JPH11139818A - Manufacturing method of high purity silica powder - Google Patents

Abstract

(57) Abstract: A method for inexpensively producing high-purity silica powder that can be used in optical-related fields such as optical quartz glass, semiconductor encapsulants, and semiconductor-related fields such as crucibles for pulling Si single crystals. I will provide a. In producing high-purity silica powder from sodium silicate, (a) a step of adding an acid to sodium silicate to adjust the pH to less than ₂ to obtain an acidic sodium silicate solution of 4 to 12% by weight as SiO ₂ ; (B) passing the acidic sodium silicate solution through a hydrogen-type cation exchange fiber having an ion exchange capacity 2.5 times or more the cation amount of the acidic sodium silicate solution obtained in (a), A step of obtaining an aqueous colloidal solution of pure active silicic acid; (c) adding an alkali to the aqueous colloidal solution of high-purity active silicic acid obtained in (b) to adjust the pH to 4 to 7;
(D) drying the high-purity silica cake obtained in (c) and then pulverizing it to obtain a high-purity silica powder. A method for producing silica powder is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical-related fields such as quartz glass for optical use, synthetic quartz glass plate for photomask, and transparent quartz glass for optical fiber, semiconductor encapsulant,
The present invention relates to a method for producing a high-purity silica powder used in a semiconductor-related field such as a crucible for pulling an i-single crystal.

[0002]

2. Description of the Related Art Conventionally, various methods have been studied for producing high-purity silica powder. For example, as a method of using silicon tetrachloride as a raw material, a method in which silicon tetrachloride is supplied into an aqueous hydrochloric acid solution and the resulting slurry is used. Is filtered, washed with water, and dried to obtain silica (Japanese Patent Application Laid-Open No. Sho 62-30613), the silicon alkoxide is hydrolyzed, and the obtained sol is gelled.
A method of drying this to obtain silica (JP-A-5-4827)
Publication). However, Japanese Patent Application Laid-Open
In the method described in JP-A-30613, silicon tetrachloride as a raw material is expensive, and a large amount of alkali is required to neutralize a large amount of hydrogen chloride generated during hydrolysis. There was a problem that it could not be obtained. Further, the method described in JP-A-5-4827 has a problem that an inexpensive product cannot be obtained because silicon alkoxide as a raw material is expensive.

On the other hand, as a method for producing high-purity silica powder using sodium silicate as a raw material, Japanese Unexamined Patent Publication (Kokai) No. 61-270209 discloses a method in which an acid is added to diluted sodium silicate to pH 3.5.
２2, which is passed through a hydrogen-type strongly acidic cation exchange resin and an OH-type weakly acidic anion exchange resin to obtain a high-purity active silicic acid solution, which is concentrated, dried and calcined. . However, in this method, it is impossible to flow a high concentration of alkali silicate to prevent gelation in the ion exchange resin because the solution is adjusted to pH 3.5 to 2, and a dilute acid having a silicic acid concentration of less than 2% by weight is impossible. There is a problem that only silicic acid can be obtained and a large amount of water needs to be evaporated in a subsequent step, which is not efficient as a production process. Further, Japanese Patent Application Laid-Open No. 1-126216 discloses a method for producing a silica sol in which a mixed solution of sodium silicate and a silica sol or an aqueous solution of silicic acid is passed through hydrogen-type ion exchange fibers. However, in this method, a mixture of sodium silicate and silica sol or an aqueous solution of silicic acid is passed through the ion-exchange fiber. When sodium silicate showing alkalinity is turned into a sol, the inclusion of impurity elements cannot be prevented, so that Fe,
There is a problem that impurities such as Al cannot be removed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of solving these problems, and an object of the present invention is to provide an optical system such as an optical quartz glass for solving the above-mentioned conventional problems. Related fields, semiconductor encapsulants, Si
An object of the present invention is to provide a method for inexpensively producing high-purity silica powder that can be used in semiconductor-related fields such as a crucible for pulling a single crystal.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, when producing high-purity silica from industrial sodium silicate, an acid was added to a sodium silicate solution or the like. By adjusting the pH to less than 2, a high-concentration acidic sodium silicate solution was obtained, and this was used to obtain an aqueous colloidal solution of high-purity active silicic acid from which sodium ions and other metal impurities were removed using hydrogen-type cation exchange fibers. After adding ₃ to adjust the pH to 4-7, separating and washing to obtain a high-purity silica cake, drying and pulverizing it to obtain a high-purity silica powder. After crushing the silica powder and firing or sintering the crushed product after granulation, they have found that they are useful as raw materials for various uses such as molten glass, and have completed the present invention.

Hereinafter, the method of the present invention will be described in detail.

First, sodium silicate used as a raw material in the present invention will be described. For example, commercially available sodium silicates for industrial use include No. 1, No. 2, No. 3, No. 4, and Na ₂ O and SiO _2.
Is only applicable to all industrial sodium silicates. An example of the chemical analysis value of commercial industrial sodium silicate is as follows.
O ₂ 29.02%, Na ₂ O 9.39%, Al ₂ O ₃
0.13% and Fe ₂ O ₃ 0.01%. Further, as the sodium silicate used as a raw material in the method of the present invention, not only such a liquid but also a solid silicate can be used. The concentration of sodium silicate is preferably high as the concentration of SiO ₂ in order to make the production process compact, facilitate gelation and increase the yield of high-purity silica powder finally obtained.

Next, a description will be given below along a manufacturing process.

Step (a) In the method of the present invention, the step (a) is carried out under acidic conditions such as SiO 2.
₍₂ ) An acidic sodium silicate solution which is stable even in a solution having a high concentration and gives sufficient fluidity and can remove sodium and other impurities in the subsequent step (b). Here, the pH of the sodium silicate solution is adjusted to less than 2 in order to be stable even at a high silicic acid concentration of 4 to 12% by weight obtained in the step (a) and to remove impurities such as aluminum and iron in the ion exchange step. It is essential to do. Within this range, it is possible to prevent gelation from occurring and the active silicic acid to contain impurities in the subsequent ion exchange step. On the other hand, when the pH is 2 or more, the rate of change from the alkali side to the acidic side is not sufficient, so that gelation may occur, and the active silicic acid contains impurities in the ion exchange step. It is not preferable because the removal of impurities may be incomplete.

The acid to be added is not particularly limited as long as the rate of change from the alkaline side to the acidic side is sufficient, and strong acids such as hydrochloric acid, sulfuric acid and nitric acid are preferably used. In order to obtain an acidic sodium silicate solution, nitric acid is preferably used. When acid is added to the sodium silicate solution, the acid is added to the sodium silicate solution with strong stirring at a stroke in order to prevent the pH from changing from the alkali side to the acid side sufficiently and prevent gelation during the addition. It is preferable that the addition be performed in several seconds to several minutes, although the time varies depending on the scale of production and cannot be unconditionally determined.

The concentration of silicic acid in the sodium silicate solution is S
range of 4 to 12 wt% is preferred as iO _2. The reason for this is that in the case of industrial use, the acid sodium silicate solution can be further prevented from gelling in terms of productivity such that the volume of the necessary solution can be reduced by increasing its concentration. It is preferable from the viewpoint of the stability of the solution. If the content is out of this range and is less than 4% by weight, the volume of the solution becomes large, and the subsequent ion exchange step takes a long time to perform the treatment.
Exceeding this is not preferred because gelation occurs.

Step (b) In the step (b) of the method of the present invention, the acidic sodium silicate solution obtained in the step (a) is passed through a hydrogen-type strongly acidic cation exchange fiber, and the cationic property in the solution is reduced. This is to obtain a high-purity aqueous colloidal solution of active silicic acid by removing metal impurities.

Here, as the hydrogen-type strongly acidic cation exchange fiber used in the step (b), the high-concentration acidic sodium silicate solution obtained in the step (a) can be quickly and efficiently purified with high-purity active silicate. It is important that it can be converted to Therefore, it is possible to avoid the occurrence of gelation during the treatment by rapidly and efficiently converting sodium silicate to active silicic acid in a hydrogen form by an ion exchanger having a strongly acidic group such as a sulfonic acid group. You can do it. In contrast, treatment with an ion exchanger having a weakly acidic group such as a sulfonic acid group instead of a strongly acidic group may reduce the efficiency of ion exchange or cause gelation during the treatment. There is not preferred.

Further, the ion exchange fiber is used as the ion exchanger because the specific surface area is large and the ion exchange rate is high. This is because by increasing the speed, the ion exchange treatment can be performed quickly and gelation can be avoided. In contrast,
When a cation exchange resin is used in the step (b), it is not preferable that a high-concentration acidic sodium silicate solution is passed through, so that a gel-like substance may precipitate in the resin. The hydrogen-type strongly acidic cation exchange fiber suitable for the step (b) can be easily obtained, for example, as a commercially available industrial product, and an example thereof is IEF-SC manufactured by Nichibi.

The exchange capacity of the ion-exchange fiber used in the method of the present invention is 2.5 times the total equivalent of cations such as sodium ions, iron ions and aluminum ions in the acidic sodium silicate solution passing therethrough. It is preferable that it is above. If the ratio is less than 2.5 times, ion exchange is insufficient and the amount of impurities after passing the solution is not less than ppm, so that high-purity acidic silicic acid cannot be obtained. Further, as the ion exchange capacity, it is preferable that the ion exchange capacity per unit weight of the ion exchange fiber is large in order to quickly and efficiently convert the high-concentration sodium silicate solution to high-purity active silicic acid. .

The conditions for liquid passing in the step (b) are as follows:
What is necessary is just to pass a high-concentration sodium silicate solution through the above-mentioned hydrogen-type strongly acidic cation exchange fiber, and the ion exchange treatment can be controlled by the space velocity as the passing speed. Here, the space velocity is obtained by, for example, the following equation (1).

Space velocity ((hour) ⁻¹ )) = flow rate (L / hour) / filled volume of ion exchange fiber (L) (1) The space velocity is a packed tower filled with ion exchange fiber. Although it fluctuates depending on the shape of silica and the concentration of silicic acid in the acidic sodium silicate solution, it cannot be said unconditionally, it is usually carried out at about 1.5 to 10 (hour) ^-1 . If this value is too small, it takes too much time for the ion exchange treatment, while if it is too large, gelation may occur in the pores of the ion exchange fiber, which is not preferable.

In this way, by subjecting a high-concentration acidic sodium silicate solution to an ion exchange treatment, a high-purity active silicic acid can be obtained as an aqueous colloidal solution stably present in water in a colloidal state.

Step (c) In the step (c) in the method of the present invention, the pH of the high-purity active silicic acid obtained in the step (b) is adjusted to 4 to 7 using an alkali for gelling. The obtained gel is separated and washed to obtain a silica cake of high purity,
The reason for adjusting the pH to 4 to 7 is that gelation does not occur outside of this pH range.

Here, the alkali to be added is pH
Can be adjusted in the range of 4 to 7, and any alkali that has been added in the subsequent step does not remain in the finally obtained high-purity silica powder, and is preferably ammonia that is volatilized by drying or firing. In addition, it is preferable that each element that can be mixed in with the purity of the alkali be as high as 0.1 ppm or less. Further, when ammonia water is used, one having a concentration of 5 to 28% by weight is easily used.

The gel obtained by the addition of the alkali is crushed with a stirring blade, a cutter, or the like, immersed in high-purity water, separated, and washed with water to remove the salt formed. A high-purity silica cake as a lump is obtained. As the high-purity water used here, since it is used in a large amount, it is preferable that each element that can be mixed has a high purity of 1 ppb or less. Known methods such as filtration, centrifugation, and decantation can be used as a method for separating the gel after immersion in high-purity water, and among these methods, the water-containing silica cake obtained in the step (c) can be used. Filtration is preferably used in order to reduce the rate and reduce the burden of drying in the subsequent step. The salt formed during the treatment by washing with water in this manner changes its form depending on the acid and alkali used in the previous step, but this salt can be removed to obtain a high-purity silica cake.

Step (d) In the step (d) in the method of the present invention, the high-purity silica cake obtained in the step (c) is dried by a known method such as hot-air drying or vacuum drying, and then dried with a hammer mill, mortar, A high-purity silica powder is obtained by crushing with a grinder, a roll crusher or the like.

In order to reduce the OH groups remaining in the pulverized powder or to reduce the specific surface area, depending on the intended use, calcination may be carried out as it is or after granulation such as by rolling granulation. You may. The baking temperature in the case of baking may be a condition usually performed, but is preferably 200 ° C. or more for the purpose of removing adsorbed water in high-purity silica powder, and for the purpose of removing silanol groups on the silica surface. Heating at 800 ° C. or higher is preferred. The firing may be performed in the atmosphere, under an inert gas, or in a vacuum.

As described above, a high-purity silica powder can be obtained, and a high-purity silica powder such as Five 9 can be obtained. Such high-purity products are used in optical-related fields where light absorption by impurities is a problem,
It is suitable for a semiconductor-related field where volatilization of impurities at a high temperature becomes a problem.

[0025]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to only these examples. In addition, each measuring method in an Example is as follows.

<Measurement Method of Chemical Composition> For SiO ₂ , the sample was heated to 1000 ° C. and the weight was measured. For Na and Al, the sample was dissolved using an acid, and then an ICP-MS device (VG Elemental) was used. Made by company, Model:
The sample was dissolved in an acid using a pharmacode 2) and then Fe was measured using an ICP-AES apparatus (Perkin Elmer, model: optima 3000DV), and these were measured using Na ₂ O and Al ₂ O. ₃ , calculated in terms of Fe ₂ O ₃ .

<Method for Measuring pH> The pH of the solution was measured with a pH meter (manufactured by DKK, Model: PHL-10).

Example 1 (a) Step The above-mentioned sodium silicate solution No. 3 (composition: SiO ₂ 2)
_{9.02%, Na 2 O9.39%,} Al 2 O 3 0.13
%, Fe ₂ O ₃ 0.01%) 35 ml of deionized water 1
05 ml was added to make 140 ml (7.25% by weight as SiO ₂ , 2.34% by weight as Na ₂ O). While vigorously stirring this diluted solution with a Teflon stirring bar,
8 ml of reagent grade concentrated nitric acid (HNO ₃ 61.3% by weight)
Was added all at once. The resulting solution was clear and showed a pH of 1.0.

Step (b) 80 ml of the above sodium acid silicate solution (61 cations)
meq) was converted to 53.2 g (202 me as an exchange capacity) on a hydrogen-based cation exchange fiber IEF-SC dry base.
The solution was passed through a column packed with q) at a space velocity of 1.5 per hour to recover activated silicic acid having a pH of 0.2.

Step (c) The activated silica was adjusted to pH 2 by adding 35 ml of 5% by weight aqueous ammonia diluted with high-purity water. After adjustment, 1
It gelled in 0 minutes. The gel was finely crushed with a Teflon rod, poured into 200 ml of high-purity water, and stirred for 30 minutes. After completion of the stirring, the mixture was filtered under reduced pressure using a Buchner filter to remove high-purity water 20.
Washed with 0 ml.

Step (d) The silica cake was dried in a clean oven at 80 ° C. for 12 hours to obtain a lump dried product. The dried product was pulverized with a quartz mortar into powder. The dried powder was calcined at 200 ° C. for one hour for the purpose of removing adsorbed water. This powder to SiO ₂ Chemical analysis, Na ₂ O 0.1ppm, Al ₂
O ₃ 2.0 ppm, was obtained in 90% become yield of high purity silica powder starting material of Fe ₂ O ₃ 0.8ppm.

Example 2 (a) Step 70 ml of ion-exchanged water was added to 35 ml of the same sodium silicate solution of No. 3 as in Example 1 to make 105 ml (9.67% by weight as SiO _{2 and} 3.13 as Na ₂ O). weight%). While the diluted solution was vigorously stirred with a Teflon stirrer, 10 ml of reagent grade concentrated nitric acid (HNO ₃ 61.3% by weight) was added at once. The resulting solution was clear and showed a pH of 0.9.

Step (b) The same procedure as in Example 1 was carried out except that the flow rate of the acidic sodium silicate solution was changed to 48 ml.

The steps (c) and (d) are the same as in the first embodiment. When the dry powder was chemically analyzed, 0.2 ppm of Na ₂ O was obtained.
High-purity silica powder of 0.9 ppm of Al ₂ O _{3 and} 0.6 ppm of Fe ₂ O ₃ was obtained at a yield of 90% of the starting material.

Example 3 The steps (a) to (c) were performed in the same manner as in Example 1.

Step (d) The silica cake was dried in a clean oven at 80 ° C. for 12 hours to obtain a lump of dried product. The dried product is pulverized with a quartz mortar, and the pulverized product is filled in a quartz boat and made into a quartz tube.
It was baked at 00 ° C. for 2 hours. The calcined product obtained was subjected to chemical analysis to find that 1 ppm of Na ₂ O, ₃ ppm of Al ₂ O 3,
High purity silica powder of 2 ppm Fe ₂ O _{3 was} used as starting material 9
Obtained in a yield of 0%.

Comparative Example 1 Step (a) 35 ml of ion-exchanged water was added to 35 ml of the sodium silicate solution of No. 3 described above to make 70 ml (1 as SiO _2).
4.51% by weight, 4.70% by weight as Na ₂ O). While strongly stirring the solution diluted twice with a Teflon stirrer, a reagent grade concentrated nitric acid (HNO ₃ 61.3% by weight) 1
0 ml was added all at once. It gelled immediately after the addition.

It has been found that when the concentration of SiO ₂ is high, gelation occurs when an acidic sodium silicate solution is obtained.

Comparative Example 2 The step (a) was performed in the same manner as in Example 1.

Step (b) 140 ml of the above acidic sodium silicate solution (1 cation)
07meq) to hydrogen-type cation exchange fiber IEF-SC
53.2g on a dry basis (202me as replacement capacity)
The solution was passed through a column packed with q) at a space velocity of 1.5 per hour to recover activated silica having a pH of 0.1.

Steps (c) to (d) were performed in the same manner as in Example 1. Chemical analysis of the dried powder revealed that Na ₂ O 10
00 ppm, Al ₂ O ₃ 100 ppm, Fe ₂ O ₃ 30
A powder having a high impurity content of ppm was obtained.

As described above, it was found that when the ion exchange capacity of the ion exchange fiber was smaller than the amount of silicic acid in the acidic sodium silicate, the ion exchange treatment was incomplete.

[0043]

According to the present invention, an acidic sodium silicate having a high silicic acid concentration is prepared from sodium silicate as a raw material, and this is passed through an ion exchange fiber to easily obtain a high-concentration and high-purity active silicic acid, which is powdered. Things. According to the present invention, a high-purity product can be obtained by efficient ion exchange even at a high silicic acid concentration, so that the reaction apparatus can be made compact,
In addition, since separation after gelation to obtain a solid content reduces the burden on drying, it is industrially useful because high-purity silica powder used in optical-related fields and semiconductor-related fields can be produced at low cost. .

Claims (3)

[Claims] (1) In producing a high-purity silica powder from sodium silicate, (a) adding acid to sodium silicate to adjust the pH to less than ₂ to obtain an acidic sodium silicate solution of 4 to 12% by weight as SiO ₂ ; (B) passing the acidic sodium silicate solution through a hydrogen-type cation exchange fiber having an ion exchange capacity 2.5 times or more the cation amount of the acidic sodium silicate solution obtained in (a), (C) obtaining an aqueous colloidal solution of active silicic acid; (c) adjusting the pH to 4 to 7 by adding an alkali to the aqueous colloidal solution of active silicic acid obtained in (b); A method for producing a high-purity silica powder, comprising: a step of obtaining a silica cake; a step of drying and then pulverizing the high-purity silica cake obtained in (d) and (c) to obtain a high-purity silica powder. 2. A method for producing high-purity silica powder, wherein the alkali is ammonia in the step (c) according to claim 1. 3. The step (d) according to claim 1 or claim 2.
The method for producing a high-purity silica powder according to any one of claims 1 to 3, wherein the high-purity silica cake is pulverized and then fired or the pulverized product is granulated and then fired.