Opaque quartz glass and method of manufacturing the same

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.

Claims

1. An opaque quartz glass wherein an average diameter of bubbles contained therein is 1 ?m or less, a density is 2.16 to 2.19 g/cm.sup.3, a whiteness is 90% or more at a thickness of 10 mm, and a reflectance of light of wavelength from 0.2 to 3 ?m at a thickness of 3 mm is above 85%, wherein the average diameter of the bubbles is determined by cutting a sample of the opaque quartz glass to provide a cut surface, observing at least 20 bubbles on the cut surface by using a scanning electron microscope, processing obtained images from the scanning electron microscope of the at least 20 bubbles and measuring an area A of each bubble wherein an average value D of the bubbles is determined by the following equation (1): $\begin{array}{cc}D={\left(4?A/?\right)}^{1/2}.& \left(1\right)\end{array}$

2. The opaque quartz glass according to claim 1, wherein a bending strength of the opaque quartz glass is equal to or above 75 MPa.

3. The opaque quartz glass according to claim 1, wherein the opaque quartz glass has a baked finished surface, and a surface roughness Ra of the baked finished surface is equal to or less than 0.5 ?m.

4. A method of manufacturing an opaque quartz glass, comprising the steps of: preparing a silica powder slurry having a silica powder concentration of 45 to 75 wt %; subjecting the silica powder slurry to wet pulverization by applying one or a combination of two or more methods selected from beads mill pulverization, ball mill pulverization, vibration mill pulverization and attritor pulverization; subjecting the silica powder slurry to spray dry granulation for forming substantially spherical granulated silica particles each having a mean particle diameter of 2 to 8 ?m, a standard deviation of the particle size of the granulated silica particles of 3 to 7 ?m and a BET specific area of 2 to 9 m.sup.2/g, to make a prepared slurry; subjecting the prepared slurry to spray drying to obtain dried granulated silica particles; and press-molding and firing the dried granulated silica particles.

5. The method of manufacturing an opaque quartz glass according to claim 4, wherein one or more type of beads is used for the wet pulverization, the beads being selected from the group consisting of quartz glass beads, zirconia beads, silicon carbide beads and alumina beads having an average particle size of 0.1-3 mm.

Description

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Hereinafter, the present invention is specifically described with reference to examples, but the present invention is not limited to the examples.

(2) A desktop scanning electron microscope is used for measuring instrument of average particle size of bubble, which is TM4000 Plus manufactured by Hitachi, Ltd., and a color difference meter used to measure whiteness, is CR-400 manufactured by Konica Minolta.

EXAMPLES 1?3

(3) A slurry in which silica powder is dispersed in water at concentration of 45 to 75 wt % is subjected to wet pulverization selected from one or a combination of two or more methods selected from the beads mill pulverization, ball mill pulverization, vibration mill pulverization or attritor pulverization so as to obtain an average particle size of 2?8 ?m, a standard deviation of the particle size of the pulverized powder of 3?7 ?m, and a BET specific surface area of solids contained in the slurry of 2?9 m.sup.2/g.

(4) Spray dry granulation is conducted to obtain silica powder having an average particle size of 30 to 200 ?m and water content of 3 wt % or less, and the granulated silica powder is press-molded and fired to obtain an opaque quartz glass ingot.

(5) The characteristics of the obtained opaque quartz glass are shown in Table 1. The average diameter of the bubbles of the opaque quartz glass is 1 ?m or less, the density is 2.16?2.19 g/cm.sup.3, the whiteness at thickness of 10 mm is 90% or more, and the reflectance of light wave length of 0.2?3 ?m is 85% or more, the bending strength is 75 MPa or more, and the surface roughness Ra of the baked surface is 0.5 ?m or less.

(6) The weight of the obtained opaque quartz glass ingot is 70 kg, and the bubbles of the opaque quartz glass ingot are confirmed to be uniformly dispersed by visual observation, which is also aesthetically excellent.

COMPARATIVE EXAMPLE 1

(7) A slurry in which silica powder is dispersed in water at concentration of 45 to 75 wt % is subjected to wet pulverization selected from one or a combination of two or more methods selected from the beads mill pulverization, ball mill pulverization, vibration mill pulverization or attritor pulverization so as to obtain an average particle size of 9 ?m, a standard deviation of the particle size of the pulverized powder of 3?7 ?m, and a BET specific surface area of solids contained in the slurry of 2?9 m.sup.2/g.

(8) Spray dry granulation is conducted to obtain silica powder having an average particle size of 30?200 ?m and water content of 3 wt % or less, and the granulated silica powder is press-molded and fired to obtain an opaque quartz glass ingot having air bubbles of mean diameter of 2 ?m and density of 2.16?2.19 g/cm.sup.3.

(9) The whiteness at thickness of 10 mm is 83%, which is lower than the lower limit 90% of the present invention and the reflectance of light of wavelength of 0.2 to 3 ?m at thickness 3 mm is 50%, which is below the lower limit 80% of the present invention. The bending strength is 67 MPa and the surface roughness Ra of the baked surface is 1.5 ?m which exceeds the upper limit of the present invention.

COMPARATIVE EXAMPLE 2

(10) A slurry in which silica powder is dispersed in water at 45 to 75 wt % is subjected to wet pulverization to obtain an average particle size of 2?8 ?m, a standard deviation of the particle size of the pulverized powder of 2 ?m, and a BET specific surface area of solids contained in the slurry of to 2?9 m.sup.2/g. After wet pulverization by one or a combination of two or more methods of beads mill pulverization, ball mill pulverization, vibration mill pulverization, and attritor pulverization so as, spray-dry granulation is performed and the average is substantially spherical.

(11) Granulated powder having a particle size of 30 to 200 ?m and a water content of 3 wt % or less is obtained and fired after press molding. As shown in Table 1, the measurement results show that the average particle size of the bubbles in the quartz glass is 0.9 ?m and the density is 2.10 g/cm.sup.3, the whiteness at a thickness of 10 mm is 92%, and the reflectance of light of wavelength of 0.2 to 3 ?m at 2 mm thick is 62%, the bending strength is 65 MPa, the surface roughness Ra of the baked surface is 0.8 ?m which exceeds the upper limit of 0.5 ?m of the present invention, and is lack in flatness.

COMPARATIVE EXAMPLE 3

(12) A slurry in which silica powder is dispersed in water at 45 to 75 wt % has an average particle size of 2 to 8 ?m, a standard deviation of the particle size of the pulverized powder of 3 to 7 ?m, and a BET specific surface area of solids contained in the slurry is 2 to 9 m.sup.2/g. After wet pulverization by one or a combination of two or more methods of beads mill pulverization, ball mill pulverization, vibration mill pulverization or attritor pulverization so as to be spray-dry granulation is performed to obtain a substantially spherical shape.

(13) Granulated powder having an average particle size of 30 to 200 ?m and a water content of 3 wt % or less was press-molded and then fired at 1510? C. for obtaining opaque quartz glass having the characteristics shown in Table 1.

(14) The average particle size of the bubbles of the obtained opaque quartz glass is 0.8 ?m, the density is 2.20 g/cm.sup.3, the bending strength is 80 MPa, the surface roughness Ra of the baked surface is 0.5 ?m, and the whiteness at a thickness of 10 mm is 79. %. The reflectance of light of wavelength of 0.2 ?m to 3 ?m is 40% at thickness of 2 mm.

(15) TABLE-US-00001 TABLE 1 Roughness Mean Three of baked diameter point surface of Reflect- White- Bending (?m) Bubble Density ance ness strength Ra (?m) (g/cm.sup.3) (%) (%) (MPa) (?m) Rmax Example 1 1.0 2.17 86 90 80 0.5 0.6 Example 2 0.9 2.19 87 91 78 0.4 0.5 Example 3 0.8 2.16 88 93 85 0.4 0.5 Comparative 2.0 2.18 50 83 67 1.5 3.0 Example 1 Comparative 0.9 2.10 62 92 65 0.8 1.5 Example 2 Comparative 0.8 2.20 40 70 80 0.5 0.6 Example 3

INDUSTRIAL APPLICABILITY

(16) The opaque quartz glass ingot according to the present invention is a large sized opaque quartz glass ingot having excellent in heat ray shielding property and light blocking property and the baked surface is smooth and has property of small roughness Ra. And the opaque quartz glass is applicable in variety of industrial fields, especially applicable in the field of members of the semi-conductor manufacturing machines and optical apparatus.