JPH03247524A - Production of quartz glass filter - Google Patents

Abstract

PURPOSE:To obtain a high-purify filter which has required dimensional precision and the fluid permeable characteristics and is expandable and porous by ammoniating the molded body of the flaky powder of quartz glass specified in the content of OH group at the specified temp. and thereafter deammoniating this molded body. CONSTITUTION:The base material of porous synthetic quartz glass is obtained by a flame hydrolytic method or a sol-gel method. This base material is ground to obtain the flaky powder of quartz glass contg. >=100ppm OH group. This flaky powder is preliminarily molded and the obtained molded body is heated at 800-1300 deg.C in a gaseous ammonia atmosphere to perform ammoniation reaction. Then deammoniation reaction is performed for this molded body under the conditions of higher temp. of 1350-1700 deg.C. An expandable glass filter having the required continuous vent holes is obtained. In order to control the size of the pore of the expanded material, the range of particle size in the flaky powder of quartz glass for the raw material is selected. Furthermore the rate of heating and temp. rise in the ammoniation reaction and the pressure of its atmosphere are selected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention can be used as a filtration member for filtering fluids that are difficult to process with ordinary filtration devices, such as high-temperature fluids and corrosive fluids. The present invention relates to a method for producing a suitable foamable porous high-purity quartz glass filter.

[Conventional technology]

Quartz glass has excellent chemical resistance, heat resistance, thermal shock resistance, etc., so it is widely used in many fields due to its excellent material properties, but it is also extremely useful as a filter material for separating and purifying fluids, especially liquids. It has traditionally been used as a variety of filters.

Conventional methods for manufacturing silica glass filters include 1, for example, a method of sintering quartz glass powder, a method of processing quartz glass fiber into woven or nonwoven fabric, or a method as disclosed in Japanese Patent Publication No. 39-20171. A method of forming a porous body by a phase separation method is typically known.

However, in the sintering method, the preformed compact generally shrinks due to heating and sintering, so it is difficult to obtain a material with a desired shape and high dimensional accuracy. It is necessary to process it. Furthermore, since the filtration characteristics of the target fluids differ, it is difficult to stably manufacture desired silica glass filters for each individual fluid. On the other hand, silica glass fiber textiles, non-woven fabrics, and other materials not only have problems with their shape retention, but also require many manufacturing steps, which eliminates the inherent advantages of quartz glass as a highly pure and stable material. It is not preferred industrially because it is easily damaged. Furthermore, the production of glass filters by the glass phase separation method reduces the purity of the glass, so it is difficult to say that it is a high-purity quartz glass filter, and the pore diameter of the resulting porous body is extremely small, for example, 20 mm.
~1,000 people, which is not acceptable from a practical point of view because the target and range of use is limited.

[Problem to be solved by the invention]

Therefore, the object or technical problem of the present invention is to provide a high-purity silica glass filter that has desired dimensional accuracy and desired fluid permeability characteristics without the disadvantages and inconveniences described above.

[Means to solve the problem]

The present inventors have developed a method for manufacturing a quartz glass filter that solves the above technical problems, particularly as a highly efficient filtration member useful for filtration of corrosive fluids such as hydrogen chloride gas and hot nitric acid, and high-temperature fluids. After repeated research focusing on high-purity silica glass filters, we have developed a manufacturing method for quartz glass filters that is highly desirable for practical use.

That is, in the present invention, silica glass flake powder containing 1100 pp or more of OH groups is preformed, and the obtained molded body is heated to 800 ppm or more in an ammonia gas atmosphere.
Heating to a temperature of 300°C to carry out an ammonification reaction,
Provided is a method for producing a foamed quartz glass filter, characterized in that the filter is deammoniated at a higher temperature condition of 1,350 to 1,700°C.

The quartz glass material used in the method of the present invention is one that is as pure as possible and contains 1100 pp or more of OH groups. Examples of such materials include, for example, a porous synthetic quartz glass matrix obtained by a well-known flame hydrolysis method of a sufficiently purified silicon compound, or a porous synthetic quartz glass matrix obtained by a sol-gel method. material is suitable. The quartz glass flake powder used in the method of the present invention is prepared by pulverizing the synthetic quartz glass porous base material using, for example, a ball mill or the like to preferably have a particle size in the range of 16 to 150 mesh. In the quartz glass base material produced by the above flame hydrolysis method, the target may be either rod-shaped or plate-shaped, but it is important that the glass fine powder formed is deposited in layers. Melted ingots are unsuitable as powder materials. In addition, a sol that forms a uniform sol by hydrolyzing alkoxysilane in an alcohol solution in the presence of an acid or basic catalyst.
In the gel method, the obtained sol is extruded through a slit-shaped nozzle to make a tape, or it is attached to the surface of a rotating drum like photographic film to make a sheet, which is then gelled, dried, and crushed. A glass flake-like powder can be prepared.

In addition, in the method of the present invention, it is important that the OH group content concentration of the silica glass flake powder prepared in this way is 1100 pp or more in the glass in connection with the ammonification and its elimination reactions described below. Therefore, the practically preferred concentration of OH groups is 300 to 1,500
It is pp+*.

The pulverized synthetic quartz glass flake powder is usually preformed into a shape close to the desired filter shape. For the preforming, an adhesive or pressure-sensitive adhesive such as polyvinyl alcohol or water is usually added. The amount used is approximately 30 to 90% of the weight of the powder, taking into consideration the particle size conditions of the glass flake powder and fluid permeability. , roll forming etc. are advantageously adopted,
In either case, a mold made of synthetic resin such as fluororesin is preferably used instead of a metal mold in consideration of the reduction in purity of quartz glass.

Preferably, the preformed body obtained in this way is preliminarily treated, for example, with a
The organic binder is thermally decomposed by heating to a relatively low temperature of about 00°C. Next, the molded body.

It is subjected to an ammonification reaction in an ammonia atmosphere at a temperature of 800 to 1,300°C. The ammonia atmosphere can be created by supplying a sufficient amount of ammonia into the heating furnace.
Practically, ammonia gas is continuously supplied using nitrogen gas as a carrier gas. Although the details of the reaction mechanism between ammonia and silica glass are unknown, it is presumed that the OH groups in quartz glass effectively act on the reaction with ammonia and effectively contribute to the formation of a foam glass filter. Ru. In this ammonification reaction, it is preferable that the reaction amount of ammonia is 0.1% by weight or more based on the glass, and in this case, it is possible to control the reaction amount to a desired value by selecting the temperature and time in the 5 reactions. can.

The ammoniated molded product is then subjected to a deammonification reaction at a higher temperature, i.e., 1,350 to 1,700°C, to obtain a foamed glass filter having the desired continuous ventilation pores. be able to.

To control the size of the pores in the foam, first select the particle size range of the quartz glass flake powder as the raw material, and then select the heating rate during the ammonification reaction (the pores will be smaller if the temperature is increased slowly). A desired permeability filter can be manufactured by selecting the pressure of the atmosphere and the pressure of the atmosphere (the smaller the pores, the larger the pores).

In addition, in the method of the present invention, a foaming precursor reacted with ammonia is filled into a carbon mold, and a desired foamed molded product according to the mold can be obtained by heating and foaming in a nitrogen gas atmosphere. I can do it. If the molded product is a simple cylinder, it can be easily fabricated into a cylindrical foam to obtain a desired shape.

[Effect]

According to the method of the present invention, a filter with a desired porosity can be easily manufactured, and it is also possible to mold the filter into a desired shape such as styrofoam.

Furthermore, the filter formed from flake powder by the method of the present invention has superior fluid permeability compared to a filter obtained by simply sintering silica glass powder, and therefore has a higher fluid permeability per unit cross-sectional area of light. Since it is expensive, it is provided as a lightweight and compact filter.

〔Example〕

Next, the method of the present invention will be explained in more detail by giving specific examples.

Example 1 Silicon tetrachloride (SiCΩ4) purified by distillation is vaporized using a bubbler, and this gaseous body is mixed with hydrogen gas and oxygen gas and supplied to an oxyhydrogen burner. The material was flame-hydrolyzed and deposited on a target to form a porous synthetic quartz glass matrix about 100 meters in diameter and about 100 meters long. The OH group content of the obtained base material glass was about L100 pp■.

This porous glass quartz glass base material was extracted from the target and ground in a ball mill for 30 minutes to obtain flaky quartz glass powder of 48 to 16 meshes.

After adding 300 g of a 5% polyvinyl alcohol aqueous solution to 500 g of the glass powder thus prepared and mixing well, the mixture was poured into a cylindrical polyvinyl chloride mold with a diameter of 50 mm and a length of 200 m, and was thoroughly dried to obtain a preform. Obtained.

Next, this preform was placed in a quartz glass furnace tube with an inner diameter of 1100II1, and about 40 ON cd/min of nitrogen gas and about 2 ON cd/min of ammonia gas were introduced into the furnace as carrier gas.
, while feeding at a feed rate of 50 ON cd/min.

The ammonification reaction was carried out at a temperature of about 1,000°C for 2 hours.

Next, the ammoniated preform is filled into a final molding mold made of carbon having a cavity with an inner diameter of φ60i+m and a length of 250cm, and the mold is heated at a heating rate of 10°C/win in a nitrogen gas atmosphere. The temperature was raised to 1,400° C., and then the temperature was raised to 1,600° C. at a rate of 1° C./win, and the temperature was maintained at this temperature for 30 minutes for heat treatment, and then allowed to cool.

The obtained cylindrical quartz glass foam with a diameter of 60 mm and a length of 250 mm was sliced into rings with a thickness of 20+ mm using a quartz glass saw to obtain 10 disc-shaped filters.

When corrosive gas containing particles was passed through this filter, there was little pressure loss and particles were removed well.

Comparative Example 1 A porous synthetic quartz glass base material prepared by the same soot method as in Example 1 was used as it was without being crushed, and the inner diameter was 10.
1,000°C while similarly supplying nitrogen carrier gas at a rate of approximately 400 N caf/min and ammonia gas at a rate of approximately 2,50 ON cd/min. The ammonification reaction was carried out at temperature for 2 hours. Then, again, the carrier gas and nitrogen gas supplies are stopped and the temperature is lowered to about 1,000 ml under atmospheric conditions.
The temperature was raised to 600° C. and heat treatment was performed for 10 minutes to obtain an expandable porous body.

A filter was made by cutting out a disk of 60 m in diameter and 20 mm in thickness from this foam.

However, no continuous permeable pores are formed in this disk;
It did not function as a filter because it did not allow fluid to pass through.

Example 2 Tetraethoxysilane 5i (Oc2H5)4 and 0. IN
of hydrochloric acid aqueous solution at a weight ratio of 1:5, the resulting homogeneous sol is extruded through a slit-shaped nozzle, heated and dried, and then ground in a ball mill to obtain 16-48
A mesh flaky synthetic quartz glass powder was prepared.

100 g of the obtained glass powder was uniformly mixed with 80 g of a 5% polyvinyl alcohol aqueous solution and molded in the same manner as in Example 1 to prepare a preform.

The preform was dried and then heated to a temperature of 800° C. for 5 hours to oxidatively decompose the polyvinyl alcohol binder. The porous molded body thus obtained was approximately 1,000
It was heated in a quartz glass tube furnace maintained at 0°C, and nitrogen gas was fed into the tube as a carrier gas at a rate of about 40 ON cd/min, and ammonia gas was fed at a rate of about 2,50 ON cd/min. The ammonification reaction was carried out at temperature for 2 hours.

Next, the supply of carrier gas and nitrogen gas was stopped, and then the temperature was raised to about 1,600° C. under atmospheric conditions and heat treatment was performed for 10 minutes to obtain a porous silica glass body.

A filter was made by cutting out a disk with a diameter of 60 mm and a thickness of 20 mm. When the concentrated aqueous hydrochloric acid solution used for cleaning was filtered through this filter, clear farm acid from which suspended fine solid particles had been completely removed was recovered.

Comparative Example 2 Tetraethoxysilane Si (OC2Hs) 4 and 0.
IN and an aqueous solution of hydrochloric acid were mixed at a weight ratio of 1:5 and hydrolyzed, the resulting homogeneous sol was heated, dried, and ground in a ball mill to prepare granular synthetic quartz glass powder with a mesh size of 16 to 48. . 100 g of this powder was mixed with 80 g of a 5% polyvinyl alcohol aqueous solution, and a preform was prepared by molding. The obtained molded body was heated at 800℃ for 5 minutes.
After heating for a period of time, the temperature was then raised to 1,600° C. in the air, and the temperature was maintained for 10 minutes, resulting in a slightly shrunken silica glass porous body.

This porous body had no function as a filter.

〔Effect of the invention〕

The high-purity quartz glass filter manufactured by the method of the present invention retains the inherent heat resistance, chemical resistance, and thermal shock resistance of the material, and can handle high-temperature fluids that are difficult to filter and clean, as well as highly corrosive fluids. Difficult fluids can be filtered without any inconvenience, and its practical value is extremely high.Also, in addition to its function as a filter, cylindrical filters can be heated and cooled on the sides to reduce their large surface area. can also be used to effectively exchange heat of the fluid passing through it.

Special permission Out wish Man Shin-Etsu Quartz Co., Ltd.

Claims (1)

[Claims] A flaky powder of quartz glass containing 1,100 ppm or more of OH groups is preformed, and the resulting molded body is heated to a temperature of 800 to 1,300°C in an ammonia gas atmosphere. Ammonification reaction is carried out, and this is 1,350 to 1
, a method for producing a foamed quartz glass filter, characterized in that deammonia treatment is carried out at higher temperature conditions of 700°C. 2. Claim 1, wherein the flaky quartz glass powder is prepared to have a particle size in the range of 16 to 150 mesh.
The method for manufacturing the quartz glass filter described. 3. The thickness of the silica glass powder flakes is 1 to 10 μm.
The method for manufacturing a quartz glass filter according to claim 1 or 2.