New synthesis route for Si2N2O ceramics based on desert sand

A new approach for synthesis and sintering of silicon oxynitride starting from a unique natural raw material, desert sand is described. The sand in a mixture with silicon metal is combusted under pressurized nitrogen gas into pure silicon oxynitride powder. Then, this powder is densified in the presence of 5 wt.% calcia-alumina mixture to a compact with about 99% of theoretical density within 6 min heating up and holding by using the spark plasma sintering technique. The dense silicon oxynitride has 18.7 GPa Vickers hardness, 3.3 MPa m1/2 fracture toughness, and 363 MPa strength. Morphology of a fractured surface shows that the grains are equiaxed and the fracture occurs in transgranular mode. The material exhibited excellent oxidation resistance at high temperatures up to 1500 °C as well as outstanding chemical resistance in acidic, alkaline and salt mediums at room temperature.