JPS62212235A - Production of glass - Google Patents

Abstract

PURPOSE:To easily obtain high-quality transparent glass having excellent functionality at a low cost, by filling SiO2 powder containing a phase-transition promoter in plural containers, heating the powder to obtain sintered articles having cristobalite crystal phase, collecting the articles to a desired form and integrating the articles by heating and melting in vacuum. CONSTITUTION:SiO2 powder containing a phase-transition promoter such as Na component is filled in plural containers made of mullite and heated at >=1,100 deg.C to obtain sintered porous articles having open cell structure and excellent processability and containing cristobalite crystal phase. A plurality of the sintered articles are collected to form a sintered aggregate having a desired shape and the aggregate is introduced into a vacuum furnace and heated at >=1,750 deg.C in vacuum of <=0.5mb. The collected plurality of sintered articles are integrated, melted and vitrified by this treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing glass by a vacuum melting method using silicon dioxide as a raw material.

(Prior art) Generally, glass as an industrial product is produced by heating raw material powder prepared at a predetermined ratio in a crucible or tank kiln to a temperature above the liquid phase, and cooling the resulting uniform solution. Manufactured. At this time, bubbles generated in the melt due to gases adsorbed to the raw material powder or gases generated during the reaction are removed by raising the temperature of the melt sufficiently to lower the viscosity of the melt and allowing it to float to the surface. It is common to make the material transparent by means such as methods.

However, when manufacturing glass using silicon dioxide as a raw material, due to its high viscosity and high melting point, constraints such as crucible and furnace refractories make it impossible to raise the temperature to an effective temperature for defoaming. If the temperature is too high, gas will be generated due to volatilization of the raw material itself and reaction between the raw material and the crucible, and conversely bubbles will be generated, so the above method cannot be adopted. For this reason, in order to obtain transparent quartz glass using silicon dioxide as a raw material, the following steps are generally taken:
How to deposit this on the table. The gas generated at this time is dissipated from the surface. (Bernoulli method) ■ A porous body made of fine powder of silicon dioxide is made,
A method of melting it into a strip from one end and turning it into glass.

The generated gas escapes through the unmolten porous body. (Normal melting method) ■ Quartz crystal powder adjusted to a particle size of 100 ham 4 yen is placed in a crucible and melted in a vacuum heating furnace to vitrify it, and the generated gas is forcibly removed. (vacuum melting method).

However, it is well known that both methods ① and ③ require an extremely long time to produce one glass block and have poor productivity.In particular, in the case of the Bernoulli method, the raw material efficiency is 30%.
~40%, which is bad. Furthermore, if an argon-oxygen plasma flame is used as the heat source, a glass with less residual -〇H groups and fewer internal bubbles can be obtained, but the energy cost is high, whereas when using an oxyhydrogen flame, which has a lower energy cost. However, there is a problem that only products with a large amount of residual -○H groups can be obtained. Moreover, the shapes of ingots that can be produced are limited to round and thin ones, which poses difficulties in subsequent processing steps.

Next, according to the vacuum melting method (■), there is little residual -08M,
It has characteristics such as high viscosity at high temperatures, and relatively large ingots can be obtained, but since raw material powder is filled in a container such as a crucible and then melted and vitrified, degassing is difficult, so it is difficult to make ingots in containers. Due to reaction gas generation due to contact with other materials, there are many internal bubbles and high quality products cannot be obtained. In addition, since crystal powder is used, there are also difficulties in supplying raw materials due to resource depletion.

In view of the above, the present applicant has proposed 11 methods for easily manufacturing high-quality transparent or functional glass at low cost. This is done by filling a suitable container with silicon dioxide powder, heating it in the presence of a phase transition accelerator such as an alkali component, and molding it into a porous body with continuous pores unified into a crystalline phase just below the melting point. (Japanese Patent Application No. 59-181586, Japanese Patent Application No. 59-181587, Japanese Patent Application No. 59-181588, - Japanese Patent Application No. 60-170663, Gansho 60-170
664@).

[Problem that the invention seeks to solve]

As described above, the method for producing glass according to the present invention includes the steps of heat-treating silicon dioxide powder to form a molded body having a cristobalite crystal phase, and vitrifying the molded body by heating and melting it under vacuum. It is something.

By the way, as is well known, crystalline silicon dioxide undergoes a phase transition from a quartz phase in a low temperature range to a tridymite phase and a cristobalite phase depending on the temperature at which it is heated during the heating process.

This phase transition is difficult to occur in silicon dioxide alone, and L i2
0. Na2O, 20°MQO, Cab, P20S,
It is known that it is effective to use a metal component such as 8203 as a phase transition promoter. On the other hand, since amorphous silicon dioxide alone is directly dissolved, metal additives such as those mentioned above are required in order to crystallize it into a cristobalite phase. Therefore, in the method of the present invention, the metal component is also used in the process of converting silicon dioxide powder into a cristobalite crystal phase, but as can be easily understood from the explanation of the prior art, generally in the glass manufacturing method, the raw material is The inclusion of metal components such as those mentioned above is not preferable, as it causes a decrease in the purity of the final product, similar to moisture and the like. That is,
In conventional glass manufacturing methods, there is a contradictory relationship between obtaining highly pure quartz glass and adding impurities to raw materials or using raw materials containing impurities.

For this reason, the glass manufacturing method of the present invention, in which a phase transition accelerator is added to silicon dioxide, or silicon dioxide containing an effective component for phase transition is selected as a raw material, is a manufacturing method that has no conventional concept. However, the reason why high-quality glass can be obtained more easily by this method than by conventional methods is that the characteristics of the sintered molded body of the cristobalite crystal phase, together with the adoption of the vacuum melting method, bring about many effects. There is a particular thing.

That is, as is well known, the sintered body of the cristobalite crystal phase has a unique melting point, so it can be heated to a temperature just below the melting point and degassed, and the sintered body of the cristobalite crystal phase is continuous. This is because it is a porous body with open pores, so that deaeration can be carried out sufficiently and easily. Therefore, if a metal component such as Na, which is easily decomposed and released and exhausted at a temperature below the melting point, is used as a phase transition accelerator, it is possible to obtain a transparent material from which impurities (including phase transition accelerators) are almost completely removed. Quartz glass can be obtained, and if a promoter that is not decomposed and removed at the melting point is selected, a functional glass containing only the promoter and other impurities removed can be obtained.

As described above, the method for producing glass according to the present invention organically combines a crystallization process using a phase transition accelerator and a vitrification process using a vacuum melting method, thereby producing a high-quality glass ingot with good productivity. is obtained. In addition, it has the effect of obtaining a relatively large glass ingot, but in order to obtain a larger ingot, the container for the sintered molded body must be made proportionally larger, and the container must be heat-resistant. This makes production difficult due to certain factors. In addition, the silicon dioxide powder used as a raw material has a low bulk density and low thermal conductivity, so when a large sintered molded body is obtained, production efficiency becomes poor or quality problems occur.

In view of the above, the present invention aims to provide a method for manufacturing larger glass ingots without reducing productivity.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention has been developed by filling a plurality of containers with silicon dioxide powder containing phase transition promoting powder, heating it to form a sintered molded body having a cristobalite crystal phase, and converting the resulting molded body into a sintered molded body having a cristobalite crystal phase. It is characterized by being aggregated into a desired shape to form a sintered aggregate, and then heated and melted under vacuum to vitrify it.

As mentioned above, the method (i) of the glass according to the present invention has an effect not seen in conventional methods by having a step of forming a sintered molded body having a cristobalite crystal phase without directly vitrifying the raw material powder. However, as mentioned above, in order to obtain a larger glass ingot, it is necessary to accept a certain reduction in production efficiency.

As a result of various studies as a means of obtaining larger glass ingots, the inventors of the present invention have found that by effectively utilizing the characteristics of the manufacturing method that produces a crystallized molded product from raw material powder, a larger glass ingot can be obtained without reducing productivity. Glass inbo!・We have found that the following benefits can be obtained. In other words, a sintered molded body with a cristobalite crystal phase has moderate base strength and excellent workability, and it is possible to utilize the characteristics that it is a crystal phase just below the melting point and has a unique melting point. There is, and the outline is explained below.

For example, when a Na component is added as a phase transition accelerator to amorphous silicon dioxide powder obtained by oxidizing silicon tetrachloride, the ratio is approximately 1.0 O.
OpI)■ Add. As a means of addition, since it is desirable to granulate the silicon dioxide powder to a large particle size without substantially changing the specific surface area, the silicon dioxide powder is immersed in an aqueous NaOI-1 solution, stirred and mixed, and then , dehydration, and drying are preferred.

The silicon dioxide powder containing Na component obtained in this manner is divided and filled into a plurality of relatively small containers made of mullite, which are easy to manufacture, and then heated to 1.100°C or less using any heating means. By doing so, a sintered body having a cristobalite crystal phase is obtained. The sintered body has a shape corresponding to a filled container, is porous with continuous open pores, and has an appropriate base strength, and these characteristics can be obtained by processing the raw material powder, etc. can.

Next, the plurality of obtained sintered bodies are assembled to form a sintered aggregate having a desired shape. The shape of the accumulation may be stacked, gathered, etc., and the size may be arbitrary, but in order to obtain the desired shape and dimensions, the shape of the sintering container is determined in advance.

It is necessary to obtain and prepare the dimensions. It is also necessary to mold the individual sintered bodies so that there are no irregularities on their contact surfaces so that the sintered bodies are densely assembled, but since the sintered bodies have good workability, molding is easy.

The sintered aggregate obtained in this way is carried into a vacuum furnace and heated to 1,750°C or higher under a vacuum of 0.5 mb or less, and the several sintered bodies are integrated into a molten glass. to become

(Example) Na content: approximately 1.0001) Ilm (Weight) 25 kg of each of two containers made of mullite having an inner diameter of 420 m and a height of 620 m+ were filled with 25 kg of silicon powder containing silica, and then heated in a heating furnace. Heating to 1,100℃ for 75 hours, 1,
Hold IFJ Ift at 100℃ at 5 o'clock, and this will reduce the outer diameter to 2.
A sintered molded body having a cristobalite crystal phase with a length of 65 m+ and a height of 3905 m was obtained. After shaping these two molded bodies by cutting the periphery with a knife etc., the outer diameter of the two molded bodies is 265 am.
A sintered aggregate with a height of 750 m1+ was prepared and heated and melted under vacuum. Heating was carried out for 12 hours to 1,730℃ and held at 1,730℃ for 3 hours, resulting in an outer diameter of 265m and a height of 400s.
An integrated transparent quartz glass weighing 49 kg of I,ffiffi was obtained.

〔Effect of the invention〕

According to the glass manufacturing method of the present invention, it is possible to eliminate the poor raw material efficiency and the poor production efficiency that required a long vitrification time, which were unavoidable in the conventional Bernoulli method, and moreover, it does not require an extremely expensive heat source. Since it is not necessary, it can be produced at low cost, and the method of the present invention further enhances this effect. That is, when a glass ingot is obtained by the method of the present invention, a large-sized glass ingot can be manufactured through a relatively easy-to-produce sintered body manufacturing process, so that productivity is not adversely affected and production costs can be reduced. Enjoy the benefits.

Claims (1)

[Claims] 1. Fill a plurality of containers with silicon dioxide powder containing a phase transition accelerator, heat it to form a sintered molded body having a cristobalite crystal phase, and shape the obtained molded body into a desired shape. A method for producing glass, which comprises accumulating them to form a sintered aggregate, then heating them under vacuum to melt them together and vitrify them. 2. The method for manufacturing glass according to claim 1, wherein the container has a relatively small diameter. 3. Claims 1 or 2, characterized in that the outer peripheral surface of the obtained sintered molded body is formed and then integrated.
Method for producing glass as described in section.