JPH11139835A - Production of synthetic quartz - Google Patents

Abstract

PROBLEM TO BE SOLVED: To industrially advantageously produce high purity and high quality synthetic quartz powder by mixing a silicon alkoxide with water, crushing and drying the resultant gel and carrying out treatment in an atmosphere of gaseous ozone and firing. SOLUTION: A silicon alkoxide is mixed with water or a water-alcohol mixture in a molar ratio of 1:3 to 1:20 and the resultant mixture is allowed to react to form gel. This gel is aged at >=40 deg.C for <=1 hr, crushed to about 10 μm to 5 mm with a suitable crusher, dried at <=300 deg.C and treated by contact with ozone in a solid-vapor contact device such as a kiln, a fluidized bed, a moving bed or a shelf type contact unit in an atmosphere of gaseous ozone having 3-100 g/m<3> concn. at 100-300 deg.C. The ozone treated gel is heated to 1,000-1,300 deg.C at 10-2,000 deg.C/hr rate in dry air and fired by holding at the temp. until the amt. of residual silanol is reduced to <=500 ppm to obtain the objective synthetic quartz powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass powder suitable as a raw material for ultra-high purity quartz glass products used in the fields of semiconductors and optical fibers. More particularly, the present invention relates to a method for producing a synthetic quartz by mixing and drying a gel formed by mixing silicon alkoxide and water (or a mixed solution of water and alcohol instead of water), treating the gel in ozone gas, and calcining the resultant. Things. Such a synthetic quartz production method enables decarbonization at low temperatures, so that not only black particles derived from carbon, which is a problem in quality generated after firing, can be significantly reduced, but also a small amount of carbon can be removed, so that foaming during melting at high temperatures is reduced. It is possible to obtain an excellent synthetic quartz having a small amount.

[0002]

2. Description of the Related Art In recent years, with respect to various glass jigs and crucibles used in the optical fiber and semiconductor industries, etc., very strict control has been performed on the purity of constituent glass materials. As a method for producing high-purity glass products applied to these applications, conventionally, silicon alkoxide and water, and in some cases, alcohol are further mixed and stirred to hydrolyze and gelate, which is then crushed, dried and calcined to produce synthetic quartz. Is generally used. For example, 'S
ol-gel Science, The Physics and Chemistry of Si-Ge
l Processing, C. Jeffrey Brinker and George W. Sche
A detailed description can be found in Academic Press, Inc. 1990 'by rer. Depending on the gelling conditions, colloidal particles are formed, which are settled, collected, and fired at a high temperature to obtain a sintered body once. However, a synthetic quartz quartz can also be obtained by pulverizing the sintered body (see, for example, JP-A-2-80329). ). According to these methods, the alkoxysilane as a starting material can be easily distilled and purified, so that high-purity synthetic quartz powder can be obtained.

[0003]

However, in the above method, black carbonaceous material often remains in the gel after firing, which causes serious problems such as foaming during melting. Once formed, this black matter is difficult to remove even after subsequent firing in a temperature range of 1000 ° C. or higher for a long time. Therefore, as means for suppressing the formation of black matter at the time of sintering, first, a gelation condition in which the amount of alikoxy remaining in the gel is small is selected in advance, or the gel is sufficiently porous so that there is a sufficient gas diffusion path into the gel. Things are needed. In addition to this, when drying after gelation and firing, it was necessary to fire at a temperature of 300 ° C. or more and 600 ° C. or less for a long time. The purpose of this operation is mainly to remove the carbon component contained in the porous particles after gelation and drying. However, there is a problem that if there is a substance in which the inner pores of the formed particles during gelation are not sufficiently developed, these pores are sealed at a low temperature, carbon is left in the pores, and blackening occurs. In addition, a trace amount of carbon of several ppm or less may remain even before blackening, and a long-time calcination treatment was required to remove this. In these treatments, the treatment temperature has an upper limit due to the problem of sealing, which has been a problem in terms of both production cost and quality.

[0004]

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the porous gel particles after gelation and drying have been brought into contact with ozone gas without being sealed with ozone gas. Found that the pore structure, which took a long time to decarbonize and easily blackened, could be easily fired without blackening by performing decarburization sufficiently quickly at low temperature even in an undeveloped low specific surface area gel

Hereinafter, the present invention will be described in more detail. Various silicon alkoxides can be used as a raw material for the sol-gel method. Preferably, tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane are used. The reaction is carried out using the above tetraalkoxysilane with water or a mixed system of water and alcohol. The molar ratio of water to silicon alkoxide may be from 3: 1 to 20: 1, preferably from 4: 1 to 15: 1. For applications of high-purity quartz, it is desirable to adjust the pH between 2 and 10 using an organic acid such as hydrochloric acid or acetic acid, ammonia, or an organic amine.

From the viewpoint of productivity, it is preferable to shorten the gelation time. Therefore, it is realistic that the amount of alcohol added is 5 mol or less per 1 mol of silicon alkoxide. The reaction temperature is usually from 20 ° C to 80 ° C. The reaction pressure is usually normal pressure. It is possible to raise the reaction pressure to, for example, about 5 atm as a usual technique. After the gelling, it is usual that the gel is left standing in a reactor and subjected to an aging treatment.

The reason for this is that unreacted components (monomers, partial hydrolysates thereof, and oligomer components such as dimers and trimers) contained in the gel are reacted and incorporated into the gel structure. is there. By doing so, not only loss and scale generation due to volatilization of unreacted substances in the subsequent drying step and the like can be suppressed, but also the gel hardness can be increased and the pulverization step can be easily performed. The retention time of this aging is longer at room temperature and may be 1 depending on the reaction composition.
0 hours or more are required. Therefore, on an industrial scale, holding at a temperature of 40 ° C. or higher for one hour or less is preferable. Further 60
It is within the ordinary technical scope to reduce the holding time by setting the temperature higher than the temperature.

After aging, the gel produced by a suitable pulverizer is pulverized to about 10 to 5 mm and dried at 300 ° C. or less. Thereafter, ozone treatment is performed. It is also possible to perform ozone treatment without alcohol and water without passing through a drying step. However, considering the danger of explosion, it is necessary to remove at least a certain amount of alcohol in advance.

The higher the concentration of ozone gas, the better, but 3g
/ M^ThreeIf it is above, a sufficient oxidation rate can be obtained. Another explosion
100g in consideration of emission and load of ozone generator
/ M ^ThreeIt is desirable to generate at the following concentration. On contact
Temperature should be higher to achieve a sufficient oxidation rate
However, the upper limit is naturally determined from the viewpoint of the aforementioned sealing.
It is. For example, if the pore radius is 10 ° or less,
Limited. Ozone gas can also decompose at high temperatures.
Considering this, in practice, it is preferable that the temperature be between 20 ° C and 400 ° C.
In other words, it is possible to carry out oxidation at
desirable.

For contact with ozone, various solid-gas contact devices such as a kiln, a vibrating fluidized bed, a fluidized bed, a moving bed, a plate-type contactor, and a stationary type can be used. The gel thus treated is further subjected to a drying air atmosphere at 2000 ° C./hr.
The temperature is raised to a temperature of 1000 ° C. or more and 1300 ° C. or less at the following speed, and the temperature is held and calcined to obtain a synthetic quartz powder.

The firing rate is generally 500 ° C./hr or less, preferably 200 ° C./hr or less, and more preferably 50 ° C./hr.
hr or less is good. The lower limit is 10 ° C. /
hr or more. This is to prevent the pores from becoming closed pores during the firing process. The amount of residual silanol can be adjusted depending on the holding time at the maximum temperature. The amount of the silanol is usually preferably 500 ppm or less because the melt viscosity of the quartz powder is reduced. Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 Tetraalkoxysilane 15
After mixing 20 cc with 640 g of methanol, the mixture was mixed with 900 cc of PH4 water adjusted with hydrochloric acid, and reacted at 45 ° C. under normal pressure with stirring in a separable flask equipped with a reflux device to form a gel. After gelling, the mixture was held at 45 ° C. for 2 hours, taken out, and then pulverized while being pressed against a 900 μm nylon mesh, and dried at 200 ° C. under an atmosphere of 10 torr for 2 hours to obtain dried gel particles having an average particle size of 250 μm. Was. The specific surface area of the particles was 300 m ² / g when measured by a nitrogen adsorption method. At this time, the residual carbon amount was about 0.2%. Take 10g of this and 500cc of 4
It was brought into contact with ozone gas in a one-necked flask.

The flask is a metal mantle heater with 20
The temperature was kept at 0 °, and ozone gas was generated at a concentration of 18 g / m ³ , introduced into the flask at a flow rate of 2 l / min, and treated for 4 hours. The ozone generator is "LABO" manufactured by Ebara Jitsugyo Co., Ltd.
OZONAIZER OZSD-3000A "was used. The carbon content of the particles after the treatment was 0.01% or less.
2 g of a quartz boat was gradually introduced into a silicone furnace heated to 800 ° C. over 5 minutes. When the sample was taken out while being kept at 800 ° C. for 2 hours, no black particles were visually observed.

Example 2 Tetraalkoxysilane 15
20 cc of the mixture was mixed with 900 cc of PH7 water and reacted at 45 ° C. under normal pressure with stirring in a separable flask equipped with a reflux condenser to form a gel. After gelation, the mixture was held at 45 ° C. for 2 hours, taken out, and then pulverized while being pressed against a 900 μm nylon mesh, and dried at 200 ° C. in an atmosphere of 10 torr for 2 hours. As a result, dried gel particles having an average particle diameter of 250 μm were obtained. . When the specific surface area of the particles was measured by a nitrogen adsorption method, it was 600 m ² / g. At this time, the residual carbon amount was about 0.13%. Take 10 g of these particles and 500
It was brought into contact with ozone gas in a cc four-necked flask.

The flask was heated with a metal mantle heater.
The temperature was kept at 0 ° C., and ozone gas was generated at a concentration of 0.3 g / m ³ , introduced into the flask at a flow rate of 1 l / min, and treated for 2 hours. The ozone generator is "LAB" manufactured by Ebara Jitsugyo Co., Ltd.
O OZONAIZER OZSD-3000A "was used. The carbon content of the treated particles was about 0.09%.

(Comparative Example 1) When the dried gel particles prepared in Example 1 were rapidly heated to 800 ° C by the method of Example 1 without ozone treatment, about 50% of the black particles were generated.

[0017]

According to the present invention, synthetic quartz powder of high purity and high quality can be industrially advantageously produced.

Claims (4)

[Claims] 1. A method for producing synthetic quartz, comprising: crushing and drying a gel formed by mixing silicon alkoxide and water; treating the gel in an ozone gas atmosphere; and firing. 2. A method for producing synthetic quartz, comprising: crushing and drying a gel formed by mixing silicon alkoxide, water and alcohol, performing a treatment in an ozone gas atmosphere, and then firing. 3. An ozone gas concentration of 3 g / m ³ or more,
The method for producing synthetic quartz according to claim 1, wherein the amount is 0 g / m ³ or less. 4. The method for producing synthetic quartz according to claim 1, wherein the temperature in the treatment in an ozone gas atmosphere is 100 ° C. or more and 300 ° C. or less.