JPH0372574B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for producing high-purity glass useful for optical and electronic devices.

[Prior art]

A solution of an oxide or a compound that decomposes or reacts to become an oxide is impregnated into the pores of a porous silicate or gelminate that has internally interconnected pores, and the dopant is further deposited by drying or baking. Methods for producing glass bodies by post-firing are known. (For example, Japanese Patent Application Laid-open No. 50-28339.) Conventionally, when glass is manufactured by this method, a porous glass such as porous Vycor (trademark of Corning Inc.) glass has been used as a matrix. Vycor glass is well known
A homogeneous glass of the SiO ₂ −B ₂ O ₃ −Na ₂ O system is made, and by heat treatment, a portion consisting mostly of SiO ₂ and a portion consisting mostly of
The glass is phase-separated into a portion consisting of B ₂ O ₃ −Na ₂ O, and the B ₂ O ₃ −Na ₂ O portion is leached with an acid such as hydrochloric acid, resulting in a glass consisting almost only of SiO ₂ . However, the porous glass obtained by this method is not 100% SiO ₂ glass, but about 4% (B ₂ O ₃ + Na ₂ O) remains, and the diameter of the pores is not uniform. When leaching is performed from the base glass of the round bar, the disadvantage is that the diameter of the pores in the center of the round bar becomes small. For this reason, when Vycor is used as a porous glass matrix when producing optical glass materials, for example, the defect is that the dopant distribution is uneven and the refractive index distribution falls at the center of the round bar. This is because the dopant was not sufficiently precipitated because the pore diameter at the center of the round rod was small. In order to avoid these problems, for example, as shown in Japanese Patent Application Laid-open No. 56-104733, a large porous Vycor is made, and the central part (where the pores are small) is rounded using a reamer. After cutting out a rod to obtain porous glass with a substantially uniform pore diameter, a dopant is precipitated into the pores and heat treatment is performed to obtain an optical glass material with no distortion in the center of the round rod.

However, recently it has become possible to produce porous glass by the so-called sol-gel method. According to this method, the distribution of pore diameters in porous glass can be made almost uniform, unlike in the case of Vycor, but in order to make glass, it is necessary to heat the glass to near its transition point. must,
At that time, there is a problem in that the pores that were present in the gel state are burned out by heating, and the pore diameter becomes smaller. In order to precipitate a sufficient amount of dopant into the porous pores, a pore diameter of about 50 to 100 Å is desirable, but the pore diameter becomes smaller when the gel is heated.

Therefore, it is desirable to pre-immerse a porous gel with a large pore size in a dopant solution to precipitate the compound in the pores, and then heat-treat the gel to obtain glass. However, if the porous gel is immersed as it is in a compound solution, the gel will break, which is a problem. It is thought that a large amount of water is adsorbed on the pore surface of the gel at once, and the porous gel is cracked by the heat of adsorption.

[Purpose of the invention]

An object of the present invention is to provide a method for manufacturing glass that does not break when impregnated with a dopant solution using the porous gel.

[Structure of the invention]

The method for producing glass of the present invention is characterized in that a porous gel having continuous pores produced by a sol-gel method is subjected to steam treatment, then immersed in a dopant solution, dried, and fired.

The sol-gel method referred to in the present invention is to generate a metal compound sol from a metal compound solution, polymerize the sol to form a gel, volatilize or decompose the solvent in the gel, and obtain a porous gel. This is a method for producing glass in which glass is vitrified by firing at a temperature above the transition point of glass and pores are crushed. Specifically, silica gel has been manufactured by adding acid to water glass while stirring to first form a sol, which is then polymerized into a gel and dried, which has been known for a long time.
As in No. 55344, silicon alcoholate and other metal alcoholates are mixed, water is added to cause hydrolysis, first a sol is produced, and the reaction is further advanced to polymerize into a gel, which is then converted into glass. A method of manufacturing.

The gel obtained by the sol-gel method contains a large amount of solvent and water, and when heated and dried, the solvent evaporates, decomposes and evaporates, or disappears by combustion, leaving behind continuous pores. JP-A-58-55344 also describes the production of multi-component glass using the sol-gel method, but depending on the combination of metal compound solutions, it is possible to arbitrarily produce multi-component glass with a uniform composition due to the difference in reaction rate between the two. I can't get it.

However, the continuous pores remaining in the porous gel are uniformly distributed throughout the gel, so by precipitating the dopant of the metal compound to be added to the pore surface and then vitrifying it, it is possible to create homogeneous glasses with various combinations of components. It is possible to manufacture.

The steam treatment referred to in the present invention refers to a relative humidity of 90% RH.
Exposure to the above atmosphere causes water to be adsorbed on the gel surface and pore surface. Gels produced by the sol-gel method are dried at high temperatures in order to remove the solvent, and as a result, the dried porous gels have the property of adsorbing water extremely easily. However, if suddenly exposed to an atmosphere with high relative humidity, it is likely to cause damage, so it is desirable to gradually increase the atmospheric humidity and eventually raise the humidity to 90% RH or higher. By treating in this manner, the gel rarely cracks even when immersed in a solution containing a dopant.

The dopant of the present invention is a substance produced by thermal decomposition of a metal oxide to be added to glass, which penetrates into the pores in the gel in the form of an aqueous solution, precipitates on the surface of the pores by drying, and is then fired. It is decomposed into oxides and vitrified together with the gel base components. Therefore, metal hydroxides and metal salts are mainly used as dopants. In the case of metal salts, nitrates are preferred in terms of solubility in water and ease of decomposition into oxides. Further, the number of metals used for the dopant is not limited to one type, but multiple types can also be used.

〔Example〕

76 g of Si(OCH ₃ ) ₄ and 73.6 g of CH ₃ OH were placed in an Erlenmeyer flask and stirred with ultrasonic waves for about 15 minutes, and then 36 g of 0.00008% aqueous ammonia was gradually added and stirred with ultrasonic waves for an additional 15 minutes. Place this mixed solution in a Teflon container with a diameter of 15 mm and a length of 150 mm, cover the top of the container with aluminum foil, and place it in a constant temperature bath at 70°C for 24 hours. After that, make one pinhole of about 0.5 mm in the aluminum foil. Open it and keep it in a thermostat at 70℃ for 14 days until it has a diameter of 7.
A silica gel with a length of 70 mm was obtained. Water and alcohol remain in this gel, so in order to remove them, the gel is heated slowly from room temperature to 400°C in a vacuum (10 ^-3 TOrr) to remove water, and then placed in an oxidizing atmosphere.
After holding at 400°C for 16 hours to burn off the alcohol, it was gradually heated again in a vacuum, held at 700°C for 16 hours, and then cooled to room temperature to obtain a siliceous porous gel. 150g of water in a 300ml beaker
Pour a solution containing 100g of CsNO ₃ and hang the silica gel rod obtained earlier on its top.
The top of the beaker was covered with a watch glass, and the beaker was placed in a water bath and gradually heated. After holding at 60°C for 4 hours to allow the pores of the silica gel rod to sufficiently adsorb water vapor, the silica gel rod was placed in a beaker.
into the _CsNO3 solution and set the temperature of the water bath to
The temperature was raised to 95° C. and held for 4 hours to allow an aqueous solution of CsNO ₃ to permeate into the pores in the silica gel rod. The round bar was taken out and dried under vacuum at room temperature for 48 hours to precipitate CsNO ₃ into the pores of the silica gel. After that, it was slowly heated in a vacuum to raise the temperature to 700℃, and then dried at 700℃ in an oxidizing atmosphere. Hold for 16 hours. Next, it was slowly heated to 1050°C in a vacuum (10 ^-3 TOrr), held for 16 hours, and then lowered to room temperature, resulting in 84% by weight of SiO ₂ .
A glass body containing 16% Cs ₂ O was obtained. The Cs component in the diametrical direction of the cross section of this glass round rod was analyzed using an X-ray microanalyzer, and the Cs component was found to have a uniform concentration in the center without a decrease in concentration.

In this example, a CsNO ₃ solution was infiltrated into the pores of silica gel and precipitated on the pore surface, and then the gel was immersed in water at 95°C for about 10 minutes to create a concentration gradient in the CsNO ₃ solution in the pores of the silica gel. After attaching it, if you perform the same vitrification operation as in this example,
SiO ₂ − with a continuous refractive index distribution in the radial direction
A Cs ₂ O-based round bar lens can be obtained.

〔Effect of the invention〕

According to the glass manufacturing method of the present invention, a dopant is precipitated into a porous gel manufactured by a sol-gel method, so that a homogeneous glass with a uniform dopant distribution can be obtained. Since the porous gel is then immersed in the dopant solution, damage to the porous gel during the immersion process can be reduced.

Claims (1)

[Claims] 1. A method for producing glass, which comprises subjecting a porous gel having continuous pores produced by a sol-gel method to steam treatment, immersing it in a solution containing a dopant, and drying and firing.