JPH0416412B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing glass articles, and more specifically, a laminate of glass fine particles having an axially symmetrical shape is heat-treated in an atmosphere containing a fluorine compound, and a fluorine-doped light is heated. A method of manufacturing a glass article suitable for use as a transmission line provides a method for imparting a uniform fluorine refractive index profile to said glass article. [Prior Art] Several proposals have already been made as methods for imparting a refractive index distribution to glass articles using fluorine.
The first method is to create a refractive index distribution during vapor phase alignment in the gas phase alignment method, and is shown in FIG. In FIG. 4, reference numeral 41 denotes a glass fine particle synthesis burner through which the raw material for a portion 44 which is the center of the glass article is flowed, and silicon tetrachloride, etc., which is the glass fine particle raw material, is flowed here. Reference numeral 42 denotes a burner for synthesizing glass fine particles through which the raw material for the outer peripheral portion 45 of the glass article is passed, and the fluorine raw material is flowed therein together with the glass fine particle raw material. 43 is a glass fine particle laminate formed by adhering glass fine particles. however,
In this method, fluorine diffuses and is uniformly added to the glass particle laminate, making it impossible to create a refractive index distribution. A second method is illustrated in FIG. In FIG. 5, the glass fine particle laminate 53 has a center portion 54,
It is made to contain many substances that lower the transparent vitrification temperature, such as GeO ₂ and P ₂ O ₅ . When this stacked body 53 is inserted into a furnace 57 maintained at a high temperature, the central portion 5
4 shrinks faster than the outer peripheral part 55, so if the concentration of the fluorine raw material and the period of fluorine addition are selected,
It is possible to add more fluorine to the outer circumferential portion 55 to create a refractive index distribution in the glass article. However, although this method makes it possible to create a refractive index distribution, it has the disadvantage that in principle, the glass article contains substances other than silica and fluorine. The third method was proposed in the Proceedings of the 1983 National Conference of the Institute of Electronics and Communication Engineers (IEICE), Optical and Radio Division, Proceedings 2-183. In this method, the glass particle laminate is produced by changing the bulk density between the center and the outer periphery. It is being
When fluorine is added to this base material in a high-temperature furnace, more fluorine is added to the outer periphery where fluorine tends to diffuse, creating a refractive index difference between the outer periphery and the center. In order to achieve a relative refractive index difference of 0.3% between the center and the outer periphery using this method, the bulk density at the outer periphery must be ~0.2 g/
cm ³ , and the bulk density at the center must be greater than 1.5 g/cm ³ . However, there was a drawback in that it was extremely difficult to remove residual moisture from a glass particle laminate having a bulk density of 1.5 g/cm ³ or more. The fourth method, as proposed by the present applicant in Japanese Patent Application No. 59-254099, involves imparting a radial particle size distribution to the glass particles constituting the glass particle laminate.
The purpose is to utilize the fact that the transparentization temperature changes as a result of this to create a distribution in the amount of fluorine added. This method has the advantage of having little residual moisture, containing no substances other than SiO ₂ and fluorine, and being able to create a wide distribution in the amount added. flame,
The disadvantage was that it required the use of carbon monoxide flame, the sol-gel method, etc. Methods 1 to 4 above have been proposed when trying to give a refractive index distribution due to fluorine, but on the contrary, you want to make the refractive index distribution due to fluorine completely uniform. There are cases. However, the change in the bulk density of the glass fine particle laminate in the radial direction is reflected in the amount of fluorine added, making it difficult to obtain a completely uniform refractive index distribution due to fluorine. [Problems to be Solved by the Invention] In view of the current situation explained above, the present invention solves the drawbacks of the conventional method and provides a method of achieving a uniform refractive index even if the bulk density of the glass particles is not uniform in the radial direction. It is an object of the present invention to provide a method for manufacturing a glass article that has a profile, is sufficiently dehydrated, and is suitable for use as an optical transmission line. [Means for Solving the Problem] The present inventors decided to change the partial pressure of the fluorine compound as the heat treatment progresses when heating the glass fine particle laminate in an atmosphere containing a fluorine compound. Therefore, we have obtained the knowledge that the radial profile of the amount of fluorine added can be controlled despite the radial change in bulk density, and we have developed a novel method for manufacturing glass articles suitable for use as optical transmission lines. I came up with a method. That is, the present invention heat-treats a laminate of glass particles having a cylindrical or cylindrical shape with a bulk density larger in the center and smaller in the periphery in an atmosphere containing a fluorine compound, thereby producing a glass article doped with fluorine. In the manufacturing method, the heat treatment consists of a first heat treatment and a second heat treatment, and the partial pressure of the fluorine compound in the first heat treatment is equal to the partial pressure of the fluorine compound in the second heat treatment. Provided is a method for manufacturing a cylindrical or cylindrical glass article, characterized in that the fluorine concentration is made approximately equal in any part of the glass article by making the pressure larger than the pressure. Particularly preferred embodiments of the present invention include the use of a silicon fluoride as the fluorine compound, and the above-mentioned method in which the heat treatment is carried out in a high-purity carbon matuffle. The method of the present invention can control the radial distribution of fluorine concentration to be approximately uniform. In the present invention, both a soaking furnace as shown in FIG. 1A and a zone furnace as shown in FIG. 1B can be used. In FIGS. 1A and 1B, 11 is a rotating shaft, 12 is a matsuru, 13 is a furnace body, 14 is a heater, 15 is a glass particle laminate, 16 is a pressure gauge, and 17 is a pressure adjustment device. When a soaking furnace is used in the present invention, as the furnace temperature rises and the glass fine particle laminate 25 shrinks,
Change the partial pressure of fluorine compounds. Further, when a zone furnace is used, the furnace temperature and the fluorine compound partial pressure are changed each time the glass fine particle laminate 25 is passed through a high temperature section and heat-treated. Examples of the fluorine compounds used in the present invention include SiF ₄ , Si ₂ F ₆ , SF ₆ , NH ₄ F, NF ₃ , PF ₅ ,
Mention may be made of chlorofluorocarbons such as CF ₄ or CCl ₂ F ₂ . Furthermore, in the present invention, prior to the heat treatment in an atmosphere containing a fluorine compound, dehydration treatment is performed under conditions that the glass fine particle deposit does not shrink, such as heating treatment at a temperature of 1150°C in a zone furnace. By doing so, the amount of water contained in the glass article can be extremely reduced. It is advantageous if the glass particle deposit is dehydrated under such conditions that it does not shrink, since this will not have any effect on the amount of fluorine added thereafter. [Examples] Example 1 Glass fine particles were laminated by VAD method around a glass rod consisting of a core made of pure silicon dioxide and silicon dioxide containing fluorine surrounding the core to obtain a composite. When the bulk density of the composite was measured non-destructively using X-ray CT, it was found that the bulk density around the rods was extremely large, as shown in the radial bulk density distribution diagram in FIG. In FIG. 2, a represents a glass fine particle laminate, and b represents a glass rod. This complex is the first
Heat treatment was performed in the zone furnace shown in Figure B under the conditions shown in Table 1 below.

[Table] The refractive index of the obtained glass article was as shown in FIG. 3A. Comparative Example The same composite as in Example 1 was heat treated in the same zone furnace under the conditions shown in Table 2 below.

[Table] The refractive index of the obtained glass article was as shown in FIG. 3B, and the amount of fluorine added around the glass rod was small. Example 2 A glass fine particle laminate having an average bulk density of 0.25 was heated in a zone furnace as shown in Figure 3B in Table 3 below.
Heat treatment was performed under the following conditions.

〔Effect of the invention〕

According to the present invention, fluorine can be uniformly added even to a glass fine particle laminate having a bulk density distribution. When the glass article according to the present invention is used as a material for an optical fiber, a fiber with excellent hydrogen resistance and radiation resistance can be obtained, and the glass fine particle laminate does not shrink prior to heat treatment in an atmosphere containing a fluorine compound. By performing dehydration under certain conditions, it is possible to extremely reduce the amount of water contained in glass articles without affecting the subsequent amount of fluorine added. It has the advantage that it does not require special equipment or methods and can be carried out using an oxyhydrogen flame or a flame containing unitary hydrogen.

[Brief explanation of drawings]

FIGS. 1A and 1B are schematic explanatory diagrams showing examples of heating apparatuses used in the present invention, in which A shows a soaking furnace and B shows a zone furnace. FIG. 2 is a graph showing the radial bulk density distribution of the composite obtained in Example 1 of the present invention. 3A, B and C are graphs showing the radial refractive index distribution of a glass article;
Figure A shows the product of the present invention obtained in Example 1, B shows the comparative product obtained in Comparative Example, and C shows the product of the present invention obtained in Example 2. FIG. 4 is a schematic explanatory diagram of a conventional method of creating a refractive index distribution during vapor phase alignment. FIG. 5 is a schematic explanatory diagram of another conventional method for creating a refractive index distribution.

Claims (1)

[Scope of Claims] 1 A laminate of glass fine particles having a columnar or cylindrical shape and having a bulk density larger in the center and smaller in the periphery is heat-treated in an atmosphere containing a fluorine compound to produce fluorine-doped glass. In the method for manufacturing an article, the heat treatment includes a first heat treatment and a second heat treatment, and the partial pressure of the fluorine compound in the first heat treatment is lowered by the partial pressure of the fluorine compound in the second heat treatment. A method for manufacturing a columnar or cylindrical glass article, characterized in that the fluorine concentration is made approximately equal in any part of the glass article by increasing the partial pressure to a value greater than . 2. A method for manufacturing a glass article according to claim 1, which uses a silicon fluoride as the fluorine compound. 3. The method for manufacturing a glass article according to claim 1 or 2, wherein the heat treatment is performed in a high-purity carbon matsufuru.