JPS6227341A - Production of fused glass - Google Patents

Abstract

PURPOSE:To obtain a fused glass body having high purity and high homogeneity with less foam in the titled process for production consisting in sintering pulverous particle glass obtd. by a vapor chemical reaction after press molding by thoroughly heating and drying the above-mentioned glass prior to the press molding. CONSTITUTION:The glass having the extremely small grain size and high purity is obtd. when the pulverous particle glass is synthesized by the gaseous phase oxidation reaction. The soot prior to the press molding is preliminarily and thoroughly heated and dried at >=100 deg.C and at the sintering initiation temp. at which the growth of a neck starts or below by using such pulverous particle glass. The adsorption of the atmospheric gas such as H2O in the reaction stage, etc. is thereby decreased. The atmosphere in the drying stage is preferably of an inert gas such as Ar, or N2 or O2 which does not react with or is not adsorbed to the glass. The drying under the reduced pressure is also possible. The intended fused glass body is obtd. when the soot is calcined after the press molding.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing molten glass, and more specifically, a method for producing a molten glass molded body with high purity and high homogeneity that can be used for optical fibers, etc. Regarding.

[Conventional technology]

Conventionally, as a glass manufacturing method proposed in JP-A-52-156640.53-48536, etc., fine particulate glass obtained by vapor phase chemical reaction etc. is once pressure-formed using a press or the like. There is a method of obtaining a molten glass body by sintering this.

[Problem that the invention seeks to solve]

However, when the conventional methods described in the above-mentioned publications were examined in detail, it was found that when the particle size of the starting glass is large, there are problems in that bubbles tend to remain after sintering and the degree of homogeneity is poor. On the other hand, if the particle size of the starting glass is small, cracks are likely to occur in the press-molded product, making it difficult to obtain a good molded product.

It is an object of the present invention to provide a method for manufacturing a glass molded article that does not have the above-mentioned drawbacks.

[Means for solving problems]

The present invention provides a method for obtaining a molten glass body by pressure forming and sintering particulate glass, in which glass obtained by a gas phase oxidation reaction is used as the particulate glass, and the particulate glass is pressure molded. The above object is achieved by a method for manufacturing a molten glass body, which is characterized in that the glass body is sufficiently heated and dried at a temperature of 100° C. or higher and a temperature below the sintering start temperature at which sintering growth begins.

The present invention will be explained in detail below based on its theory.

The soot obtained by the gas phase oxidation reaction is, for example, 5ic
Sin particles obtained by introducing a 710 genide such as z4 into an oxyhydrogen flame or a plasma flame and reacting as shown in the following formula (1) or formula 12) can be used.

In case of oxyhydrogen flame S i C4+ 2Hz + 0 → 8i0! +4HC
t...(1) In the case of plasma flame, 5iC4+O, → SiO+2C't,
(2) By the way, the shrinkage rate of a glass molded body due to sintering largely depends on its particle size, as shown by the following equation (3).

I, dη k : proportionality constant d : particle diameter η : viscosity coefficient γ : surface energy t : time and the sintering rate of the glass molded body is expressed by the following equation (4).

However, the smaller the particle size, the faster the shrinkage occurs, so the faster the sintering speed is, the faster the sintering and melting can be completed at a lower temperature and in a shorter time, making it easier to obtain a transparent glass body. When fine particle glass is synthesized by a gas phase reaction, a highly pure material with extremely small particle size, usually 1 μm or less, can be obtained. That is, if fine particulate glass is sintered by a gas phase reaction, a glass body with extremely high purity and less foxing can be obtained, but there is a drawback that cracks occur during pressure molding of soot.

The inventors of the present invention have intensively investigated the causes and solutions for this problem, and have found that the soot obtained in the gas phase reaction has a small particle size, and therefore has a large specific surface area, which increases the adsorption amount of atmospheric gases such as H80 during the reaction. It was learned that this adsorbed gas causes cracks in the compact when the pressure is released after pressurization.

It was also found that as a countermeasure to this problem, this cracking can be prevented by sufficiently drying the soot before pressure molding. The drying conditions include a temperature of 100°C or higher, and a temperature up to the point at which particle neck growth (a state in which after heating for a predetermined period of time, material transfer occurs to the areas where the particles are in contact and sintering begins). Preferably, it is carried out under temperature conditions.

If it is below 100°C, H,0 of the main adsorbed substance cannot be removed, and if it is dried under conditions that cause neck growth, it will be difficult to obtain a uniform molded product during pressure molding in the subsequent process. be.

Note that the temperature at which neck growth starts is, for example, approximately (L1 μm
In the case of a suit with a diameter of 810 mm, the temperature is about 900°C. As a guideline for this temperature, in the case of glass particles obtained by a gas phase reaction, it can be represented by its viscosity value η, and is a temperature at which η is about 101S.

Further, the drying atmosphere is Ar or He.

It is preferable to carry out the process in an inert gas atmosphere such as N, or in a gas atmosphere such as O3 that does not react with or adsorb to glass. Furthermore, drying can also be carried out under reduced pressure. [Example] Example 1 5i02 soot with a particle size (11 to α01 μm) obtained by introducing 5iC4 into an oxyhydrogen burner was dried in an open oven at a temperature of 250°C. The reactor was kept in the reactor for 3 hours, during which time dry N was flowed at a rate of 1 t/min.

This soot was poured into a cylindrical rubber container, the inside of the rubber container was reduced in pressure and sealed, and then molded using a static pressure molding machine under 300 atmospheres, resulting in a molded product without cracks. This molded body was placed in a heat treatment furnace, dehydrated in an atmosphere of He and C4 gases, and then melted and vitrified at a temperature of 1600°C.

The resulting molten glass body was completely transparent glass and had almost no wrinkles. A plastic clad fiber was made using this glass as a core material, and just in case, the 0.
The transmission loss at a wavelength of 8 μm was f OdB/krn, a good characteristic, and it was found that this glass could be used as a material for optical fibers.

Comparative Example 1 When the same Sin and soot as in Example 1 were pressure-molded under the same conditions as in Example 1 without being heat-dried, the molded product had many cracks.
Also, when external force was applied, it broke into many small pieces.

Comparative Example 2 Commercially available 400 mesh (particle size approximately 64 μm)
When the S 10z powder of rn) was pressure-molded under the same conditions as in Example 1 without being heat-dried, a good molded body was obtained.

This was melted and vitrified in the same manner as in Example 1, but a completely transparent glass body was not obtained, and bubbles were scattered that were visible to the naked eye.

〔Effect of the invention〕

According to the present invention, molten glass with extremely high purity and high homogeneity can be obtained with good productivity.

Claims (1)

[Claims] In a method of obtaining a molten glass body by sintering fine particulate glass after pressure forming, the particulate glass is glass obtained by a gas phase oxidation reaction, and before pressure forming the particulate glass, , a method for producing a molten glass body, which comprises sufficiently heating and drying at a temperature of 100° C. or higher and below a sintering start temperature at which neck growth begins.