Synthetic opaque quartz glass and method for producing the same

Abstract

Provided is a method for producing a synthetic opaque quartz glass where flame processing can be performed in high purity with a simple way and even a large sized one can be produced, and the synthetic opaque quartz glass. A method for producing a synthetic opaque quartz glass which comprises the step of heating and burning a quartz glass porous body under a pressure of from 0.15 MPa to 1000 MPa at a temperature of from 1200 C. The quartz glass porous body is prepared by depositing quartz glass particles which are produced by hydrolyzing a silicon compound with an oxyhydrogen flame.

Claims

1. A method for producing a synthetic opaque quartz glass, consisting essentially of: hydrolyzing a silicon compound with an oxyhydrogen flame to form quartz glass soot, depositing the quartz glass soot onto a rotating base body to produce a quartz glass porous body; setting the quartz glass porous body in a furnace; pressurizing an atmosphere of the furnace containing the quartz glass porous body to a pressure within a range of 0.15 MPa to 1000 MPa, the atmosphere of the furnace containing an inert gas; heating the furnace containing the quartz glass porous body to a temperature within a range of 1200 C. to 2000 C.: and maintaining said pressure and said temperature for 30 minutes to 10 hours, thereby burning the quartz glass porous body into the synthetic opaque quartz glass having a nitrogen concentration that is in a range of 0 to 10 ppm, wherein the synthetic opaque quartz glass comprises bubbles spread uniformly throughout an entirety of the synthetic opaque quartz glass, and wherein an average diameter of the bubbles is 1 to 50 m.

2. The method of claim 1, wherein the silicon compound includes silicon tetrachloride.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a photograph showing a result of Example 1.

(2) FIG. 2 is a photograph showing a result of Comparative Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

(3) Hereinafter, embodiments of the present invention will be described. It is needless to say that the embodiments are illustrative and can be modified in various ways without departing from the technical idea of the present invention.

(4) The present invention will be described below in detail.

(5) A synthetic opaque quartz glass can be obtained by heating and burning a quartz glass porous body under a pressure of from 0.15 MPa to 1000 MPa at a temperature of from 1200 C. to 2000 C. In the present invention, a quartz glass where permeability of light having a wavelength of 200 to 5000 nm is less than 5% at 1 mm thick is referred to as a synthetic quartz glass.

(6) The quartz glass porous body is not particularly limited but is suitably a synthetic quartz glass porous body which is prepared by depositing quartz glass particles (soot) obtained by hydrolyzing raw material for forming glass with an oxyhydrogen flame. As glass forming raw material, a silicon compound is preferable, and as the silicon compound, for example, silicon tetrachloride, monosilane, trichlorosilane, dichlorosilane, and methyltrimethoxysilane can be used. Other compounds may be used such as a porous body prepared by a sol-gel method. It is preferable that the quartz glass porous body contains no nitrogen compound.

(7) An atmosphere during heating and burning is not particularly limited, but includes, for example, reducing gases such as an inert gas and hydrogen, oxygen and chlorine, an inert gas being preferable, and nitrogen, Ar or the mixed gas thereof being more preferable.

(8) A pressurizing range is between 0.15 and 1000 MPa, preferably between 0.3 and 1 MPa, and more preferably between 0.5 and 1.0 MPa. A pressure in pressurizing level between 1 and 1000 MPa requires an extremely strict safety measure on the device, resulting in a cost increase. The reason why the higher pressure is preferable is that, in correlation with the extent of the pressure, the number of fine bubbles contained in the quartz glass porous body is increased, the bubbles spread uniformly in the whole glass body, whereby opacity and uniformity thereof increase, and also uniformity in other various properties of the glass body as well as mechanical strength thereof increases.

(9) As to the heating temperature, at lowest a temperature of 1200 C. or more is required to densify the glass body; however at a temperature of over 2000 C. the glass body is softened and the bubbles thereof are broken, resulting in being a transparent glass body. Therefore, the temperature range during heating and burning is between 1200 C. and 2000 C., preferably between 1300 C. and 1700 C. in the present invention. Time for heat treatment may be selected appropriately depending on conditions such as a pressure and a temperature, and in particular, it is preferable to keep it for 30 minutes to 10 hours, more preferably for 1 hour to 4 hours within the above-mentioned ranges of temperature and pressure.

(10) A sintered body after the heating and burning step is completely densified so that a synthetic opaque quartz glass body can be obtained which has uniform fine bubbles in the whole glass body and is excellent in a shading effect by the method of the present invention.

(11) In particular, the synthetic opaque quartz glass can be obtained by the method of the present invention wherein the density thereof is 1.0 g/cm.sup.3 or more and 2.20 g/cm.sup.3 or less, preferably over 2.1 g/cm.sup.3 and 2.20 g/cm.sup.3 or less, the porosity thereof is 1 to 50%, preferably 2 to 10%, an average diameter of isolated bubbles contained therein is 1 m or more and 50 m or less, preferably 1 m or more and 30 m or less, more preferably 1 m or more and less than 10 m, the number of the isolated bubbles is 110.sup.6 to 110.sup.9/cm.sup.3, preferably 110.sup.7 to 110.sup.9/cm.sup.3, more preferably over 610.sup.7/cm.sup.3 and 110.sup.9/cm.sup.3 or less.

(12) The synthetic opaque quartz glass having high purity also can be obtained according to the method of the present invention wherein the contents of metal impurities of Li, Na, K, Mg, Ti, Fe, Cu, Ni, Cr and Al are 0.05 ppm or less (including 0 ppm), respectively.

(13) In the present invention, a nitrogen concentration contained in the obtained synthetic opaque quartz glass is preferably 0 to 50 ppm, more preferably 0 to 10 ppm, further preferably 0 or more and less than 1 ppm. The nitrogen content of 50 ppm or less solves a problem such as clacking caused by flame processing treatment, whereby flame processing treatment can be performed easily.

(14) In addition, in the method of the present invention, using a synthetic quartz glass porous body which is prepared by depositing quartz glass particles synthesized by hydrolyzing raw material for forming glass with an oxyhydrogen flame, there may be obtained the synthetic opaque quartz glass where bubble layers containing the number of 210.sup.6 to 510.sup.9/cm.sup.3 of isolated bubbles and bubble-free layers containing the number of 0 to 110.sup.3/cm.sup.3 of isolated bubbles are alternately deposited. The above-described silicon compounds are preferably used as glass forming raw material.

(15) The thickness of the bubble layer is preferably 1 to 100 m, more preferably 1 to 50 m. The thickness of the bubble-free layer is preferably 1 to 200 m, more preferably 1 to 100 m.

EXAMPLES

(16) Hereinafter, the present invention will be described more specifically by way of examples. However, it should be appreciated that these examples are shown for illustrative purposes, and should not be interpreted in a limiting manner.

Example 1

(17) Quartz glass particules formed by hydrolyzing silicon tetrachloride were deposited onto a rotating base body to produce a quartz glass porous body (length: 2000 mm, diameter: 400 mm). The quartz glass porous body was set into a heating furnace, which was vacuum-evacuated and thereafter pressurized to 0.6 MPa with filling nitrogen gas therein. Next, the furnace was heated to a temperature of 1500 C. in the next 2 hours and kept for 2 hours, followed by cooling spontaneously to a room temperature and then the quartz glass porous body was taken out therefrom after the pressure being reduced to an atmospheric pressure. The obtained quartz glass porous body was densified and the whole body was whitened.

(18) As a result of measuring permeability of the obtained white opaque quartz glass, permeability of light with a wavelength of 200 to 5000 nm at a thickness of 1 mm was 0.5 to 2.0%.

(19) A photograph of the obtained white opaque quartz glass was shown in FIG. 1. As shown in FIG. 1, in the obtained opaque quartz glass the bubble layers having the thickness of 10 m and bubble-free layers having the thickness of 50 m were deposited alternately.

(20) The results of measuring the diameter and the content of the isolated bubbles contained in the obtained white opaque quartz glass were that the diameter of the isolated bubbles was ranging between 1 and 40 m, the average diameter was 9 m, the number of the isolated bubbles was 910.sup.7/cm.sup.3 and the bubble rate was 6.0%. The number of the isolated bubbles in the bubble layers was 110.sup.8/cm.sup.3 and the number of the isolated bubbles in the bubble-free layers was 110.sup.2/cm.sup.3.

(21) In addition, the results of measuring the density, the porosity, the content of the metal impurities, the concentrations of the OH group and nitrogen of the obtained white opaque quartz glass were that the density was 2.16 g/cm.sup.3, the porosity was 8%, the content of each metal impurities of Li, Na, K, Mg, Ti, Fe, Cu, Ni, Cr and Al was 0.005 ppm or less, the OH group concentration was 200 ppm and the nitrogen concentration was 0.5 ppm.

(22) When flame processing treatment such as welding was applied to the obtained synthetic opaque quartz glass, the synthetic opaque quartz glass was easily processed with no problem at all as in the case of the conventional transparent quartz glass body.

Example 2

(23) An experiment was conducted in the same way as in Example 1 except that the pressure during heat treatment to densify was 0.15 MPa and the same result as Example 1 was obtained.

Example 3

(24) An experiment was conducted in the same way as in Example 1 except that the pressure during heat treatment to densify was 800 MPa and the same result as Example 1 was obtained.

Example 4

(25) An experiment was conducted in the same way as in Example 1 except that the atmosphere during heat treatment to densify was Ar and the same result as Example 1 was obtained.

Example 5

(26) An experiment was conducted in the same way as in Example 1 except that the temperature during heat treatment to densify was 1600 C. and the same result as Example 1 was obtained.

Example 6

(27) An experiment was conducted in the same way as in Example 1 except that the condition during heat treatment to densify was changed to keeping a temperature of 1200 C. for 4 hours and the same result as Example 1 was obtained.

Example 7

(28) An experiment was conducted in the same way as in Example 1 except that the condition during heat treatment to densify was changed to keeping a temperature of 1900 C. for 1 hour and the same result as Example 1 was obtained.

Comparative Example 1

(29) Quartz glass particles formed by hydrolyzing silicon tetrachloride were deposited onto a rotating base body to produce a synthetic quartz glass porous body (length: 2000 mm, diameter: 400 mm). The quartz glass porous body was set into a heating furnace, which was vacuum-evacuated and thereafter pressurized to 0.01 MPa with filling nitrogen gas therein. Next, the furnace was heated to a temperature of 1500 C. in the next 2 hours and kept for 2 hours, followed by cooling spontaneously to a room temperature, and then the quartz glass porous body was taken out therefrom after the pressure being reduced to an atmospheric pressure. The obtained quartz glass porous body was densified but the whole body was transparentized.

(30) The content of each metal impurities of Li, Na, K, Mg, Ti, Fe, Cu, Ni, Cr and Al was 0.005 ppm or less, and the OH group content in the glass body was 200 ppm.

Comparative Example 2

(31) A starting material was used where silicon nitride powder was mixed and dispersed into amorphous silica powder having an average diameter of 10 m in an amount of 0.01 parts by weight of per 100 parts by weight of the silica powder. The starting material was loaded into a casting mold which has an inside diameter of 500 mm and an inside height of 300 mm and the casting mold was set into a heating furnace to heat it under an oxygen-free atmosphere at a temperature of 1800 C. in an atmospheric pressure for 30 minutes to form bubbles by vitrifying and foaming, whereby an opaque quartz glass was obtained.

(32) A photograph of the obtained opaque quartz glass was shown in FIG. 2. The results of measuring the density of the obtained opaque quartz glass, the porosity, the average diameter and the content of the isolated bubbles contained therein were that the density was 2.0 g/cm.sup.3, the porosity was 14%, the average diameter of the isolated bubbles contained therein was 60 m, and the number of the isolated bubbles was 210.sup.6/cm.sup.3.

(33) In the obtained white opaque quartz glass, the content of each the metal impurities of Li, Na, K, Mg, Ti, Fe, Cu, Ni, Cr and Al was identified in a range of 0.1 to 0.3 ppm due to diffusion of the metal impurities from the casting mold. The nitrogen content thereof was 300 ppm.

(34) When flame processing treatment such as welding was applied to the obtained synthetic opaque quartz glass, a large amount of bubbles were generated in the interface and strength thereof was significantly declined.