PREPARATION AND PROPERTIES OF NITRIDE-CONTAINING COMPOSITES DURING COMBUSTION OF THE «SILICON – ZIRCON» MIXTURE IN NITROGEN

Abstract

Nitriding of silicon with the addition of zircon (10-70%) was performed by the self-propagating high-temperature synthesis (SHS) method. The nitriding potential and the combustion rate were studied versus the mixture composition, nitrogen pressure, and the sample diameter. The maximum nitriding potential is achieved with the addition of 40 – 50% zircon to the starting mixture. Nitriding of the «silicon – zircon» mixture by the SHS method occurs in the autoscillatory mode. The macrostructure of the burned samples was shown to be heterogeneous. Combustion was impossible for the «50% silicon – 50% zircon» mixture with a sample diameter less than 30 mm and a nitrogen pressure less than 1.5 MPa. Varying the synthesis parameters (nitrogen pressure 1.5-6 MPa, sample diameter 30-60 mm), the phase composition of the synthesized products consists of α,β-Si3N4, ZrO2, Si2N2O and ZrSi2. The high-temperature interaction of the «40% silicon – 60% zircon» mixture with gaseous nitrogen was studied using the complex DSC-TG- analysis. It was found that zircon does not undergo physical and chemical transformations involving a weight change under controlled heating conditions in the range of 20 – 1500 °С. Silicon in the «silicon – zircon – nitrogen» system exhibits the properties of both a nitride-forming agent (Si3N4, Si2N2O phases are identified in the synthesized products), and a reducing agent ZrO2 with the formation of ZrSi2. The mechanism of chemical transformations during SHS nitriding of silicon with zircon is presented. The properties of the nitride-containing composites were investigated depending on the zircon content in the mixture.