| 摘要 |
PROBLEM TO BE SOLVED: To provide a glass preform material having optical constants in a specific range, low transition temperature (Tg) and used for precision press forming by comprehensively eliminating various defects of the optical glass which are known in the conventional technique and to provide the optical glass suitable for the precision press forming. SOLUTION: The optical glass contains, as essential components, SiO<SB>2</SB>, B<SB>2</SB>O<SB>3</SB>, La<SB>2</SB>O<SB>3</SB>, Gd<SB>2</SB>O<SB>3</SB>and Li<SB>2</SB>O wherein the total amount of SiO<SB>2</SB>, B<SB>2</SB>O<SB>3</SB>, La<SB>2</SB>O<SB>3</SB>, Gd<SB>2</SB>O<SB>3</SB>and Li<SB>2</SB>O to the total mass of the glass composition is≥91 mass% and has the optical constant of refractive index (nd) within a range from 1.65 to 1.71 and Abbe number (νd) within a range from >55 to 60, the logarithm logηof viscosity (dPa×s) of≥0.5 in a liquidus temperature and the glass transition temperature (Tg) within a range from 550 to 630°C. COPYRIGHT: (C)2006,JPO&NCIPI
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