JPS6090836A - Manufacture of synthetic quartz - Google Patents

Abstract

PURPOSE:To manufacture synthetic quartz contg. no Cl by burning specified ester silane, depositing produced silica on a substrate, and melting the resulting sintered body of porous silica by heating. CONSTITUTION:Ester silane represented by the formula (where R is H, methyl or ethyl, R' is methyl or ethyl, and n is 0-4) is fed from a tank 1 to an evaporator 3, where it is vaporized and mixed with an inert gas blown from a pipe 4. The mixture is optionally mixed with gaseous O2 introduced from a pipe 5, and it is fed to a burner 6. The vaporized ester silane is burned with gaseous O2 and gaseous H2 or gas of a combustible contg. no Cl fed from pipes 7-9 to produce silica, and this silica is deposited on a heat resistant substrate 10 to form a sintered body 11 of porous silica having 0.05-1.0g/cm<3> density. The sintered body 11 is dehydrated by heating to about 1,000 deg.C in a furnace kept at <=1X 10<-2>Torr degree of vacuum, and it is vitrified by heating to 1,400-1,600 deg.C in vacuum or an inert gaseous atmosphere contg. no moisture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing synthetic quartz, particularly synthetic quartz that does not contain elemental or compound chlorine.

The method for producing synthetic quartz is to make silica tetrachloride into a gas, decompose it in an oxyhydrogen flame, and spray the silica (Si04) generated from this onto a heat-resistant substrate together with the flame. There is a method in which silica is melted and grown using the sensible heat of a flame (see U.S. Pat. No. 2,272,342), and another method is to grow silica as a porous mass without melting it, and then This was heated to t40 in an electric furnace.
A method of melting and vitrifying by heating to 0 to 1700°C (see US Pat. No. 3,806,570) is known, but the synthetic quartz obtained by this former method has an original crystalline shape. Or compound chlorine is 1O~200ppm, OH
Group is 700-I200. ppm is also included, and those obtained by the latter method also contain OH koto.
It becomes less than about m, but the chlorine σ) average is 10 to 100 p'
pm, which is quite high. -! In addition, as for the manufacturing method of this quartz, it is also known that the decomposition reaction of tetrachloride quartz is carried out using sword heat using high-frequency plasma, and according to this method, the OH group content can be lowered to below IOppm. Stingy 1. However, even in this case, the amount of chlorine is not reduced and is still quite high, between 10 and 500'ppni.

However, synthetic quartz that contains a large amount of chlorine is colored yellow, although the degree of chlorine content varies depending on its content, which has the disadvantage of impairing its properties for optical communication and optical applications. They also have the disadvantage of being inferior in chemical resistance compared to those that do not contain chlorine.

The present invention solves such disadvantages and relates to a method for producing synthetic quartz that does not substantially contain chlorine.This invention has the general formula RnSi (OR')4-r3, where R is a hydrogen atom or a methyl group. , ethyl group -R/ is a methyl group or ethyl group, n is a positive number from 0 to 4) or a mixture gas of this and a vaporized combustible substance that does not contain hydrogen gas or chlorine is combusted. , the resulting silica is deposited on the substrate, and the resulting porous silica sintered body is immediately melted under vacuum or in an inert gas atmosphere that does not contain water. That is.

To explain this, the present inventors focused on various methods of manufacturing synthetic quartz that do not use chlorine, and conducted research on this subject.
Although the silane represented by 4 can also be used, it has an extremely low boiling point of -111.2°C, and is a dangerous substance that can explode and burn in confined air. The ester silane produced does not contain chlorine, has a combustion rate of approximately 100°C or higher, has a low combustion rate, and is easy to handle.Moreover, it can be supplied to industrial rFJ at a low cost. After conducting repeated experiments on this, it was confirmed that chlorine-free synthetic quartz could be easily and reliably produced using this method, and the present invention was completed.

As mentioned above, the ester silane used as the starting material in the method of the present invention may be one represented by the general formula Rn5i (OR4-n), and examples thereof include methyltrimethoxysilane-dimethyldimethoxysilane, trimethylmethoxysilane, Examples include -tetramethoxysilane, methyltriethoxysilane, and tetraethoxysilane, but from an industrial standpoint, methyltrimethoxysilane and tetramethoxysilane are preferable because they are inexpensive and easy to handle. This ester silane is a by-product of the synthesis of dimethyldiglorosilane, which is the main raw material for silicone rubber, silicone varnish, and silicone oil, and is produced by the direct reaction between methyl glolide and safe silicon (trimethyl).
The general formula (CH3) n8 is produced by reacting with alcohol such as 7 alcohol or ethanol, or from the production process of this dimethyldiglomerate ν run.
1mCtxOy polymethylborigo copolysilane, a mixture of monomethyl trig σ-silane-dimethyl diglo-v run, trimethylgu-anolan, monomethyl di-g σ-rosilane obtained by thermally decomposing polymethyl polygloloborosiloxane. It can be easily obtained by reacting with alcohol, and this tetramethoxysilane can be obtained by reacting residual silicon and methyl alcohol in the presence of NaOCH3 as a catalyst to obtain the following formula: Si+40H10H-! i (OCH
3) 4+:2H2” can also be produced by 100~ttU°C, so this is an industrial IT]
VC can be supplied at low cost.It can also be easily obtained as a purified product free of impurities by rectification of glo-A silane, which is the raw material, or rectification of ester silane. C has the advantage that synthetic quartz with high purity can be obtained.

In the method of the present invention, the ester silane is first burned to generate silica, which is deposited on a substrate to form a porous sintered silica body.

For example, it may be carried by argon gas or the like and burned in air. This combustion occurs because the ester silane is the IC in the needle.
[It has a methyl group, an ethyl group, and an alkoxy group as materials.1. In addition, since oxygen can be mixed with the ester silane in advance, it exhibits extremely high combustion efficiency, and complete combustion can be achieved.
According to this method, it is possible to obtain a sufficiently high temperature to obtain a porous silica sintered body made of fine silica that has been sintered with moderate VC, and since this ester silane does not contain chlorine, there is no chlorine Easily produce silica sintered bodies that do not contain
c can be obtained.

The bulk density of the porous silica sintered body thus obtained differs depending on the reaction conditions such as the ester silane supply rate and reaction temperature for producing this phosphoric acid. If it is less than d, it is extremely easy to sag, and when it is melted and vitrified, the shrinkage rate is large, resulting in an irregular shape after vitrification, which is disadvantageous. ! In order to exceed ', the formation temperature of this sintered body must be considerably high, which causes the disadvantage that it becomes partially vitrified, which becomes bubbles when melted. Ofl/ea is often in the range 0.05 to 1, Ofl/ea, for which the ester silane as the starting material is doped with hydrogen gas as an auxiliary fuel, or the ester silane as the starting material is enriched with hydrogen gas as an auxiliary fuel, or a vaporized combustible material, e.g. methane, ethane,
It is preferable to use a volatile hydrocarbon that does not contain chlorine, such as propane.

Incidentally, the silica produced by the combustion of this ester silane is grown on a heat-resistant substrate.
If this is a quartz rod manufactured by the same method, it has the advantage that a solid glass body can be manufactured by melting, which will be described later. However, this quartz rod
It may also be doped with e-P-B-F-TI A4 or the like, which allows the base portion and the portion attached thereon to be glass bodies with different refractive indexes. Further, this substrate may be a rod-shaped body made of carbon or graphite, and by this, a hollow glass body can be obtained by extracting the rod after melting and cooling.

Next, the method for producing a porous sintered silica body by the method of the present invention will be explained based on the drawings. FIG. 1 shows a system diagram thereof, and FIG. 2 is a vertical cross-sectional view of the main part showing another aspect thereof. ,
Figure 3 shows a burner used in carrying out the method of the present invention. To carry out the method for producing a sintered body, first, as shown in Fig. 1, ester silane stored in a raw material tank 1 is sent to an evaporator 3 by a metering pump 2.The ester silane is vaporized in this evaporator. If this is carried out at a high temperature, the ester silane will decompose and polymerize, so an inert gas such as argon or nitrogen is blown into the atmosphere from the vibrator 4 to vaporize the ester silane at a low 7iMIf. In order to completely burn out the ester silane that is being carried out, and furthermore, in order to reduce or eliminate the use of hydrogen gas and flammable substances as hydraulic fuel,
Oxygen gas from the vibrator 5 is mixed in if necessary, but the amount of oxygen does not necessarily have to be the stoichiometric amount required for complete combustion of the raw material, and the remaining amount may be supplied to the burner 6. (So this burner 6 is further supplied with oxygen gas or inert gas from a vibrator 7, oxygen gas from a vibrator 8, and hydrogen gas or combustible gas from a vibrator 9 as required. The structure of this burner is shown in Figure 3. As shown in Figure 2, it has a concentric multiple ring structure, and a prefectural gas containing ester silane is supplied from the center, and oxygen gas, inert gas, -element gas, hydrogen gas, or combustible gas is supplied around it. The ester silane supplied from this burner 6 is completely combusted in coexistence with gas from the surrounding area, and silica is generated in the reactor. 11 porous sintered bodies are formed. FIG. 2 shows another embodiment of this, in which the rotating heat-resistant base 10' is It is designed to repeatedly move back and forth in the horizontal direction relative to the burner 6', and according to this, the porous silica sintered body can be formed into a cylindrical shape along the length direction of the base body 10'. I can do it.

In the method of the present invention, the porous silica sintered body obtained in this way is then melted and vitrified to obtain synthetic quartz. The vitrification temperature in the furnace is about 1400℃ vc/I
I] Heat and melt treatmentf l
This dehydration process is carried out by maintaining the degree of vacuum below Xl0)-1 and keeping the inside of the furnace at around 1000°C, which is below the vitrification temperature of 1400°C. After doing this, increase the temperature inside the furnace to 14
00~1600℃ IC heat to vitrify vc-
f is enough. However, when this sintered body is bath-fused vitrified under a high nitrogen atmosphere, the silica evaporates, and a small amount of foreign matter present in the sinter becomes bubbles and remains in the glass. Therefore, this includes an inert gas that does not contain water, such as helium. Vitrification may be carried out while enclosing or circulating a gas such as nitrogen or carbon, and by this method, the OH group content can be reduced to 50 ppm or less.

In short, the present invention generates silica using ester silane, which does not contain any chlorine, as a starting material, obtains this as a porous sintered silica, and then melts it to produce synthetic quartz. According to this method, it is possible to easily obtain synthetic quartz that does not contain any chlorine, and it is possible to reduce the OH group content to 50 ppm or less if sufficient dehydration is performed in the vacuum treatment in the fusing and vitrification process. For optical equipment such as lenses and prisms.

Furthermore, base materials for optical communication can be easily obtained,
The hollow quartz tube obtained in this manner is said to be useful as an internal CvP tube for manufacturing low-loss optical fibers.

Next, examples of the method of the present invention will be given.

Example 1゜Methyltrimethoxysilane (0H3S i (OCH3
)It boiling point 1-2℃] Argon gas as a carrier gas is blown into the evaporator containing 20℃ of argon gas.
A raw material gas containing 1'oofllb of methyltrimethoxysilane in Nt/h is prepared, and 50% of oxygen gas is added to it.
Send the mixture at a rate of N t/h to a burner, and add hydrogen gas for auxiliary fuel to this burner] OO'N t
/h - By supplying 80 Nt/h of oxygen gas for combustion, a porous sintered body of silica was made on a synthetic quartz matrix using the method shown in Figure 1, and this was continued for 2 hours. As a result, a sintered body weighing 58 g was obtained, and the sintered body had a skein density of 0.55. ! It was 9/Cd.

Next, this sintered body is placed in a vacuum furnace.
After holding at i]oo'C for 2 hours in a vacuum of 2 torr, the vacuum was maintained and the IL was immediately heated to 61,550°C to vitrify it, yielding 53g of synthetic quartz, which contained no chlorine. It does not contain any OH group, and its OH group content is 25
It was ppm.

Shoganii 12 Argon gas as a carrier gas was blown into an evaporator containing tetramethoxysilane (Si (OOH) + boiling point 4 121°C) to form 130.!9/h of tetramethoxysilane in 5ONt/h of argon gas. A raw material gas containing 1.2 ONt/h of oxygen gas is mixed with 30 Nt/b of oxygen gas and sent to the burner. A porous silica sintered body was prepared on a synthetic quartz substrate using the method shown in FIG. 94 g of sintered body of 33 g/crI was obtained.

Next, this sintered body was placed in a vacuum furnace, left open for 2 hours at 1100°C under a vacuum of 1XIO), and then filled with helium gas up to atmospheric pressure.
When vitrified by raising the temperature to 1560°C while flowing at a rate of Nt/h, 91 g of synthetic quartz was obtained, which contained no chlorine at all and had an OH group content of 45 ppm.
Met.

Example 3: Using methyltritoxysilane or tetramethoxysilane as a raw material, it is transported with argon gas as a carrier gas, mixed with oxygen gas, and then supplied to a burner, and the burner is auxiliary. The ester silane is combusted by supplying hydrogen gas for fuel, and the resulting Lika is placed on a rotating graphite rod-shaped body with a diameter of 20 mm held horizontally as shown in Figure 2. It was deposited in At this time, the burner is placed in the same horizontal plane as the substrate, and the 400I
A reciprocating motion is made at a distance of llI+.

A porous silica sintered body in which silica was deposited with a substantially uniform thickness on the substrate was obtained, and this was then heated in a vacuum furnace using IX.
The substrate was held at 1150°C for 2 hours under the heavy atmosphere of an IF2)-cooler, then melted and vitrified in helium gas or under vacuum, and after cooling, the substrate was extracted and a pipe-shaped synthetic quartz was obtained. It was done.

The combustion conditions, melting conditions, and properties of the obtained sintered body and synthetic quartz were as shown in Table 1 below.

Table 1

[Brief explanation of drawings]

Fig. 1 is a system diagram of the method of the present invention, Fig. 2 is a vertical cross-sectional view of the main part showing another aspect of the present invention, and Fig. 3 is a diagram showing the burner used in the present invention 1C (al is its Top view -+b+
is a partial vertical sectional view thereof. 1... Raw material tank, 2... Metering pump. 3... Evaporator. 11-11" ... Porous silica sintered body. Figure 2 Figure 3 Display of procedural amendment case 1982 Patent Application No. 198268 Name of the invention Relationship with the person who amends the manufacturing method of synthetic quartz case Patent applicant name (206) Shin-Etsu Chemical Co., Ltd. Address: 4-9 Nihonbashi Honmachi, Chuo-ku, Tokyo 103 Date of amendment order Sent date: January 31, 1980 Subject of amendment

Claims (1)

[Claims] 1 In the general formula RnSi (OR'), \KR is a hydrogen atom or a methyl group or an ethyl group, R' is a methyl group or an ethyl group, and n is a positive number from 0 to 4). This is obtained by burning ester silane or a mixed gas of this with hydrogen gas or a vaporized combustible substance that does not contain chlorine, and depositing the silica generated by 1C on a substrate. 1. A method for producing synthetic quartz, which comprises immediately melting a porous sintered silica body under vacuum or in an inert gas atmosphere containing no water. 2. Claims in which the ester silane is methyltrimethoxysilane or tetramethoxysilane! A method for producing synthetic quartz according to item 1. 3. The method for producing synthetic quartz according to claim 1 or 2, wherein the substrate is a carbon or graphite product.