JPH10287416A - Production of synthetic quartz powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a synthetic quartz powder that can enhance the productivity and can reduce the production cost by increasing a bulk density of the powder charged to a crucible, by successively charging silica gel from one end of a rotary kiln, heat treating the charged silica gel while fluidizing the silica gel, and further charging oxygen-containing gas thereto. SOLUTION: The objective synthetic quartz powder is obtained by firing a silica gel powder to make the silica gel powder have no pore. The production method is preferably a sol-gel method by hydrolysis and gelation of an alkoxysilane, etc. The alkoxysilane is preferably a 1-4C lower alkoxysilane or an oligomer thereof. The amount of water is 1-10 times as much as that of the alkoxy group. A highly pure water, a catalyst, etc., are introduced to a hydrolyzing reaction system, carrying out gelation of the product in a heated state or a normal temperature state to obtain wet silica gel containing an alcohol, and subdividing and drying the wet silica gel to provide dried silica gel powder having 10-1,000 μm diameter. Further, the obtained dried silica gel powder is thermally treated in a rotary kiln, and allowed to flow down by lifting the powder by the contact surface between the powder 1 and the wall of a reactor core pipe 2 and flowing down the powder over the angle of repose.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently producing synthetic quartz powder. In recent years, the optical communication field,
In glass products used in the semiconductor industry and the like, very strict control is performed on trace impurities and micro bubbles in the products. Such high quality glass is mainly
A method for purifying natural quartz, a method for attaching and growing fumes generated by decomposition of silicon tetrachloride in an oxyhydrogen flame to a substrate, and a method for sintering silica gel obtained by hydrolysis and gelation of silicon alkoxide and the like. Generated by such a method. However, the method (1) has a limit in reducing the content of trace impurities, and the method (2) has problems such as extremely high manufacturing cost. On the other hand, in the method using silica gel, in particular, the method using silicon alkoxide as a raw material, a synthetic quartz powder having a low trace impurity content can be obtained at a lower cost than the method, but it does not necessarily satisfy the required level. In other words, the method using the silicon alkoxide has a problem that, in some cases, microbubbles are generated in the molded product of the final product.

[0002]

SUMMARY OF THE INVENTION As a result of the earnest study of the present inventors, a method for producing a synthetic quartz powder using silicon alkoxide is inexpensive compared with the conventional method, and extremely small bubbles are generated when producing a molded product. It has been found that the following problems can be solved in order to industrially produce a small amount of synthetic quartz powder.

[0003] That is, the firing of silica gel is generally carried out by a method in which silica gel is charged into a quartz container and heated in an electric furnace or the like in order to eliminate contamination of impurities from the container. In particular, when industrially manufactured, a large-diameter quartz crucible is used. However, since silica gel has a lower bulk density than quartz powder, a container used for baking cannot be used efficiently, productivity is poor, and production cost is high. Therefore, increasing the bulk density of the powder charged into the crucible is an important issue for improving productivity.

On the other hand, in the production of a molded body using quartz powder, the generation of microbubbles during the production of the molded body is affected by the heating process in the firing step in the production of quartz powder. The silica gel powder obtained by hydrolyzing the silicon alkoxide retains unreacted alkoxy groups and a part of the by-produced alcohol even if the by-produced alcohol is removed by drying. Actually, when the carbon concentration in the dried silica gel powder is measured, it is 1 to 3% depending on the drying conditions. When this silica gel powder is calcined in an oxygen-containing gas, most of the carbon is burned and removed in the course of raising the temperature, but part of the carbon is sometimes trapped as unburned carbon in the synthetic quartz powder. If synthetic quartz powder containing this unburned carbon is used, CO or CO ₂ gas is generated during melt molding, which causes the generation of bubbles. Therefore, it is necessary to remove substantially all of the unburned carbon before sealing the silica gel, and the rate of temperature increase during the temperature increase process is important.

However, as described above, when synthetic quartz powder is manufactured industrially, a large-diameter quartz crucible is used.
Since the temperature in the crucible during the temperature raising process becomes uneven, it is difficult to raise the temperature of all parts in the container in a predetermined temperature pattern. As a result, in some cases, a phenomenon is observed in which synthetic quartz powder in which carbon remains is partially generated, and microbubbles are generated in a molded body using the synthetic quartz powder.

[0006]

Means for Solving the Problems In view of the above problems, the present inventors have conducted further intensive studies. As a result, the silica gel is subjected to heat treatment under appropriate conditions and operations before firing, so that the powder to be fired is obtained. It has been found that the bulk density can be made equal to that after firing, and that the alkoxy group and the hydroxyl group can be sufficiently removed, and the present invention has been completed. That is, the present invention is a method of producing a synthetic quartz powder by heating while flowing while continuously supplying silica gel powder from one end of a rotary kiln, and supplying an oxygen-containing gas to the rotary kiln. A method for producing a synthetic quartz powder.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
Synthetic quartz powder targeted in the present invention, silica gel powder,
It is a synthetic quartz powder made nonporous by firing.
The method for producing the silica gel powder is not particularly limited, and various known methods can be adopted, but from the viewpoint of easily achieving high purity, hydrolysis and gelation of alkoxysilane and the like,
The so-called sol-gel method is preferred. The hydrolysis of alkoxysilane by the sol-gel method is performed by reacting alkoxysilane with water according to a known method.

The alkoxysilane used as a raw material is preferably a C1-4 lower alkoxysilane such as tetraalkoxysilane and tetraethoxysilane or an oligomer thereof. The amount of water used is usually selected from the range of 1 to 10 equivalents of the alkoxy group in the alkoxysilane. At this time, if necessary, an organic solvent such as an alcohol or an ether which is compatible with water may be mixed and used. Representative examples of the alcohol used include lower aliphatic alcohols such as methanol and ethanol.

In this hydrolysis reaction, hydrochloric acid is used as a catalyst.
An acid such as acetic acid or an alkali such as ammonia may be added as a catalyst. It is needless to say that all substances to be introduced into the reaction system, such as water and catalyst used here, need to be of high purity. Gelation of the hydrolysis product is performed under heating or at room temperature. When heating,
Since the speed of gelation can be improved, the gelation time can be adjusted by adjusting the degree of heating.

The obtained gel is a wet silica gel containing a large amount of water and an alcohol formed by hydrolysis, and may be finely divided and then dried, or may be dried and then finely divided. In any case, the particle size after drying is 10 to 1000 μm, preferably 100 to 600 μm.
Subdivision is performed to a size of μm. Drying is performed while heating under normal pressure or reduced pressure. The heating temperature varies depending on the conditions, but is usually 50 to 200 ° C. The operation can be performed either batchwise or continuously. The degree of drying is usually 1 to 30% by weight.
Done until. The term “liquid content” as used herein refers to a weight reduction rate when a constant weight is reached at 160 ° C.

The dried silica gel powder thus obtained is heat-treated under the following specific conditions. That is, the silica gel powder is heated in a rotary kiln under a specific gas supply condition while rotating the rotary kiln to flow the silica gel powder. This heat treatment may be performed using a plurality of rotary kilns. The term “flow of powder” as used herein refers to, for example, the powder (see FIG. 2 which shows a cross section of a rotary kiln in a rotating state in which powder is charged, compared to FIG. 1 which shows a cross section of a stationary rotary kiln). There is substantially no slippage between 1) and the powder contact surface (3) of the core tube (2) wall, the powder is lifted by the core tube wall, and the powder leaves the wall surface at a repose angle or more, and the core leaves. Flowing down the bottom of the pipe wall (in the direction of the black arrow in FIG. 2)
Say.

It is necessary to select a material for the furnace tube that does not cause contamination of the material to the treated powder, and is preferably made of quartz. In the case of quartz, there is a limit in the size of the furnace tube in terms of manufacturing, so that heat treatment is performed using a multi-stage rotary kiln depending on conditions. The temperature range in which the heat treatment is performed is 50 to 1100 ° C. Usually, heating is performed by a heater.

[0013] By the heat treatment, first, water and alcohol contained in the silica gel are volatilized. Subsequently, the temperature is raised to the combustion temperature range of the remaining carbon component. This temperature range is 300 to 600 ° C. However, the present inventors have found that when heating at 300 to 430 ° C. for burning the remaining carbon component is performed in a rotary kiln, the fluidity of the powder in the rotary kiln is extremely poor. Therefore, the combustion of the remaining carbon component is performed at a temperature of 450 ° C. or higher.

In the powder heated to a temperature range of 450 ° C. or higher, the residual carbon decreases. If the powder temperature is 60
When the temperature reaches 0 ° C. or higher, sealing of the silica gel starts, so that almost all of the remaining carbon must be eliminated before the temperature reaches this temperature range. Otherwise, unburned carbon remains in the obtained synthetic quartz powder, and bubbles are generated during melt molding.

For this purpose, it is necessary to appropriately control the time during which the powder passes through the temperature range of 450 to 550 ° C. In a rotary kiln, powder moves in a piston flow substantially in the traveling direction. Therefore, the passage time in the predetermined temperature zone is naturally determined from the length of the predetermined temperature zone in the rotary kiln and the moving speed in the traveling direction of the powder. For example, if the length of the predetermined temperature zone is 1 m and the moving speed of the powder in the traveling direction is 0.5 m / Hr,
The passing time is 2 hours.

Usually, the passage time in this temperature range is 0.5
10 to 10 hours, preferably 1 to 5 hours. If it is shorter than this range, it is very difficult to sufficiently reduce unburned carbon, and if the passage time is longer than this, there is no difference in the amount of unburned carbon, and the apparatus is large and not economical. . Next, a control method of the heat treatment described above will be described.

In the present invention, since the operation is performed continuously, the heating zone of the furnace tube is divided into a plurality of zones in accordance with the traveling direction of the processing powder, and the heaters of each zone are set so that the temperature of the powder becomes a predetermined region. This can be achieved by adjusting the heating intensity. The present invention is characterized in that the powder is heated while supplying the oxygen-containing gas to the rotary kiln. Specifically, a method is employed in which the oxygen-containing gas is supplied from one end of the furnace tube and discharged from the other end. The supply end of the oxygen-containing gas may be either the supply end or the discharge end of the powder, but it is easier and preferable to make the supply end of the powder and the supply end of the oxygen-containing gas the same from the viewpoint of making the apparatus. .

By supplying the oxygen-containing gas, the reduction of the carbon present in the silica gel is promoted, and the residual carbon in the obtained synthetic quartz powder is substantially disappeared. Decreases sharply. The oxygen concentration of the oxygen-containing gas is usually 5 to 50%. Components other than oxygen are usually inert gases such as nitrogen, helium, and argon. Oxygen-containing gas can be prepared by mixing oxygen and these inert gases at a predetermined ratio,
Air may be used as the oxygen-containing gas, and the use of air is economically preferable. It is also possible to use air diluted with an inert gas. If the oxygen concentration is lower than 5%, the effect of improving the speed of carbon reduction is reduced, and if the oxygen concentration is higher than 50%, an explosive composition may be formed with the organic component volatilized from silica gel, which is not preferable.

The supply amount of the oxygen-containing gas is determined by the amount of carbon contained in the silica gel and the oxygen concentration of the oxygen-containing gas. That is, 1 of the amount necessary for complete oxidation of carbon
Supply 30 to 300 liters at 10 to 10 times. It is preferable that dust is removed from the oxygen-containing gas using a filter or the like in advance. If the dust is not removed, the dust adheres to the powder to be treated, and the quality of the synthetic quartz powder may be greatly reduced. The degree of dust removal is desirably through a filter having an absolute filtration accuracy of preferably 10 μm or less, preferably 5 μm or less, particularly preferably 2 μm or less. As a result, the present inventors have made it clear that dust that adversely affects the quality of the synthetic quartz powder can be almost completely removed.

By the above heat treatment, the carbon concentration in the silica gel is reduced to about 50 to 1000 ppm.
The treated powder from which the remaining carbon has almost disappeared is continuously heated, and the final powder temperature is 900 to 1100.
° C, preferably up to 950-1050 ° C. The heating rate at this time is usually 100 to 1000 ° C / Hr. In the rotary kiln, the powder flows substantially in a piston flow in the traveling direction, so that the temperature of the supplied powder increases as it moves in the rotary kiln in the traveling direction. Therefore, the temperature rise rate of the powder is such that the distance between the temperature measurement points in the rotary kiln is 1 m and the temperature difference is
And the moving speed in the traveling direction of the powder is 0.5 m /
In the case of Hr, the heating rate is 400 ° C./Hr.

In the heat treatment in this temperature range, the powder is also heat-treated while supplying the oxygen-containing gas to the rotary kiln. Specifically, a method is employed in which an oxygen-containing gas is supplied from one end of the core tube and discharged from the other end. In this temperature range, the amount of carbon remaining in the powder is 50 to 1000 ppm.
Although the reason is not clearly understood by supplying the oxygen mixed gas, the bubbles generated at the time of melt-molding the obtained synthetic quartz powder are drastically reduced.

The supply amount of the oxygen-containing gas is determined by the amount of carbon contained in the silica gel and the oxygen concentration of the oxygen-containing gas, but it is preferable to remove dust using a filter or the like in advance. If the dust is not removed, it adheres to the powder to be treated, greatly reducing the quality of the synthetic quartz powder. The degree of dust removal is preferably 10μ absolute filtration accuracy
m, preferably 5 μm or less, particularly preferably 2 μm
It is desirable to remove dust through the following filters. It has been clarified by the study of the present inventors that the dust which adversely affects the quality of the synthetic quartz powder can be almost completely removed.

It is desirable that the heat treatment at this temperature is also performed while the powder is fluidized using a rotary kiln. By performing the process while the powder is flowing using a rotary kiln, uniform heating is performed, and a uniform processed powder is obtained. This treatment almost completes the sealing of the silica gel,
The tap bulk density of the powder, which was about 0.7 to 0.8 g / ml (hereinafter referred to as bulk density), is 1.0 to 1.2 g / ml.
Rise to the extent.

When the silica gel powder is subjected to a heat treatment according to the present invention, a synthetic quartz powder is obtained.
000 ppm or more remains. Therefore, firing is performed in a further elevated temperature range. As a container used for firing, a material that does not generate contamination of the synthetic quartz powder with impurities, for example, a crucible made of quartz is used. In this firing, it is not necessary to pay special attention to the heating rate because substantially all of the carbon in the powder used for firing has already been removed. Therefore, since the variation in the heating rate in the container does not affect the quality, a homogeneous product can be obtained, and a container having a larger capacity can be used as compared with the related art. In addition, since the bulk density of the powder has been sufficiently increased in advance, there is no significant change in the bulk density of the powder before firing and the bulk density of the powder after firing, and the container can be used efficiently. The performance is improved.

The firing temperature is usually from 1100 to 1300 ° C.
It is. The heating rate is not particularly limited, and is 100 to 2000.
It is appropriately selected from the range of ° C / Hr. The calcination time depends on the calcination temperature, but is usually 10 to 100 hours, and the silanol concentration in the synthetic quartz powder is 100 ppm or less, preferably,
It is continued until it becomes 60 ppm or less. In addition, it is preferable that the heating be performed while flowing air or substantially inert gas which does not substantially contain water, since the reduction rate of the silanol group is accelerated. Naturally, carbon does not substantially exist in the synthetic quartz powder after firing.

The synthetic quartz powder thus obtained is formed into a compact. The molding method varies depending on the use of the molded body. For example, when the use is a crucible, the arc melt method is used, and when the use is an IC jig,
Examples thereof include a method of forming an ingot by the Bernoulli method using an acid / hydrogen flame, and a method of heating and melting under vacuum using a carbon mold.

In any case, when the synthetic quartz powder obtained by the method of the present invention is used, a molded article with very few bubbles can be obtained, so that the quality of the molded article and the product yield are greatly improved. Hereinafter, the present invention will be described more specifically with reference to examples.

[0028]

[Example 1]

(Preparation of dry silica gel) High-purity tetramethoxysilane was reacted with water to obtain a lump wet gel. Subsequently, after crushing this massive wet gel with a mesh pulverizer,
The resultant was dried by heating under reduced pressure to obtain powdery dry silica gel.
This powdery dry silica gel is classified by a vibrating sieve to obtain 5
Particles of 00 μm or less and 100 μm or more were obtained. When the powdery dry silica gel was analyzed, the liquid content was 16.7% by weight and the carbon concentration was 1.0% by weight. The bulk density of this powdery dry silica gel is
0.90 g / ml.

The following heat treatment was performed using a rotary kiln schematically shown in FIG. In FIG. 3, 6 is a dry gel hopper, 7 is a table feeder, 8 is a furnace tube, 9 is a supply port, 10 is a supply port donut-shaped weir, 11 is an air supply pipe, 12 is a discharge port, and 13 is a donut-shaped discharge port. Weir, 14 is a processing powder receiver, 15 is a first heater, 16 is a second heater, 17 is a third heater, 18 is a fourth heater, and 19 is a fifth heater. The furnace tube is made of quartz, length (heating zone): 2m, inner diameter: 200m
m, opening diameter of the supply port donut-shaped weir: 15 mm, opening diameter of the discharge-nut donut-shaped weir: 22 mm, and the maximum layer height is 90 m.
m. The core tube was adjusted so that the inclination angle was 0.2 °.

(Heat treatment-previous stage) First, the heaters were heated (first heater: 330 ° C, second heater: 330 ° C, third heater: 455 ° C, fourth heater: 455 ° C, Fifth heater: 455 ° C),
While the furnace tube was rotated at 8 rpm, powdered dry silica gel was supplied at a rate of 11 kg / hour, and air passed through a filter (“MCG-045” manufactured by Advantech) at a rate of 100 liter / minute from a supply port. The powder in the furnace tube was flowing continuously and continuously. The powder discharged at 4, 6, and 8 hours after the start of the supply operation was analyzed.

[0031]

[Table 1]

As can be seen from Table 1, the analytical values of the powder were stable. (Heat Treatment-Latter Stage) Subsequently, the powder obtained by the above operation was subjected to a heat treatment under the following conditions using the same rotary kiln. The first heater: 500 ° C., the second heater: 500 ° C., the third heater: 500 ° C., the fourth heater: 1000 ° C., the fifth heater: 1030 ° C., and the furnace tube was rotated at 8 rpm. While powdering 9.
At 2 kg / Hr, a filter (Advantech “M”
(CG-045 type) was supplied from the supply port at 110 liter / min.

The final temperature of the heat-treated powder is 1020 ° C.
Met. The powder in the furnace tube was flowing continuously and continuously. When the synthetic quartz powder discharged at 4, 6, and 8 hours after the start of the supply operation was analyzed, the values shown in Table 2 were obtained.

[0034]

[Table 2]

(Firing) Synthetic quartz powder 1 obtained by heat treatment
30 kg was charged into a quartz crucible having a diameter of 550 mm, and heated and fired in an electric furnace. Furnace heating rate 200 ℃ /
After the temperature was increased to an ultimate temperature of 1200 ° C. with Hr, the temperature was maintained at the same temperature for 40 hours. At this time, clean dry air having a dew point of −60 ° C. was passed through the crucible at 780 liter / Hr. After the completion of the holding, the heating was stopped and the temperature was cooled to room temperature. During the cooling, clean dry air circulated. The amount of the synthetic quartz powder obtained after firing was 115 kg. When the obtained synthetic quartz powder was analyzed for each sampling location, the values shown in Table 3 were obtained.

[0036]

[Table 3]

(Forming) The synthetic quartz powder obtained by firing was formed into an ingot by the Bernoulli method at each sampling location. No foaming was observed during the ingot.

Example 2 The air supply amount before and after the heat treatment was 50 liters /
The powdery dry silica gel obtained in Example 1 was subjected to a heat treatment using the same rotary kiln as used in Example 1 except that the amount was changed to minutes. Heat treatment-The residual carbon concentration in the powder obtained in the former stage was 1200 ppm. The heat treatment—the residual carbon concentration in the powder obtained in the latter stage was 5 ppm or less, and the number of black particles was 1/10 g. The synthetic quartz powder obtained by the heat treatment was fired and molded in the same operation as in Example 1. 1/10 g of fine bubbles were observed in the ingot.

Example 3 Example 1 (dry silica gel) was prepared in the same manner as in Example 1 except that the same rotary kiln as in Example 1 was used, and the air supply rates at the first and second stages of the heat treatment were changed to 25 L / min. The heat treatment was performed on the powdery dry silica gel obtained in (Creation).

Heat treatment-The residual carbon concentration in the powder obtained in the preceding stage was 1350 ppm. The heat treatment—the residual carbon concentration in the powder obtained in the latter stage was 5 ppm or less, and the number of black particles was 2/10 g. Firing and molding were performed by the same operation as in Example 1 using the synthetic quartz powder obtained by the heat treatment. 5/10 g of fine bubbles were observed in the ingot.

Comparative Example 1 The same operation as in Example 1 was carried out except that the same rotary kiln as used in Example 1 was used, and nitrogen was used in place of air as the supply gas before and after the heat treatment.
The powdery dry silica gel obtained in (Preparation of dry silica gel) was subjected to a heat treatment.

Heat treatment-The residual carbon concentration in the powder obtained in the former stage was 3000 ppm. The heat treatment—the residual carbon concentration in the powder obtained in the latter stage was 5 ppm or less, and the number of black particles was 25/10 g. Firing and molding were performed by the same operation as in Example 1 using the synthetic quartz powder obtained by the heat treatment. Countless microbubbles were observed in the ingot.

[0043]

According to the present invention, it is possible to easily obtain a synthetic quartz powder having a small amount of residual carbon which causes foaming during melting.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a stationary rotary kiln charged with powder.

FIG. 2 is a cross-sectional view of a rotating rotary kiln in which charged powder is in a flowing state.

FIG. 3 is a diagram schematically showing a rotary kiln that can be used in the present invention.

[Explanation of symbols]

 1: powder 2: furnace tube 3: powder contact surface 4: void in furnace tube 5: powder surface 6: dry gel hopper 7: table feeder 8: furnace tube 9: supply port 10: supply port donut weir 11: Air supply pipe 12: Outlet 13: Outlet donut-shaped weir 14: Processing powder receiver 15: First heater 16: Second heater 17: Third heater 18: Fourth heater 19: Fifth heater

Claims (8)

[Claims] 1. A method for producing a synthetic quartz powder by continuously heating silica gel from one end of a rotary kiln and heating it while flowing, wherein oxygen-containing gas is supplied to the rotary kiln. Method for producing synthetic quartz powder. 2. The method according to claim 1, wherein the oxygen-containing gas is air. 3. The method for producing synthetic quartz powder according to claim 1, wherein the oxygen-containing gas is a clean gas from which dust has been removed. 4. The final temperature of the heat treatment is 900 to 1100.
The method for producing a synthetic quartz powder according to any one of claims 1 to 3, wherein the temperature is ℃. 5. After performing the heat treatment at 1100 ° C. or less,
The method for producing synthetic quartz powder according to any one of claims 1 to 4, further comprising firing at a temperature exceeding 1100 ° C. 6. The method for producing synthetic quartz powder according to claim 1, wherein the method is performed using a multi-stage rotary kiln. 7. The method for producing synthetic quartz powder according to claim 1, wherein the material of the core tube of the rotary kiln is quartz. 8. The method for producing synthetic quartz powder according to claim 1, wherein the silica gel powder is obtained by hydrolysis of tetraalkoxysilane.