| 摘要 |
1408087 Silicon nitride NORTON CO 19 Jan 1973 [20 Jan 1972] 2936/73 Heading C1A The invention comprises high density silicon nitride, predominantly in the #-phase, containing a complex magnesium silicate having a liquidus above 1400‹ C., the total oxygen content of the composition being between 2 and 5% by wt. The density is from 3À1 to 3À3 g./c.c., and the rupture modulus in excess of 90,000 p.s.i. at 1200‹ C. and in excess of 45,000 p.s.i. at 1375‹ C. The complex silicate may be of formula RO.Al 2 O 3 .SiO 2 wherein RO represents the aggregate of the oxides of iron, calcium, magnesium and manganese. The MgO/CaO ratio should be greater than 4 and the calcium content less than 0À1% by weight. The magnesium content may be from 0À25 to 2À0% the iron content less than 0À3% and the aluminium content less than 0À5%, all by weight of the product. The product may be prepared by mixing a commercialα-silicon nitride powder of average particle size 1 to 3 microns having a surface layer containing silica and traces of iron, calcium, aluminium and magnesium with 0À25 to 2% of MgO or a compound yielding MgO on heating and hot-pressing the mixture. The product consists predominately of #-silicon nitride particles of average size less than 1 micron bonded together with a non-crystalline complex magnesium silicate. |
