JPS60200844A - Dehydration treatment of optical material by glow discharge - Google Patents

Abstract

PURPOSE:To dehydrate optical material contg. OH group without contg. impurities by arranging the optical material contg. OH group in the atmosphere of halogen atom isolated by glow discharge in the state wherein said material is subjected to high-frequency electric heating and substituting the halogen atom for the OH group. CONSTITUTION:When for example, gaseous fluorine is introduced in a reaction tube 3 from a gas introduction port 7 and glow discharge is caused from high frequency coils 8, plasma 9 contg. fluorine atom in nascent state is uniformly formed in the inside of the coil 8. On the other hand, the material 5 to be treated which is optical material is heated with the eddy current of high-frequency current flowing through coil 8 to give thermal energy necessary to a chemical reaction. Therefore, the fluorine atom isolated in the nascent state is substituted for the OH group of said material 5 and furthermore the OH group is allowed to react with fluorine atom to produce hydrogen halide and H2O molecule and these are discharged from an exhaust port 6. In this manner, the material is dehydrated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for dehydrating optical materials, and particularly to a method for dehydrating optical materials using glow discharge.

(Prior Art) Optical communication has been particularly in the spotlight in recent years because it allows broadband transmission and reduces loss. Low-loss silica glass fibers are mainly used as transmission media for optical communications, but the transmission loss has almost reached the theoretical limit, so new fiber materials are being developed. Among them, fluoride glass fiber is estimated to have a transmission loss of about one hundredth of that of silica glass fiber in the wavelength band of 3 to 4 μm, and is considered the most promising as a next-generation fiber. In addition, KBr and KCt have high light transmittance in the infrared region near this wavelength.

Lenses and prisms using crystals such as CaF2 are used as optical components in optical measuring instruments and the like.

However, these optical materials contain extremely small amounts of 820 molecules and OH.
It is known that when groups are mixed in as impurities, light in the near-infrared region is absorbed due to the molecular vibrations of 820 molecules and OH groups, significantly degrading light transmittance. Therefore, in order to construct a low-loss optical communication system or optical component, a method for removing 820 molecules and OR groups from the optical materials used is extremely important. The method of chemically removing H20 molecules and OH groups from optical materials in this way is called a chemical dehydration treatment method.

FIG. 1 is a basic configuration diagram of an apparatus using a conventional chemical dehydration treatment method. In the chemical dehydration treatment method shown in the figure, H
It utilizes a substitution reaction between 20 molecules or OH groups and a nitrogen element, and 1 is an inlet for an inert gas such as He or Ar, and 2 is an inlet for a nitrogen gas such as fluorine, chlorine, or bromine. The halogenating agent supplied from the introduction port 2 and the introduction port 1 are also supplied. mixed with the inert gas and introduced into the reaction tube 3,
It is heated to a desired temperature by the heater 4. Of the inert gas heated to the desired temperature and the no-logeflating agent,
For example, a chemical agent such as fluorine gas (F2) is dissociated from a molecular state (F2) into an extremely reactive atomic state (2F) (hereinafter referred to as the "nascent state") by thermal energy. . This resolved halogen atom (F) replaces the OH group contained in the object to be treated 5.

The substituted OH group further reacts with the floating hydrogen atom (F), and hydrogen halide (I (F) and H20
It becomes molecules and is discharged from the exhaust port 6 together with the inert gas.

In this way, in the conventional technology, by heating the 7. rogogenating agent to a desired temperature with a heat source such as the heater 4, it is dissociated into highly reactive nascent rogen atoms and treated. The method used was to replace the OH group contained in Product 5. Therefore, this chemical dehydration treatment method simply heat-treats the substance to be treated in an atmosphere containing the 7-rogen element, and is widely used.

However, in the conventional chemical dehydration treatment method, in which fluorine gas and other fluorine gases are dissociated into nascent atoms through heat treatment, fluorine gases in a steady state have a strong intermolecular bonding force, so temperatures of approximately 1200 degrees or higher It is necessary to raise the temperature to Therefore, at the heating temperature to dissociate the gas,
The optical material with a low melting point evaporated, making it impossible to dehydrate the optical material with a low melting point.

Furthermore, in conventional dehydration treatment for optical materials with low melting points, halogenated methane gas such as carbon tetrachloride has been used instead of halogen gas such as fluorine gas.

Halogenated methane gas such as carbon tetrachloride (CCt4) does not produce chlorine (C
It is possible to dissociate in step t), and the dehydration treatment effect is also improved.

However, when dissociating a molecule by thermal decomposition reaction, a reaction that dissociates one chlorine atom (CG) (CCt4→CCt30C
In addition to t), a reaction (CCt4→C+2Ct2) in which two or more chlorines are simultaneously dissociated to liberate carbon atoms also occurs, which has the disadvantage that carbon atoms (C) are mixed into the treated material as an impurity. In addition, methane such as carbon tetrachloride generates carbon dioxide gas during the dehydration reaction, and most of it is exhausted together with inert gas, but some of it is highly reactive like fluoride. It has the disadvantage that it reacts with substance 5, liberates carbon, and generates a new source of impurities.

As described above, with the prior art, it has been impossible to dehydrate optical materials with low melting points without containing impurities.

(Object of the Invention) The present invention was made in view of the above-mentioned drawbacks of the prior art, and is a dehydration treatment of optical materials using glow discharge, which can be applied to optical materials with a low melting point and a high melting point, and can be dehydrated without containing impurities. The purpose is to provide a method.

(Structure and operation of the invention) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 2 is a schematic diagram for explaining the principle of the dehydration treatment method according to the present invention, and shows how plasma is generated in the reaction tube by glow discharge. In the figure, 7 is a gas inlet for supplying a halogenating agent and an inert gas, 3 is a reaction tube, 8 is a high-frequency coil for causing glow discharge, and 9
indicates the part where glow discharge occurs. For example, fluorine gas (F) supplied from the gas introduction lower is dissociated by glow discharge regardless of the ambient temperature, and a plasma 9 containing F atoms in a nascent state is formed almost uniformly inside the high-frequency coil 8. Ru. On the other hand, the object to be processed 5 is heated by the eddy current of the high frequency current flowing through the high frequency coil 8, and thermal energy necessary for the chemical reaction is provided. in this way,
The F atoms dissociated into a nascent state by the glow discharge replace the OH groups of the heated workpiece, and further react with the F atoms to form hydrogen halide and H20 molecules, which are then discharged from the exhaust port 6 along with the inert gas. is exhausted from. Further, by heating the object 5 to be treated, 20 molecules of impurities (2) are also evaporated and exhausted from the exhaust port 6.

As described above, when a halogenating agent is supplied into the atmosphere undergoing glow discharge, the halogenating agent is dissociated into atoms in the nascent state at a high concentration regardless of the temperature, and the halogenating agent is dissociated into atoms in the nascent state at a high concentration, and the By setting the temperature at which the object to be treated can undergo a chemical reaction and at a temperature that does not evaporate due to heat, the OH groups of the object to be treated are replaced and removed. Therefore, this treatment method can also be applied to low-melting point optical materials such as fluoride glass or germanium oxide fiber, which could not be produced using the conventional method of dissociating halogen gas by thermal decomposition reaction and reacting with OH groups. Note that Table 1 shows the temperatures required for chemical reactions of main optical materials.

Table 1 FIG. 3 shows a specific example of an apparatus for carrying out the dehydration treatment method according to the present invention. In the figure, 10 is a susceptor support rod made of an insulating material such as quartz glass or alumina;
1 is a susceptor made of metal or graphite, etc.;
2 is a crucible, 13 is a fluoride glass which is the object to be treated, 1
Reference numeral 4 indicates a joint where flanges are joined via a seal.

Note that, as an initial setting, the height of the high-frequency coil 8 is adjusted so that the crucible 12 enters inside the high-frequency coil 8.

In addition, the inside of the reaction tube 3 is 1O-3torr (1torr
= 1/760 atm) or less.

After completing the above initial settings, argon (A
An inert gas such as helium (He) or helium (He) is introduced to maintain the pressure in the reaction tube 3 between 0.03 and 1 torr. Next, when a high frequency current is applied to the high frequency coil 8,
A glow discharge is generated inside the reaction tube 3, and the susceptor 11 is heated by an eddy current caused by the high-frequency current.

By adjusting the amount of high frequency current, the temperature is set to be above the melting point of fluoride glass (approximately 460 degrees) and below the temperature at which fluoride glass does not evaporate (approximately 900 degrees). In this state, a gas consisting of an inert gas mixed with a halogenating agent is supplied from the gas introduction lower. The halogenating agent supplied into the reaction tube 3 is dissociated by glow discharge, and the ionized halogen atoms in the nascent state at a high concentration in the plasma react with the OH groups in the fluoride glass 13 to be halogenated. hydrogen and H
20 molecules are produced. These hydrogen halides and H2
The 0 molecules are exhausted from the exhaust port 6 along with the inert gas, and dehydration processing is performed.

In the above embodiment, a case was explained in which fluoride glass was used as the object to be treated, but low melting point optical materials such as germanium oxide fiber, chalcogenide glass fiber, multi-component glass fiber, potassium bromide or chloride kareem were also used. Of course, it goes without saying that it can be applied to dehydration treatment of high melting point optical materials such as quartz fibers.

(Effects of the Invention) As explained above, according to the present invention, glow discharge is used to dissociate the logeflating agent to generate halogen atoms in a nascent state, and heating of the object to be treated is performed using glow discharge. This is done using high frequency current to generate discharge. Therefore, the halogenating agent can be dissociated to generate nascent halogen atoms, regardless of the processing temperature, as long as the temperature is set to the temperature required for the chemical reaction of the solid optical material. It is also applicable to dehydration treatment that does not contain impurities, so it is extremely effective in reducing the loss of optical materials used in the near-infrared region.

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional chemical dehydration treatment device, Figure 2 is a schematic diagram for explaining the glow discharge dehydration method of the present invention, and Figure 3 is a diagram of the glow discharge dehydration treatment device of the present invention. It is a sectional view showing an example. DESCRIPTION OF SYMBOLS 1... Inert gas inlet, 2... Halogenating agent inlet, 3... Reaction tube, 4... Heater, 5...
Object to be treated, 6... Exhaust port, 7... Gas inlet, 8.
... High frequency coil, 9... Part where plasma is generated by glow discharge, 10... Susceptor support rod, 11.
... Susceptor, 12... Crucible, 13... 7-node glass, 14... Joining part. Patent Applicant: International Telegraph and Telephone Co., Ltd. Agent Inuzuka, 1 external person, 1st item 1, 2 drawings, 3 drawings, procedural amendment (voluntary) May 22, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi, 1. Indication of the case Patent Application No. 59-57312 2, Name of the invention: Method for dehydrating optical materials by glow discharge 3, Relationship with the amended case Applicant (121) Kokusai Telegraph and Telephone Co., Ltd. 4, Agent Nishi, Shinjuku-ku, Tokyo Shinjuku 1-23-1

Claims (1)

[Claims] By placing an optical material containing an OH group in an atmosphere of halogen atoms dissociated by glow discharge under high-frequency heating to a desired temperature for chemical reaction, the OH groups and halogen atoms are replaced. 1. A method for dehydrating an optical material using glow discharge, the method comprising dehydrating the optical material using a glow discharge.