JPH06122533A - Silica glass containing silicon carbide and its production - Google Patents

Abstract

PURPOSE:To obtain the subject glass having high strength, rigidity and heat- resistance by adsorbing vapor of an organochlorosilane to deposited silica soot, baking the soot in hydrogen to form silicon carbide and heating the obtained porous material in a non-oxidizing atmosphere to effect the vitrification of the material. CONSTITUTION:An organochlorosilane [e.g. (CH3)2SiCl3 or (CH3)2SiCl2] or its mixture with an inert gas (e.g. helium) is made to contact with deposited silica soot in gaseous phase at 800-1000 deg.C for >=30min and the excess organochlorosilane adsorbed to the surface is removed by applying an inert gas (e.g. helium). The product is converted into silicon carbide by baking in hydrogen atmosphere at 800-1700 deg.C. The obtained porous material is fused and completely densified in a non-oxidizing atmosphere at >=1700 deg.C to obtain a silica glass containing 0.5-10wt.% of silicon carbide fine particles having an average particle diameter of <=20nm and dispersed in the silica glass. The glass has an OH group content of <=50ppm, a free carbon content of 200ppm and a density of 2.22-2.30g/cm<3>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to silicon carbide-containing silica glass and a method for producing the same.

[0002]

2. Description of the Related Art Carbon-containing glass is expected as a material excellent in high strength, high rigidity and heat resistance, and is currently being actively researched. The carbon-containing glass reported so far is C
Carbon-containing glass obtained by sintering a gel obtained by a sol-gel method using H ₃ Si (OC ₂ H ₅ ) ₃ or the like in an inert gas, or a mixture of silicon carbide powder and silica powder For example, carbon-containing glass obtained by melting powder. However, in the carbon-containing glass produced by the sol-gel method, since it contains a large amount of OH groups and a large amount of free carbon, the heat resistance is not good, and in the carbon-containing glass produced by the melting method, It is difficult to stably produce a carbon-containing glass because of the gas generation accompanying the reaction between silicon carbide and silica at a temperature of 1400 ° C. or higher.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a silica glass having a high density, a high rigidity, and a high heat resistance, which contains a small amount of OH groups, does not contain free carbon, and has a high density. And a manufacturing method for stably manufacturing the same.

[0004]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems.

That is, the present invention is a silica glass in which 0.5 to 10 weight percent of silicon carbide fine particles having an average particle size of 20 nm or less are dispersed, and the silica glass contains 50 OH groups.
It is a silica glass containing high density silicon carbide, characterized in that it is below ppm, free carbon below 200 ppm, and density is 2.22 to 2.30 g / cm ³ . Less than,
The present invention will be described in more detail.

The silicon carbide-containing silica glass of the present invention has a silicon carbide content of 0.5 to 10 weight percent. 0.5
If the silicon carbide content is less than percent, high strength, high rigidity,
Does not become silica glass with excellent heat resistance. Further, if the content of silicon carbide exceeds 10% by weight, the difference in heat shrinkage between silicon carbide and silica becomes prominent and the production becomes difficult. In order to obtain the effect of inclusion and to manufacture stably,
It preferably contains 1 to 5 weight percent of silicon carbide.

Further, the free carbon in the silicon carbide-containing silica glass of the present invention is 200 ppm or less, which is substantially not contained. Therefore, the appearance of the glass body is not green but light green. In addition, since it does not contain free carbon, it is stable against heating in an oxidizing atmosphere and is unlikely to foam even when heated by, for example, an oxyhydrogen flame.

Silicon carbide dispersed in glass can be identified by X-ray diffraction and NMR. The average particle diameter of the silicon carbide fine particles is 20 nm or less, and usually 5 to 10 n.
m. Silicon carbide particles having a large particle size exceeding 20 nm are difficult to stably exist in silica glass at high temperatures.

In the silica glass of the present invention, it is presumed that all carbon is present in the form of SiC or SiOxCy, and a high density silica glass having a density of 2.22 to 2.30 g / cm ³ is obtained.

Furthermore, the OH groups contained in the silica glass containing silicon carbide of the present invention is 50 ppm or less, more preferably 30 ppm or less. It is known that the OH group in glass significantly lowers the heat resistance, but if the OH group is 50 ppm or less, it has sufficient heat resistance,
It is more preferable if it is ppm or less.

The present invention is also a method for stably producing the above silica glass containing silicon carbide. That is, it is possible to use the organochlorosilane gas as a gas in the silica fine powder deposit 700
Adsorb at ℃ or more, then calcinate in hydrogen atmosphere to convert organochlorosilane to silicon carbide, and treat the obtained porous body at a temperature of 1700 ° C or more in a non-oxidizing atmosphere to form a dense glass. And a method for producing silica glass containing silicon carbide. The details will be described below.

Organochlorosilane as a gas is brought into contact with the silica fine powder deposit produced by a known method to be adsorbed on the silica fine powder deposit. As the organochlorosilane, those containing a lower alkyl group are used, and examples thereof include those containing a methyl group or an ethyl group, specifically CH ₃ SiCl ₃ and (CH ₃ ) ₂ SiCl ₂ . There is no particular limitation on the concentration when these are brought into contact with the silica fine powder volume body, and only organochlorosilane may be brought into contact therewith, or an inert gas such as helium may be mixed and brought into contact therewith. The contact / adsorption time depends on the balance with the organochlorosilane concentration and is not particularly limited.

As a result, the OH groups present in the original silica fine powder deposits are replaced with organochlorosilanes,
The group is reduced. The adsorption temperature is 700 ° C. or higher.
It is preferably carried out at 800 to 1000 ° C. from the viewpoint of the adsorption amount and decomposition of organochlorosilane and the reduction amount of OH groups. The contact time is preferably 30 minutes or longer. After absorbing again,
An inert gas such as He may be applied to remove the excess organochlorosilane adsorbed on the surface.

Then, it is fired in a hydrogen atmosphere to reduce the adsorbed organochlorosilane portion of organic groups such as CH ₃ and C ₂ H ₅ to form silicon carbide. Without this hydrogen treatment, the organochlorosilane cannot be converted to silicon carbide, free carbon is likely to be generated, the density will not be high, and the silica glass will not be excellent in high strength, high rigidity and heat resistance. The temperature of the hydrogen treatment is preferably 700 ° C. or higher, but more preferably 800 to 1700 ° C. in order to sufficiently contain silicon carbide. The hydrogen concentration in the hydrogen atmosphere is not particularly limited, and may be an atmosphere composed of only hydrogen, or an atmosphere in which hydrogen having a large diffusion coefficient such as helium and having no reactivity is mixed with hydrogen.

The silica fine powder deposit which has been subjected to the above-mentioned hydrogen treatment at a temperature of 700 ° C. or higher is not completely densified at a temperature of less than 1700 ° C. Therefore, the silicon carbide-containing silica glass of the present invention can be obtained by melting and completely densifying at a temperature of 1700 ° C. or higher in a non-oxidizing atmosphere to prevent the oxidation of silicon carbide.

[0016]

EXAMPLES In order to explain the present invention in more detail, examples will be given below, but the present invention is not limited thereto.

Example 1 The silica fine powder deposit obtained by the flame hydrolysis method was mounted in an electric furnace and heated to 800 ° C. in a He atmosphere. Then add 8 to CH ₃ SiCl ₃ .
What bubbled He gas at a rate of 00 ml / min was introduced into the furnace, and was held for one and a half hours while CH ₃ SiCl ₃ acting as a gas in the furnace. Then, bubbling was stopped, supply of CH ₃ SiCl ₃ was stopped, and only He gas was supplied and held for 1 hour.

Subsequently, H ₂ gas of 550 ml / min,
And 230 ml / min of He gas were supplied, the temperature was raised to 1450 ° C., and this temperature was maintained for 1 hour for vitrification. The obtained glass body was in a porous state and was heated to 1800 ° C. in a nitrogen atmosphere and kept for 1 hour to be completely densified.

The glass thus obtained has a light green color,
X-ray diffraction reveals that it contains silicon carbide,
The content was 1.3 weight percent. The average particle size of silicon carbide obtained from the TEM photograph was 10 nm. No free carbon was found and the density was 2.238 g / cm ³ . Further, according to the IR absorption spectrum, the OH group is 21
It was ppm.

(Examples 2 and 3) CH ₃ SiCl ₃ treatment, H
₂ The same glass making experiment was conducted by changing the treatment conditions as shown in Table 1. The results are shown in Table 1. In each of the examples, the obtained glass was light green, and it was found by X-ray diffraction that silicon carbide was contained, and no free carbon was found. Also, in any of the examples,
OH group is 10 ppm by IR absorption spectrum, TEM
The average particle size of silicon carbide obtained from the photograph was 10 nm.

(Comparative Example 1) The silica fine powder deposit obtained by the flame hydrolysis method was mounted in an electric furnace and heated to 650 ° C in a He atmosphere. Then add 8 to CH ₃ SiCl ₃ .
A bubbling He gas at a rate of 00 ml / min was introduced into the furnace, and the furnace was kept for 1 hour while CH ₃ SiCl ₃ acting as a gas. Then, bubbling was stopped, supply of CH ₃ SiCl ₃ was stopped, and only He gas was supplied and held for 1 hour.

Subsequently, H ₂ gas of 550 ml / min,
And He gas of 230 ml / min are supplied and 1450 ° C
The temperature was raised up to and maintained at this temperature for 1 hour to obtain a dense glass. The glass thus obtained has a black color and is 0.03
It contained weight percent free carbon but no silicon carbide was observed by X-ray diffraction. Density is 2.2
It was 02 g / cm ³ . Further, according to the IR absorption spectrum, the OH group was 30 ppm.

Comparative Example 2 A silica fine powder deposit obtained by the flame hydrolysis method was mounted in an electric furnace and heated to 700 ° C. in a He atmosphere. Then add 8 to CH ₃ SiCl ₃ .
What bubbled He gas at a rate of 00 ml / min was introduced into the furnace, and the furnace was kept for 1 hour while CH ₃ SiCl ₃ acting as a gas. Then, bubbling was stopped, supply of CH ₃ SiCl ₃ was stopped, and only He gas was supplied and maintained for 1 hour.

Subsequently, only He gas was added at 230 ml / m.
In was supplied, the temperature was raised to 1450 ° C., and the temperature was maintained for 1 hour to obtain a dense glass.

The glass thus obtained has a black color,
It contained 0.04 weight percent free carbon but no silicon carbide was observed by X-ray diffraction. The density was 2.205 g / cm ³ . Further, according to the IR absorption spectrum, the OH group was 30 ppm.

[0026]

[Table 1]

[0027]

As described in detail above, according to the method of the present invention, free carbon is not contained, the content of OH groups is small, the density is high, and the strength, rigidity and heat resistance of the present invention are excellent. It is possible to stably produce silicon carbide-containing silica glass.

Claims (2)

[Claims] 1. A silica glass in which 0.5 to 10% by weight of silicon carbide fine particles having an average particle diameter of 20 nm or less are dispersed, the OH groups contained in the silica glass are 50 ppm or less, and the free carbon is 200 ppm or less, and Density is 2.22
2.30 g / cm ³ of high density silicon carbide-containing silica glass. 2. A silica fine powder deposit is adsorbed with organochlorosilane as a gas at a temperature of 700 ° C. or higher, and then fired in a hydrogen atmosphere to convert the organochlorosilane into silicon carbide, and the resulting porous body is subjected to a non-oxidizing atmosphere. Medium 1700 ° C
The method for producing silicon carbide-containing silica glass according to claim 1, wherein the glass is treated at the above temperature to obtain a dense glass.