JPH07267660A - Foamed quartz glass structure and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Object] To provide a foamed silica glass structure having a multilayer structure and excellent in purity, lightness and heat insulation performance. [Structure] Constituting at least two portions containing closed cells and having different porosities due to different foaming states, and the adjoining surfaces of the two portions are completely continuous in a glass state, and The part having the lowest porosity is the expanded silica glass structure located on the outer surface of the structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed quartz glass structure and a method for manufacturing the same, and in particular, it has a multilayer structure and is
TECHNICAL FIELD The present invention relates to a foamed quartz glass structure having high purity and excellent heat insulating performance, and a method for producing the same.

[0002]

2. Description of the Related Art At present, a structure having a bulk density of 0.2 to 0.4 g / cm ³ and a porosity of 80 to 90% by volume is known as a foamed quartz glass. These structures are 200
It is a foam having a single structure containing closed cells having a bubble diameter of ˜800 μm, and the porosities of all parts are almost the same. As a manufacturing method thereof, a method is known in which ammonia gas is brought into contact with a silica fine particle deposit at a high temperature to be vitrified, and then foamed at a higher temperature.

[0003]

The conventional foam having a single structure has a brittle surface and is easily peeled off, so that the mechanical strength is inferior and dust is liable to be generated. In addition, although conduction heat transfer can be suppressed, radiant heat transfer may not be suppressed in some cases, and in all cases, there are various problems such as not having excellent heat insulating properties.

In the case of a single structure in which the expanded quartz glass structure is a foam having a high porosity, a large number of large bubbles are present on the surface, chipping and peeling are likely to occur, and the overall mechanical strength is reduced. Further, such a structure as a heat insulator lowers the conductive heat transfer, but at a high temperature of about 1000 ° C., it is easily affected by the radiant heat transfer, and the total heat transfer does not necessarily have a relatively high porosity. Does not decrease compared to low foam. On the other hand, when the foamed quartz glass structure is a foam with a low porosity, it is composed of relatively small bubbles, has high mechanical strength, and surface peeling does not easily occur, but since it has a high specific gravity and it takes time to raise and lower the temperature. However, it is not suitable for heat insulation for heat retention.

In order to solve these problems, the surface of the foam is melted by a flame or the like to provide a dense layer, but the layer has a thickness of 1 mm or less and is called a multilayer structure. It was difficult and its effect was not sufficient.

In addition, in the conventional manufacturing method using ammonia gas, it is difficult to partially contain different amounts of ammonia in the fine particle deposit body, and it is very difficult to manufacture a multilayer structure having different foaming degrees. It was

Therefore, it is an object of the present invention to provide a foamed quartz glass structure having a multi-layered structure, which is excellent in purity, light weight and heat insulation performance, and a method for producing the same.

[0008]

As a result of intensive research to solve the above-mentioned problems, the inventors of the present invention have made foamed quartz glass into a multilayer structure composed of layers having different porosities, and particularly,
It was discovered that by forming a layer with a high porosity inside the center and forming a layer with the lowest porosity on the outer surface, it is possible to obtain a foamed silica glass structure excellent in purity, lightness and heat insulation performance, and completed the present invention. did.

That is, the expanded silica glass structure of the present invention containing closed cells is composed of at least two parts having different porosities due to different foaming states, and the adjacent surfaces of the two parts are adjacent to each other. It is characterized in that it is completely continuous in the glass state and the portion having the lowest porosity is located on the outer surface portion of the structure.

Further, the method for producing a foamed quartz glass structure of the present invention comprises at least two kinds of silica powder containing 0.1 to 2% by weight of silicon nitride and having different silicon nitride contents from each other. In order to have a powder with a low silicon nitride content, and a powder with a high silicon nitride content inside,
It is filled in a container made of a material that does not easily react with silica, and heated at a temperature of 1700 ° C to 1850 ° C in an oxygen-free atmosphere,
Characterized by foaming.

The present invention will be described in detail below. [1] Foamed quartz glass structure The foamed quartz glass structure of the present invention is composed of at least two portions having different foaming states, in other words, different porosities, and the adjacent surfaces of each portion are in a glass state. Is a completely continuous multilayer structure. A “multilayer structure composed of at least two or more portions having different porosities” means that the distribution of porosity is apparently continuous because it is composed of two or more layers having different porosities. By anything from 10 or more layers that appear to have a gradient is meant. "Adjacent surfaces are completely continuous in a glass state" means that the skeleton structure of silica glass that constitutes the porous body is seamless and continuous in the boundary region with different porosity, and is completely integrated as a structure. Means
A structure in which two types of foams having different porosities are mechanically fitted is not applicable.

The multilayer structure of the present invention comprises a layer having the lowest porosity at the outer surface. By forming the outer surface portion with a layer having the lowest porosity, it is possible to improve mechanical strength and prevent surface defects. In addition, by forming the layer with a high porosity inside, it is possible to achieve an increase in the total heat insulating effect due to the reduction of radiative heat transfer, the maintenance of light weight, and the securing of heat retention performance. In order to make these effects significant, the difference between the porosity of the outer surface portion and the porosity of the central portion is 2%.
Or more, preferably 3% or more, more preferably 4 to 1
0%

[2] Manufacturing Method A method for manufacturing a foamed quartz glass structure of the present invention comprises filling silica powders having different silicon nitride contents so as to form a desired layered structure, and heating to obtain a porosity. Realize the difference between.

(1) Starting Raw Material The raw material used in the present invention is two or more kinds of powders having different silicon nitride contents selected from silica powder containing 0.1 to 2% by weight of silicon nitride. is there. As these raw materials, for example, commercially available silicon nitride powder and synthetic silica powder can be mixed in a predetermined amount and used.

(A) Silica powder The silica powder may be of any type as long as it has a high purity. For example, it can be obtained from silicon tetrachloride, silicon alkoxide, or other silicon compounds. Also,
In order to improve the dispersibility with silicon nitride, it is preferable that the silica powder be finely pulverized to an average particle size of about 0.01 to 200 μm, particularly about 0.01 to 100 μm by a process such as ball milling.

(B) Silicon Nitride Powder As the silicon nitride powder, it is preferable to use silicon tetrachloride, silicon, silica or the like as a raw material and a high-purity product obtained by nitriding them. Further, since the particle diameter of the silicon nitride powder affects the bubble diameter at the time of foaming, the silicon nitride powder is 0.1 to 1 by a process such as ball milling.
Those capable of being pulverized to an average particle size of about .mu.m, particularly about 0.1 to 0.5 .mu.m are preferable.

(2) Mixing A predetermined amount of the above silicon nitride powder and silica powder are mixed with a mixer such as a ball mill. Since the dispersibility of silicon nitride in a mixed powder of silica powder and silicon nitride powder affects the bubble size and its distribution during foaming, use a mortar, ball mill, etc. to prevent aggregation of the silicon nitride powder. Need to mix. The mixing may be performed by a dry method or a wet method using a dispersion medium such as water or alcohol, but a pulverization step is separately provided or a mixing step is performed to prevent aggregation, improve dispersibility and make the particle diameter uniform. And crushing are preferably performed at the same time.

(3) Filling the mold with the filling powder is carried out by sequentially putting different types of contents into a container made of a material that does not easily react with silica so that a desired multilayer structure is obtained. Be seen. At this time, the portion corresponding to the outer surface portion of the structure is filled with a raw material having the smallest porosity, that is, a raw material having a low silicon nitride content. The material of the container is preferably at least one selected from carbon, boron nitride, silicon carbide, silicon nitride and the like. Further, it is preferable to use carbon felt or the like in order to improve the slippage between the inner surface of the container and the raw material powder. The density of the mixed powder filled in the container is 0.2-1.0.
About g / cm ³ is preferable, and it is preferable that the filling density be uniform in order to uniformly foam. that time,
Of course, the powder may be formed into a desired shape in advance by a molding machine such as a rubber press.

(4) Foaming The foaming treatment is performed at a temperature of 1700 to 1850 ° C. in an oxygen-free atmosphere. At 1700 ° C. or lower, solid solution of silicon nitride in silica does not occur and foaming becomes insufficient. Also, 18
At temperatures above 50 ° C, the evaporation of silica becomes severe, which is not suitable. Further, up to 1000 ° C. or lower, a vacuum state is preferable for the purpose of removing water contained in the silicon nitride-containing silica powder. The heating atmosphere is preferably an oxygen-free atmosphere in order to prevent oxidation of silicon nitride. As such an oxygen-free atmosphere, an inert gas such as nitrogen, helium, or argon, or a mixed gas thereof can be used, but a vacuum state may be used. The heating time is not particularly limited as long as the quartz glass can be sufficiently foamed,
Generally, it is preferably about 0.5 to 2 hours.

In order to confine the decomposed gas of silicon nitride in glass, silica powder is bound (vitrifies).
It is necessary to decompose silicon nitride above the temperature. Since the decomposition temperature of silicon nitride is changed by pressure, it is preferably added to 10 kgf / cm ² or less pressure against the powder mixture in the mold, preferably in particular to add the pressure of 1~6kgf / cm ^2.
To pressurize in this way, a weight or the like may be placed on the mixed powder, or the pressure of the atmosphere may be adjusted.

(5) Foam The foamed quartz glass structure of the present invention has a content of 0.2 to 0.6 g /
cm ³ , in particular, a bulk density of 0.3 to 0.4 g / cm ³ , 7
0-95%, especially 80-85% porosity, 100-50
It has a bubble diameter of 00 μm, especially 600 to 2000 μm.

[0022]

In the present invention, the foamed quartz glass is composed of layers having different porosities, and the central interior is composed of a layer having a high porosity and the outer surface is composed of a layer having the lowest porosity.
It is possible to obtain a foamed quartz glass structure having high mechanical strength on the surface and excellent in purity, lightness and heat insulation performance.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

In order to obtain a desired multilayer structure by the production method of the present invention, it is necessary to know in advance the porosity of the foam obtained from each powder having a different silicon nitride content. The relationship between the silicon nitride content and the porosity of the foam was obtained by preliminary experiments of the following Reference Examples 1 to 4, and used as the basis for setting the powder filling amount and filling density in the subsequent Examples.

Reference Examples 1 to 4 Commercially available silicon nitride powder and silica powder were dry-mixed in a ball mill to obtain starting materials. The content of silicon nitride powder is 0.3% by weight (Reference Example 1), 0.5% by weight (Reference Example 2), 1.0% by weight (Reference Example 3), and 1.5% by weight (Reference Example 4). ) (Table 1). This starting material was placed in a carbon container having an inner diameter of 85 mm and a height of 200 mm, which was heated in an electric furnace in vacuum at a temperature rising rate of 300 ° C./hr for 10 minutes.
After raising the temperature to 00 ° C. and holding it for 1 hour, nitrogen gas was introduced into the furnace, the temperature was raised to 1800 ° C. at a temperature rising rate of 300 ° C./hr, the temperature was kept for 2 hours, and then allowed to cool. A foaming process was performed.

It was confirmed by X-ray analysis that the glass thus obtained was foaming and was in a glass state. Table 1 shows the bulk density of the foamed quartz glass, the porosity calculated using the bulk density, and the evaluated values of the heat insulating property. For the heat insulation evaluation test, the apparatus shown in FIG. 1 was used to place the prepared glass sample in contact with an electric furnace at 900 ° C., and a thermocouple was placed 9 cm from the surface of the sample in contact with the electric furnace into the sample. It was installed and the temperature of the sample was measured and used as the evaluation temperature for heat insulation. These data were used to make the multilayer structures of Examples 1-3 shown below.

Table 1 Reference Example 1 Reference Example 2 Reference Example 3 Reference Example 4 Silicon nitride (wt%) 0.3 0.5 1.0 1.5 Bulk density (g / cm ³ ) 0.40 0.350 .30 0.28 Porosity (%) 81.8 84.1 86.4 87.3 Adiabatic evaluation temperature (° C.) 340 395 445 480

Example 1 Commercially available silicon nitride powder and silica powder were dry mixed in a ball mill to obtain two starting materials having silicon nitride powder contents of 0.5% by weight and 1.5% by weight, respectively. These starting materials were filled in a carbon container having an inner diameter of 250 mm and a height of 300 mm in the arrangement shown in FIG. Place the carbon container containing the powder in an electric furnace and vacuum it to 300
After raising the temperature to 1000 ° C. at a temperature rising rate of ° C./hr and holding for 1 hour, introducing nitrogen gas into the furnace and raising the temperature to 1800 ° C. at a temperature rising rate of 300 ° C./hr and holding for 2 hours Then, the foaming treatment was performed by the procedure of allowing to cool. The bulk density of the obtained glass is shown in Table 2, and the shape is shown in FIG. When the heat insulating property was evaluated in the same manner as the reference example, the temperature was 362 ° C., and the heat insulating property was better than that of the conventional glass having the same bulk density.

Example 2 The content of silicon nitride powder was 0.3% by weight, respectively.
Silica powder and silicon nitride powder were dry mixed by a ball mill so as to be 5% by weight, 1.0% by weight, and 1.5% by weight to prepare four types of starting materials. These starting materials were filled in a carbon container having an inner diameter of 250 mm and a height of 300 mm in the arrangement shown in FIG. The carbon container containing the powder was placed in an electric furnace, heated to 1000 ° C. at a heating rate of 300 ° C./hr in vacuum, held for 1 hour, and then nitrogen gas was introduced into the furnace to 300 ° C./hr. At a heating rate of 1800 ℃
After the temperature was raised to 2, the temperature was maintained for 2 hours, and then allowed to cool, the foaming treatment was performed. The bulk density of the obtained glass is shown in Table 2, and the shape is shown in FIG. When the heat insulating property was evaluated in the same manner as in Example 1, the temperature was 340 ° C., and the heat insulating property was better than that of the conventional glass having the same bulk density.

Example 3 The content of silicon nitride powder was 0.3% by weight, respectively.
Silica powder and silicon nitride powder were dry-mixed by a ball mill so as to be 5% by weight, 1.0% by weight, and 1.5% by weight to prepare four types of starting materials. These starting materials were filled in a carbon container having an inner diameter of 250 mm and a height of 300 mm in the arrangement shown in FIG. The carbon container containing the powder was put into an electric furnace, heated to 1000 ° C. at a heating rate of 300 ° C./hr in vacuum, and held for 1 hour, and then nitrogen gas was introduced into the furnace to give 300 ° C./hour. 1800 at a heating rate of hr
The foaming treatment was performed by the procedure of raising the temperature to 0 ° C., holding for 2 hours, and then allowing to cool. The bulk density of the obtained glass is shown in Table 2, and the shape is shown in FIG. When the heat insulating property was evaluated in the same manner as in Example 1, the temperature was 373 ° C., and the heat insulating property was better than that of the conventional glass having the same bulk density.

Table 2 Example No. Bulk density (g / cm ³ ) Example 1 0.31 Example 2 0.38 Example 3 0.36

[0032]

As described above in detail, the expanded silica glass structure of the present invention is a multilayer structure composed of at least two portions having different porosities, and the porosity can be freely changed. Therefore, it is possible to have an ideal structure as a heat insulating material in which a layer having a high mechanical strength and a high heat insulating property and having a low porosity is on the outer surface, and a light layer having a high porosity is inside. The expanded silica glass structure of the present invention can be utilized as various heat insulating members used particularly in the field of semiconductor manufacturing.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring an evaluation temperature for heat insulation.

FIG. 2 is a schematic diagram showing a filling shape of a starting material in Example 1.

FIG. 3 is a schematic view showing a filling shape of the foam glass obtained in Example 1.

FIG. 4 is a schematic diagram showing a filling shape of a starting material in Example 2.

FIG. 5 is a schematic view showing a filling shape of the foam glass obtained in Example 2.

FIG. 6 is a schematic diagram showing a filling shape of a starting material in Example 3.

FIG. 7 is a schematic diagram showing a filling shape of the foam glass obtained in Example 3.

[Explanation of symbols]

 1 ... Foamed quartz glass sample 2 ... Electric furnace 3 ... Recorder 4 ... Thermocouple a ... Layer with silicon nitride content of 0.3 wt% b ... Silicon nitride content 0 .5 wt% layer c ... Silicon nitride content 1.0 wt% layer d ... Silicon nitride content 1.5 wt% layer

Front page continuation (72) Inventor Kazuhito Sudo 3-2-25-407 Jonan-cho, Yamagata City, Yamagata Prefecture (72) Minako Goto 2-29 Enouji-cho, Yamagata City, Yamagata Prefecture (72) Yoshikazu Kikuchi Yamagata Prefecture 43-7 Tsuruta, Sagae-shi, Sagae-shi

Claims (3)

[Claims] 1. A foamed quartz glass structure containing closed cells, comprising at least two portions having different porosities due to different foaming states, and the adjoining surfaces of the two portions are in a glass state. A foamed quartz glass structure, which is completely continuous and has the lowest porosity at the outer surface of the structure. 2. The expanded silica glass structure according to claim 1, wherein the difference in porosity between the central portion and the outer surface portion of the structure is at least 2% or more. body. 3. At least 2 containing 0.1 to 2% by weight of silicon nitride and different in silicon nitride content from each other.
At least 1700 kinds of silica powders were filled in a container made of a material that does not easily react with silica so that the powder having a low content of silicon nitride on the outside and the powder having a high content of silicon nitride on the inside were filled with the silica powder. A method for producing a foamed quartz glass structure, which comprises heating at a temperature of ℃ to 1850 ℃ to foam.