SPS sintering of amorphous nano-sized Si₂N₂O powders and characterization of its sintered bulks

Through XRD analysis, the obtained amorphous nano-sized Si₂N₂O powders, with the size of about 20 nm, began to crystallize at 1 100 ℃. By further investigating the oxidation resistance and mechanical properties of the ceramics sintered at different temperatures, the study found that the weight gain of dense bulks was only 1.1% after twenty-hour oxidation at 1 600 ℃. The mechanical properties of sintered bulks increased rapidly with the increase of sintering temperature. When the temperature was over 1 500 ℃, the increasing tendency of the mechanical properties became slowly with the rise of temperature. The Vickers hardness, flexural strength and fracture toughness of the sintered samples at 1 500 ℃ reached 19.6 GPa, 440 MPa and 4.1 MPa·m1/2respectively. When Si₂OCl₆ was taken as raw materials and sodium solution as the reducing agent, amorphous nano-sized Si₂N₂O powders were successfully synthesized in liquid ammonia solution through low temperature reduction. Thus dense ceramic bulks were obtained via spark plasma sintering without any sintering additives.