JP2000169162A - Production of quartz glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process for quartz glass having higher degrees of freedom with respect to the product shape and a lower degree of contamination. SOLUTION: This production process comprise introducing a gas for plasma formation into an electric insulator tube 1 from a plasma formation gas source 11, forming a plasma space 15 containing an inductive coupling type thermal plasma obtained by applying a high frequency electric field that is caused with a high frequency induction coil to the introduced plasma formation gas, supplying powdery quartz to the plasma space 15 through a powder introduction port 5 to heat and melt the powdery quartz by the inductive coupling type thermal plasma, and allowing the resulting molten quartz particles 13 to collide with a rotatable and movable table 9 placed below the plasma space 15, to obtain a quartz glass deposit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a quartz glass molded product by fusing quartz powder, and more particularly to a method for producing quartz glass using high-frequency inductively coupled thermal plasma.

[0002]

_2. Description of the Related Art A molded product of quartz (SiO ₂ ) glass is mainly manufactured by the following three types of manufacturing methods. The first method is a method in which quartz powder is used as a raw material and is melted and solidified by an electric furnace using an electric heater as a heat source.
A second method is a method of obtaining a quartz molded product by a chemical reaction using SiCl ₄ as a raw material and an oxyhydrogen flame as a heat source. Further, the third method is a method in which rough quartz particles are used as a raw material and are melted and formed in a crucible using a DC arc plasma as a heat source.

[0003]

When the first method is used among the above-mentioned manufacturing methods, a large block can be obtained. However, since the shape of the obtained glass molded product depends on the structure of the furnace body, there are many cases. Not suitable for the production of varieties of glass moldings. Therefore, there is a disadvantage that a secondary processing step is required to obtain a desired plate material, round bar, or the like. In the second method, since the raw material is a gas, the growth rate of the quartz block is low, and a post-annealing step is required to form the quartz block into a glass state. This method is also unsuitable for the production of many kinds because the shape of the obtained quartz block is limited. Further, in the third method, there is a problem in that the electrode of the DC arc plasma undergoes thermal evaporation, is mixed in the fused quartz, and is contaminated. An object of the present invention is to solve the above-described problems of the prior art, and to increase the degree of freedom in shape.
Another object of the present invention is to provide a method for producing quartz glass with low contamination.

[0004]

Means for Solving the Problems To solve the above-mentioned problems, in the present invention, (1) As described in claim 1, quartz powder is melted by using inductively coupled thermal plasma, and quartz glass is melted. It shall be manufactured. Since thermal plasma has a high temperature of about 10,000K, it has a high capability as a heating source. Therefore, if this is used, the quartz powder can be effectively melted. In addition, unlike the DC arc plasma, the inductively coupled thermal plasma can generate plasma without an electrode, so that there is no thermal evaporation of the electrode as in the third conventional method, and there is no risk of contamination. .

(2) Further, as described in claim 2, gas is introduced from above into an insulating tube having a central axis in the vertical direction, and is introduced by a high-frequency coil coaxially arranged outside the insulating tube. The gas thus produced is turned into plasma, quartz powder is introduced into the plasma from the outside, and the quartz powder is melted by the heat of the plasma to produce quartz glass. In this way, the quartz powder is effectively heated and melted from room temperature to the softening point in the plasma space.
Therefore, since a crucible is not required, quartz glass having an arbitrary shape can be manufactured.

(3) Further, as described in claim 3, the quartz powder is introduced into the plasma by an introduction tube having an open end in the plasma. Thermal plasma is a gas fluid with very high viscosity due to its very high temperature, and the resistance increases when a low-temperature gas or powder having a temperature of about room temperature is introduced into the plasma. If it is fed by an inlet tube having an open end, the resistance is reduced, and it can be easily introduced into the plasma.

Further, if the quartz powder to be introduced into the plasma is transported and introduced by a gas flow as described in claim 4, the quartz powder is dispersed as individual particles. Heating can be performed efficiently. Further, since the gas used for transport also acts as a heating medium for the quartz powder, the heating conditions can be adjusted by selecting the type of gas.

(4) Further, as described in claim 5, the fused quartz powder is deposited on a table arranged below the insulating tube. In this way, it is possible to manufacture quartz glass of any shape. For example, according to the sixth aspect, quartz deposits of various shapes can be manufactured, and according to the seventh aspect, a quartz deposit symmetrical to the rotation axis can be manufactured. Further, according to the eighth aspect, a quartz deposit having a larger diameter can be manufactured.

[0009]

FIG. 1 is a longitudinal sectional view showing the basic structure of an inductively coupled plasma apparatus used in the method of manufacturing quartz glass according to the present invention. In FIG. 1, reference numeral 1 denotes a cylindrical insulating tube. Usually, it is formed of quartz having electrical insulation and heat resistance. The insulating tube 1 has a double structure, in which a cooling medium (not shown) is passed between the inner cylinder 1a and the outer cylinder 1b to cool it. The inner diameter of the insulating tube 1 is φ160
mm. Reference numeral 2 denotes a high-frequency induction coil coaxially wound on the insulating tube 1 and is usually wound three to six turns. Reference numeral 3 denotes a high-frequency inverter power supply for supplying a high-frequency current to the high-frequency induction coil 2 and has an output frequency of 450 kHz.
The rated output is 100 kW. At the upper part of the insulating tube 1, a gas introduction unit 4 having a nozzle that blows out in a circumferential direction of the insulating tube 1 and a nozzle that blows out in a radial direction of the insulating tube 1 is incorporated. Further, a powder inlet 5 for feeding quartz powder into the plasma is provided on the central axis at the upper part of the insulating tube 1. The powder inlet 5 has an outer diameter of 25 mm and an inner diameter of 4 mm.
mm, cooled by a coolant and protected from the heat of the plasma. The open end of the powder inlet 5 is located at a position of about 70 mm into the plasma space 15. The powder introduction port 5 is connected to the powder supply unit 6 by a tube, and a predetermined amount of quartz powder is sent to the powder introduction port 5 by adjusting the amount of the carrier powder and the flow rate of the carrier gas with the powder supply unit 6.

Below the inductively coupled plasma torch constructed as described above, a furnace vessel 7 having an opening of φ160 mm which is the same as the inner diameter of the insulating tube 1 is arranged. The furnace container 7
It consists of a metal cylinder with a heat-insulating refractory 8 stuck inside,
A water cooling mechanism (not shown) is provided. Further, the furnace container 7 is connected to a vacuum exhaust device (not shown) via a gas exhaust port 14, so that the inside of the container can be adjusted to an arbitrary pressure equal to or lower than the atmospheric pressure. A rotatable table 9 is installed inside the furnace vessel 7, and inside the insulating tube 1 of the inductively coupled plasma torch, the quartz fused particles 13 that have passed through the plasma space 15 and melted are placed on the table 9. Deposits on top of 9. In addition, the rotation axis of the table 9 is configured to be eccentric with respect to the center axis of the insulating tube 1.

In this configuration, helium gas as an ignition gas is supplied from a helium gas supply source 10 to a gas introduction section 4.
To the upper part of the insulating tube 1, and a high-frequency current flows through the high-frequency induction coil 2 from the high-frequency inverter power supply 3. The helium gas introduced into the insulating tube 1 is discharged by a capacitive coupling electric field formed by the high frequency induction coil 2. In this state, the plasma gas, for example, argon gas is supplied from the plasma gas supply source 11 to maintain the discharge, then the introduction of helium gas is stopped, and the argon gas concentration is increased and the argon gas arc plasma is formed. Migrate. After that, energy is supplied to the plasma 15 by a high-frequency induction electric field generated by the high-frequency induction coil 2. This plasma is generally called an inductively coupled plasma. The resulting plasma depends on the strength and shape of the electric field and the gas flow. An example of the plasma generation conditions in the above apparatus is as follows: argon gas flow rate: 55 L / min, nitrogen gas flow rate: 12 L / min, coil current: 150 A, input power: 50 kW, pressure: 26.6 kPa.

In the state where the inductively coupled plasma is thus obtained, the quartz powder is sent from the powder supplier 6 to the powder inlet 5 together with the argon gas. The particle size of the supplied quartz powder is 44 to 74 μm. The quartz powder is blown from the powder inlet 5 into the plasma space 15 inside the insulating tube 1 and flies downstream in the plasma space 15. In the meantime, the quartz powder is heated by the plasma to be in a molten state, and collides with the table 9 as fused silica particles 13 to form the quartz glass deposit 1.
Deposited as 6.

FIG. 2 is a characteristic diagram showing the height distribution of the quartz glass deposit 16 deposited on the table 9. In the figure, the distribution indicated by the broken line indicated by A is the distribution when the rotation axis of the table 9 is made to coincide with the center axis of the insulating tube 1, and the distribution indicated by the solid line indicated by B is the rotation of the table 9. This is the distribution when the shaft is eccentric with respect to the center axis of the insulating tube 1 by 30 mm and deposited. As can be seen from the characteristic A, the fused quartz particles 13 in the plasma space 15 are deposited in an extremely narrow range, and the half width of the distribution is about φ35 mm. On the other hand, in the characteristic B, the spread becomes large and the half width is about φ80 mm.
It can be seen that a larger quartz glass can be obtained by depositing the rotating shaft of the table 9 eccentrically with respect to the central axis of the insulating tube 1. Therefore, the table 9 is placed on the horizontal plane by X
If the structure is such that the quartz glass can be freely moved in the direction and the Y direction and is deposited while moving, the quartz glass can be deposited in an arbitrary shape. Even when post-processing is required, processing becomes easier than before, and the amount of offcuts generated is reduced.

In the apparatus shown in FIG. 1, the particle diameter of the quartz powder is 44 to 74 μm, and the supply speed of the quartz powder is 0.5.
4 kg / h, input power: 50 kW, plasma gas: Ar + N
The specific gravity of quartz glass manufactured under the condition of ₂ (26.6 kPa) is 2.1
It was 1-2.17. The specific gravity of commercially available quartz glass is 2.07 to 2.12 for the opaque type and 2.02 for the transparent type.
It can be seen that the quartz glass obtained by this method using inductively coupled thermal plasma also has a specific gravity similar to that of a commercial product.

Further, in the present method, the melting state of the quartz powder can be controlled by lowering the plasma input power. Therefore, contrary to the above quartz glass,
It is also possible to produce quartz glass deposits with a low density and a high porosity. This kind of glass can be used as a heat insulating material having high heat resistance.

[0016]

As described above, in the present invention, quartz powder is melted by using inductively coupled thermal plasma to produce quartz glass, so that the quartz powder is effectively melted and an arbitrary shape is obtained. Quartz glass can be produced, and quartz glass with a low degree of contamination can be produced. Further, according to the present method, it is possible to produce a porous quartz glass block having a small specific gravity.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a basic configuration of an inductively coupled plasma device used in a method for producing quartz glass of the present invention.

FIG. 2 is a characteristic diagram showing a height distribution of a quartz glass deposit 16 deposited on a table 9 in the method for producing quartz glass of the present invention using the inductively coupled plasma apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation pipe 2 High frequency induction coil 3 High frequency inverter power supply 4 Gas introduction part 5 Powder introduction port 6 Powder supply device 7 Furnace vessel 8 Insulated refractory 9 Table 10 Helium gas supply source 11 Plasma gas supply source 13 Quartz fused particles 14 Gas exhaust Mouth 15 Plasma space 16 Quartz glass deposit

Claims (8)

[Claims] 1. A method for producing quartz glass by melting quartz powder using inductively coupled thermal plasma to obtain quartz glass. 2. A gas is introduced from above into an insulating tube having a central axis in a vertical direction, the introduced gas is converted into plasma by a high-frequency coil disposed coaxially outside the insulating tube, and quartz powder is externally applied to the tube. 2. The method for producing quartz glass according to claim 1, wherein the quartz powder is introduced into the plasma, and the quartz powder is melted by the heat of the plasma. 3. The method for producing quartz glass according to claim 2, wherein the quartz powder is introduced into the plasma by an introduction tube having an open end in the plasma. 4. The method for producing quartz glass according to claim 3, wherein the quartz powder introduced into the plasma by the introduction tube is transported and introduced by a gas flow. 5. The method for producing quartz glass according to claim 2, wherein the fused quartz powder is deposited on a table arranged below the insulating tube. 6. The method for producing quartz glass according to claim 5, wherein the fused quartz powder is deposited while moving the table. 7. The method for producing quartz glass according to claim 6, wherein the fused quartz powder is deposited while rotating the table. 8. The quartz glass according to claim 7, wherein the fused quartz powder is deposited while rotating the table around a rotation axis eccentric to the center axis of the insulating tube. Production method.