초록 ▼

Glass compositions have been found which, with a low linear thermal expansion coefficient of 33.9-53.2×10-7/°C. at 20-300°C. will pre-stress to a much higher extent under similar prestressing conditions than known glasses of the same thermal expansion, and which consequently result in crumbling unde

Glass compositions have been found which, with a low linear thermal expansion coefficient of 33.9-53.2×10-7/°C. at 20-300°C. will pre-stress to a much higher extent under similar prestressing conditions than known glasses of the same thermal expansion, and which consequently result in crumbling under forced fracture. The glasses possess the following properties: the transformation temperatures (Tg) are between 566°and 660°C., the softening temperatures (Ew) are between 821°and 845°C. and working temperatures are between 1211°and 1370°C., the temperature differential Ew-Tg being 232°to 298°C., the ratio aaaa2 61.60-79.50 percent by weight B2O3 1.00-10.50 Al2O3 2.50-14.00 Na2O 1.50-6.00 CaO 0-4.20 MgO 0-3.19 BaO 0-9.60 ZnO 0-12.00 Total CaO +MgO BaO +ZnO 3.20-17.90 ZrO2 0-1.50 As2O3 0-0.50 NaCl 0-0.75 ________________________________ .

대표청구항 ▼

Thermally high prestressable glasses with high temperative shock resistance and thermal expansion coefficients in the temperature range 20°-300°C. of from 37.8 to 53.1×10-7/°C., characterized in that the transformation temperatures (Tg) are from 571°to 608°C., the softening temperatures (Ew) are fro

Thermally high prestressable glasses with high temperative shock resistance and thermal expansion coefficients in the temperature range 20°-300°C. of from 37.8 to 53.1×10-7/°C., characterized in that the transformation temperatures (Tg) are from 571°to 608°C., the softening temperatures (Ew) are from 821°to 897°C., the working temperatures (VA) are from 1211°to 1355°C., the temperature differential Ew-Tg is from 232 to 294°C., the thermal stress factor R is greater than 300 for undamaged glass surfaces under a quench blowing pressure of one bar and the ratio aaaa4.6 to 9.4 whereby said glass exhibits a high compression prestressing and crumbles into small pieces upon forced fracture, wherein the composition of said glasses, in oxides percent by weight, consists essentially of: ________________________________ -SiO2 73.40-79.50 B2O3 1.00-10.50 Al2O3 2.50-9.00 Na2O 4.00-6.00 CaO 0-3.00 MgO 0-2.10 BaO 0-9.60 ZnO 0-5.10 total CaO +MgO +BaO +ZnO 3.20-13.50 ZrO2 0-1.50 As2O3 0-0.50 and NaCl 0-0.75. ________________________________