| 摘要 |
Glass compositions have been found which, with a low linear thermal expansion coefficient of 33.9-53.2x10-7/ DEG C. at 20-300 DEG 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 DEG and 660 DEG C., the softening temperatures (Ew) are between 821 DEG and 845 DEG C. and working temperatures are between 1211 DEG and 1370 DEG C., the temperature differential Ew-Tg being 232 DEG to 298 DEG C., the ratio alpha '/ alpha of the thermal expansion coefficient above Tg ( alpha ') to expansion below Tg ( alpha ) being between 4.1 and 9.4 and the formation comprising: -SiO2 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 - .
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