JPH0776098B2 - Method for producing high-purity quartz glass - Google Patents

Description

The present invention relates to a method for producing high-purity quartz glass.

[Prior Art] Conventionally, as one of the methods for producing synthetic quartz glass, a method of forming a porous quartz glass base material by a gas phase reaction method and heating the base material to vitrify has been adopted. . That is, a raw material gas such as a silicon compound, hydrogen, and oxygen is supplied from a burner toward a rotating starting member (hereinafter also referred to as a seed rod) that is vertically suspended, and a silicon compound such as silicon tetrachloride is supplied as an acid. The silica fine particles produced by hydrolysis in a hydrogen flame are adhered and deposited on the lower end of the seed rod made of quartz or the like to form a porous quartz glass base material. Then, this porous quartz glass base material is put into a heating furnace, and the base material is sintered to be vitrified. This method can produce extremely high-purity quartz glass, but since the shape is usually a cylindrical rod, if a prismatic block is required, heat it using a graphite container or the like. In some cases, molding is performed to obtain a quartz glass ingot.

[Problems to be Solved by the Invention] When quartz glass is produced by this method, although the purity is extremely high, in some cases, the outer peripheral portion of the glass rod (having a thickness of 0 to 10 mm from the outer surface) When cristobalite microcrystals (diameter of 10 to 100 μm) are deposited on (1), and defect-free products such as optical applications are required, the product yield is reduced. The cause of generation of the fine crystals in the outer peripheral portion is not necessarily clear, but is considered to be due to inclusion of foreign silica fine particles in the porous base material.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and is provided on a starting member for rotating silica fine particles produced by hydrolyzing a silicon compound in an oxyhydrogen flame. A high-purity quartz glass rod obtained by depositing on a porous matrix to form a porous base material, or a quartz glass ingot obtained by molding this at a high temperature, has an ambient temperature of 300 ° C / hr or more. The temperature is raised to 1730 ° C or higher at this rate for 1 to 4 hours.
After heat treatment at a high temperature of 1730 ℃ or higher, the ambient temperature
A method for producing high-purity quartz glass without defects, characterized by removing crystalline microscopic defects contained in the outer peripheral portion of the glass by cooling the range of 1200 to 1000 ° C at a heating rate of 30 ° C / hr or less Is provided. A high-purity quartz glass rod obtained by firing the above-mentioned porous base material and a quartz glass ingot obtained by molding it at a high temperature will be generically referred to as a synthetic quartz glass ingot below.

The quartz glass to be heat-treated in the present invention is a cylindrical rod or prismatic block of the synthetic quartz glass ingot produced by the above-mentioned method, which is treated with an organic solvent and 10 to 20% hydrofluoric acid and adhered to the glass. It is preferable to remove the organic substances and metal oxides other than SiO ₂ and metal ions, wash with pure water, and then dry the product. This is set in, for example, a graphite container as shown in FIG. 1, and the space between the container and glass is filled with carbon black or high-purity SiC powder or the like, and then installed in a furnace.
It is preferable to use a resistance heating type furnace using a graphite heater or an induction heating furnace.

Next, the atmosphere in the furnace is replaced with an inert gas atmosphere such as argon, and then the temperature rise is started. The heating rate is usually 300 ℃ / hr
The above is preferable. If this is slow, 1400 ~
Since the residence time of the quartz glass at 1600 ° C tends to devitrify for a long period of time, the surface of the synthetic quartz glass ingot that has been devitrified partially devitrifies and bubbles are entrained on the glass surface at the end of the heat treatment. , Not preferable.

The heat treatment temperature is preferably 1730 ° C. or higher. This is because 1730 ° C. or higher is required for the crystals of cristobalite to substantially disappear by dissolution. The holding time at 1730 ° C or higher is not generally determined depending on the size of the cristobalite-like defects and the size of the glass, but is usually 1 to 4 hours. When the length is shorter than this, the heat transfer of the glass is not feasible, the dissolution disappearance speed is frustrating, and the defects are not eliminated, and it is not usually necessary to treat for a longer time. The temperature lowering rate after holding at 1730 ° C or higher is optional, but it is 1200 to prevent thermal strain from remaining in the glass.
It is necessary to cool in the range of up to 1000 ° C at a rate of 30 ° C / hr or less.

[Example] A diameter of 120 mm and a length of 480 m manufactured by using silicon tetrachloride as a raw material
m, 11.9 kg in weight synthetic quartz glass ingot (including about 500 cristobalite-like defects within 5 mm from the rod surface) is washed and dried by ordinary treatment to remove deposits on the surface, and then the inner diameter is 150 mmφ, After setting it in a graphite container with a height of 500 mm as shown in Fig. 1, and filling carbon black powder (manufactured by Toyo Carbon Co., Ltd., which was heat-treated with Seast 3H in advance) between the glass and the container. , 400mm with carbon heater with maximum output 140KW
It was set in an electric furnace having an effective size of (inner diameter) × 700 mm (height).

Then, the inside of the furnace was evacuated by a vacuum pump to reduce the pressure to 0.05 Torr, and then the temperature was increased while continuing to reduce the pressure.
When the temperature was raised to 1000 ° C. in 2 hours, the vacuum pump was stopped and argon gas was introduced into the furnace to 1 atm. After this, the temperature was raised to 1750 ° C. in 2 hours and kept for 2 hours.

After this, the temperature is lowered to 1250 ° C in 1 hour and then to 1000 ° C 30
The temperature was lowered at ° C / hr, the electric furnace power was turned off, and the system was allowed to cool. After confirming that the temperature inside the furnace had cooled to room temperature, the graphite container was taken out of the furnace and the synthetic quartz glass ingot was taken out. The weight of this ingot was 11.8 kg, and there was no change in shape or the like. Both ends of this were polished, and defects were observed using a high-intensity light source. As a result, all of the cristobalite-shaped defects on the outer peripheral part disappeared and the glass was defect-free.

[Effects of the Invention] As described above, according to the present invention, it is possible to remove microscopic crystalline defects contained in the outer peripheral portion of a synthetic quartz glass ingot, and to manufacture high-purity quartz glass with good yield and no defects. I can do things. Moreover, the effect that a homogeneous glass having no striae or distortion can be obtained because the treatment is performed at a high temperature.

[Brief description of drawings]

 FIG. 1 is an explanatory view showing an embodiment of the present invention. 1 ... Synthetic quartz glass ingot 2 ... Graphite container for heat treatment 3 ... Filling material filled between container and glass

Claims (1)

[Claims] 1. A high-purity quartz glass obtained by depositing silica fine particles produced by hydrolyzing a silicon compound in an oxyhydrogen flame on a rotating starting member to form a porous base material and firing the porous base material. The ambient temperature of the rod or quartz glass ingot obtained by molding this at high temperature is 30
1 to 4 at a heating rate of 0 ° C / hr or more to 1730 ° C or more
After heat treatment at a high temperature of 1730 ° C or higher for a period of time, by cooling the atmosphere temperature range of 1200 to 1000 ° C at a cooling rate of 30 ° C / hr or less, crystalline micro defects contained in the outer periphery of the glass are removed A method for producing high-purity quartz glass without defects, which comprises: