JPS62202826A - Production of glass - Google Patents

Abstract

PURPOSE:To produce high-quality glass in high efficiency, by producing SiO2 powder containing a phase-transition promoter by a specific method, heat- treating the powder to obtain grown cristobalite crystal phase and melting the phase by heating in vacuum. CONSTITUTION:SiO2 powder containing excess phase-transfer promoter necessary in crystallization (e.g. metallic component such as Na2O, MgO, etc.) is uniformly mixed with SiO2 powder free from the promoter to obtain SiO2 containing prescribed amount of the phase-transition promoter. The obtained SiO2 is filled in a vessel and heated to obtain a sintered form containing cristobalite crystal phase. The sintered material is vitrified by heating and melting in vacuum. Since the amount of the promoter for crystallization can be controlled and uniformly distributed by this process, a high-quality transparent or functional glass can be easily produced at a low cost.

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 in a predetermined ratio above the liquidus temperature in a crucible or tank kiln to form a uniform solution f&.
′? Manufactured by l. 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 would be an exaggeration to try to make things transparent by such means.

However, when producing glass using 1F elemental dioxide as a raw material, it is difficult to raise the temperature to a temperature that is effective for degassing due to constraints such as crucible and furnace refractories due to its high viscosity and high melting point. If you do not raise the temperature, the raw material itself will volatilize,
The above method cannot be adopted because gas is generated due to the reaction between the raw material and the crucible, and conversely bubbles are generated. For this reason, in order to obtain transparent quartz glass using carbon dioxide as a raw material, generally silicon dioxide powder is fed little by little into an argon-oxygen, plasma flame, or oxyhydrogen flame, and then melted and vitrified.
How to make this on a stand. 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 about 100J1+11 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 (2) 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 extremely poor. In addition, if an argon-oxygen plasma flame is used as the heat source, a glass with less residual -〇H groups and comparatively fewer internal bubbles can be obtained, but the energy cost is high, and an oxyhydrogen flame with a low energy cost is used. If it is, there is a problem that only a product with a large amount of residual -OH groups can be obtained. Moreover, the shape of the ingot that can be manufactured is limited to round and narrow shapes, which poses difficulties in subsequent processing steps.

Next, according to the vacuum melting method (■), a comparatively large ingot can be obtained with characteristics such as a small amount of residual -〇8 bases and high viscosity at high temperatures. Since it is melted and vitrified, it is difficult to degas it, and moreover, it produces a lot of internal bubbles due to reaction gas generation due to contact with the container, making it difficult to obtain high-quality products. 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 applicant has developed a method for easily manufacturing high-quality transparent or functional glass at an inexpensive 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 metal component, forming it into a porous body with continuous pores that has a uniform crystalline phase just below the melting point, and then vacuuming. It is characterized by being melted and vitrified. 60-1706
No. 64).

[Problem that the invention seeks to solve]

The yJ@ method for 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 as described above, and vitrifying the molded body by heating and melting the molded body under vacuum. It is what it is.

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 with silicon dioxide alone, and Li
20. Naz O, 20°M (JO, Cab, P20
It is known that it is effective to use a metal component of S, [3203'8 as a phase transition accelerator. On the other hand, since amorphous 11-cumulium 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 presence of metal components such as those mentioned above is undesirable because 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 pure silica glass and adding impurities to raw materials or using raw materials containing impurities.

For this reason, it is necessary to add a phase transition accelerator to silicon dioxide, or to add silicon dioxide containing a component effective for phase transition.
The glass manufacturing method according to the present invention, which uses f elements as raw materials, is a WJ manufacturing method that has not been previously conceived, but the reason why high-quality glass can be easily obtained by this method compared to the conventional method is as follows.
The characteristics of the sintered body of the cristobalite crystal phase, together with the use of the pure air 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 temperature just below the melting point and then subjected to deaeration treatment. This is because deaeration can be carried out sufficiently and easily due to the porous body having a continuous amount of pores. Therefore, it decomposes easily at temperatures below the melting point and separates 1B2.
If a metal component such as Na, which is highly sensitive to metals, is used as a phase transition accelerator, transparent quartz glass from which impurities (including phase transition accelerators) are almost completely removed can be obtained, and it will not be decomposed and removed at the melting point. By selecting a promoter, it is possible to obtain a functional glass that contains only the promoter and removes other impurities.

As mentioned above, the method for producing glass according to the present invention is characterized in that it includes a crystallization step and that a phase transition accelerator is used for crystallization, but in the vitrification step, impurities are removed. For this reason, the phase transition accelerator added to the silicon dioxide powder, which is a raw material, is in an unnecessary amount, and it is desirable that it be uniform. This is particularly important when obtaining transparent quartz glass, and the glass manufacturing method according to the present invention is characterized by the ability to obtain relatively large glass ingots, making this a problem. Become.

The object of the present invention is to provide a method in which this phase transition accelerator, which is an essential loss, can be easily homogenized and high-quality glass can be efficiently produced.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention blends silicon dioxide powder containing an excessive amount of phase transition accelerator necessary for crystallization and Ij dioxide raw powder that does not substantially contain the accelerator, and uniformly The obtained silicon dioxide powder containing the desired amount of phase transition accelerator is filled into a container and heated to form a sintered molded body having a cristobalite crystal phase, which is then heated and melted under vacuum. It is characterized by being vitrified.

As described above, in the method for producing glass according to the present invention, a sintered molded body having a cristobalite crystal phase is obtained by heat-treating silicon dioxide powder containing a phase transition accelerator. The method of addition to the accelerator is usually by mixing raw material powder into the accelerator-containing solution and stirring the mixture. That is, when a Na component is used as a phase transition accelerator, the component is added to a water-dioxide mixture in the form of an aqueous NaOH solution, stirred and mixed, and then water is removed and dried to accelerate the phase transition. A silicon dioxide powder substantially containing the agent is obtained. At this time, it is desirable that the weight ratio of the Na component added to the raw material powder be 100 DDI to 2,000901, and that silicon dioxide powder containing about 500 pp1m to 1.000 EIDl of Na component can be obtained.

However, when mixing and stirring silicon dioxide powder in the above-mentioned NaOH aqueous solution to achieve homogenization, it has been found that adding a desired amount of Na component results in poor stirring performance and does not easily homogenize the mixture.

The figure shows the experimentally determined relationship between the amount of Na added and the stirring torque when silicon dioxide powder is mixed and stirred in an NaO Hinaga solution using a stirrer.As is clear from the figure, The vicinity of the desired addition Ja shows the maximum torque, and thereafter, as the addition amount increases, the torque decreases to about 2.3
001) It becomes almost the minimum value at the addition amount of fl-. For this reason, in order to improve the stirring performance and make it uniform, Naf
Either the f1 load was set excessively and stirring was performed with low torque, or the desired amount of Na was added and stirred, and the mixture had to be used in a non-uniform state. Therefore, if excessive Na component is added, the deaeration efficiency will be poor in the vitrification process.
Alternatively, it may result in a product with insufficient degassing, and even if raw material powders that are mixed non-uniformly are used, a high-quality product cannot be obtained.

The method of the present invention is based on such knowledge, and an example of manufacturing transparent quartz glass will be described below.
Add silicon dioxide powder to deionized water and mix with W1.

Next, a Na component is added as a phase transition accelerator in the form of an aqueous NaOH solution and stirred. Based on the above findings, the amount of Na component added is determined by the excess a1 (for example, 2.300 as a weight ratio to the silicon dioxide powder). pOm or more), and HlJf
, m with less torque is added. After a sufficient stirring operation, the solid-liquid mixture is frozen and then thawed to form a solid-liquid fraction, or solid-liquid separation is performed using a pressing means such as a filter press, and the resulting solid is dried to form a powder. to obtain silicon dioxide powder containing an excessive amount of Na component. Meanwhile, add silicon dioxide powder to deionized water, stir,
The mixture is separated using the solid-liquid separation means and dried to obtain a secondary powder of silicon dioxide containing no phase transition accelerator. The reason for performing the above treatment on the silicon dioxide powder without or without addition of a phase transition accelerator is to make the sintered molded body of the cristobalite crystal phase self-supporting and more porous. It's for a reason.

The respective silicon dioxide powders obtained in this way are mixed, and the mixing ratio is substantially N to the mixed powder in terms of weight ratio.
a component is 5001) Elm ~1 , 0001) I'1
Adjusted to contain m. Then, after filling the mixed silicon dioxide powder into a container, it is heated to 1,000°C by any heating means.
It is heated to the above temperature to form a sintered molded body having a cristobalite crystal phase. This sintered product is a porous molded product with continuous open pores in a shape corresponding to a filled container, and has enough base strength to be self-supporting and transportable. Next, this sintered product is placed on a dish-shaped tray and heated to 1,740°C or higher under reduced pressure of 0°5+eb or less in a vacuum heating furnace to vitrify it, but as mentioned above, the sintered product is Since it is porous with continuous open pores, the impurity components contained and the Na components added to the raw material powder are easily separated and exhausted by being heated to their respective thermal decomposition temperatures. Further, the sintered product is a cristobalite crystal phase just below the melting point, and since the melting point is unique, degassing treatment is extremely effective. That is, if melting occurs in stages, the porous state partially collapses and degassing becomes insufficient, but since the melting point is unique, there is no such problem, and as long as a decomposition reaction does not occur, high temperatures are not required. , Adsorption 1 is effective for removing residual gas from the reaction, and is effective because it can be heated to a temperature just below the melting point to degas it. Therefore, by the vacuum heat treatment, the inside of the sintered product is almost evacuated before it is melted, and the Na component added for crystallization is finally reduced to several E.
lf) l or less, and transparent quartz glass with few impurities and no bubbles can be obtained.

The above is a case of obtaining transparent quartz glass, but a well-known component for functionalization is added together with a phase transition accelerator, leaving only the functionalized component and removing other impurity components and phase transition V progression. By doing so, high quality mtw glass can be obtained. It is also possible to selectively use a metal component that promotes crystallization as well as functionalization, and adjust it without removing it using VIViA.

In addition, in order to uniformly add the desired amount of phase transition accelerator, in the above explanation, silicon dioxide powder containing an excessive amount of the accelerator was mixed with silicon dioxide powder containing no accelerator at all, but as is clear from the explanation of the figure. It is also possible to do this by appropriately preparing a mixture that has been treated with a small amount of stirring torque. That is, 2
．． Even if powder of ooowt, ppl is mixed with powder of 100wt, ppm, a raw material powder containing a desired amount of phase transition accelerator can be obtained depending on the mixing ratio. Furthermore, silicon dioxide powder containing no phase transition accelerator may be used without the above treatment.

〔Example〕

Inner diameter 260#+1. 5 J of deionized water was put into a 1-4134 stainless steel cylindrical container, and 500 g of amorphous silicon dioxide powder was added while stirring the deionized water at room temperature and under normal pressure to obtain a water-silicon dioxide mixed system. Next, 50 d of Na component was added as a phase transition accelerator in the form of a 1N NaOH aqueous solution. The addition ω of the Na component was 2,300111)1 in terms of weight relative to silicon dioxide, and the stirring torque was approximately the lowest value. After stirring for about 60 minutes, this solid-liquid dispersion was separated into solid and liquid using a filter press, and then dried to obtain silicon dioxide powder containing 1.50011 pl of Na component.

On the other hand, the open-chain amorphous silicon dioxide powder was stirred in deionized water, the t7-treated water-silicon dioxide mixture was subjected to solid-liquid separation, and then dried powder was prepared. It was added to silicon powder and mixed.

Next, this mixed powder was made into a powder with an inner diameter of 1201N11 and a height of 150#.
After filling a cylindrical container made of No. 111 Murai I-quality, the mixture was heated to 1,100° C. in an electric furnace. As a result, 76 shoesφ
A cylindrical sintered body having a cristobalite crystal phase of ×91jIIl was obtained, which was maintained at a temperature of 500°C or higher, transported into a vacuum furnace, and heated under a vacuum of 0.5 + eb or less to 1.
It was heated to 750°C to vitrify it.

The temperature increase balance at this time is 3 hours to 1,600℃ and 1 hour to 1,750℃, which results in 80m1
A transparent quartz glass with a weight of about 500 g was obtained using Iφ×45 glasses.

〔Effect of the invention〕

According to the glass manufacturing method of the present invention, it is possible to eliminate the poor raw material efficiency that was unavoidable with the conventional Bernoulli method, or the poor production efficiency that required a long vitrification time, and moreover, it does not require an extremely expensive heat source. Since it is not required, it can be produced at low cost. However, the method of the present invention further enhances its effects. That is, as is clear from the above explanation, one of the factors contributing to the production of high-quality glass is that the degassing treatment in the vitrification process can be carried out sufficiently, but according to the method of the present invention, the promotion of crystallization is Since the amount of additive added can be controlled and made uniform, this requirement can be easily met.

[Brief explanation of drawings]

The figure does not show the relationship between Na addition and stirring torque.

Claims (1)

[Claims] 1. A silicon dioxide powder containing an excess of a phase transition accelerator necessary for crystallization and a silicon dioxide powder substantially free of the accelerator are prepared and uniformly mixed. By filling a container with silicon dioxide powder containing a desired amount of phase transition accelerator and heating it, a sintered molded body having a cristobalite crystal phase is obtained, which is then heated and melted under vacuum to vitrify it. Characteristic glass manufacturing method. 2. The method for producing glass according to claim 1, wherein the phase transition accelerator is an Na component. 3. Claim 1, characterized in that the silicon dioxide powder containing the phase transition accelerator is mixed in a solution containing a desired amount or more of the phase transition accelerator, and subjected to dehydration and drying treatment. A method for manufacturing the glass according to item 1 or 2. 4. Claim 1, characterized in that the silicon dioxide powder that does not substantially contain the phase transition accelerator is untreated or mixed in water and subjected to dehydration and drying treatment. A method for manufacturing the glass according to item 1 or 2.