JP2015205782A - Silica gel particles and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase silica gel filled amount to a firing furnace per 1 patch by obtaining silica gel particles having reduced whole pore volume from a silica slurry having concentration easy to handle without increasing raw material cost of the silica gel using a fumed silica.SOLUTION: A silica slurry having the silica particle concentration of 25 to 35 mass% by mixing fumed silica particles having a specific surface area of 90 to 300 m/g and water. A silica dried body is obtained by adding ammonium water or ammonium carbonate solution to silica slurry so that the ammonia concentration or the ammonium carbonate in the slurry is 100 to 500 mass.ppm and mixing and removing moisture from the silica slurry. Silica gel particles are obtained by degrading, pulverizing and sizing the dried body.

Description

  The present invention relates to silica gel particles suitable as a precursor of a synthetic amorphous silica powder used as a raw material for producing a synthetic silica glass product such as a crucible for pulling up a silicon single crystal, and a method for producing the same.

  Conventionally, a method for producing silica gel by drying a silica slurry in which fumed silica particles are dispersed in a water dispersion medium and a silica gel have been disclosed (for example, see Patent Document 1). However, this method has a problem that when silica gel is produced by gelling a silica slurry, the gel shrinks greatly, and the shrinkage and cracking are easily caused by the shrinkage.

  In addition, when this type of silica gel particles is placed in a firing furnace and baked into a synthetic amorphous silica powder, if the amount of pores (hereinafter referred to as pores) in the silica gel particles is large, The density was low, and there was a problem that the amount of silica gel that could be charged into the firing furnace at one time, that is, the amount of silica gel charged per batch into the firing furnace could not be increased. In order to avoid these problems, a method for producing silica gel by using fused silica particles instead of fumed silica particles has been disclosed (for example, see Patent Document 2).

  The method for producing silica gel disclosed in Patent Document 2 is a method in which a dispersion medium is removed from a dispersion having a fused silica particle concentration of 60% by weight or more to form aggregates of the fused silica particles. In this dispersion, fused silica particles having a particle size of less than 0.1 μm are present in an amount of 5% by weight or less of the total particles, and fused silica particles having a particle size of 0.1 to 5 μm are present in an amount of 20% by weight or more of the total particles. . The silica gel obtained by this method is composed of an aggregate of fused silica particles, and among pores having a pore diameter of 0.004 to 10 μm measured by a mercury porosimeter, the pore diameter is 0.05 to 0.5 μm. The proportion of pores is 50% or more, and the total pore volume is 0.1 to 0.5 cc / g. The pore distribution characteristics are set to enable efficient gas replacement. It is said that it is optimized and has excellent dimensional stability that does not easily cause cracking or chipping.

  In Patent Document 2, by using substantially spherical fused silica particles different from fumed silica particles, it is possible to obtain a dispersion having a high slurry concentration that could not be achieved with fumed silica particles, and drying this. It has been found that chipping and cracking of the silica gel obtained in this way can be extremely effectively suppressed, and the invention of Patent Document 2 has been completed.

JP 5-505167 A (Claims) JP 2002-137913 (Claim 1, Claim 2, Claim 7, Abstract, Paragraph [0011])

  Since the silica gel shown in Patent Document 2 has a total pore volume of 0.1 to 0.5 cc / g, the bulk density is high, and there is an advantage that the amount of silica gel charged per batch into the firing furnace can be increased. In the production, it is necessary to prepare a dispersion of fused silica particles having a concentration of 60% by weight or more by using substantially spherical fused silica particles different from fumed silica particles. The fused silica particles require a more complicated manufacturing process than the fumed silica particles, and have the disadvantage of increasing the raw material cost of the silica gel. In addition, in order to prepare a dispersion of fused silica particles having a concentration of 60% by weight or more, an expensive kneading apparatus is required, and the dispersion is too viscous to be handled. There was a disadvantage that the property could not be increased.

  An object of the present invention is to obtain silica gel particles having a reduced total pore volume from a silica slurry having a concentration that is easily prepared and easy to handle without using a complicated process by using fumed silica particles. An object of the present invention is to provide silica gel particles that can increase the amount of silica gel per batch into a firing furnace and a method for producing the same.

  The present inventors added ammonia water or an ammonium carbonate aqueous solution at an appropriate ammonia concentration or an appropriate ammonium carbonate concentration when preparing a silica slurry using fumed silica particles conventionally used. The present inventors have found that silica gel particles having a reduced total pore volume can be obtained, and reached the present invention.

According to a first aspect of the present invention, fumed silica particles having a specific surface area of 90 to 300 m ² / g and water as a dispersion medium are mixed to prepare a silica slurry having a concentration of 25 to 35% by mass of the silica particles. And a step of adding and mixing ammonia water or an aqueous ammonium carbonate solution as an additive to the silica slurry such that the ammonia concentration or ammonium carbonate concentration in the silica slurry is 100 to 500 ppm by mass, and the additive A method for producing silica gel particles, comprising: a step of removing moisture from a silica slurry to obtain a dried silica product; and a step of pulverizing and classifying the dried silica product to obtain silica gel particles.

  The second aspect of the present invention is that the total pore volume in the range of pore diameter in the range of 0.003 to 3 μm measured by mercury porosimeter is in the range of 1.030 to 1.173 ml / g, and Of the range of pore diameters in the particles of 0.003 to 3 μm, the proportion of pores in the range of pore diameters in the range of 0.01 to 0.1 μm is 74.1 to 80.5%. Silica gel particles in the range of

  A third aspect of the present invention is a silica gel particle according to the second aspect, which is a precursor of a synthetic amorphous silica powder.

  According to the method for producing silica gel particles of the first aspect of the present invention, since the fumed silica particle concentration of the silica slurry is 25 to 35% by mass, the preparation of the silica slurry is simple and easy to handle. . And the repulsive force which acts between the fumed silica particles in a silica slurry is weakened by adding the ammonia water or ammonium carbonate aqueous solution of moderate ammonia concentration or ammonium carbonate concentration, and it becomes easy for particles to approach. As a result, silica gel particles with a reduced total pore volume can be obtained, and the amount of silica gel charged per batch into the firing furnace can be increased. Further, since fumed silica particles are used instead of the fused silica particles, which are expensive in raw material cost, the raw material cost of silica gel is not increased.

  The silica gel particles according to the second aspect of the present invention have a total pore volume in the range of 0.003 to 3 μm and a total pore volume in the range of 1.030 to 1.173 ml / g as measured with a mercury porosimeter. And the ratio of the pores having a pore diameter in the range of 0.01 to 0.1 μm in the range of 0.003 to 3 μm of the pore diameter in the particle is 74.1 to 80 Since it is in the range of 5%, it is possible to increase the silica gel filling amount per batch into the baking furnace.

  According to the silica gel particles of the third aspect of the present invention, the amount of silica gel charged per batch into the baking furnace can be increased. The productivity of the crystalline silica powder can be increased.

It is a figure which shows the relationship between the pore diameter of the silica gel particle of Example 1-1 of this invention, and a log differential pore volume. FIG. 2 is an integrated pore volume distribution diagram in which the pore volumes of silica gel particles based on FIG. 1 are integrated.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings.

[Method for producing silica gel particles]
In the method for producing silica gel particles of the present invention, fumed silica particles having a specific surface area of 90 to 300 m ² / g and water as a dispersion medium are mixed to obtain a silica slurry having a concentration of 25 to 35% by mass of the silica particles. A step of preparing, a step of adding and mixing ammonia water or an aqueous ammonium carbonate solution as an additive to the silica slurry such that an ammonia concentration or an ammonium carbonate concentration in the silica slurry becomes 100 to 500 ppm by mass, and the additive The method includes a step of removing moisture from the silica slurry, and obtaining a silica dried product, and a step of crushing the silica dried product and then pulverizing and classifying to obtain silica gel particles.

[Preparation of silica slurry]
First, fumed silica particles having an average particle diameter D _{50 of 7} to 20 nm and a specific surface area of 90 to 300 m ² / g, preferably 90 to 120 m ² / g, are prepared as starting materials. When the specific surface area decreases, the primary particle size of fumed silica increases. When the specific surface area is less than 90 m ² / g, there is a problem that the silica slurry is separated into silica and solvent with the passage of time. When the specific surface area exceeds 300 m ² / g, There is a problem that it is difficult to mix with the dispersion medium during mixing. This average particle diameter _{D 50} of 7 to 20 nm, concentration of 25 to 35% by weight of water and mixed to the silica particles of the fumed silica particles is the specific surface area is 90~300m ² / g as the dispersion medium, preferably A 30-35% by weight silica slurry is prepared. In this preparation, fumed silica particles are added to ultrapure water at room temperature in an air atmosphere so that the concentration of the silica particles is 25 to 35% by mass, and the mixture is stirred by a kneader. It is performed by mixing uniformly in water. When the concentration of the silica particles is less than 25% by mass, the drying efficiency decreases, and when it exceeds 35% by mass, the viscosity of the slurry increases and it becomes difficult to handle. In this specification, the average particle diameter D _50, a laser diffraction scattering type particle distribution measuring apparatus (model name: HORIBA LA-950) was measured by a particle distribution median (diameter) was measured three times, the average value Say.

[Addition of additive to silica slurry]
Ammonia water or an aqueous ammonium carbonate solution is added as an additive to the silica slurry in which the concentration of silica particles is adjusted. This addition is carried out by adding the aqueous ammonia or ammonium carbonate at room temperature so that the ammonia concentration or ammonium carbonate concentration in the silica slurry is 100 to 500 ppm by mass, preferably 200 to 400 ppm by mass, in the atmosphere at room temperature. This is done by adding an aqueous solution. If this concentration is less than 100 ppm by mass, the effect of adding an additive is insufficient, and if it exceeds 500 ppm by mass, the viscosity of the slurry increases and it becomes difficult to handle. In addition, the said additive may be previously added and mixed with the ultrapure water mentioned above, and a fumed silica particle may be added and mixed with the ultrapure water containing this additive, and a silica slurry may be prepared.

[Removal of water from silica slurry containing additives]
The silica slurry containing the additive is transferred to a drying container having an opening at the top, and this is introduced into a dryer, and while flowing dry air at a flow rate of preferably 1 to 20 liters / minute in the dryer, Dry at a temperature for 12 to 48 hours to obtain a dried silica.

[From silica dried product to silica gel particle production]
The obtained dried silica is taken out from the drying container, crushed by a pulverizer having a structure in which a quartz comb rotates, and pulverized using a pulverizer such as a roll crusher. When a roll crusher is used, the roll gap is adjusted to 0.5 to 2.0 mm, and the roll rotation speed is adjusted to 3 to 200 rpm and pulverized. Lastly, the pulverized silica dried body is classified using a vibrating screen or the like, whereby silica gel particles are obtained.

[Physical properties of silica gel particles]
The resulting gel particles may, 200 to 400, preferably have an average particle diameter _{D 50} of 300～350Myuemu, a mercury porosimeter (manufactured by Shimadzu Corporation, model number Autopore IV 9500) is measured intraparticle pore diameter 0.003 Among the pores in the range of ˜3 μm, the proportion A of the pores in which the pore diameter in the particles is in the range of 0.01 to 0.1 μm is in the range of 74.1 to 80.5%. The pore volume is in the range of 1.030 to 1.173 ml / g. If the total pore volume is less than 1.030 ml / g, there is a problem that the time required for degassing during firing is prolonged, and if it exceeds 1.173 ml / g, the silica crucible becomes silica crucible. There is a defect in the filling property. Similarly, when the ratio A is less than 74.1%, there is a problem that the time required for degassing during the subsequent process becomes long, and when the ratio A exceeds 80.5%, the silica gel particles are converted into a quartz crucible. There is a defect in filling property. In the present invention, the additive is added so that the total pore volume is 1.030 to 1.173 ml / g when the ratio A is in the range of 74.1 to 80.5%.

[Uses of silica gel particles]
The obtained silica gel particles are baked to become a synthetic silica amorphous silica powder, which is suitably used as a raw material for producing a synthetic silica glass product such as a crucible for pulling up a silicon single crystal. That is, the obtained silica gel particles are suitably used as a precursor of synthetic amorphous silica powder.

  Next, examples of the present invention will be described in detail together with comparative examples.

[Preparation of silica slurry]
<Examples 1-1 to 1-6>
Fumed silica particles having an average particle diameter D ₅₀ of 20 nm and a specific surface area of 90 m ² / g were prepared. The fumed silica particles were added to an aqueous solution in which ammonia water was added to and mixed with ultrapure water at 25 ° C. in an air atmosphere, and stirred with a continuous kneader to prepare a silica slurry. At this time, the fumed silica particles and the ammonia water were added so that the silica particle concentration and the ammonia concentration shown in Table 1 below were obtained.

<Examples 2-1 to 2-6>
Fumed silica particles having an average particle diameter D ₅₀ of 20 nm and a specific surface area of 90 m ² / g were prepared. The fumed silica particles were added to an aqueous solution obtained by adding and mixing an ammonium carbonate aqueous solution to ultrapure water at 25 ° C. in an air atmosphere, and stirred with a continuous kneader to prepare a silica slurry. At this time, the fumed silica particles and the aqueous ammonium carbonate solution were added so that the silica particle concentration and the ammonium carbonate concentration in the following Table 1 were obtained.

<Examples 3-1 to 3-6>
Fumed silica particles having an average particle diameter D ₅₀ of 7 nm and a specific surface area of 300 m ² / g were prepared. The fumed silica particles were added to an aqueous solution in which ammonia water was added to and mixed with ultrapure water at 25 ° C. in an air atmosphere, and stirred with a continuous kneader to prepare a silica slurry. At this time, the fumed silica particles and the ammonia water were added so that the silica particle concentration and the ammonia concentration shown in Table 1 below were obtained.

<Examples 4-1 to 4-6>
Fumed silica particles having an average particle diameter D ₅₀ of 7 nm and a specific surface area of 300 m ² / g were prepared. The fumed silica particles were added to an aqueous solution obtained by adding and mixing an ammonium carbonate aqueous solution to ultrapure water at 25 ° C. in an air atmosphere, and stirred with a continuous kneader to prepare a silica slurry. At this time, the fumed silica particles and the aqueous ammonium carbonate solution were added so that the silica particle concentration and the ammonium carbonate concentration in the following Table 1 were obtained.

<Comparative Examples 1-1 and 1-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 1-1 and 1-2 except that ammonia water was not added.

<Comparative Examples 2-1 and 2-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 3-1 and 3-2 except that ammonia water was not added.

<Comparative Examples 3-1 and 3-2>
As shown in the following Table 2, silica slurry was prepared in the same manner as in Examples 1-1 and 1-2 except that ammonia water was added so that the ammonia concentration in the silica slurry was 90 ppm by mass.

<Comparative Examples 4-1 and 4-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 3-1 and 3-2 except that ammonia water was added so that the ammonia concentration in the silica slurry was 90 mass ppm.

<Comparative Examples 5-1 and 5-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 2-1 and 2-2, except that an aqueous ammonium carbonate solution was added so that the ammonium carbonate concentration in the silica slurry was 90 ppm by mass. did.

<Comparative Examples 6-1 and 6-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 4-1 and 4-2, except that an aqueous ammonium carbonate solution was added so that the ammonium carbonate concentration in the silica slurry was 90 ppm by mass. did.

<Comparative Examples 7-1 and 7-2>
As shown in the following Table 2, silica slurry was prepared in the same manner as in Examples 1-1 and 1-2 except that ammonia water was added so that the ammonia concentration in the silica slurry was 550 mass ppm.

<Comparative Examples 8-1 and 8-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 3-1 and 3-2 except that ammonia water was added so that the ammonia concentration in the silica slurry was 550 mass ppm.

<Comparative Examples 9-1 and 9-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 2-1 and 2-2 except that an aqueous ammonium carbonate solution was added so that the ammonium carbonate concentration in the silica slurry was 550 mass ppm. did.

<Comparative Examples 10-1 and 10-2>
As shown in the following Table 2, a silica slurry was prepared in the same manner as in Examples 4-1 and 4-2, except that an aqueous ammonium carbonate solution was added so that the ammonium carbonate concentration in the silica slurry was 550 mass ppm. did.

[Moisture removal from silica slurry]
In the 36 types of silica slurries obtained in Example 1-1 to Example 4-6 and Comparative Example 1-1 to Comparative Example 6-2, the silica particles in the slurry are dispersed to the state of secondary particles. The fluidity was such that it could easily be fed with a tube pump. Each of these silica slurries was transferred to a flat plate made of Pyrex (trademark), which was a drying container, and placed in a constant temperature dryer. The temperature of this dryer was set to 200 ° C. and left for 24 hours and dried until the water content was 0.5% by mass or less to obtain 28 types of dried silica. When these silica dried bodies were taken out from the flat dish, all the silica dried bodies maintained the shape of the flat dish with almost no shrinkage.
On the other hand, the eight types of silica slurries of Comparative Examples 7-1 to 10-2 having an ammonia concentration and an ammonium carbonate concentration of 550 ppm by mass have excessively increased slurry viscosity and are not fluid. Could not be transferred to. For this reason, only Comparative Example 7-1 was transferred to a flat dish with a resin scoop and dried in the same manner as in the Examples, and drying of the other seven types of silica slurry was abandoned. The viscosities of 44 types of silica slurries obtained in Examples 1-1 to 4-6 and Comparative Examples 1-1 to 10-2 were measured using a B-type viscometer (model number BM-, manufactured by Toki Sangyo Co., Ltd.). It was measured in II). The results are shown in Tables 1 and 2. When the slurry viscosity exceeds 300 cP, the fluidity is lost and liquid feeding with a tube pump becomes substantially impossible.

[From crushing to classification of dried silica]
36 types of dried silica were separately pulverized to a mass of about 5 to 20 mm by a pulverizer and then pulverized by a roll crusher made of high-density polypropylene resin. The pulverized product was passed through a vibration sieve composed of a nylon resin net and classified to obtain 28 types of silica gel particles. The range of classification of all silica gel particles was 150 to 600 μm.

[Physical properties of silica gel particles]
(1) The pore distribution of 36 types of silica gel particles was measured with a mercury porosimeter (manufactured by Shimadzu Corporation, model number Autopore IV9500). From the measured pore distribution, the range of pore diameters in the particles and the range of pore diameters between the particles were determined. It was found that the pore diameter range in the particles was in the range of 0.03 to 3 μm, and the main pore diameters were in the range of 0.03 to 0.04 μm. The pore distributions of the 24 types of silica gel particles of Example 1-1 to Example 4-6 were almost equal to each other. FIG. 1 shows the relationship between the pore diameter of the silica gel particles of Example 1-1 and the log differential pore volume.

  (2) A relationship diagram between pore diameter and accumulated pore volume was created from the pore distribution measurement data, and the total pore volume (ml / g) in the range of pore diameter in the particle range of 0.003 to 3 μm Asked. Further, the ratio A (%) occupied by pores having a pore diameter of 0.01 to 0.1 μm out of 0.003 to 3 μm which is a range of pore diameters in the particles was determined. Specifically, it is a value obtained by dividing the cumulative pore volume in the range of 0.01 to 0.1 μm by the cumulative pore volume in the range of 0.003 to 3 μm. FIG. 2 shows an integrated pore volume distribution diagram in which the pore volumes of the silica gel particles based on FIG. 1 are integrated.

(3) Each of 36 types of silica gel particles is filled in a quartz baking container (effective volume: 5 liters), its mass (g) is obtained, and the mass is divided by the effective volume to obtain a bulk density (g / Ml) was calculated. These results are shown in Tables 1 and 2.
(4) A quartz firing container filled with 36 types of silica gel particles was placed in an electric furnace as a firing furnace, heated to 1250 ° C. over 2 hours, held for 20 hours, and then naturally cooled.

  As is clear from Tables 1 and 2, (a) with respect to the proportion A of the pores having a pore diameter in the range of 0.01 to 0.1 μm, the comparative example 1-1 to 6-2 The obtained silica gel particles were 80.6-90.0%. On the other hand, the silica gel particles obtained in Examples 1-1 to 4-6 were 74.1 to 80.5%. From this, it can be inferred that although the diameter of the pores is not significantly changed by the addition of the additive, the total pore volume is reduced by reducing the number of pores.

  (b) Regarding the total pore volume, the silica gel particles obtained in Comparative Examples 1-1 to 6-2 were 1.172 to 1.388 ml / g. On the other hand, the silica gel particles obtained in Example 1-1 to Example 4-6 are 1.030 to 1.173 ml / g, and the silica gel obtained in Example 1-1 to Example 4-6. The particles were about 12-15% smaller than the silica gel particles obtained in Comparative Examples 1-1 to 6-2.

  (c) Further, although the silica gel particles of Comparative Examples 1-1 to 6-2 having a bulk density of 0.27 to 0.29 g / ml could only be filled into a firing container from 1.35 to 1.45 kg. On the other hand, the silica gel particles of Examples 1-1 to 4-6 having a bulk density of 0.31 to 0.32 g / ml can be filled in a container for baking from 1.55 to 1.60 kg, 10 to 15% more could be filled in the firing furnace. That is, it was found that the productivity of the firing process can be improved by increasing the amount of silica gel per batch into the firing furnace.

Claims (3)

A step of preparing fumed silica particles having a specific surface area of 90 to 300 m ² / g and water as a dispersion medium to prepare a silica slurry having a concentration of the silica particles of 25 to 35% by mass;
Adding and mixing ammonia water or an aqueous ammonium carbonate solution as an additive to the silica slurry such that the ammonia concentration or ammonium carbonate concentration in the silica slurry is 100 to 500 ppm by mass;
Removing water from the silica slurry containing the additive to obtain a dried silica,
And crushing and classifying the dried silica product to obtain silica gel particles.   The total pore volume in the range of 0.003 to 3 μm of pore diameter in the particle measured with a mercury porosimeter is in the range of 1.030 to 1.173 ml / g, and the pore diameter in the particle is 0. The ratio of the pores having a pore diameter in the range of 0.01 to 0.1 μm in the range of 0.003 to 3 μm is in the range of 74.1 to 80.5%. Silica gel particles.   3. Silica gel particles according to claim 2, which is a precursor of synthetic amorphous silica powder.

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