igniting agents. The addition of Mg also was necessary for reaching the combustion. Sodium azide as a good reactant addition for preparing both combustion and nitrogen supply was tested. Beta-Si 3 N 4 powder acted as diluting agent and by reducing the adiabatic temperature helped the nitrogen diffusion into the melted reactants which was not agglomerated. NH 4 Cl in some cases was used as a catalyst which showed good results for reaching SiAlON. For comparison possibility some experiments were made using silica powder instead of sodium silicate gel. These materials were mixed by pestle and mortar and laid into the combustion chamber cavity without pressing. The compound was heated by electrical element until the ignition happened by gases which were produced from urea and aluminum nitrate hydrate. The pressure of nitrogen in combustion chamber was kept constant near 0.1 Mpa. The products of syntheses were of agglomerated one mostly O′-SiAlON & β and β′-SiAlON. Effects of NH 4 Cl were examined by XRD results. TGA and DTA graphs showed the thermodynamics of reaction which were analyzed in some parts by XRD spectroscopy. In some cases nano material of SiAlON was produced which is demonstrated by XRD and FTIR spectroscopy.