JPH04238808A - Production of highly pure crystalline silica - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing synthetic crystalline silica of high purity and low content of silanol groups.

0002

[Prior Art] Natural quartz has traditionally been used as a raw material for fused quartz glass, but in recent years this quartz glass has come to be used as a material for electronic parts, etc. Due to the need to obtain high purity quartz glass,
The use of high-purity synthetic silica as a raw material is being considered (JP-A-51-77,612, JP-A-61-
186,232, etc.).

However, synthetically produced silica generally has a pore diameter of several angstroms to several tens of angstroms depending on its manufacturing conditions, and dehydration begins upon heating, and further 1,1
The pores are sealed by firing at 00°C to 1,300°C for several hours, and adsorbed water and condensed water are released during the firing process until the pores are sealed.
Further, dehydration occurs due to a condensation reaction of silanol groups, etc. However, the isolated silanol group inside the silica
During this firing process, a condensation reaction cannot occur, and the pores are sealed with moisture remaining inside. If silica with residual silanol groups is used as a raw material for quartz glass, a problem arises in that silica glass with excellent heat resistance cannot be obtained.

[0004] Therefore, as a method for removing these silanol groups, silica gel is baked in a mixed gas flow of a halogen-based OH deOH base and a carrier gas, and the silanol groups are removed using a reaction that replaces the silanol groups with halogen atoms. A method is known (Japanese Unexamined Patent Publication No. 61-186,232), but even in this method, halogen groups remain in place of silano groups, and when it is made into quartz glass, it is caused by the residual halogen. Problems such as decreased heat resistance and corrosive properties occur.

[0005] Although it is possible to remove the silanol groups by crystallizing high-purity synthetic amorphous silica powder, high-purity amorphous silica containing all metal impurities of 1 ppm or less has few impurity defects. Since crystal nucleus generation is difficult to occur, even if high temperature firing is performed, sintering of the silica powder occurs before crystallization occurs, and the powder state cannot be maintained. Furthermore, as a means of crystallizing at a low temperature, there is a method of adding a crystallization promoter, such as an alkali metal carbonate, and then firing, but this naturally results in the addition of impurities, making it impossible to maintain the desired high purity. It is also well known to obtain synthetic quartz crystals by hydrothermal synthesis, but this method is economically too expensive for this purpose.

[0006]

[Problems to be Solved by the Invention] Therefore, the present inventors have worked hard to solve the problems of these conventional techniques and to develop a method that can efficiently and stably produce high-purity synthetic anhydrous silica. As a result of research, it was found that 0.1% by weight or more of crystalline fine powder silica, which becomes a crystal nucleus, is added and mixed into amorphous synthetic silica or synthetic silica gel, and preferably 1.
Either by calcining at a temperature of 200°C or higher, or by adding 0.1% by weight or more of crystalline fine powder silica to serve as crystal nuclei when hydrolyzing silicon alkoxide into a gel, and drying the resulting silica gel. , then preferably 1,100
It has been discovered that by firing at a temperature of 0.degree. C. or higher, the silanol groups present in silica can be removed from the crystal structure while maintaining high purity, and the present invention has been completed.

[0007] Accordingly, an object of the present invention is to provide synthetic crystalline silica of high purity and low content of silanol groups, which is suitable as a raw material for producing high-purity fused silica glass, and a method for producing the same. In addition, in the present invention, the silanol group in silica is considered to be water contained in silica.

[0008]

[Means for Solving the Problems] That is, the present invention provides synthetic amorphous silica powder or synthetic silica gel powder containing
This is a method for producing high-purity crystalline silica in which 0.1% by weight or more of crystalline fine powder silica is added and fired to serve as crystal nuclei, and the crystal fine powder that serves as crystal nuclei is used when silicon alkoxide is hydrolyzed and gelled. This is a method for producing high-purity crystalline silica, in which 0.1% by weight or more of silica is added in advance, and the obtained silica gel powder is dried and then fired. Hereinafter, the method for producing synthetic crystalline silica of the present invention will be specifically explained.

[0009] Finely crystalline silica powder serving as a crystal nucleus that can be used in the present invention includes natural or synthetic quartz, cristobalite, tridymite, and the like. If the purity of the crystal nuclei is poor, the desired product can be obtained by repeating the process several times to add the crystal nuclei to high-purity synthetic amorphous silica and then sintering to produce high-purity synthetic crystalline silica. I can do it.

In the present invention, the amount of crystalline fine powder silica used as crystal nuclei is 0.1% by weight or more, more preferably 0.5% by weight or more, based on the synthetic amorphous silica. The amount of crystalline fine powder silica used as crystal nuclei is 0.1% by weight.
If the water content is less than 1, the crystallization of amorphous silica or silica gel will not substantially proceed sufficiently, making it impossible to obtain silica with a low water content. As the amount of crystalline fine powder silica that serves as crystal nuclei increases, it tends to be possible to obtain completely crystalline, highly pure anhydrous silica at a substantially lower temperature and in a shorter time.

The high-purity amorphous silica and silica gel that can be used in the present invention include silica obtained by hydrolyzing silicon alkoxide or silicon tetrachloride, and silica obtained by refining natural raw materials by the sodium silicate method. Any silica or silica gel can be used.

[0012] In the production of anhydrous silica by crystallization according to the present invention, 0.1% by weight or more of crystalline fine powder silica serving as a crystal nucleus is added to high purity amorphous silica or silica gel and mixed, preferably 1,200% by weight or more. Either by baking at a temperature of ℃ or higher, or by adding 0.1% by weight or more of crystalline fine powder silica that will become crystal nuclei in advance when hydrolyzing and gelling silicon alkoxide, and drying the obtained silica gel, This can then be carried out by firing preferably at a temperature of 1,100° C. or higher. If the firing temperature is too low, the crystallization rate will be slow and it will be difficult to achieve substantially complete crystallization.

[0013] As a specific manufacturing method, for example, 100 parts by weight of high-purity amorphous silica powder obtained from silicon alkoxide as a raw material is pulverized with high-purity natural crystal to an average particle diameter of several μm. A method of adding 1 part by weight of, mixing, and baking in a muffle furnace in the air at 1,300°C for 10 hours.Also, to 253 parts by weight of tetramethyl orthosilicate, 140 parts by weight of water, 53 parts by weight of methanol, and high purity natural There is a method in which 1 part by weight of quartz is crushed to an average particle diameter of several μm, stirred, gelled, dried, and fired in the air at 1,200° C. for 10 hours in a muffle furnace. The hydrolysis and gelation reaction of the silicon alkoxide at this time can be carried out by a generally known method (eg, "Science of Sol-Gel Method", published by Agne Seifu-sha, pp. 8-13). Further, the finer the particle size of the crystalline fine powder silica that becomes the crystal nucleus, the greater the effect of crystallization even when added in a small amount, and crystalline high-purity synthetic anhydrous silica can be obtained at a lower temperature.

The synthetic crystalline silica thus obtained is
When used as a raw material for fused silica glass, it not only has the characteristics of high purity and low moisture content, but also has the characteristics of high purity and low moisture content when compared with amorphous silica of the same high purity and low moisture content obtained by other methods. Crystalline materials have a wide melting temperature range, while crystalline materials have a fixed melting point and therefore have a narrow melting temperature range, melting instantly. Therefore, it also has the characteristic that fewer bubbles remain in the glass during melting.

[0015]

EXAMPLES The present invention will be explained in detail below based on examples.

Example 1 A mineralizing agent was added to high-purity synthetic silica, and the mixture was fired at 1,200°C for 5 hours to form cristobalite, which was then ground to an average particle size of 2 μm using an agate planetary ball mill to form crystal nuclei. And so. Next, highly pure synthetic amorphous silica with a water content of about 10% was calcined at 1,100° C. for 10 hours to obtain amorphous silica with an OH group content of 760 ppm.

[0017] Crystal nuclei are added to this amorphous silica by 0.5
% by weight was added and calcined at 1,300° C. for 10 hours to obtain crystalline silica with a low water content. The above operation is repeated twice using the obtained crystalline silica as the next crystal nucleus to produce crystalline silica (cristobalite) with high purity and low water content.
I got it.

Table 1 shows the OH group content of the cristobalite obtained, and Table 2 shows the purity analysis results. Note that the concentration of OH groups is as follows: 20% of adsorbed water in a quartz tube.
After desorption for 30 minutes under reduced pressure at 0°C, it was melted by heating with a burner in a vacuum state, and after cooling, a test piece was cut out and F
Transmittance was measured by T-IR and Lambert-Beer
It was determined from the law of

Example 2 Silicon alkoxide is hydrolyzed to have a water content of 10%
Synthesize high-purity synthetic silica gel of about 1.10
After firing at 0° C. for 10 hours, amorphous silica having an OH group content of 760 ppm was obtained.

0.5% by weight of the crystal nuclei obtained in Example 1 was added to this amorphous silica, and the mixture was calcined at 1,300° C. for 10 hours to obtain crystalline silica with a low water content. The above operation was repeated twice using the obtained crystalline silica as the next crystal nucleus to obtain crystalline silica (cristobalite) with high purity and low water content. Table 1 shows the amount of OH groups in the obtained cristobalite, and Table 2 shows the purity analysis results.

Example 3 To 253 parts by weight of tetramethyl orthosilicate, 24 parts by weight of water was added.
0 parts by weight, 53 parts by weight of methanol, and 0.5 parts by weight of the crystal nuclei obtained in Example 1 were added, stirred, gelled, and dried. The obtained silica gel was calcined at 1,200°C for 10 hours. Crystalline silica with low water content was obtained. The above operation was repeated twice using the obtained crystalline silica as the next crystal nucleus to obtain crystalline silica (cristobalite) with high purity and low water content. Table 1 shows the amount of OH groups in the obtained cristobalite, and Table 2 shows the purity analysis results.

Comparative Example 1 After adding crystal nuclei to high-purity amorphous silica, calcination was carried out in 1,
The same operation as in Example 1 was performed except that the temperature was 100°C. Table 3 shows the OH group content of the obtained mixture of amorphous and cristobalite.

Comparative Example 2 The same operation as in Example 3 was carried out except that the silica gel was calcined at 1,000°C. Table 3 shows the OH group content of the obtained mixture of amorphous and cristobalite.

Comparative Example 3 High purity synthetic amorphous silica to which no crystal nuclei were added
, 10 hours at 500°C, the silica was sintered. Table 3 shows the OH group content of the obtained mixture of amorphous and cristobalite.

Comparative Example 4 Silica gel obtained in the same manner as in Example 3 except that no crystal nuclei were added was calcined at 1,300° C. for 10 hours. Table 3 shows the amount of OH groups in the obtained amorphous silica.

[Table 1]

[Table 2]

[Table 3]

According to the method of the present invention, synthetic crystalline silica powder of high purity and low content of silanol groups can be efficiently and stably produced. Such synthetic crystalline silica powder is particularly useful as a raw material for high purity fused silica glass.

Claims (3)

[Claims] Claim 1: Synthetic amorphous silica powder or synthetic silica gel powder contains zero crystalline fine powder silica, which will serve as crystal nuclei.
．． A method for producing high-purity crystalline silica, which comprises adding 1% by weight or more and firing. [Claim 2] When silicon alkoxide is hydrolyzed to form a gel, fine crystalline powder silica, which will serve as crystal nuclei, is added in advance to a concentration of 0.1
1. A method for producing high-purity crystalline silica, which comprises adding silica gel powder in an amount of at least % by weight, drying the obtained silica gel powder, and then firing the obtained silica gel powder. 3. The crystalline silica obtained by the method according to claim 1 or 2 has a content of all metal impurity elements of 1 ppm or less and a silanol group content of 50 ppm.
pm or less.