JPH0426530A - Surface treatment of fluoride glass - Google Patents

Abstract

PURPOSE:To enable treatment for preventing crystallization in a fiber forming device when the title glass is formed into a fiber and to simplify a process by using F2 under specified conditions. CONSTITUTION:Gas having <=30vol.% F2 concn. is brought into contact with fluoride glass at <=50 deg.C or gas having 3-50% HF concn. may be brought into contact with the fluoride glass at <=40 deg.C. The fluoride glass has a polished surface or water, hydroxyl groups and oxide formed by a reaction may remain on the surface of the glass. Gas having <=30vol.% F2 concn. is effective in inhibiting crystallization but gas having about 1vol.% F2 concn. is most effective and crystallization is nearly halved. The effect is enhanced in accordance with the reduction of treatment temp. but crystallization is well inhibited at ordinary temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for surface treatment of fluoride glass.

[Prior art] Fluoride glass has a wide range of '/l from ultraviolet to infrared range.
It has a transmission range and is used as optical window materials, laser matrix materials, optical fiber materials, etc.

Fluoride glass is made into a molded product by melting fluorides such as zirconium tetrafluoride, barium difluoride, and aluminum trifluoride, pouring it into a mold, etc., and rapidly cooling it.
The surface is then smoothed and cleaned. A water polishing method is generally applied for this smoothing and cleaning.

Fluoride glasses have a small difference (Tx - Tg) between glass transition temperature (Tg) and crystallization temperature (Tx) (and have significantly worse thermal stability than oxide glasses; for example, fluoride glasses When converting glass into fibers, the temperature is raised to about 320°C to soften the glass, but the surface tends to crystallize due to the effects of surface dirt and adhering moisture.This crystallization causes the fibers to form. This results in a significant decrease in the mechanical strength of the fiber, making it impossible to manufacture products of stable quality.Furthermore, crystallization increases scattering loss, which increases the transmission loss of the fiber.

In order to prevent such crystallization, various methods have been proposed as surface treatment methods for fluoride glass, such as plasma treatment with fluorine gas such as NF3 [P, H,
Klein, 5th 1nternatiOnal S
Symposium on Halide Glasse
s (1988)], -NF3, CF4, etc.,!
Sputtering treatment using l-based gas, etc.
49), a method of heat treatment at approximately 260°C using a fluorine gas such as NF3, ClF3, F2 (Japanese Patent Laid-Open No. 64
-28252) etc. are known.

However, these methods involve processing under reduced pressure or heat treatment, and the processing cannot be carried out within the fiberization equipment, resulting in additional steps and the need for separate processing equipment. .

"Specific means for solving the problem" The present inventors
As a result of intensive study in view of these problems with the conventional method,
The present invention was achieved by discovering that by using F or F2 under specific conditions, fluoride glass can be efficiently treated and crystallization during fiberization can be suppressed.

That is, the present invention provides a surface treatment method for fluoride glass in which a gas with an F2'a degree of 30 vol% or less is brought into contact with fluoride glass at a temperature of 50°C or less, and a) a gas with an IF concentration of 3 to 50 vol% is brought into contact with fluoride glass at a temperature of 40°C or less. This is a method for surface treatment of fluoride glass.

The fluoride glasses targeted by the method of the present invention include those whose surfaces have been polished, those which have been washed with water, or those in which moisture, hydroxyl groups, and oxides produced by reaction remain on the surfaces. In addition, it is not limited to cast-molded preforms, etc., but can also be applied to completed fluoride glasses such as lenses and prisms, and does not apply to all products that undergo heat treatment that can cause crystallization. Become.

In the method of the present invention, F2 or HF is used as the processing gas.
However, conventional methods include heat treatment using F2 at a temperature at which fluoride glass does not crystallize;
Specifically, a method of processing at around 260°C is known, and from the viewpoint of reaction activity, it is common to perform processing at higher temperatures, but as a result of our investigation, we found that However, it has been found that a lower treatment temperature is more effective in suppressing the crystallization of fluoride glass, and a lower treatment gas concentration is also more effective. A treatment gas concentration of 30 vol% or less has the effect of suppressing crystallization, and a concentration of about 1 vol% is most effective, suppressing crystallization to about half that of an untreated gas.

Although the lower the treatment temperature, the better the effect, treatment at room temperature is sufficient without using any particular cooling means.

1 (Almost the same conditions are applied when processing with F gas, but the processing gas concentration is in the range of 3 to 50 vol%, more preferably in the range of 20 to 40 vol%, compared to the untreated one. Crystallization is suppressed by about 20%.The effect of suppressing crystallization is reduced when the temperature is lower or higher than this range.As with F2, the lower the treatment temperature, the more effective it is.
Room temperature is sufficient.

These processing gases preferably contain as little moisture as possible. Further, as the diluent gas, an inert gas such as Ar or 82 is preferable.

The apparatus for implementing the method of the present invention is not particularly limited,
When using a glass fiber processing furnace as is, it is sufficient that it has an inlet and an exhaust port for processing gas, and that the inside of the equipment can be made into a closed system. . Also,
Although the treatment time depends on the treatment concentration and gas flow rate, about one hour is sufficient.

The processing effect is better exhibited when these processing gases are passed continuously, and a flow type processing is particularly effective in the case of IF processing. In the case of F2, if it is made into a flow type,
The processing effect still improves, but it is not as noticeable in the case of 1(F).

Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples.

In the following examples and comparative examples, fluoride glass having the following composition was used.

ZrFa (51)-8aF2 (20n-L
aF3(4,5)-~aF(20)f() indicates mol%] An optically polished glass rod is placed in a processing device integrated with a fiber drawing furnace. Vacuum degas the inside of the processing equipment,
F2 or HF4 at a predetermined concentration after replacing with Ar gas
Therefore, the treatment was performed at a predetermined temperature and for a predetermined time. After the treatment, the inside of the apparatus was vacuum degassed and replaced with Ar gas, and then heated to 325° C. in Ar gas. As a result, the number of crystals generated on the surface of the glass rod was measured, and the untreated glass rod was similarly heated in Ar to measure the number of crystals generated on the surface. The value of the number of crystals in the untreated rod was used as the crystal number ratio, and this was evaluated as the treatment effect.

The results of measuring the crystal number ratio by changing the processing gas concentration and processing temperature with a processing time of 1 hour are shown in Table 1.
It is shown in Table 4.

Note: Processing temperature is room temperature.

Note: The treatment concentration is 1 vol%.

Note: XXX in the table indicates that the number of crystals is extremely large and evaluation is difficult.

The processing temperature is room temperature.

Note: The treatment concentration is 25νof%.

As is clear from Table 1, a decrease in the number of crystals is seen at a concentration of 30 vol% or less, and the most effective is seen at a concentration of 1 vol% or less, with the number of crystals decreasing by half compared to the untreated case.

Furthermore, as is clear from Table 2, a lower temperature is more effective than when the F2 concentration is fixed at 1 νOI% and the processing temperature is varied, and the number of crystals can be reduced to 1/2 at a processing temperature below room temperature.

When the HF treatment concentration was changed as shown in Table 3, 5
A decrease in the number of crystals was observed at 0 vol% or less. Especially from 20~
A range of 30vo 1% is effective, and 1% compared to untreated
The number of crystals can be reduced to about /5.

When the 11F treatment concentration was fixed at 25VO 1% and the treatment temperature was varied, as shown in Table 4, lower temperatures were more effective.

[Effects of the Invention] According to the method of the present invention, crystallization during fiberization of fluoride glass can be easily suppressed, reduction in transmission loss can be suppressed, and fiberization can be stably achieved. It is.

Claims (2)

[Claims] (1) A method for surface treatment of fluoride glass, which comprises bringing a gas having an F_2 concentration of 30 vol % or less into contact with the fluoride glass at a temperature of 50° C. or less. (2) A method for surface treatment of fluoride glass, which comprises bringing a gas having an HF concentration of 3 to 50 vol% into contact with the fluoride glass at 40°C or lower.