Patent ID: 7429546
Filing Date: 2008-09-30
Classification: C03B,C03C

Abstract:
1. A silica glass comprising TiO2, which has a fictive temperature of at most 1,000° C., a F concentration of at least 100 ppm and a coefficient of thermal expansion of 0±200 ppb/° C., from 0 to 100° C., and produced by one of the following processes: (a) forming a porous glass body by depositing and growing on a target quartz glass particles obtained by flame hydrolysis of glass-forming materials; (b) holding the porous glass body in a fluorine-containing atmosphere to obtain a fluorine-containing porous glass body; (c) heating the fluorine-containing porous glass body to a vitrification temperature to obtain a fluorine-containing vitrified glass body; (d) heating the fluorine-containing vitrified glass body to a temperature of at least the softening temperature and forming it in a shape to obtain a fluorine-containing formed glass body; and (e) carrying out annealing treatment wherein the formed glass body is held at a temperature exceeding 500° C., for at least 5 hours, and then, the temperature is lowered to 500° C., at an average cooling rate of at most 10° C./hr, or a step of carrying out annealing treatment wherein the formed glass body at a temperature of at least 1,200° C., is cooled to 500° C., at an average cooling rate of at most 10° C./hr, or (a) forming a porous glass body by depositing and growing on a target quartz glass particles obtained by flame hydrolysis of glass-forming materials; (b) holding the porous glass body in a fluorine-containing atmosphere to obtain a fluorine-containing porous glass body; (c) holding the fluorine-containing porous glass body in an atmosphere containing oxygen at from 300 to 1,300° C., for at least 5 hours, and then heating it to a vitrification temperature to obtain a fluorine-containing vitrified glass body; (d) heating the fluorine-containing vitrified glass body to a temperature of at least the softening temperature and forming it in a shape to obtain a fluorine-containing formed glass body; and (e) carrying out annealing treatment wherein the formed glass body is held at a temperature exceeding 500° C., for at least 5 hours, and then, the temperature is lowered to 500° C., at an average cooling rate of at most 10° C./hr, or a step of carrying out annealing treatment wherein the formed glass body at a temperature of at least 1,200° C., is cooled to 500° C., at an average cooling rate of at most 10° C./hr.