OPAQUE QUARTZ GLASS AND METHOD FOR MANUFACTURING THE SAME

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/cm.sup.3, 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.

Claims

1. Opaque quarts glass having independent spherical shape bubbles with a mean diameter of 2 to 30 m and a density of 1.90 to 2.20 g/cm.sup.3, a whiteness of 80 or more, and a reflectance of light of a wavelength of 0.2 to 3 m at a thickness of 3 mm is 80% or more. The whiteness is defined as the lightness measured according to JIS Z 8722 using a colorimeter.

2. The opaque quartz glass according to claim 1, wherein the bending strength is greater 70 MPa or more.

3. The opaque quartz glass according to claim 1, wherein the surface roughness Ra of the baked surface is 0.7 m or less.

4. A method of manufacturing any one of the opaque quartz glass of claim 1, comprising the steps of mixing a silica powder with a foaming agent and melting the mixture, wherein silicon nitride beads having a mean diameter of 0.1 mm to 3 mm is mixed with the silica powder slurry in which the silica powder dispersed in water at 45 to 75 wt %, pulverizing the silicon nitride beads and generating silicon nitride powder which works as foaming agent and the mixture is melted to manufacture the opaque quartz glass.

5. A method of manufacturing the opaque quartz glass of claim 4, wherein controlling the pulverizing time of silicon nitride beads with silica powder for adjusting the amount of foaming agent generated by abrasion of the silicon nitride beads from 0.1 to 100 ppm, pulverizing the mixture adding one or a plurality of beads selected from the quartz glass beads, zirconia beads, silicon carbide beads, or alumina beads, except the silicon nitride beads, having a mean diameter of 0.1 to 3 mm, abrading the silica powder slurry until the BET specific surface area of the solids in the slurry becomes 2 m.sup.2/g or more, and the slurry is spray-dried for obtaining granulated silica powder having a mean particle diameter of 30 to 200 m and water content of 3 wt % or less, and the granulated silica powder is melted to manufacture the opaque quartz glass.

6. The method of manufacturing an opaque quartz glass of claim 4, wherein diluting the silica powder slurry having silica nitride concentration of 200 to 10000 ppm with respect to the silica powder, thereby adjusting the foaming agent ratio with respect to silica powder from 0.1 to 500 ppm, wet-pulverizing by adding the pulverizing beads having mean diameter of 0.1 mm to 3 mm other than silicon nitride beads until the BET specific surface area of solids contained in the slurry is adjusted to 2 m.sup.2/g or more, and the slurry is spray-dried for granulating substantially spherical shapes having a mean particle diameter of 30 to 200 m and water content of 3 wt % or less.

7. The method of manufacturing the opaque quartz glass according to claim 5, wherein one or a combination of two or more types of a beads mill pulverization method is selected from a ball mill pulverization, a vibration mill pulverization, or an attritor pulverization.

8. The method of manufacturing the opaque quartz glass according to claim 5, wherein the molten raw material is melted with an oxyhydrogen flame.

9. An opaque quartz glass manufactured by the method according to claim 8, which has an OH group concentration of 100 to 1000 ppm.

10. The method of manufacturing opaque quartz glass according to claim 5, wherein the molten raw material is heated and melted under vacuum atmosphere.

11. An opaque quartz glass manufactured according to claim 10, which has an OH group concentration of 10 ppm or less.

Description

PREFERRED EMBODIMENT OF THE INVENTION

[0043] The present invention will be specifically described with reference to the examples described below, but the present invention is not limited to the examples.

Example 1

[0044] Fumed silica (D.sub.10: 2.5 m, D.sub.50: 10.1 m, D.sub.90: 28.1 m) is used as the silica raw material powder. Fumed silica is dispersed in water to form slurry, and the concentration is adjusted to 67 wt %. Next, the prepared fumed silica slurry is put into a bead mill and wet-milled using silicon nitride beads having a mean particle diameter of 2.0 mm until the silicon nitride concentration with respect to the silica powder in the slurry becomes 250 ppm, and the slurry (A) is obtained. On the other hand, slurry (B) with no foaming agent having a silica solid content of 67 wt % is prepared using a silica raw material powder. Then, as the slurry for pulverization and granulation, the slurry (A) is diluted with addition of the slurry (B) so that the concentration of silicon nitride with respect to the silica powder in the slurry becomes 1 ppm. The slurry for pulverization and granulation is wet-pulverized using zirconia beads having a mean particle diameter of 2.0 mm until the BET specific surface area becomes 6.0 m.sup.2/g.

[0045] Next, the slurry for pulverization and granulation produced by the above process is spray-dried to obtain granulated powder. The obtained granulated powder has a mean diameter of 80 m and water content of 1 wt %. The obtained granulated powder is melted with an oxyhydrogen flame to produce a column-shaped opaque quartz glass ingot.

Example 2

[0046] A column-shaped opaque quartz glass ingot is manufactured according to example 1 except that the amount of silicon nitride added is 5 ppm.

[0047] The air bubbles of the obtained opaque quartz glass are observed evenly distributed and the obtained opaque glass looks good.

Example 3

[0048] A column-shaped opaque quartz glass ingot is manufactured according to example 1 except that the amount of silicon nitride added is 0.3 ppm.

[0049] Bubbles of the obtained column-shaped opaque quartz glass ingot are observed to be evenly distributed by visual observation, and the obtained opaque glass looks good.

Example 4

[0050] Same as in the example 1, fumed silica as a silica raw material powder is dispersed in water and its concentration is adjusted to 50%. Then, the prepared slurry is put into a bead mill and wet-milled using silicon nitride beads having a mean particle diameter of 0.3 mm until the concentration of silicon nitride in the slurry becomes 1 ppm. Then, the silicon nitride beads are removed, and the slurry to which the foaming agent is added is wet-milled using zirconia beads having a mean particle diameter of 0.3 mm until the BET specific surface area becomes 3.0 m.sup.2/g. Next, the slurry prepared by the above described procedure is dried and sprayed to obtain granulated powder. The obtained granulated powder has a mean diameter of 40 m and a water content of 1 wt %. The obtained granulated powder is melted with an oxyhydrogen flame to produce a column-shaped opaque quartz glass ingot.

[0051] Bubbles inside the obtained column-shaped opaque quartz glass ingot are observed to be evenly distributed, and the appearance of the product looks good.

Example 5

[0052] Fumed silica as a silica raw material powder used in the example 1 is dispersed in water and the concentration thereof was adjusted to 70%. Next, the prepared slurry is put into a bead mill and wet-milled using silicon nitride beads having a mean particle diameter of 1.0 mm until the concentration of silicon nitride in the slurry becomes 1 ppm. Then, the silicon nitride beads are removed, and the slurry to which the foaming agent is added is wet-milled using zirconia beads having a mean particle diameter of 1.0 mm until the BET specific surface area becomes 8.0 m.sup.2/g.

[0053] Next, the slurry prepared by the above procedure is dried and sprayed to obtain granulated powder. The obtained granulated powder has a mean content of 150 m and a water content of 1 wt %. The obtained granulated powder is melted with an oxyhydrogen flame to produce a column-shaped opaque quartz glass ingot. Bubbles of the obtained column-shaped opaque quartz glass ingot are observed to be evenly distributed and the appearance of the obtained opaque glass looks good.

Example 6

[0054] Fumed silica (D.sub.10: 2.5 m, D.sub.50: 10.1 m, D.sub.90: 28.1 m) is used as the silica raw material powder. Fumed silica is dispersed in water to form slurry, and the concentration is adjusted to 67 wt %. Next, the adjusted slurry is put into a bead mill and wet-milled using silicon nitride beads having a mean particle diameter of 2.0 mm until the silicon nitride concentration with respect to the silica powder in the slurry becomes 250 ppm, and the slurry (A) is prepared. On the other hand, a slurry (B) having a solid content of 67 wt % is prepared using a silica raw material powder containing no foaming agent. Then, as the slurry for pulverization and granulation, the slurry (A) is diluted with the slurry (B) so that the concentration of silicon nitride with respect to the silica powder in the slurry is 1 ppm. The slurry for pulverization and granulation is wet-pulverized using zirconia beads having a mean particle diameter of 2.0 mm until the BET specific surface area becomes 6.0 m.sup.2/g. Next, the slurry for pulverization and granulation produced by the above procedure is spray-dried to obtain granulated powder. The obtained granulated powder has a mean diameter of 80 m and a water content of 1 wt %. The obtained granulated powder is melted with an oxyhydrogen flame to produce a slab-shaped opaque quartz glass ingot.

[0055] The air bubbles of the obtained slab-like opaque quartz glass ingot are observed to be uniformly dispersed, which is excellent in appearance.

Example 7

[0056] A slab-shaped opaque quartz glass ingot is manufactured according to example 1 except that the amount of silicon nitride added is 5 ppm.

[0057] The air bubbles of the obtained slab-like opaque quartz glass ingot are observed to be uniformly dispersed, which is excellent in appearance as opaque silicon glass.

Example 8

[0058] A slab-shaped opaque quartz glass ingot is manufactured according to example 1 except that the amount of silicon nitride added is 0.3 ppm.

[0059] The air bubbles of the slab-shaped opaque quartz glass obtained are observed to be evenly distributed, which is excellent in appearance as opaque silicon glass.

Example 9

[0060] As in example 1, fumed silica as a silica raw material powder is dispersed in water and its concentration is adjusted to 50%. Then, the prepared slurry is put into a bead mill and wet-milled using silicon nitride beads having a mean particle diameter of 0.3 mm until the concentration of silicon nitride in the slurry is 1 ppm. Then, the silicon nitride beads are removed, and the slurry to which the foaming agent is added is wet-milled using zirconia beads having a mean particle diameter of 0.3 mm until the BET specific surface area becomes 3.0 m.sup.2/g. Next, the slurry prepared by the above procedure is dried and sprayed to obtain granulated powder. The obtained is dried and sprayed to obtain granulated powder. The obtained granulated powder has a mean diameter of 40 m and a water content of 1 wt %. The obtained granulated powder is melted with an oxyhydrogen flame to produce a slab-shaped opaque quartz glass ingot.

[0061] The air bubbles of the obtained opaque quartz glass are observed to be evenly distributed and which is excellent in appearance as opaque silicon glass.

Example 10

[0062] Fumed silica as silica raw material powder same as the example 1 is dispersed in water and the concentration thereof is adjusted to 70%. Next, the prepared slurry is put into a bead mill and wet-milled using silicon nitride beads having a mean particle diameter of 1.0 mm until the concentration of silicon nitride in the slurry becomes 1 ppm. Then, the silicon nitride beads are removed, and the slurry to which the foaming agent is added is wet-milled using zirconia beads having a mean particle diameter of 1.0 mm until the BET specific surface area becomes 8.0 m.sup.2/g. Next, the slurry prepared by the above procedure is dried and sprayed to obtain granulated powder. The obtained granulated powder has a mean content of 150 m and a water content of 1 wt %. The obtained granulated powder is melted with an oxyhydrogen flame to produce a slab-shaped opaque quartz glass ingot.

[0063] The air bubbles of the obtained slab-like opaque quartz glass ingot are observed to be uniformly dispersed and the appearance of the opaque glass looks good.

Comparative Example 1

[0064] Quartz powder having a mean particle size of 150 m is used as the silica raw material powder. Further, silicon nitride having a mean particle diameter of 2 m is used as a foaming agent. The mixing concentration of silicon nitride with respect to the crystal powder is 0.2 wt %, and the mixed powder is well mixed and then melted by an oxyhydrogen flame to obtain a column-shaped opaque quartz glass ingot.

Comparative Example 2

[0065] The same fumed silica of example 1 is used as the silica raw material powder. Fumed silica is dispersed in water to form slurry, and its concentration is adjusted to 40 wt %. Next, the prepared fumed silica slurry is put into a bead mill and wet-milled using silicon nitride beads having a mean particle diameter of 3.5 mm until the silicon nitride concentration with respect to the silica powder in the slurry becomes 20000 ppm, and the slurry (A) is obtained. On the other hand, slurry (B) having a solid concentration of 40 wt % is prepared using a silica raw material powder containing no foaming agent.

[0066] Then, slurry for pulverization and granulation, slurry (A) is diluted by adding slurry (B) so that the concentration of silicon nitride with respect to the silica powder in the slurry is 0.5 ppm. The slurry for pulverization and granulation is wet-pulverized using zirconia beads having a mean particle diameter of 3.5 mm until the BET specific surface area becomes 1.8 m.sup.2/g.

[0067] Next, the slurry for pulverization and granulation produced by the above described process is spray-dried to obtain granulated powder. The obtained granulated powder has a mean diameter of 25 m and water content of 4 wt %. This granulated powder is melted with an oxyhydrogen flame to produce a column-shaped opaque quartz glass ingot.

[0068] The BET specific surface area of the slurry is 1.8 m.sup.2/g, which is rather small, the strength of the granulated powder is low, the granulated powder becomes collapsible, and consequently the yield of opaque quartz glass with oxyhydrogen flame melting is low.

Comparative Example 3

[0069] The same fumed silica as in example 1 is used as the silica raw material powder. Fumed silica is dispersed in water and its concentration is adjusted to 40%. Next, the concentration-adjusted silica fume slurry is put into a bead mill and wet-milled with silicon nitride beads having a mean particle diameter of 3.5 mm until the concentration of silicon nitride in the slurry reaches 150 ppm, and then the silicon nitride beads are removed. Then, the slurry to which the foaming agent is added is wet pulverized by using zirconia beads having a mean particle diameter of 3.5 mm until the BET specific surface area becomes 1.8 m.sup.2/g.

[0070] Next, the obtained slurry is spray-dried to obtain granulated powder. The obtained granulated powder has a mean particle size of 250 m and a water content of 4 wt %. The obtained granulated powder is melted with an oxyhydrogen flame to produce a column-shaped opaque quartz glass ingot.

[0071] The BET specific surface area of the slurry is 1.8 m.sup.2/g, which is rather small value, and the strength of the granulated powder tends to be low, and the granulated powder is likely to collapse. And the yield of the opaque quartz glass by oxyhydrogen flame is low.

[0072] The manufacturing conditions of the above described examples and comparative examples are shown in Table 1, and the characteristics (mean diameter of the foam, density, reflectance, whiteness, bending strength, and surface roughness Ra of baked surface) of the obtained opaque quartz glass ingot are shown in Table 2.

INDUSTRIAL APPLICABILITY

[0073] The opaque quartz glass of the present invention has excellent heat insulating property, mechanical strength, and surface smoothness, and is applicable to members of semiconductor manufacturing equipment, parts of optical equipment, and the like.

[0074] Further, according to the method for manufacturing opaque quartz glass of the present invention, it becomes possible to manufacture opaque quartz glass having excellent heat insulating property, mechanical strength, and surface smoothness.

TABLE-US-00001 TABLE 1 Mean diameter Concen- Mean Mean Concen- of tration diameter BET diameter tration Silicon of of specific of of Nitride Silicon Zirconia surface Granulated Water Shape Slurry Beads Nitride beads area Powder content of (wt %) (mm) (ppm) (mm) (m.sup.2/g) (m) (wt %) Ingot Example 1 67 2.0 1 2.0 6 80 1 Column Example 2 67 2.0 5 2.0 6 80 1 Column Example 3 67 2.0 0.3 2.0 6 80 1 Column Example 4 50 0.3 1 0.3 3 40 1 Column Example 5 70 1.0 1 1.0 8 150 1 Column Example 6 67 2.0 1 2.0 6 80 1 Slab Example 7 67 2.0 5 2.0 6 80 1 Slab Example 8 67 2.0 0.3 2.0 6 80 1 Slab Example 9 50 0.3 1 0.3 3 40 1 Slab Example 10 70 1.0 1 1.0 8 150 1 Slab Comparative 0.2 Column Example 1 (wt %) Comparative 40 3.5 0.5 3.5 1.8 25 4 Column Example 2 Comparative 40 3.5 150 3.5 1.8 250 4 Column Examaple 3

TABLE-US-00002 TABLE 2 Mean Density of Burnished diameter Opaque surface of Shape quartz Re- Bending Roughness air foam of glass flectance Whit- Strength Ra (m) air foam (g/cm.sup.3) (%) ness (MPa) (m) Example 1 10 Independent 2.19 86 95 75 0.5 Sphere Example 2 18 Independent 2.15 81 90 71 0.6 Sphere Example 3 2 Independent 2.20 88 98 76 0.4 Sphere Example 4 10 Independent 2.19 86 95 75 0.5 Sphere Example 5 10 Independent 2.19 86 95 75 0.5 Sphere Example 6 25 Independent 2.19 82 84 72 0.7 Sphere Example 7 28 Independent 2.15 80 80 70 0.7 Sphere Example 8 15 Independent 2.20 83 92 73 0.6 Sphere Example 9 25 Independent 2.19 82 84 72 0.7 Sphere Example 10 25 Independent 2.19 82 84 72 0.7 Sphere Comparative 80 Independent 2.10 40 50 67 3.0 Example 1 spherical Comparative 1 Independent 2.21 70 70 77 0.4 Example 2 Sphere Comparative 100 Combined 1.17 70 70 30 50 Examaple 3 Sphere