JPS6230634A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To obtain a high-purity ingot having relatively large size, without problems of the supply of raw materials, by using SiO2 powder as a raw material, carrying out the secondary pulverization of the raw material in the presence of a phase-transition accelerator, converting secondary powder to a sintered material having cristobalite phase, and producing a quartz glass from the sintered material by vacuum-melting process. CONSTITUTION:SiO2 powder is mixed to a solution containing a phase-transition accelerator, the mixture is frozen and thawed to effect the separation of the SiO2 powder dispersion into solid phase and liquid phase and the supernatant water is discarded. The coagulated SiO2 powder settled at the bottom is dried by dehydration means. The dried powder is pulverized again, and the particle size is adjusted by a simple crushing means. The powder produced by the secondary pulverization process is filled in a vessel having sufficient strength at high temperature and calcined to obtain a porous sintered product having cristobalite crystal phase. The sintered product is vitrified by heating and melting in vacuum. The deaeration in melting process can be carried out easily and completely by this process.

Description

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

[Conventional technology]

Currently, the methods for manufacturing transparent quartz glass are as follows:
The Bernoulli method involves feeding silicon dioxide powder little by little into an argon-oxygen plasma flame or an oxy-hydrogen flame to generate a stone. The sol-gel method involves placing quartz powder in a graphite crucible and melting it under vacuum to turn it into glass. After depositing on the target to obtain a porous glass body, 1,5
Methods such as C, V, D, etc. in which sintering is performed at around 00°C are well known.

(Problems to be Solved by the Invention) However, according to the Bernoulli method, if an argon-oxygen plasma flame is used as a heat source, a product with fewer residual -0 H groups and fewer internal bubbles can be obtained, but the energy cost is high. There are disadvantages.Also, if an oxyhydrogen flame is used as a heat source, the energy cost will be lower, but the residual -01111
You can only buy products with a lot of Moreover, as described above, this method has disadvantages such as a limit on the speed of raw material supply, poor productivity, and the ingots obtained are limited to thin round ingots. Next, it is said that the sol-gel method is not technically established, as it is prone to cracking and breakage during the reheating process, and it is difficult to obtain the desired glass lump.

In addition, the vacuum melting method is carried out on an industrial scale and has the characteristics of having few residual OH- groups and high viscosity at high temperatures. High purity cannot be expected. Moreover, as is well known, there is a problem of depletion of the raw materials themselves, making it difficult to supply them. Also, C, V, O, law is light fu? Although this is a well-known method for producing the fiber base material, it is also well known that the production quality is poor.

For these reasons, the present invention uses silicon dioxide powder with no concerns about raw material supply, provides high purity and relatively large ingots, and provides transparent glass that is easy to manufacture and has high productivity. The purpose is to provide a manufacturing method.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention relates to a method of producing quartz glass by a vacuum melting method using silicon dioxide, which has no resource constraints, as a raw material.
A secondary powdering process in which silicon dioxide powder containing a phase transition accelerator is obtained by mixing it in a solution containing a phase transition accelerator, freezing it, thawing it, dehydrating it, and drying it to obtain a silicon dioxide powder containing a phase transition accelerator; A calcination step in which the powder is filled in a container and heated to form a porous sintered molded body having a β-cristobalite crystal phase; This process is characterized by a vitrification step of heating and melting in a vacuum while maintaining the temperature above the transition humidity to .

〔Example〕

Hereinafter, the glass manufacturing method according to the present invention will be explained in detail.

As described above, when producing glass using silicon dioxide as a raw material, the Bernoulli method, which produces relatively high quality glass, has drawbacks such as productivity.

On the other hand, in the vacuum melting method, which allows relatively large ingots to be obtained, there is a difficulty in degassing, and high quality ingots cannot be obtained. The present inventors took advantage of the characteristics of the vacuum melting method and conducted various studies on the immediate problem of degassing, which could not be solved by conventional methods, and the problem of raw material supply difficulties due to the use of quartz powder. It has been discovered that sufficient degassing can be achieved by using silicon as a raw material, forming a sintered molded body having a cristobalite crystal phase, and then melting it in a vacuum.

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 due to the humidity heated during the heating process. This phase transition is difficult to occur with silicon dioxide alone, but it can be easily achieved by adding a polarizing metal element or using silicon dioxide containing a metal element. For example, Li2O, N
a2O.

k20. MGO, cao, P20S, 8203
It is known that these are effective as phase transition accelerators. 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. However, as can be easily understood from the explanation of the prior art, in the conventional method, the inclusion of the above-mentioned metal elements in the raw materials is a factor that causes a decrease in the purity of the final product, similar to other impurities such as moisture. This is not desirable. That is, in the conventional method, obtaining a highly pure quartz glass and adding impurities to the raw material are in a contradictory relationship, so a raw material with a high purity is required. Therefore, the concept of containing a metal element in a raw material or using a raw material containing a metal element, as in the method of the present invention, does not exist in the prior art.

For this reason, the method of the present invention, in which silicon dioxide is intensified with a phase transition accelerator, or silicon dioxide containing an effective component for phase transition is selectively used, can be said to be unique. The characteristics of the sintered molded body, combined with the adoption of the vacuum melting method, bring about many effects. 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 humidity just below the melting point and deaerated, and the sintered body of the cristobalite crystal phase is Since it is a porous body having a continuous amount of pores, deaeration can be carried out sufficiently and easily.

In addition, polarized phase transition accelerators are easily exhausted at humidity below the melting point, so if these are selected and used, transparent quartz glass from which impurities are almost completely removed can be obtained, and they can be decomposed and removed. If you choose an accelerator that does not
A hydrophilic glass containing only the accelerator can be obtained. In short, metal components that are considered impurities in the prior art are indispensable to the present invention and work effectively for carrying out the invention.

Next, as an example, a method for manufacturing a transparent quartz glass ink bottle 1- will be described using amorphous silicon dioxide powder as a raw material.

For example, a phase transition accelerator is added to and mixed with fine powder of amorphous silicon dioxide obtained by oxidizing silicon tetrachloride.

One type of alkali metal is selected as the phase transition accelerator, and the present inventors have found that when obtaining transparent quartz glass, the Na component is effective as it is the easiest to degas. In addition, the addition of Na component is easy to obtain a sintered molded body of cristobalite crystal phase, and according to the experiments of the present inventors, the weight ratio to the raw material powder is 100 Fl,
1), 1. ~2,00Of), 1), 1. If it is less than this, there will be problems with crystallization, and if it is more than this, there will be problems with degassing. Therefore, considering workability etc., the weight ratio to the raw material powder is 1,0001), El,
1. It is desirable to synthesize amorphous silicon dioxide powder containing a certain amount of Na component.

Next, as a means of adding the Na component, if you add amorphous silicon dioxide powder to deionized water and stir it, a dispersion system that is difficult to separate into solid and liquid will be obtained, so the Na component is added and mixed in the form of NaOH to this. Alternatively, if amorphous silicon dioxide powder is placed in deionized water to which NaOH has been added and mixed in advance and mixed and stirred, Na will uniformly adhere to the powder as ions. As mentioned above, this adhesion layer has a weight ratio of 1. o o o p, p,
For this purpose, the Na component may be adjusted to a weight ratio of about 2.300 p, p, m in the solution. The solution containing the amorphous silicon dioxide powder to which the Na component has been attached in this manner is dehydrated and dried by an appropriate means and re-pulverized. What is important here is that commercially available amorphous silicon dioxide powder has a particle size of about 0.02 Jll11.
This is the following fine powder, and when it is used to crystallize by heating, sintering progresses rapidly and a dense sintered body is likely to be formed (this must be avoided. In other words, the obtained It is desirable that the sintered body of the cristobalite crystal phase has pores large enough to allow residual gas to escape, yet small enough to have adequate base strength and shrinkage during melting during the vitrification process. In order to meet this demand, the solution containing the amorphous silicon dioxide to which the Na component has been attached is divided into appropriate containers and frozen in a freezer, or frozen using a well-known ice making device.Next, this solution is When the amorphous silicon dioxide powder is thawed by any method such as natural or heating, the dispersion system of amorphous silicon dioxide powder separates into solid-liquid two phases, so discard the supernatant water and dehydrate the silicon dioxide powder aggregates remaining at the bottom. Drying. By adjusting the particle size of the dried and re-powdered amorphous silicon dioxide powder using a simple crushing method, the fine powder is agglomerated, and the initially particle size of 0.02 μm or less becomes , a powder having a particle size of approximately 50 μm to 500 μm is obtained.

After filling the amorphous silicon dioxide powder obtained in this manner into a container made of, for example, mullite, which has high temperature strength, it is heated to 1,000°C or higher using any heating means to form a cristobalite crystal phase. Make it a sintered body. At this time, it is desirable to reduce the temperature increase rate as much as possible. The obtained sintered product is a porous molded product having a continuous number of pores in a shape corresponding to a filled container, and has sufficient support strength for self-supporting and transportation. Most of this sintered body is a β-type cristobalite crystal phase, and if it is a high-temperature type of cristobalite crystal, the obtained sintered body is cooled to form a low-temperature type α
When the crystal phase is transformed into a type of cristobalite crystal phase, a small rack is generated due to a volume reduction of about 6%. When this crack occurs, the cracks will further progress when melted and vitrified, so that it is often impossible to obtain a desired product. As is well known, the transition from the β-type cristobalite crystal phase to the α-type occurs between 220°C and 275°C, so the sintered body obtained by heating to about 1,000°C as described above is It is desirable to maintain the temperature above this transition humidity and send it to the vitrification process.

The vitrification process is carried out by a method similar to the well-known vacuum melting method, in which the sintered molded body having the cristobalite crystal phase obtained by the calcination process is heated and melted under vacuum to vitrify it. . At this time, due to the above-mentioned reason, the β-cristobalite crystal form is maintained (approximately 30
The mixture is placed in a vacuum heating furnace (maintained at 0° C. or higher) and simply placed on a shallow dish-shaped tray without placing it in a crucible or the like. This is possible because the sintered body has sufficient support strength for transportation and can stand on its own, facilitating degassing and preventing contamination due to contact with the container.

In a vacuum heating furnace, 1.
The temperature is raised to 750°C or higher to vitrify it, but since the sintered body is porous with a continuous amount of pores, impurities in the sintered body and Na components added for crystal shaping are removed. II easily by being heated to the respective pyrolysis humidity! It comes off and is exhausted. Further, the sintered body has a cristobalite crystal phase just below the melting point, and since the melting point of the crystal phase is unique, it acts extremely effectively on degassing treatment.

That is, if melting occurs in stages, the porous state partially collapses, blocking the escape route for gas and preventing sufficient degassing, but since the melting point is unique, there is no such inconvenience. Further, as long as a decomposition reaction does not occur, high humidity is effective in removing residual gas from the adsorption 9 reaction, but degassing can be achieved by raising the temperature to a humidity just below the melting point. Therefore, by the vacuum heat treatment,
The inside of the sintered body was almost evacuated until it was melted, and 1, OO01), 1), 1. In terms of Rt/4, the Na component is reduced to several p, p, m or less, and transparent quartz glass with few impurities and no bubble cracks can be obtained.

The above explanation was given as an example in which Na component was added as a phase transition accelerator to amorphous silicon dioxide powder, but materials containing Na component such as colloidal silica may also be used as the starting material. can. In addition, when obtaining transparent quartz glass, a phase transition accelerator is selected that is easily decomposed, desorbed, and exhausted at a humidity just below the melting point of the sintered body, but according to experiments conducted by the present inventors, alkali metals Among these, Na has been confirmed to be effective as the component that can shorten the vitrification time the most.

As is clear from the above description, the feature of the present invention is that after silicon dioxide powder is made into a sintered body having a cristobalite crystal phase,
Since vitrification is carried out by a vacuum melting method, a functionalized glass can be obtained by adding a phase transition accelerator for cristobalite formation and well-known components for linearization, leaving only the functionalized components remaining. It is also possible to selectively use a phase transition accelerator that also serves as a functionalization agent, and to adjust it without actively removing it. For example, Nd2O3
Silicon dioxide powder containing 0.3 mol % of P2O5 and 3 mol % of P2O5 is granulated into secondary particles by the above-described pretreatment, and then calcined at about 1.300° C. to form cristobalite. By heating and melting the obtained sintered body to 1.700° C. in a vacuum furnace, laser glass can be efficiently manufactured. Therefore, by doping various active ions, laser glass, photochromic glass, filter glass, etc.
It can be applied to the production of various functional glasses such as heat ray absorbing glass.

〔Effect of the invention〕

As described above, the glass manufacturing method according to the present invention includes a secondary powdering step in which silicon dioxide powder is made to contain a phase transition accelerator, and a sintered body having a cristobalite crystal phase is produced by heating the obtained powder. This is a glass manufacturing process that combines a calcination process and a vitrification process in which the sintered body is heated and melted under vacuum while maintaining the sintered body at a transfer humidity of β-α or higher.
It has many features and effects not found in conventional methods. In other words, when producing highly viscous glass such as quartz glass, it is possible to eliminate the inefficiency of raw materials that could not be avoided with conventional methods or the inefficiency of production that required a long vitrification time, and at the same time, it is extremely expensive. Coupled with the fact that it does not require a heat source, it can be manufactured at low cost.

Furthermore, although a vacuum melting method is used, bubbles are generated due to insufficient degassing, which could not be solved with conventional methods.

All problems of contamination caused by contact with containers can be solved, and a glass ingot with high purity can be obtained.

Claims (1)

[Claims] 1. Silicon dioxide powder is mixed into a solution containing a phase transition accelerator, then frozen, thawed, dehydrated, and dried to obtain a silicon dioxide powder containing a phase transition accelerator. a secondary powdering step; a calcination step in which the powder obtained in the secondary powdering step is filled into a container and heated to form a porous sintered molded body having a cristobalite crystal phase; and the calcination step. A method for producing quartz glass, comprising a vitrification step of heating and melting the sintered molded body obtained in the step under vacuum. 2. The method for producing quartz glass according to claim 1, wherein a functionalizing component is added in the secondary powdering step. 3. The method for producing quartz glass according to claim 1 or 2, wherein the particle size of the silicon dioxide powder obtained in the secondary powdering step is 50 μm to 500 μm. 4. Claims characterized in that the sintered molded body obtained in the calcination step is treated in a vitrification step while being maintained at a humidity higher than that at which the β-cristobalite crystal phase transitions to the α-cristobalite crystal phase. A method for producing quartz glass according to any one of items 1 to 3.