| 摘要 |
To suppress breakage of glass for an electric lamp in a process in which the glass that has already been formed is processed further, a glass composition for an electric lamp is provided. The glass composition contains, expressed in mol %, 70 to 85% of SiO2, 12 to 17% of R2O, and 2 to 8.5% of MO (where R represents at least one selected from Li, Na and K, and M represents at least one selected from Mg, Ca, Sr, Ba, Zn and Pb). In the glass composition, the respective contents of CaO, MgO, BaO and SrO satisfy the relationship, CaO+MgO>BaO+SrO. The glass composition has a brittleness index value B determined by the Vickers hardness test of 7,000 m<-1/2>. Preferably, the contents of SrO and BaO are 0 to 0.5% and 0.1 to 1%, respectively. More preferably, the respective contents of K2O and Na2O satisfy the relationship, K2O>Na2O.
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