JPS6197141A - Preparation of synthetic quartz glass - Google Patents

Abstract

PURPOSE:To prepare the titled glass contg. less defects such as bubbles in the surfacial layer part by regulating the density distribution in the diametral direction by calcining a porous quartz glass parent material, then converting the parent material to transparent glass. CONSTITUTION:A porous quartz glass parent material 11 formed at an end of a seed rod 10 by a vapor phase reaction process, is inserted into a heating furnace 21 provided with an annular heater 22 and the inside being held in an atmosphere contg. >=50% gaseous He. The parent material 11 is calcined at 1,100-1,300 deg.C for 1-10hr while revolving the parent material 11 to regulate thus the density distribution in the diametral direction, and calcined thereafter at 1,400-1,600 deg.C for 1-5hr in an atmosphere contg. >=80% He gas to convert to transparent glass.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a porous quartz glass for obtaining transparent synthetic quartz glass by heating a porous quartz glass base material produced by a gas phase reaction synthesis method in a heating furnace. This invention relates to a method for vitrifying a base material.

"Prior art and its problems" One of the conventional methods for manufacturing synthetic quartz glass is to form a porous quartz glass base material by a gas phase reaction method, and heat this base material to vitrify it. has been adopted.

That is, raw material gases such as silicon compounds, hydrogen, and oxygen are supplied from a burner to a vertically suspended seed rod, and silicon compounds such as silicon tetrachloride are hydrolyzed in an acidic water flame. Fine silica particles are attached and deposited on the lower end of the seed rod to form a porous quartz glass matrix. Then, this porous quartz glass base material is placed in a heating furnace and heated with a heater to sinter the base material, thereby vitrifying it.

When attempting to manufacture large-diameter synthetic quartz glass using this method, a large-diameter burner is used, but the flame emitted from the burner is hot at the center, but the temperature at the outer periphery is lower than the center. Due to the difference in The density of the outer periphery where Si02 fine particles adhere at low temperatures is 0.
．． 10~O, 15g/cc.

The density at the center is about 0.30 to 0.401/cc. When a porous quartz glass base material with such a density distribution is put into a heating furnace and heated to 1,400 to 1,600°C to vitrify it, the center of the vitrified quartz glass base material has no defects such as bubbles. It was found that a large number of defects such as bubbles having a diameter of several tens of bubbles occurred in the surface layer 5 to 10 mm from the surface. One reason for the occurrence of such defects is that when the porous quartz glass base material is sintered and vitrified, the outer periphery, which has a lower density, shrinks first, so the gas generated during vitrification occurs. It is recognized that the removal of the silica glass was insufficient and that it remained on the surface layer of the vitrified quartz glass base material. Another reason is that some high-density silica particles enter the outer circumference where the density is low, and the vitrification is not uniform with the surrounding area, resulting in a defect as foreign matter. It is possible to make the radial density distribution of the porous quartz glass base material constant as described above to make the shrinkage of the base material uniform and prevent the occurrence of defects, but it is also possible to make the temperature distribution of the flame uniform. It is extremely difficult to obtain a porous base material with a constant density distribution in the radial direction.

"Objective and Summary of the Invention" The present invention solves the above-mentioned problems of the prior art, and even when a large-diameter porous quartz glass base material is vitrified, the resulting quartz glass does not contain defects such as bubbles. It was invented as a result of research with the aim of providing a method for vitrifying a porous quartz glass base material that avoids the formation of porous silica glass. In a method of producing synthetic quartz glass by heating a porous quartz glass base material to make it transparent, the porous quartz glass base material is calcined in advance at 1100 to 1300°C to adjust the radial density distribution of the base material. After.

The present invention relates to a method for producing synthetic quartz glass, which is characterized by firing at 1400-1800°C to form transparent glass.

"Structure of the Invention" In the present invention, a porous quartz glass base material is manufactured by, for example, an apparatus as shown in FIG.

That is, hydrogen and oxygen are supplied from the cylinder 1 and the cylinder 2 to the multi-tube burner 5 through the flow controllers 3 and 41. Further, a gas of a silicon compound such as silicon tetrachloride, trichlorosilane, silicon tetrabromide, etc. is supplied from the tank 6 to the multi-tube burner 5 by a pump 7 through a heat exchanger 8.

The multi-tube burner 5 forms an oxyhydrogen flame in the reaction chamber s, and hydrolyzes the silicon compound to produce silica fine particles. Although not shown, inert gases such as nitrogen and argon are also supplied to the burner 5, and these are used as a carrier gas for the silicon compound or as an air curtain in the oxyhydrogen flame. The chemical formula for this hydrolysis reaction when the silicon compound is silicon tetrachloride is as follows.

2H2◆02 groan 2H20・・・・・・・・・l)S i
c 14◆2H20→S i02+4001・・・・・・
...2) These silica particles are suspended vertically in the reaction chamber 9 made of quartz! i-rod 1 (plant at the lower end of l, grow sequentially, have a large diameter (e.g. diameter 2001~3 scm)
A porous quartz glass base material 11 is formed. Note that 101 (generated by the reaction) is absorbed and removed by contacting the Mail (Na0) 1 liquid circulated from the liquid storage tank 12 in countercurrent contact with the cleaning tower 13.

In the present invention, the porous quartz glass base material produced by the method described above is pre-calcined in the range of 1100 to 1300°C before being vitrified by firing at 1400 to 1800°C. Adjust the radial density distribution of the material. This calcination contains at least 50% He gas.
Under an atmosphere containing the above.

The calcination time, which is carried out in the heating furnace at the above temperature range, is suitably 1 to 10 hours, although it depends on the calcination temperature and the size, density, etc. of the porous quartz glass base material. The porous quartz glass base material subjected to such calcination is transferred to the same heating furnace or another heating furnace, and is subjected to main sintering and vitrification immediately or after a predetermined period of time. This book sintering is.

140 in a heating furnace containing at least 80% He gas.
The time for zero-strand sintering, which is carried out in the temperature range of 0 to 1600°C, also depends on the size, density, etc. of the porous quartz glass base material, but a suitable time is 1 to 5 hours.

In the calcination and final sintering of the porous quartz glass base material, it is optimal to gradually perform the calcination and final sintering by heating from the lower end of the porous quartz glass base material.

In this way, since the porous quartz glass base material is heated from the lower end to perform vitrification through calcination and final sintering, the vicinity of the lower end of the seed rod does not soften first.
The base material can be supported without falling until calcination and main sintering are completed. Further, the seed rod can be prevented from being thermally deformed and can withstand repeated use. Furthermore, since the air bubbles that flow out due to vitrification can escape to the upper part of the base material that has not yet been vitrified, it is possible to prevent air bubbles from being contained in the obtained quartz glass.

In addition, in the calcination or main sintering of the present invention, the base material is heated by rotating the porous quartz glass base material and gradually inserting it into the heating furnace from above while rotating the seed rod. It is best to do this by stopping the heater a little before the top of the heater. By heating in this way, the base material can be calcined and vitrified as it is while being supported by the seed rod, and heating can be averaged by rotating it once, so that the vicinity of the first seed rod is not heated. This can reliably prevent the base material from falling and the seed rod from being deformed by heat.

Furthermore, it is preferable that the heater in the heating furnace for main sintering is provided with a temperature gradient that increases from the top to the bottom. The heating efficiency can be improved by gradually increasing the temperature of the base material when inserting the base material into the base material. In addition, since the vitrification temperature of the porous quartz glass base material is 1410°C or higher, it is appropriate to set the temperature gradient at around 1200°C at the upper part of the heater, around 1430°C at the middle part, and around 1400°C at the lower part. It is.

"Embodiments of the Invention" A cylindrical porous quartz glass base material (diameter 2
5c11. Length is 80 cm, center (1 cm diameter from center)
The average density of the part (m) is 0.40 g/cc, and the average density of the surface part (2 cm from the surface layer) is 0.12 g/cc.
) was placed from above into a heating furnace maintained at 1250° C. and controlled to have an atmosphere containing 80% He gas, sealed, and held for 5 hours to perform calcination. After this calcining, the porous quartz glass base material has become translucent, with an average density of 0.508/cc at the center and 0.508/cc at the surface.
Immediately after calcining, as shown in Fig. 2, the calcined porous quartz glass base material 11 of the quartz seed rod 10 + tons was heated.
was inserted from above into a heating furnace 21 into which 80% helium gas and 10% N2 gas were introduced and an annular heater 22 was disposed inside. This heater 22 has a size that allows insertion of this porous quartz glass base material II.
The heater 22 has an E section of 120 mm.
Around 0℃.

The type 0 rod 10, which has a temperature gradient of about 1430°C in the middle part and about 1400'Q in the lower part, is lowered while rotating as shown by the arrow in the figure, and the porous quartz glass base material 11
was gradually inserted into the heater 22 from its lower end. This porous glass base material 11 was gradually heated and melted from the lower end, defoamed, and became transparent vitrified to become quartz glass 23 having a smaller diameter than the base material 11.

The thus vitrified quartz glass base material has no defects in the inner center from its surface layer (5 m-thickness), and the air bubbles generated in this surface layer have a surface area of 1 cm2.
The average number of pieces per serving was 1.3. On the other hand, the quartz glass base material that was fired and vitrified by the above method without calcination did not have any defects in the inner center from the surface layer (lc-thickness); There were a large number of particles on average, 10 pieces per 1cm2m of surface area.

"Effects of the Invention" As explained above, according to the present invention, the density distribution in the radial direction of the pre-calcined porous quartz glass base material is obtained before the vitrification treatment by main sintering. Even if vitrification treatment is performed by main sintering, the number of defects that occur not only in the center but also in the surface layer can be significantly reduced, resulting in 1 quality improvement and 1 yield. can be improved.

In particular, the method of the present invention is most suitable for vitrifying large-diameter porous quartz glass base materials.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus for obtaining a porous quartz glass base material, and FIG. 2 is an explanatory diagram showing an example of the vitrification method according to the present invention. In the figure, lO is a seed rod, 11 is a porous quartz glass base material, 21
2 is a heating furnace, 22 is a heater, and 23 is quartz glass.

Claims (1)

[Claims] (1) In a method of producing synthetic quartz glass by heating and transparent vitrifying a porous quartz glass base material deposited and grown on one end of a seed rod for quartz glass production, the porous quartz glass base material is pre-heated to a temperature of 1100 to A method for producing synthetic quartz glass, which comprises calcining at 1,300°C to adjust the density distribution in the radial direction of the base material, and then firing at 1,400 to 1,600°C to form transparent glass.