JPH08188411A - Synthetic quartz powder and glass molding - Google Patents

Abstract

PURPOSE: To obtain a synthetic quartz powder of high quality with bubble formation reduced on fusing and glass formed products therefrom by reducing the number of the particles including black points in the powdery bodies lower than a specific level in the production of synthetic quartz by the sol-gel process. CONSTITUTION: This synthetic quartz powder is produced by the sol-gel process and includes five particles having black points/50 grams among the powder particles. When this synthetic quartz powder is melt-formed, a glass formed product including extremely reduced bubbles is given. In order to produce such synthetic quartz powder, the thickness of scales stuck on the inner walls of the producer composed of silica precursor is controlled within a limited value and the concentration of the oxygen gas is controlled so that the scales may be sufficiently fired on the firing process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity and high-quality synthetic quartz powder, and a glass molded body formed by melting the powder having extremely few bubbles.

[0002]

2. Description of the Related Art In recent years, glass products used in the optical communication field, semiconductor industry, etc. have been subjected to extremely strict control regarding the purity thereof. Such high-purity glass is mainly produced by using sand-like natural quartz powder (so-called so-called sand) obtained by crushing natural quartz as a raw material, and in the case of higher purity, silicon tetrachloride. The oxyhydrogen flame method using a mass of fumes obtained by adhering and growing fumes generated by decomposition in oxyhydrogen flame on a substrate, using a gel obtained from an organometallic compound such as a metal alkoxide as a raw material, It is manufactured by the so-called sol-gel method or the like. However, each of these manufacturing methods has advantages and disadvantages.

When natural quartz is used as a raw material, metallic elements such as aluminum and iron are essentially contained inside the quartz particles, and it is difficult to highly purify it to 10 ppb or less even if purification such as acid washing is repeated. Is. Further, although high purity can be achieved by the oxyhydrogen flame method of silicon tetrachloride, it is not mass-produced because it is difficult to cost industrially. On the other hand, although the sol-gel method can be mass-produced, there is a fate that raw materials, intermediates, and products come into contact with the manufacturing apparatus, and there is a problem that impurities are mixed due to contact with the apparatus. In particular, organometallic compounds, which are raw materials, and particles (sols, gels) and wet gels produced by the reaction of alkoxide and water come into contact with the inner wall of the device and repeatedly adhere, peel, and fall off, and are mixed in the product. It was extremely difficult to separate and remove it. Such a scaled product becomes a black spot foreign substance in which carbon aggregates after firing, which significantly deteriorates the quality of the product.

[0004]

The scaling material adhered to the inner wall of the apparatus is a hard and dense silica precursor, and unlike normal reaction product gel, decarbonization does not occur easily even during drying and firing, and it appears as a black dot. It remains in the product. These black-spotted particles contain bubbles because the black-spotted carbon burns to generate gas when the synthetic quartz powder is melt-processed.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in view of the above-mentioned problems, and as a result, reduce the amount of the device deposits mixed in the product and ensure that the mixed device deposits are appropriate. By subjecting it to heat treatment, it is possible to obtain the desired high-quality synthetic quartz powder, and then by melting the synthetic quartz powder of the present invention having a low content of black spot particles, it is possible to obtain a glass molded body with very few bubbles. The present invention has been found. That is, an object of the present invention is to maintain the purity and quality of the synthetic quartz powder and granules to a very high level, and obtain a glass molded body having almost no bubbles. Therefore, the object is the synthetic quartz powder produced by the sol-gel reaction, which is the gist of the present invention, and the number of black spot particles in the powder is 5/50 g.
This is achieved by the following synthetic quartz powder and a glass molded body obtained by melting the present quartz powder.

The main source of black spot particles in synthetic quartz is silica precursor such as hydroxyalkoxy siloxane produced by sol-gel reaction, which adheres to the inner wall of the apparatus, and the adhered scaling material peels off and falls off during the manufacturing process. It is a substance mixed in the gel. As such an apparatus, at least a reactor, a crusher, a dryer, a pipe section, and the like, a series of apparatuses for producing synthetic quartz having a portion in contact with a liquid or a wet gel, a dry gel, or these individual apparatuses are targeted. . A part of the scaling substance (abnormal particles) separated and dropped is not sufficiently combusted during the constitution process and remains as unburned carbon in the quartz powder to become black spot particles. The present invention is a means for controlling the number of sunspot particles to be 5/50 g or less within the scaling limit thickness, and controlling the oxygen gas concentration so that the mixed scaling material is sufficiently burned in the firing process. Achieved by

Hereinafter, the present invention will be described in detail. First, the synthetic quartz powder of the present invention is obtained by a so-called sol-gel method. For example, alkoxysilane and high-purity water are charged into a reactor in an amount of 10 to 10 equivalents, and after performing a sol-gel reaction, the silica gel precursor can be obtained by pulverizing and drying. As the alkoxysilane, tetramethoxysilane or tetraethoxysilane is generally used, but it is not limited to this as long as the hydrolysis reaction is an alkoxysilane. As a method of promoting the reaction, an acid or alkali catalyst may be used. In this case, a metal-free catalyst is preferable, and organic acids, aqueous ammonia, etc. are generally used. The obtained wet gel is adjusted to an arbitrary particle size by pulverization. In particular, the particle size distribution of the milling here governs the particle size distribution of the final product. The optimum particle size of the wet gel may be determined in consideration of the particle size distribution of the target product and the shrinkage of the particles due to drying and firing.

For example, a wet gel is demethanol,
After dehydration and drying to give a dry gel having a particle size distribution of 100 to 500 microns, it is calcined to remove carbon and silanol as residues. Normal product silica gel glass powder, for example, exhibits a particle size distribution of 75-400 microns with less than 5 ppm carbon and less than 50 ppm silanol. However, in the prior art, even if a small amount of the scaling material adhering to the inner wall of the apparatus is mixed in the product, it is difficult to remove it, so that the quality of the product is significantly deteriorated. In the present invention, when mixed in the product gel at the stage of dry gel, it is quickly detected to prevent further mixing from the device,
Alternatively, when mixed, air can be sufficiently supplied in the firing process so that unburned carbon does not remain, and the object can be achieved by controlling the number of black spot particles in the product to be 5 particles / 50 g or less.

A method for detecting abnormal scaling substances (abnormal particles) in dry gel is, for example, that carbon is abnormally contained, and therefore abnormal particles are detected as black spots by heat treatment under low oxygen and high temperature. I can. Further, even with the mixed scaling material, carbon can be removed by sufficiently supplying air during the firing process. At this time, it is important to reduce the dense scaling material remaining as unburned carbon so that the number of black spot particles in the product is 5 particles / 50 g or less. Since the black spot particles can be easily confirmed with the naked eye, 50 g of the product is thin in a container such as a petri dish and a bat so that the number of black spots can be confirmed (specifically, about several mm, preferably about 1 mm. The following) makes it easy to count the number of sunspot particles if they are uniformly spread. Further, in the present invention, a glass molded body is manufactured by a conventional method, for example, a melting method using an oxyhydrogen flame, that is, a so-called Bernoulli method is used to melt synthetic quartz powder having a small content of black spot particles to produce a glass molded body. Produces a high quality product with less foaming when melted.

[0010]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 A jacket-heated SUS304 reactor was charged with tetramethoxysilane and water in an amount of 5 times the equivalent amount of the tetramethoxysilane.
The mixture was reacted at 30 ° C. for 30 minutes to obtain a wet gel as a silica precursor. Then, the wet gel was crushed with a SUS304 cone mill type crusher, and the crushed wet gel thus obtained was subjected to S
The gel was placed in a US304 conical dryer and, while rolling, dried at 140 ° C. for 3 hours, and subsequently this gel was washed with water and dried in a conical dryer for 4 hours. The dry gel was classified to obtain a particle size distribution of 75 to 400 microns.

When the above-mentioned operations (reaction, crushing, drying, washing with water, drying, and classification) were repeated 1 to 50 times, adhesion of a scaling material composed of a silica precursor was observed on the inner wall of the apparatus. The 10th, 20th, 30th, 40th, and 50th classification dry gels 10 g among these 1 to 50 times were precisely weighed, and were placed in an electric furnace under a nitrogen gas flow,
After heat-treating at 800 ° C for 15 minutes, it was taken out from the electric furnace and the number of all black spot particles, that is, abnormal particles was examined. The number of abnormal particles (black dots) in the classified dry gel was 1 each.
50 at 0th, 45 at 20th, 55 at 30th
The number was 60 at the 40th time and 70 at the 50th time. Then, 10th, 20th, 30th, 40th, 50
The second classification dry gel was placed in a rotary quartz inner cylinder electric furnace (core diameter 200 mm; powder bed height 60 mm; rotation speed 4 rpm).
The temperature was raised from room temperature to 1000 ° C. in 2 hours under a flow of 45 liters / minute of air to obtain a synthetic quartz glass powder. When 50 g of each of these powders was precisely weighed and the number of black spot particles was examined, it was 2 at the 10th time, 1 at the 20th time, 4 at the 30th time, 2 at the 40th time, and 3 at the 50th time. there were. or,
Bernoulli melting method was applied to each powder at 1700 ℃
And was melted at 10 g to obtain a glass molded body of 10 g. The foam content of each of these molded products was extremely small and less than one, which was a practical value.

Comparative Example 1 The same operations as in Example 1 (reaction, pulverization, drying, washing with water, drying, classification) were repeated 100 times. Classification dry gel 10g
Was weighed accurately, and at 15 ° C in an electric furnace under nitrogen gas flow at 15 ° C.
After heat treatment for a minute, remove it from the electric furnace and
That is, when the number of abnormal particles was examined, the number of abnormal particles (black dots) in the classified dry gel was 255. Then 1
The 00th classification dry gel was placed in a rotary quartz inner cylinder electric furnace,
It was calcined under air flow in the same manner as in Example 1, 50 g of the powder was precisely weighed, and the number of black spot particles was examined. As a result, it was 21.
Further, this powder was melted at 1700 ° C. using a Bernoulli melting method to obtain 10 g of a glass molded body. This molded product had a very large amount of bubbles (about 100 bubbles per molded product) and was not put to practical use.

[0014]

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a high-quality synthetic quartz powder and a glass molded product which are less likely to generate bubbles during melting.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Shimoyama 1-1 Kurosaki Shiroishi, Hachimannishi-ku, Kitakyushu City Mitsubishi Chemical Corporation Kurosaki Development Laboratory

Claims (2)

[Claims] 1. A synthetic quartz powder produced by a sol-gel reaction, wherein the number of black spot particles in the powder is 5/50 g or less. 2. A glass molded body, which is obtained by melting the synthetic quartz powder according to claim 1.