JPS5854102B2 - Doped silica glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing optically high-quality doped silica glass with a controlled refractive index by adding oxides of other elements to pure silica glass.

Doped silica glass is a high melting point glass that is mainly composed of silicon dioxide and is obtained by adding small amounts of oxides of other elements.

By selecting an appropriate oxide, glass with an extremely small coefficient of thermal expansion or glass with a controlled refractive index can be obtained.

For example, regarding the former, a glass having a substantially zero coefficient of thermal expansion has been realized by adding several percent of niobium oxide or kuntal oxide, as disclosed in U.S. Pat. No. 3,031,318 by B. V. Janakirama-Rao.

The latter doped silica glass with a controlled refractive index has recently been viewed as extremely promising for application as a transmission medium in optical communication systems.

Conventionally, such doped silica glass has been obtained by mixing silicon dioxide as a main component and powder of an additive metal oxide in a predetermined composition ratio, heating the mixture to a temperature above the melting point, and converting the mixture into molten glass.

However, with this method, since silicon dioxide is the main component, its melting point is extremely high, and it is difficult to reduce the viscosity and turn it into vitrification. Therefore, it is difficult to obtain high-quality glass that has a uniform composition and does not contain bubbles. It is difficult.

Another synthesis method is a method in which silicon or a halide compound of an additive metal is introduced into an oxyhydrogen flame and oxidized and melted (J, F, Heide,
U.S. Patent No. 2,272,342) and a method of oxidizing vitrification of halide compounds using high-frequency plasma (J, A
.

Wincoburn, British Patent No. 37273/71).

All of these methods obtain glass lumps by sequential deposition from gaseous raw materials, but they have drawbacks such as a low yield of glass, a long synthesis time, and difficulty in obtaining large lumps.

The object of the present invention is to obtain a large-sized doped silica glass of high quality and uniform composition by mixing additive metal lumps into silicon dioxide powder and performing direct melting using high frequency waves through the mixture.

The present invention will be explained below using the drawings.

The drawings are cross-sectional views illustrating an example of synthesis of doped silica glass according to the present invention.

1 is powdered silicon dioxide which is the main component of doped silica glass, and 2 is a predetermined amount of metal lump to be added.

These are mixed appropriately and placed in a container 3 which is water-cooled by a cooler 4.

Then, it is heated from the outside by a high frequency coil 5.

Powdered oxides have low electrical conductivity, so a high frequency electric field cannot generate current in the raw material, and self-heating due to high frequencies is therefore impossible.

However, since the mixed metal lump has low resistance, it easily generates heat due to the high frequency electric field and reaches a high temperature.

At this time, the silicon dioxide surrounding the metal lump that is generating heat also becomes high temperature and becomes conductive.

Then, a high-frequency current is gradually generated near the metal lump, which reaches a high temperature and begins to melt.

At this time, the metal lump also reacts with the oxygen gas in the atmosphere or the oxygen introduced, changes into an oxide, and is uniformly mixed with the surrounding silicon dioxide.

In this way, a metal oxide-doped silicon dioxide melt is obtained in a container, kept at a high temperature for a suitable period of time, and then cooled to take out the doped silica glass in the form of a block.

The container containing the molten material is water-cooled from its surroundings, preventing it from reaching high temperatures and preventing impurities from leaching out of the container or reacting with the molten material.

Next, the present invention will be explained in more detail with reference to Examples.

In Example, 20 dice-shaped pieces of metal aluminum each having a side of about 51 nm were mixed into 225 g of silicon oxide powder, and these were placed in a quartz glass crucible surrounded by a water-cooled pipe and placed in a high-frequency heating coil.

The output frequency of the high frequency oscillator was 3.9 MHz.

As the high-frequency power is increased, the lump of metal aluminum initially generates heat and reacts with the surrounding silicon dioxide, gradually increasing the molten area until the entire crucible except for the periphery becomes liquefied.

At this time, metal aluminum reacted with oxygen in the atmosphere and changed into aluminum oxide.

The temperature of the melt was measured by optical pyrometer to be approximately 200,000.

This state was maintained for 5 hours to continue melting. After the aluminum oxide and silicon oxide were uniformly mixed, the mixture was rapidly cooled to obtain a lump of aluminum oxide doped silica glass.

This was optically polished and the refractive index was measured.
The wavelength of the Um D line was 1.465.

Example 2 Titanium metal was mixed with silicon dioxide in the same manner as in Example 1 to obtain titanium oxide doped silica glass.

In other words, a dice-shaped titanium metal 1 with a side of approximately 5 mm.
Eight pieces were mixed with 380 g of silicon dioxide powder and subjected to high frequency induction heating.

As a result, a transparent glass body with a refractive index of 1.473 was obtained.

It is clear that the method can be applied to doped silica glasses with other additives as well.

That is, germanium is used as the starting material for the additive oxide.
By using zinc, lead, vanadine, chromium, iron, cobalt, nickel, etc., doped silica glasses having various properties with metal oxides added thereto can be obtained.

As explained above, the manufacturing method of the present invention has the advantage that transparent, high-quality, uniform doped silica glass can be easily manufactured in bulk by high-frequency induction heating.

The manufacturing method of the present invention is effective for mass production of glass fibers as optical transmission lines.

The embodiments of the present invention are as follows.

(1) The manufacturing method according to the claims, wherein the metal lump to be added is at least one of aluminum, titanium, germanium, zinc, lead, vanadine, chromium, iron, cobalt, and nickel.

(2) The manufacturing method according to the claims, wherein oxygen is included in the manufacturing atmosphere.

(3) A manufacturing method according to the claims, wherein the mixture is melted and vitrified using a container whose surroundings are cooled.

[Brief explanation of the drawing]

The drawings are explanatory cross-sectional views of the method for manufacturing doped silica glass of the present invention. 1... Powdered silicon dioxide, 2... Metal lump, 3... Container, 4... Cooler, 5...
...High frequency coil.

Claims (1)

[Claims] 1. In a method for producing doped silica glass in which a metal oxide is added to silicon dioxide, an additive metal lump is mixed into silicon dioxide powder, heated and melted through the metal lump by high-frequency induction heating, and the metal is oxidized. A method for producing doped silica glass, which comprises cooling a silicon dioxide melt in which additives are uniformly mixed.