JP3770412B2 - Manufacturing method of high strength quartz glass foam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a quartz glass foam, and more particularly to a method for producing a high strength quartz glass foam having a plurality of dense layers.
[0002]
[Prior art]
Conventionally, quartz glass foam has been widely used as a heat insulating and heat insulating structural material of a furnace, a base of a lightweight reflector, and the like because of its light weight, excellent heat insulation, and low expansion. The quartz glass foam is a method in which a foaming agent such as carbon powder or Si ₃ N ₄ is added to and mixed with quartz powder or glass powder, or a porous quartz glass base material and ammonia are reacted, It has been produced by a method of heating and foaming at a high temperature (Japanese Patent Publication No. 6-24999). However, the quartz glass foam manufactured by the above-described manufacturing method is lightweight and excellent in heat insulation, but is originally a vitreous porous structure, so it can be easily applied with local force or a large bending load. Or the cell collapses and the foam collapses, resulting in insufficient mechanical strength as a structural material. Further, when the quartz glass foam is used as a structural material for a furnace, for example, there is a drawback that it is softened and deformed at a high temperature of 1200 ° C. or more and lacks in shape stability.
[0003]
[Problems to be solved by the invention]
In view of the present situation, the present inventors have conducted intensive research. As a result, soot-like silica fine particles produced by oxidative hydrolysis of silicon halides in an oxyhydrogen flame burner are obtained, for example, physical property values such as the amount and density of hydroxyl groups. The present invention has been completed by finding that a high-strength quartz glass foam can be obtained by depositing on a target so as to form a discontinuous layer and heating and foaming it.
[0004]
That is, an object of the present invention is to provide a method for producing a lightweight, high-strength quartz glass foam.
[0005]
Another object of the present invention is to provide a method for producing a quartz glass foam containing uniform bubbles having a plurality of dense layers.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a porous quartz glass base material having a multilayer structure in which soot-like silica fine particles produced by oxidative hydrolysis of silicon halide are deposited on a target in layers having discontinuous physical property values. And a method for producing a high-strength quartz glass foam, characterized in that a foam precursor is formed by treatment with ammonia gas and then heated and foamed.
[0007]
Examples of the silicon halide include monosilane (SiH ₄ ), trichlorosilane (SiHCl ₃ ), dichlorosilane (SiH ₂ Cl ₂ ), and the like. The present invention supplies the silicon halide together with oxygen and hydrogen to a hydrolysis burner, and hydrolyzes it with an oxyhydrogen flame to produce soot-like silica fine particles, which have a layered physical property value on a target made of alumina or the like. The porous silica base material is manufactured by depositing differently, and then the porous silica base material is treated with ammonia and then heated and foamed. As a deposition method for varying the physical property values of the porous silica base material in layers, a method of changing the moving speed of the burner (hereinafter referred to as a burner moving method), a method of changing the flow rate of the feedstock (hereinafter referred to as a raw material supply change method) ), A method in which the former two are used together, or a method in which soot-like silica fine particles deposited on a target are periodically heated with an oxyhydrogen flame. On the other hand, it is preferable that each deposited layer forming the porous silica base material has a constant physical property value. When the physical property value of the deposited layer varies, the generated gas varies during high-temperature foaming, resulting in a dense portion or cavity that is not controlled in a direction parallel to each deposited layer of the foam, and foaming occurs. The mechanical strength of the whole body is reduced. Therefore, for the formation of each deposited layer, it is preferable that the moving speed is a fluctuation rate of ± 15% or less in the burner moving method, and the supply flow rate is a changing rate of ± 10% or less in the source gas supply method.
[0008]
As a target used in the production of the porous silica base material, those having various shapes, for example, a cylindrical shape, a polygonal shape, a disk shape, a polygonal pyramid, and the like can be used. By selecting a target, a porous silica base material having an arbitrary shape can be formed. If the porous silica base material is foamed, a structural material having a shape corresponding to the purpose of use can be produced.
[0009]
Furthermore, a porous silica preform as shown in FIGS. 1 (a) to 1 (c) can be produced by changing the angle or arrangement of the hydrolysis burner in the production of a porous silica glass preform having a multilayer structure. By combining the displacement of the hydrolysis burner and the shape of the target, it is possible to produce a quartz glass foam having an arbitrary density layer angle, so that the quartz glass foam structural material to be finally used can exhibit the most strength. Therefore, it is extremely advantageous industrially.
[0010]
In the present invention, the porous silica base material obtained by the above production method is then treated with ammonia gas to form a foam precursor. As the ammonia gas processing method, the porous silica base material is treated with an ammonia gas atmosphere. Among them, it is preferable to heat and hold at 600 to 1300 ° C. If the ammonia treatment temperature is lower than 600 ° C., the reaction is too slow and impractical, and if it exceeds 1300 ° C., the ammonia or nitrogen-containing gas bound by the substitution reaction is liberated again, which adversely affects the subsequent foaming process. It is.
[0011]
The foam precursor formed by the ammonia treatment is heat-treated at 1350 to 1800 ° C., preferably 1600 ° C. or more for 30 to 120 minutes, and foam-molded to produce a quartz glass foam mainly composed of closed cells. . The foam molding may be performed under reduced pressure or atmospheric pressure, but atmospheric pressure is preferable because abnormal foaming can be suppressed. The preferred degree of foaming is in the range of an apparent density of 0.25 to 1.7 g / cm ³ . When the apparent density is less than 0.25 g / cm ³ , the compression and bending strength are poor, and when the apparent density exceeds 1.7 g / cm ³ , the layered structure disappears and the heat insulation and lightness are impaired. The foam having an apparent density in the above range has a density of a sparse layer of 0.1 to 1.4 g / cm ³ and a density of a dense layer of 0.5 to 2.2 g / cm ³ .
[0012]
The foam obtained by the above foam molding is a quartz glass foam having a multi-layered structure having a plurality of dense layers and having uniform bubbles in which almost no voids are observed. The degree of foaming is high in the direction perpendicular to the layer and low in the parallel direction. Therefore, since only one direction needs to be considered, a sealing mold is not particularly required for foam molding, and the foam may be set so as to foam in the vertical direction. Light weight when the sparse layer thickness of the quartz glass foam obtained by the foam molding is 1 or more than the dense layer thickness and the density of the dense layer is 0.3 g / cm ³ or more larger than the density of the sparse layer. The mechanical strength such as bending fracture strength, compressive strength, and high temperature bending strength is improved while maintaining stability, and shape stability at high temperature is also improved. Therefore, the quartz glass foam is useful as various structural materials. When the foaming temperature in the foam molding is less than 1350 ° C., not only sufficient foaming is performed, but also active ammonia gas remains in the closed cells without being thermally decomposed, and when it exceeds 1800 ° C., foaming proceeds. This is inconvenient because a foam having open cells is formed.
[0013]
In the manufacturing method of the present invention, since the dimensions are almost the same except in the foaming direction, considering the processing in the subsequent process, the porous silica base material is formed in a slightly larger size, and the desired dimensions are obtained. If processed, a high-purity quartz glass foam with high dimensional accuracy can be produced.
[0014]
Embodiment
Next, the present invention will be described in detail based on specific examples, but the present invention is not limited thereto.
[0016]
Example 1
Soot-like silica fine particles are produced by supplying gaseous silicon tetrachloride 1500 g / h containing oxygen 0.4 Nm ³ / h, hydrogen 1.8 Nm ³ / h and oxygen 0.2 Nm ³ / h to an oxyhydrogen flame burner. Then, it was deposited on an alumina plate target having a thickness of 30 mm and a diameter of 400 mm. The target was rotated at 65 rpm, and the burner reciprocated with an amplitude of 100 mm at a moving speed of 300 mm / min so as to pass through the rotation axis. Further, silicon tetrachloride was repeatedly deposited alternately for 3 minutes and non-supply for 1 minute. As a result, a porous silica base material having a thickness of 150 mm and a diameter of 350 mmφ was produced. The porous silica base material is heated and held at 1200 ° C. for 4.5 hours in an electric furnace while flowing ammonia gas 0.2 Nm ³ / h using nitrogen gas 0.5 Nm ³ / h as a carrier gas, and a foamed body A precursor was formed. When the obtained foam precursor was heated and held at 1750 ° C. for 30 minutes, a quartz glass foam having a layered structure having a thickness of 280 mm, a diameter of 370 mmφ, and an apparent density of 0.4 g / cm ³ was obtained. When the foam was divided into two equal parts, no cavities were generated at any of the cut edges, and parallel layered patterns were observed. Moreover, when the dense layer was cut out and investigated about the foam, the thickness was about 1-2 mm and the density was 1.02 g / cm < ³ > (sample average).
[0017]
The quartz glass foam was subjected to a two-point bending fracture test, a compression test, and a high temperature bending test. The results are shown in Table 1. Of each test, the two-point bending fracture test was performed with a 140 mm span as a sample of a rectangular column having a length of 150 mm, a width of 50 mm, and a vertical height of 50 mm in a direction parallel to the layer. In addition, the compression test was performed using a cube having a length of 20 mm in a direction parallel to the layer, a width of 20 mm, and a height of 20 mm in a direction perpendicular to the layer as a sample. Further, in the high temperature bending test, a rectangular column having a length of 210 mm, a width of 30 mm, and a vertical height of 30 mm was used as a sample in a direction parallel to the layer, and a heating test was performed at a span of 200 mm, 1280 ° C. for 20 hours.
[0018]
<Comparative example>
Comparative Example 1
Soot-like silica fine particles generated by supplying gaseous silicon tetrachloride 1500 g / h using oxygen 0.4 Nm ³ / h, hydrogen 1.8 Nm ³ / h and oxygen 0.2 Nm ³ / h as carrier gases to an oxyhydrogen flame burner And put in a quartz glass container (inner diameter 400 × depth 300), and nitrogen gas 0.5Nm ³ / h as a carrier gas and ammonia gas 0.2Nm ³ / h while flowing in an electric furnace at 850 ° C. The foam precursor was formed by heating for 4.5 hours. Next, the foam precursor was pressed in a carbon mold having an inner diameter of 370 mm at a pressure of 100 g / cm ² , and then heated and held at 1750 ° C. for 30 minutes in the same mold for foaming. The obtained quartz glass foam was a foam having a thickness of 300 mm and a diameter of 370 mm and an apparent density of 0.4 g / cm ³ . When this foam was divided into two equal parts and observed in the same manner as in Example 2, there was no layer structure and many cavities of 10 to 20 mm were observed. Further, the bending fracture test, compression test and high temperature bending test were carried out in the same manner as in Example 2. The results are shown in Table 1.
[0019]
[Table 1]
[0020]
As is clear from Table 1 above, the foam of Example 2 has a bending strength that is about 2 to 3 times that of the foam of Comparative Example 1 and a compressive strength that is about 2 times higher in the direction perpendicular to the layer. . Furthermore, it can be seen that the amount of warping at high temperature is about 1/2 that of the foam of Comparative Example 1 and the high temperature shape stability is excellent.
[0021]
【The invention's effect】
The production method of the present invention has a plurality of dense layers, high bending strength perpendicular to the dense layers, and high tensile strength in the parallel direction, and excellent structural stability at high temperatures. It is particularly useful as a structural material for furnaces.
Brief Description of Drawings]
FIG. 1 shows a schematic diagram for producing porous silica preforms of various shapes by arrangement of hydrolysis burners.

Claims (8)

A soot-like silica fine particle produced by oxidative hydrolysis of silicon halide is repeatedly deposited on a target to produce a multilayer porous silica glass base material having discontinuous layers with different densities , and then treated with ammonia gas. Forming a foam precursor, and heating and foaming the foam precursor. 2. The method for producing a high-strength quartz glass foam according to claim 1, wherein the porous quartz glass base material having a multilayer structure is formed by changing the moving speed of the oxyhydrogen flame burner. 3. The method for producing a high-strength quartz glass foam according to claim 2, wherein each layer of the multilayer structure is formed with a fluctuation rate of the moving speed of the oxyhydrogen flame burner ± 15% or less. 2. The method for producing a high-strength quartz glass foam according to claim 1, wherein the porous quartz glass base material of the multilayer structure is formed by changing the flow rate of the raw material supplied to the oxyhydrogen flame burner. 5. The method for producing a high-strength quartz glass foam according to claim 4, wherein each layer of the multilayer structure is formed with a rate of change of the flow rate of the feedstock ± 10% or less. 2. The method for producing a high-strength quartz glass foam according to claim 1, wherein the porous quartz glass base material of the multilayer structure is formed by the moving speed of the oxyhydrogen flame burner and the flow rate fluctuation of the feedstock. 7. The high-strength quartz glass according to claim 6, wherein each layer of the multilayer structure is formed with a rate of change of flow rate of the feedstock ± 10% or less and a rate of change of moving speed of the oxyhydrogen flame burner ± 15% or less. A method for producing a foam. 2. The method for producing a high-strength quartz glass foam according to claim 1, wherein the soot-like silica fine particles on which a porous quartz glass base material having a multilayer structure is deposited are periodically heated with an oxyhydrogen flame burner. .