Abstract: A large sized opaque quartz glass ingot having an excellent heat ray shielding property, an outstanding light blocking property, high mechanical strength and small roughness of a baked finished smooth surface. The shape of bubbles inside the quartz glass are almost complete spheres and the average particle size of the bubbles is 1 ?m or less, such that the strength of the opaque quartz glass ingot is increased as the stress concentration at the edges of the bubbles is eliminated and an increase of surface roughness caused by baking is alleviated.

Abstract: A quartz glass provides an opaque quartz glass having high light-shielding property, excellent mechanical strength and excellent cleaning resistance against hydrofluoric acid. By setting the maximum width of the amorphous bubbles existing in the opaque quartz glass to an average of 3 to 15 ?m and the density to 2.15 g/cm3 or more, the mechanical strength after baking and the cleaning resistance by hydrofluoric acid are improved. The opaque quartz glass has a whiteness at a thickness of 10 mm of 75 to 90%, the reflectance of light with a wavelength of 0.24 to 2.6 ?m at a thickness of 4 mm is 60 to 85%, and the bending strength after baking is 95 MPa. In addition, a foaming agent may be mixed in the opaque quartz glass. An opaque quartz glass having cleaning resistance against acid can be obtained.

Abstract: A quartz glass provides an opaque quartz glass having high light-shielding property, excellent mechanical strength and excellent cleaning resistance against hydrofluoric acid. By setting the maximum width of the amorphous bubbles existing in the opaque quartz glass to an average of 3 to 15 ?m and the density to 2.15 g/cm3 or more, the mechanical strength after baking and the cleaning resistance by hydrofluoric acid are improved. The opaque quartz glass has a whiteness at a thickness of 10 mm of 75 to 90%, the reflectance of light with a wavelength of 0.24 to 2.6 ?m at a thickness of 4 mm is 60 to 85%, and the bending strength after baking is 95 MPa. In addition, a foaming agent may be mixed in the opaque quartz glass. An opaque quartz glass having cleaning resistance against acid can be obtained.

Abstract: A large sized opaque quartz glass ingot having an excellent heat ray shielding property, an outstanding light blocking property, high mechanical strength and small roughness of a baked finished smooth surface. The shape of bubbles inside the quartz glass are almost complete spheres and the average particle size of the bubbles is 1 ?m or less, such that the strength of the opaque quartz glass ingot is increased as the stress concentration at the edges of the bubbles is eliminated and an increase of surface roughness caused by baking is alleviated.

Abstract: A method for manufacturing a large sized opaque quartz glass ingot having excellent heat ray shielding and light blocking properties without using a foaming agent. The obtained opaque quartz glass has small diameter spherical bubbles and a preferable mechanical strength. Silica powder is dispersed in water to form a slurry having a silica powder concentration of 45 to 75 wt % and the average particle size of the silica powder is adjusted to 8 ?m or less and the standard deviation of the particle size is adjusted to 6 ?m or more by wet pulverization. The slurry is sprayed for forming granules of the silica powder. An opaque quartz glass ingot with a small bubble diameter and high mechanical strength is obtained by melting the granulated silica powder.

Abstract: To provide an opaque quartz glass having excellent heat insulating property, mechanical strength and surface smoothness, a silica powder water slurry of concentration of 45 to 75 wt % is subjected to wet pulverization with silicon nitride beads having a mean diameter of 0.1 mm to 3 mm. The silica powder and silicon nitride beads are subjected to abrasion and the silicon nitride powder works as foaming agent and independent spherical bubbles are formed for manufacturing opaque quartz glass which has air cells having a mean diameter of 2 to 30 ?m and are independent spherical, having a density of 1.90 to 2.20 g/cm3, a whiteness of 80 or more, a reflectance of 80% or more for light of a wavelength of 0.2 to 3 ?m at thickness of 3 mm, a bending strength of 70 MPa or more, a surface roughness Ra of the baked surface of 0.7 ?m or less.