JP2003104716A - Method for producing low-boron silica particle and low- boron silica particle using it and method for producing low-boron quartz glass using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a low-boron silica particle with high purity and in which boron content is reduced sufficiently even if an inexpensive alkali metal silicate solution is used as a raw material, the low-boron silica particle obtained by the method and a method for producing a low-boron quartz glass particle using the low-boron silica particle. SOLUTION: An acidic silica solution whose pH is 2.0 or less is obtained from the alkali metal silicate solution. The method for producing the low-boron silica particle is comprised of the first step to obtain a hydrated silica gel by leaving the solution in the conditions of pH 2.0 or less and 60 deg.C or less to change it to a gel, the second step to obtain a hydrated silica particle in which water content is decreased by thawing it after freezing and the third step to wash the obtained hydrated silica particle at 60 deg.C or less.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing low-boron silica particles, a low-boron silica particle obtained by this method, and a method for producing low-boron silica glass particles using the same, and particularly to a silicon single crystal for semiconductors. The present invention relates to low-boron silica particles capable of obtaining low-boron silica glass particles used as a raw material for a crucible for pulling, a method for producing the same, and a method for producing the low-boron quartz glass particles.

[0002]

2. Description of the Related Art Although natural quartz has long been used as a quartz raw material, synthetic quartz has come to be used recently due to variations in purity, exhaustion of resources, and environmental pollution caused by development. There is. Conventionally, synthetic quartz powder is made from tetramethoxysilane, tetraethoxysilane, silicon tetrachloride, etc. as a raw material, so it is highly pure but expensive.
If synthetic quartz glass particles are produced using this, the cost will be very high, and therefore it was not industrially suitable.

On the other hand, at the present time when semiconductor products are highly integrated, especially for crucible members for pulling silicon single crystals for semiconductors, high-purity synthetic quartz glass with extremely few metal impurities is required.

In response to these demands, various attempts have recently been made to obtain high-purity synthetic silica glass powder at low cost, and silica particles are obtained by using inexpensive water glass (alkali metal silicate aqueous solution) as a raw material. Japanese Patent Laid-Open No. 59-54632 discloses a method of obtaining quartz glass powder using the same.
JP-A-4-349126, JP-A-11-1192
No. 9 publication and the like.

[0005]

However, the silica particles or synthetic quartz powder obtained by these methods cannot sufficiently remove a trace amount of boron. For example, when synthetic quartz is used as a crucible member for pulling a silicon single crystal for semiconductors, if the boron in the synthetic quartz is not sufficiently reduced, the resistance value of the single crystal silicon will be as designed when it is used in the production of single crystal silicon. Can no longer be manufactured. Therefore, there has been a demand for a technique capable of reducing the content of boron in the silica particles, and further in the synthetic quartz powder, to a more sufficient level.

Therefore, an object of the present invention is to obtain high-purity silica particles even when an inexpensive alkali metal silicate aqueous solution is used as a raw material, and particularly to obtain low-boron silica particles having a sufficiently reduced boron content. It is an object of the present invention to provide a method for producing low-boron silica particles that can be produced and low-boron silica particles obtained by this method. Another object of the present invention is to provide a method for producing low boron silica glass particles using the low boron silica particles.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the content of boron has never been higher by setting predetermined conditions in the production process of silica particles. The inventors have found that it can be reduced, and have completed the present invention. That is, the present invention is as follows.

The method for producing low-boron silica particles of the present invention (hereinafter referred to as "present first invention") is to obtain an acidic silica aqueous solution having a pH of 2.0 or less from an alkali metal silicate aqueous solution,
The acidic silica aqueous solution is allowed to stand under conditions of pH 2.0 or lower and 60 ° C. or lower to cause gelation to obtain hydrous silica gel, and the obtained hydrous silica gel is frozen, thawed and allowed to separate water. The method is characterized by including a second step of reducing water content to obtain hydrous silica particles, and a third step of washing the obtained hydrous silica particles under conditions of 60 ° C. or lower.

In the first aspect of the present invention, the acidic silica aqueous solution having a pH of 2.0 or less is added to the following (1) or (2):
(1) A product obtained by subjecting the alkali metal silicate aqueous solution to at least a cation exchange treatment after dealkalizing metal treatment and / or acidification treatment or without any treatment, or the cation It is preferably obtained as any one of a product obtained by adding an acid after the exchange treatment and a product obtained by (2) electrodialyzing the alkali metal silicate aqueous solution and adding an acid. You can

The low-boron silica particles of the present invention (hereinafter referred to as "the second invention") are obtained by the above-mentioned production method of the present invention and have a boron content of 0.05 ppm or less, preferably 0.01 ppm. It is characterized by the following.

Furthermore, the method for producing low-boron silica glass particles of the present invention (hereinafter referred to as "the third invention") is based on the second invention.
The low boron silica particles of the invention are subjected to a treatment including a firing step.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of the present invention will be described in detail below. First, the first invention will be described. The first step in the first invention is to obtain an acidic silica aqueous solution having a pH of 2.0 or less from an alkali metal silicate aqueous solution,
This aqueous acidic silica solution is allowed to stand under conditions of pH 2.0 or lower and 60 ° C. or lower to cause gelation to obtain hydrous silica gel.

The alkali metal silicate aqueous solution used in the first step is not particularly limited, and any alkali metal silicate aqueous solution can be used, but SiO ₂ / M ₂ O (M is Na, K or Li, which is industrially easily available Na), has a molar ratio of 0.
An aqueous alkali metal silicate solution having a concentration of 4 to 10.0, preferably 0.5 to 8.0 can be used. If the molar ratio is less than the above, excessive equipment is required over the entire process, and if it exceeds the above, industrially stable aqueous alkali metal silicate solution cannot be obtained, and it becomes difficult to obtain it. It is easy to lack.

The concentration of SiO ₂ in the alkali metal silicate aqueous solution is preferably 2 to 30% by weight, more preferably 3 to 15% by weight. When the concentration is less than the above, it is difficult to obtain hydrous silica gel, and when the concentration is more than the above, the silica tends to be unstable, and any of them tends to lack industrial suitability.

There are several methods for obtaining an alkali metal silicate aqueous solution having the above concentration. The simplest method is to use the alkali metal silicate aqueous solution having the above concentration as it is. The concentration of this may be adjusted in the production of the alkali metal silicate aqueous solution. Next, a method of diluting an aqueous solution of an alkali metal silicate having a concentration higher than the above concentration with water, preferably pure water. Powdered water-soluble alkali silicate is also commercially available, and it can be obtained by dissolving it in water, preferably pure water, to the above concentration.

In the first step, an acidic silica aqueous solution having a pH of 2.0 or less is obtained from such an alkali metal silicate aqueous solution, and the method can be the following method (1) or (2).

(1) is an aqueous solution of an alkali metal silicate,
After dealkalizing metal treatment and / or acidification treatment,
Alternatively, it is a method of obtaining an acidic silica aqueous solution having a pH of 2.0 or less by performing at least cation exchange treatment without performing any treatment, or adding an acid after the cation exchange treatment.

The dealkalizing metal treatment is, for example, a cation exchange method, an electrophoresis method, an electrodialysis method (electrolytic dialysis method).
This is a treatment for removing or reducing the alkali metal content by, for example, By this dealkalizing metal treatment, most of the alkali metal components can be removed until the Na ₂ O concentration becomes approximately 1% or less.
In particular, it is preferable in that the polyvalent metal impurities are reduced as much as possible and the low boron silica particles can be used in a wide range of applications.

The above acidification treatment is, for example, acidification by adjusting the pH using hydrochloric acid, sulfuric acid, nitric acid alone or a combination thereof.
From the viewpoint of improving the ion exchange capacity, it is preferable to use a combination of acids containing at least nitric acid, and more preferable to use nitric acid alone. In the acidification treatment, the pH may be in the acidic region, but from the viewpoint of low boron, it is preferably p.
H3.0 or less.

In the method (1), the alkali metal silicate aqueous solution may be subjected to the dealkalizing metal treatment and / or the acidifying treatment as desired, and then subjected to a cation exchange treatment using a cation exchange resin or the like. The cation exchange resin used for this cation exchange treatment is not particularly limited, and commercially available strong acid type bead-like, fibrous, cloth-like hydrogen type cation-exchange resin, etc. may be used. it can. In addition, the used cation exchange resin is treated by the usual method, that is,
It can be regenerated using an acid such as hydrochloric acid, sulfuric acid or nitric acid.

The method of passing the aqueous solution of the alkali metal silicate through these cation exchange resins is not limited in any way. For example, a method of filling the column with the cation exchange resin and passing the solution, or an alkali metal silicate. Well-known methods such as treating the aqueous solution and the cation exchange resin in a batch system can be used. The conditions such as the above-mentioned cation exchange resin and the method for passing the alkali metal silicate aqueous solution are as follows.
The same applies to the case of performing the cation exchange treatment in the dealkalizing metal treatment.

In carrying out the cation exchange treatment, if the pH is set to 0.3 to 3.0, particularly 0.5 to 2.0,
It is preferable because the ionization of the polyvalent metal is promoted, the removal ability thereof is improved in the cation exchange treatment, and the content of not only boron but also the polyvalent metal impurity can be reduced. The same acid as described above may be used to adjust the pH. If the pH is less than 0.5, gelation occurs over a long period of time, for example, in about half a day, so a rapid operation is preferable.

The alkali metal silicate aqueous solution treated as described above becomes an acidic silica aqueous solution. Here, when the pH is not 2.0 or less, preferably 1.0 or less by the cation exchange treatment, the pH is adjusted by adding the same acid as described above to adjust the pH to 2.0 or less. An acidic silica aqueous solution can be obtained.

(2) is an aqueous solution of an alkali metal silicate,
This is a method in which an acid is added to a silica aqueous solution obtained by a treatment such as an electrodialysis method (electrolytic dialysis method) to obtain an acidic silica aqueous solution having a pH of 2.0 or less.

In this method, when the pH is acidic on the electrodialysis treatment, the electrodialysis treatment requires a relatively long time, and gelation or colloidation is likely to occur. Is pH
Is set to 10.5 or more.

Since the degree to which the pH is lowered by the electrodialysis treatment is small, it is usually necessary to adjust the pH using the same acid as described above after performing the electrodialysis treatment. It is possible to obtain an acidic silica aqueous solution of preferably 1.0 or less.

The first step is the pH thus obtained.
An aqueous solution of acidic silica of 2.0 or less, preferably 1.0 or less is allowed to stand under the conditions of pH 2.0 or less and 60 ° C. or less to cause gelation to obtain hydrous silica gel.

Usually, an acidic silica aqueous solution gels when left to stand, and tends to gel at higher temperatures. In the present invention, however, the pH is 2.0 or less, preferably p.
The boron content can be finally reduced by allowing the gel to stand while keeping H1.0 or less. This is because when the pH exceeds the above, boron becomes Si-O.
This is because the -B bond is formed and it is difficult to remove it even by the cleaning described later.

Further, it is important that the temperature at the time of standing is kept at 60 ° C. or lower, preferably 40 ° C. or lower to allow it to gel, so that the boron content is finally lowered. it can. This is because, as in the case of pH, when the temperature exceeds 60 ° C., boron forms Si—O—B bonds, which makes it difficult to remove even by the cleaning described later.

In the second step of the first invention, the hydrous silica gel obtained in the first step is frozen, thawed, and water is removed to reduce water content to obtain hydrous silica particles.

The hydrated silica gel may be frozen at a temperature below the temperature at which the hydrated silica gel begins to freeze. The temperature at which the hydrous silica gel begins to freeze varies depending on the silica concentration and pH in the hydrous silica gel, but is approximately -2 ° C.
Since freezing starts at a temperature of -15 ° C, freezing may be performed at a temperature below the temperature at which such hydrous silica gel begins to freeze. Here, the freezing method, freezing speed, etc. are not particularly limited.

Next, the frozen hydrous silica gel is thawed. The method of thawing is not limited at all, and it is sufficient to simply leave it at room temperature, but it is possible to heat it for thawing in a shorter time. The heating may be performed with, for example, warm water or warm air, but in this case as well, the temperature of the hydrous silica gel is 60 ° C. or less, particularly 40 ° C., for the reason described above.
The following is preferable.

When the frozen hydrous silica gel is thawed, the frozen water content is released so that the original hydrous silica gel does not return to its original state. That is, hydrous silica gel becomes particles when it is crushed by water separation by thawing, and separates into free water and silica particles. Therefore, by separating the free water by a conventionally known method such as filtration, the water content is reduced. The hydrous silica particles thus obtained can be obtained.

By the series of processes of freezing, thawing, and removal of separated water, trace impurities in the hydrous silica gel are transferred to the free water side and removed.

In the third step, the hydrous silica particles obtained in the second step are washed under the conditions of 60 ° C. or lower, preferably 40 ° C. or lower. By washing the hydrous silica particles obtained in the second step, the boron content can be satisfactorily reduced. The reason why the temperature is 60 ° C. or lower, preferably 40 ° C. or lower is the same as above.

The washing may be washing with water, preferably ultrapure water. This is because boron in the hydrous silica particles is present as boric acid because the treatment up to the above is performed under sufficient acidic conditions, and it is possible to sufficiently remove boron even by washing with water. However, in order to further reduce the content of boron, and also to effectively remove metal element impurities other than boron, particularly polyvalent metal element impurities, to reduce the content thereof. It is preferable to wash with a washing liquid containing an acid.

The acid may be hydrochloric acid, nitric acid, sulfuric acid or the like, alone or in combination. The concentration of the acid is not particularly limited, but it is preferably 2 to 20% by weight. Two
If it is less than wt%, the effect of using an acid is not remarkable, and
Even if it exceeds 20% by weight, the effect is not further improved, which is industrially disadvantageous.

Further, when hydrogen peroxide is added to the cleaning liquid and a cleaning liquid containing acid and hydrogen peroxide is used, more metal element impurities, particularly polyvalent metal element impurities can be effectively removed. preferable.

Although the concentration of hydrogen peroxide is not particularly limited,
Even if it is used in an amount of 2% by weight or more, the effect is not further improved, which is industrially disadvantageous. Although the effect of using hydrogen peroxide occurs even in a very small amount, the effect is particularly remarkable when it is 100 ppm or more, which is preferable.

Needless to say, it is preferable that the cleaning liquid containing hydrogen peroxide and the acid is a cleaning liquid of high purity as much as possible.

In the first aspect of the present invention, it is preferable to dry the hydrous silica particles prior to the washing in the third step under the conditions of 60 ° C. or lower.

Explaining the drying, by drying the hydrated silica particles, the boron contained in the hydrated silica particles (provided that they are present as boric acid because they have undergone treatment under acidic conditions) and other metals. It is considered that the impurities move to the surface layer of the hydrous silica particles as the water moves. Therefore, it is considered that the boron and impurities that have moved to the surface layer portion are removed by performing the above-mentioned cleaning thereafter, so that the boron content can be further lowered and the purity can be further increased.

Since boron can be sufficiently removed only by the above-mentioned washing, the advantage of performing the drying treatment is mainly that the metal element impurities, especially the polyvalent metal element impurities can be reduced.

The degree of drying is not particularly limited as long as the free water in the hydrous silica particles is reduced, but the migration of boron and metal impurities to the surface layer of the hydrous silica particles is caused by the drying. Since it depends on the reduction amount of free water, slight movement of boron and metal impurities occurs in the slight drying, and therefore, the boron and metal impurity amounts decrease only slightly after the above-mentioned washing. It is preferable to perform sufficient drying as much as possible.

The drying method is not particularly limited and may be a conventionally known method. The drying temperature is, for example,
It can be dried at room temperature to 200 ° C. However, since drying at a relatively low temperature may take a long time even if the atmosphere is set to low humidity, if drying in a short time is desired, the temperature is about 100 to 200 ° C., for example, hot air drying. It may be dried by, for example. Also, the drying temperature is room temperature to 1
When the temperature is lower than 00 ° C, it is preferable to perform drying under reduced pressure.

If a temperature above 60 ° C. is used,
As described above, the boron in the hydrous silica particles is Si-O-
Since the B bond is formed and the removal becomes difficult even by washing, in the present invention, even in the drying treatment, 6
Drying is preferably carried out at a temperature of 0 ° C. or lower, particularly 40 ° C. or lower.

However, if the hydrous silica particles are washed prior to the above-mentioned drying treatment, boron can be sufficiently removed by this washing, so that the drying can be performed at a temperature of 60 ° C. or higher. The washing method and the like in this case are the same as above. Therefore, it is preferable to wash the hydrous silica particles once, dry them, and wash them again because both the boron and the metal elements can be effectively reduced.
In this case, when the washing prior to drying is washing under the condition of 60 ° C. or less, the washing prior to such drying is the above essential cleaning in the present invention, that is, any treatment after the essential cleaning. As a result, it is synonymous with performing drying and subsequent washing treatment.

The hydrous silica particles are treated with a treatment solution containing hydrogen peroxide or subjected to a peroxide treatment before being subjected to a drying treatment or in any step until obtaining hydrous silica gel. The addition of hydrogen promotes the ionization of metal impurities, especially polyvalent metals by drying, facilitates the transfer of these hydrous silica particles to the surface layer during the drying step, and the washing of metal impurities, especially polyvalent metals. It is preferable in that the metal is effectively removed.

The second invention is a silica particle derived from an alkali metal silicate obtained by the method for producing low boron silica particles according to the first invention, which has a boron content of 0.05 pp.
m or less, preferably 0.01 ppm or less.

As described above, the conventional low-boron silica particles are made of tetramethoxysilane, tetraethoxysilane, silicon tetrachloride, etc. as raw materials, so that they are highly pure but expensive, and are synthesized using these. Since the production of the quartz glass particles is high cost, it was not industrially highly suitable, but the low boron silica particles of the present invention are industrially low cost by using an alkali metal silicate as a starting material. The silica particles are highly suitable and have a low boron content of 0.05 ppm or less, preferably 0.01 ppm or less.

The third invention is a method for producing low-boron silica glass particles, which comprises subjecting the low-boron silica particles of the second invention to a treatment having a firing step. As described above, the low-boron silica particles of the present second invention are not limited to the case of containing substantially no free water and may contain a small amount of free water. The low-boron silica particles of the second invention may be subjected to the calcination step as they are, if the low-boron silica particles of the second invention do not substantially contain the free water or if they contain only a trace amount of free water that does not affect the calcination step. 2 If the low boron silica particles of the invention contain free water, it is preferably dried to remove the free water prior to the firing step. This is because when silica gel containing free water is fired, bubbles may occur in the quartz glass particles. Quartz glass containing bubbles is limited in its use. Therefore, quartz glass particles having no bubbles are preferable.

The firing step in the third aspect of the invention is not particularly limited as long as it can convert silica particles into quartz glass particles, and the firing step is the same as that conventionally performed to obtain high-purity quartz. The temperature and time may be used, and a conventionally known method can be used. It is preferable that the high-purity quartz glass particles have as low an OH content as possible, and if firing is performed at a higher temperature for a longer time, quartz having a lower OH content can be obtained. Just set it.

[0053]

EXAMPLES Example 1 An aqueous solution of sodium silicate (1) (SiO ₂ concentration 29% by weight) having a molar ratio of SiO ₂ / Na ₂ O = 3.0 (SiO ₂ concentration 29% by weight) was diluted with pure water to obtain an SiO ₂ concentration of 13% by weight. % Sodium silicate aqueous solution. After adding 0.7% of hydrogen peroxide to the weight of SiO ₂ to the aqueous solution of sodium silicate and mixing it with nitric acid to adjust the pH to 2, a hydrogen type cation exchange resin (Amberlite IR-120B manufactured by Organo Corporation) was used. ) Through a column filled with), SiO ₂ concentration 9.3 wt%, pH
An aqueous silica solution (1) of 0.0 was obtained.

The resulting silica aqueous solution (1) was allowed to stand for 5 hours while maintaining the temperature (room temperature) and pH to obtain hydrous silica gel.

The obtained silica gel was placed in an atmosphere of −30 ° C. for 15 hours to be frozen, and then it was placed in an atmosphere of 35 ° C. for 5 hours.
After thawing for a while, water was removed and water was removed by filtration to obtain hydrous silica particles (1).

Hydrochloric acid was added to the obtained hydrous silica particles in an amount of 10
1% at room temperature using a cleaning solution (aqueous solution) containing 1% by weight and 0.7% by weight of hydrogen peroxide (based on the weight of SiO ₂ ).
The time wash was repeated 3 times.

After that, it was left at 120 ° C. for 15 hours to be dried, and then washed in the same manner as above to obtain low boron silica particles. The obtained low boron silica particles are 12
After drying at 0 ° C. for 15 hours, the amount of impurities was measured by a conventional method. The results are shown in Table 1 below.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 2 Low boron silica particles were obtained in the same manner as in Example 1 except that the sodium silicate aqueous solution (1) was mixed with sulfuric acid instead of nitric acid. However, the pH after the cation exchange treatment was 0.4. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 3 Similar to Example 1, except that the aqueous solution of sodium silicate was mixed with hydrochloric acid instead of nitric acid to adjust the pH to 0.9 and the standing time in gelation was set to 15 hours. Low boron silica particles were obtained. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 4 Example 4 was repeated except that a sodium silicate aqueous solution (1) was replaced with a sodium silicate aqueous solution (SiO ₂ concentration 10% by weight) having a molar ratio of SiO ₂ / Na ₂ O = 1.0. Low boron silica particles were obtained in the same manner as in 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 5 A sodium silicate aqueous solution (1) was diluted with pure water to obtain a sodium silicate aqueous solution having a SiO ₂ concentration of 6% by weight. Hydrogen peroxide is added to this aqueous solution of sodium silicate by SiO 2.
After adding 0.7% to ₂ weight, hydrogen type cation exchange resin (Amberlite IR-120 manufactured by Organo Corporation)
The solution was passed through a column packed with B) to obtain a SiO ₂ concentration of 5.5.
A silica aqueous solution having a weight% of 2.5 was obtained, which was mixed with hydrochloric acid to obtain a silica aqueous solution having a pH of 0.3.

The obtained silica aqueous solution was allowed to stand for 5 hours while maintaining the temperature (room temperature) and pH to obtain hydrous silica gel.

Then, low boron silica particles were obtained in the same manner as in Example 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 6 A sodium silicate aqueous solution (1) was diluted with pure water to obtain a sodium silicate aqueous solution having a SiO ₂ concentration of 6% by weight. This aqueous solution of sodium silicate was used as a hydrogen type cation exchange resin (Amberlite IR-120B manufactured by Organo Corporation).
The solution was passed through a column packed with to obtain a silica aqueous solution having a SiO ₂ concentration of 5.5% by weight and a pH of 2.5. P with this with nitric acid
The column was adjusted to H1.0 and passed through a column packed with a hydrogen type cation exchange resin (Amberlite IR-120B manufactured by Organo Corporation) to give a SiO ₂ concentration of 5.5% by weight and a pH of 1.
0 silica aqueous solution was obtained and mixed with hydrochloric acid to obtain a pH of 0.
An aqueous silica solution of 3 was obtained.

The obtained silica aqueous solution was allowed to stand for 5 hours while maintaining the temperature (room temperature) and pH to obtain hydrous silica gel.

Then, low boron silica particles were obtained in the same manner as in Example 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 7 A sodium silicate aqueous solution (1) was diluted with pure water to obtain a sodium silicate aqueous solution having a SiO ₂ concentration of 10% by weight. Hydrogen peroxide is added to this sodium silicate solution as Si.
After adding 0.7% to O ₂ weight, an electrodialysis tank with four anion and cation exchange membranes alternately arranged was used to apply a direct current of 3 A / dm ^{2 to} the aqueous sodium silicate solution to adjust pH.
The resulting solution was dialyzed to deal with 11 to dealkalize, and then passed through a column packed with a hydrogen type cation exchange resin (Amberlite IR-120B manufactured by Organo Corporation),
An aqueous silica solution (2) having a SiO ₂ concentration of 9.5% by weight and a pH of 1.5 was obtained.

The obtained aqueous silica solution was allowed to stand for 15 hours while maintaining the temperature (room temperature) and pH to obtain hydrous silica gel.

Then, low boron silica particles were obtained in the same manner as in Example 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 8 The silica aqueous solution (2) was mixed with hydrochloric acid to obtain a silica aqueous solution having a pH of 0.0.

The obtained silica aqueous solution was allowed to stand for 5 hours while maintaining the temperature (room temperature) and pH to obtain hydrous silica gel.

Then, low boron silica particles were obtained in the same manner as in Example 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 9 A sodium silicate aqueous solution (1) was diluted with pure water to obtain a sodium silicate aqueous solution having a SiO ₂ concentration of 13% by weight. Using this sodium silicate aqueous solution, an electrodialysis tank in which four anion and cation exchange membranes are alternately arranged is used, and 3 A /
A direct current of dm ² is applied to perform dialysis so as to have a pH of 11, and 0.7% of hydrogen peroxide is added to the weight of SiO ₂ , and the mixture is mixed with nitric acid to a pH of 0.5 to obtain a silica aqueous solution of pH 0.5. Got

The silica aqueous solution thus obtained was allowed to stand for 5 hours while maintaining the temperature (room temperature) and pH to obtain hydrous silica gel.

Then, low boron silica particles were obtained in the same manner as in Example 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 10 The hydrous silica particles (1) were washed in ultrapure water at 35 ° C. for 1 hour three times to obtain low boron silica particles. The obtained low boron silica particles were dried at 120 ° C. for 15 hours, and the amount of impurities was measured by a conventional method. The measurement results of the amount of impurities are shown in Table 1 below.
Shown in.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 11 The hydrous silica particles (1) were washed with a cleaning solution (aqueous solution) containing 10% by weight of hydrochloric acid at room temperature for 1 hour three times to obtain low boron silica particles. The obtained low boron silica particles are silica particles 1
After drying at 20 ° C. for 15 hours, the amount of impurities was measured by a conventional method. The measurement results of the amount of impurities are shown in Table 1 below.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 12 With respect to the hydrous silica particles (1), hydrochloric acid 10% by weight and hydrogen peroxide 0.7% by weight (SiO 2
_A low-boron silica particle was obtained by repeating washing for 1 hour at room temperature three times with a cleaning liquid (aqueous solution) containing ₂ weight parts). The obtained low boron silica particles were heated at 120 ° C. for 15
After drying for an hour, the amount of impurities was measured according to a conventional method. The measurement results of the amount of impurities are shown in Table 1 below.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Example 13 Hydrous silica particles (1)
After drying under reduced pressure (about 1 kPa) for 10 hours at a temperature of 35 ° C., a cleaning solution (aqueous solution) containing 10% by weight of hydrochloric acid and 0.7% by weight of hydrogen peroxide (based on SiO ₂ weight) was used. After that, washing at room temperature for 1 hour was repeated 3 times to obtain low boron silica particles. 1 for the obtained low boron silica particles
After drying at 20 ° C. for 15 hours, the amount of impurities was measured by a conventional method. The measurement results of the amount of impurities are shown in Table 1 below.

The obtained low boron silica particles were treated at 1250 ° C.
After that, it was baked for 24 hours to obtain low boron quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

[Comparative Example 1] Aqueous silica solution (1) was mixed with ammonia to adjust the pH to 6.0 and allowed to stand for 1 hour to obtain hydrous silica gel.

Thereafter, silica particles were obtained in the same manner as in Example 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained silica particles were treated at 1250 ° C. for 24 hours.
Firing was carried out for a period of time to obtain quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

Comparative Example 2 Aqueous silica solution (1) was added to 80
The temperature was raised to ° C, and the mixture was allowed to stand for 3 hours while maintaining the temperature and pH to obtain hydrous silica gel.

Thereafter, silica particles were obtained in the same manner as in Example 1. The measurement results of the amount of impurities are as shown in Table 1.

The obtained silica particles were heated at 1250 ° C. for 24 hours.
Firing was carried out for a period of time to obtain quartz glass particles. The amount of impurities in the obtained quartz glass particles did not change from that of silica particles.

[0099]

[Table 1] The unit in the table is ppm by weight.

[0100]

As described above, according to the present invention, high-purity silica particles can be obtained even when an inexpensive aqueous alkali metal silicate solution is used as a raw material, and particularly, the boron content is sufficiently reduced. The obtained low boron silica particles can be obtained. Further, by using the low boron silica particles obtained by this method, inexpensive and highly pure low boron silica glass particles can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C03B 20/00 C03B 20/00 D C03C 3/06 C03C 3/06 (72) Inventor Hiroyuki Watanabe Central Tokyo 4-2-16 Nihonbashi Muromachi, Ltd., Watanabe Shoten, Ltd. (72) Inventor, Keishi Uehara 4-2-16 Nihonbashi Muromachi, Chuo-ku, Tokyo Incorporated, Watanabe, Ltd. (72) Keiko Sanbe 4 Nihonbashi Muromachi, Chuo-ku, Tokyo -2-16 Watanabe Shokai Co., Ltd. (72) Inventor Ariyasu Kurita 7-35, Higashiohisa, Arakawa-ku, Tokyo Within Asahi Denka Kogyo Co., Ltd. (72) Initiator, Niichi Omi Hisaichi Higashio, Arakawa-ku, Tokyo Asahi Denka Kogyo Co., Ltd. (2-35) Inventor Maki Takahashi Makio Takahashi 7-35 Higashiohisa Arakawa-ku, Tokyo Asahi Denka Kogyo Co., Ltd. (72) Inventor Hiroshi Morita Asahi Denka Kogyo Co., Ltd. 7-35, Higashiokyu, Arakawa-ku, Tokyo (72) Inventor Tsugutaka Asahioka 7-35, Higashiohisa, Higashiokyu, Arakawa-ku, Tokyo F-Term (Reference) 4G014 AH02 AH04 AH06 4G062 AA10 BB02 CC01 CC05 DA08 MM01 NN40 4G072 AA27 AA28 AA34 BB05 BB15 CC10 GG01 GG03 HH22 JJ13 MM01 MM23 MM24 MM31 PP05 PP13 TT19 UU21

Claims (8)

[Claims] 1. A pH of 2. from an alkali metal silicate aqueous solution.
The acidic silica aqueous solution of 0 or less is obtained, and the acidic silica aqueous solution is allowed to stand under conditions of pH 2.0 or lower and 60 ° C. or lower to cause gelation to obtain hydrous silica gel. Including a second step of freezing, thawing and allowing water to reduce water content to obtain water-containing silica particles, and a third step of washing the obtained water-containing silica particles at a temperature of 60 ° C. or lower. A method for producing low boron silica particles. 2. The acidic silica aqueous solution having a pH of 2.0 or less after (1) or (2) below, (1) the alkali metal silicate aqueous solution is dealkalized and / or acidified, or Those obtained by at least cation exchange treatment without any treatment, or
One obtained by adding an acid after the cation exchange treatment, or (2) obtained by electrodialysis of the aqueous alkali metal silicate solution and adding an acid. The method for producing low boron silica particles according to claim 1. 3. The method for producing low boron silica particles according to claim 1, wherein the cleaning is performed with a cleaning solution containing an acid or a cleaning solution containing hydrogen peroxide and an acid. 4. The method for producing low boron silica particles according to claim 1, wherein the hydrous silica particles are dried prior to the washing in the third step under the condition of 60 ° C. or lower. . 5. The method for producing low boron silica particles according to claim 4, wherein the hydrous silica particles are washed prior to drying the hydrous silica particles. 6. The method according to claim 1, wherein the boron content is 0.05 ppm.
A low-boron silica particle characterized by being: 7. The low-boron silica particles according to claim 6, wherein the boron content is 0.01 ppm or less. 8. A method for producing low-boron silica glass particles, which comprises subjecting the low-boron silica particles according to claim 6 or 7 to a treatment including a firing step.