silicon nitrides ceramics prepared by sintering of dense, self reinforced sintering without pressure or the low pressure gas.the composition comprises (a) a silicon azide, with at least 20% are in the form of surface silicon azide beta related to mean high, (b) 2 to 10% by weight of a vitreous phase control of grain containing magnesium oxide, oxide yttrium, silicon dioxide, and optionally zirconia.an oxide selected from the group consisting of calcium oxide, gallium, indium, and hafnium, and (c) a second crystalline phase in a quantity of between 0.5 and 5.0% by weight of zirconium oxide, and (d) of the crystal phases of zirconium silicide mu00e9talliqu e and / or zirconium silicon metal azide in a combined total of between 0.1 and 3.0% by weight, in which the metal is calcium, tantalum, hafnium, gallium or indium, and when the metal is calcium, hafnium, gallium or indium, a metal is in the form of a metal oxide in the glass phase.the ceramic has a high strength and a toughness fracture, it has a density of at least 98% of theoretical.
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