JPH0246543B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to a highly heat-resistant and high-strength fibrous molded article and to improvements in a method for producing the same. Conventional technology Conventionally, heat-resistant fibrous molded products have been produced by adding inorganic binders, organic binders, inorganic fillers, etc. alone or in combination to inorganic fibers such as ceramic fibers and rock wool, molding them in a dry or wet method, drying, and firing. things are commonly used. Among these molded bodies, for example, those in which inorganic fibers are bonded with an organic binder do not have sufficient strength at high temperatures, and in the case of inorganic binders, the binder effect is small, so the density of the molded body must be increased considerably. Otherwise, it will be difficult to obtain strength at room temperature and high temperature. In addition, there are those that impair heat resistance, such as alkali silicates, and those that cause a significant decrease in strength at high temperatures, such as alumina cement and Portland cement.Also, even colloidal silica, alumina sol, and aluminum phosphate, etc.
It also has drawbacks such as migration that occurs during drying after molding, making it difficult to obtain uniform strength. Even if an inorganic filler is used, it has the effect of slightly improving strength and heat resistance, but it is difficult to significantly improve it, and it also has the disadvantage of increasing density. Summary of the Invention In order to improve the above-mentioned drawbacks, the present applicant treated the surface of siliceous fibers with acid to dealkalize the surface layer to form a silica layer, and after dispersing the fibers in an aqueous solution of boron oxide. A highly heat-resistant, high-strength fibrous molded product in which a borosilicate glass film is formed on the fiber surface by dehydration molding, followed by drying and firing, and the contact points between the fibers are fused, and the production thereof. A patent application has been filed regarding the method, and this invention is a further development of the method. In the invention of a highly heat-resistant, high-strength fibrous molded article and a method for producing the same according to the above application, heat resistance,
A molded product with excellent strength and thermal shock resistance can be obtained, but
Since we use a method of impregnating and firing boron oxide as a binder, it takes time and effort to process the acidic boron oxide aqueous solution, and migration tends to occur due to drying, making the binder distribution likely to be quite uneven. However, in order to obtain a completely uniform distribution, special drying methods such as high-frequency drying were required, leaving some problems with productivity and product quality stability. Means for Solving the Problems This invention was made in view of the above-mentioned problems, and uses boron nitride (BN), boron carbide (B ₄ C), A finely powdered insoluble boron compound, such as boron oxide coated with a water-insoluble organic film, is used, and only boron oxide (B ₂ O ₃ ) remains without being volatilized through oxidation or decomposition when heated in an oxidizing atmosphere. The above-mentioned problems can be solved by dispersing the treated fibers in water, fixing them on the fiber surfaces, dehydrating them, drying them, and baking them to form a borosilicate glass film on the fiber surfaces and fusing the contact points between the fibers. It is resolved. EXAMPLES Hereinafter, the present invention will be described in detail based on Examples, Experimental Examples, Comparative Examples, etc. The silicic acid fiber that can be used in this invention is SiO ₂ 40%
It must have heat resistance above the temperature (at least 500°C) at which the contact points of fibers are fused together by firing. Examples include ceramic fiber, rock wool, and glass fiber. These fibers are then treated with an acid, for example hydrochloric acid, sulfuric acid, nitric acid, etc. can be used for this treatment. Specifically, the treatment is performed using a 3-50% acid solution, preferably at a temperature of 10-80°C for 1-48 hours. By this acid treatment, the surface layer of the siliceous fiber is dealkalized and a siliceous layer is formed. However, if the thickness of the surface layer to be treated is less than 0.1 μm, the effect will be weak, so the thickness of the surface layer must be 0.1 μm or more. After acid treatment, the fibers with a siliceous surface layer are washed with water, optionally dried or fired, and then
Boron nitride (BN), boron carbide (B ₄ C), which is a source of B ₂ O ₃ to form a borosilicate glassy film, and boron oxide coated with a water-insoluble organic film, undergo oxidative decomposition when heated in an oxidizing atmosphere. Boron oxide (B ₂ O ₃ )
It is dispersed in water together with a finely powdered insoluble boron compound that remains without volatilization. Thereafter, the boron compound is fixed onto the fiber surface using a suitable fixing agent. As the fixing agent, it is possible to use, for example, a band represented by aluminum sulfate, a polymer flocculant, an activator, or a combination thereof. BN, B ₄ C fixed on the fiber surface as above,
B ₂ O ₃ and the like act as a binder.
That is, it is oxidized and decomposed in the subsequent firing process,
Only B ₂ O ₃ remains on the fiber surface and reacts with the silica layer on the surface of the fiber to form borosilicate glass, and the contact points between the fibers are firmly fused. Furthermore, the borosilicate glass surface layer formed by this reaction has the effect of preventing the silicic acid fibers from crystallizing when exposed to temperatures around 1000°C. When dispersing and mixing the siliceous fibers and BN, B ₄ C, B ₂ O _3, etc. in water, it is also possible to add an inorganic filler to improve heat resistance and strength. Furthermore, various additives may be added to improve dispersibility and moldability. Furthermore, it is also possible to add other binders to improve the dry strength after molding. The particle size of BN, B ₄ C, and B ₂ O ₃ used in the above method is preferably 5 μm or less, particularly 1 μm or less, and in that case, the following effects are obtained. is obtained. That is, (1) It is easy to uniformly adhere to the surface of the fibers and the contact points of the fibers. (2) Due to its large specific surface area, when heated in an oxidizing atmosphere, boron oxide (B ₂ O ₃ ) is quickly and reliably converted.
Changes to (3) Due to the above-mentioned item (1), a molded article with high heat resistance can be obtained because the fiber fusion effect is exhibited even with a small amount. Since boron oxide (B ₂ O ₃ ) has a low melting point, adding a large amount will impair the heat resistance of the molded product, but in the case of the present invention, fibers can be fused together with a small amount. (4) Due to the above item (1), since the fiber surface is coated, weakening of the fiber due to fiber crystallization (cristobalite) is suppressed, and a molded article with good spalling resistance can be obtained. (5) Since a uniform internal structure is obtained in which only the contact points between the fibers are fused together, a molded product with good processing conditions (particularly with a smooth surface) can be obtained. The amount added to the fiber is suitably 0.5 to 20% by weight, calculated as the amount of B ₂ O ₃ upon oxidative decomposition, and a particularly preferred range is 1 to 8% by weight. If it is less than 0.5%, it will not be possible to obtain sufficient strength as a binder, and if it is more than 20%, the heat resistance of the molded product will be significantly impaired. Siliceous fibers and BN dispersed in water,
B ₄ C, B ₂ O ₃ , etc. are then fixed, aggregated, dehydrated, and dried. The dried molded body is then preferably calcined at a temperature of 500 to 1500°C for 1 to 20 hours. The molded product finally obtained as described above is
Only the surface layer is made into borosilicate vitrification while the heat-resistant fiber skeleton remains, creating a structure in which the contact points between the fibers are fused together. Next, examples of this invention will be shown. Example 1 100 parts of ceramic fiber was dissolved in a 10% aqueous solution of hydrochloric acid.
Pour into 3000 parts, heat to about 60℃, and stir while stirring.
After processing for a time and washing the fibers thoroughly with water, 105
After drying by heating at ℃ for 10 hours, this fiber and 3 parts of boron nitride powder (in terms of boron oxide) with an average particle size of 0.38 μm were added.
4.2 parts) were added to water and mixed to make an approximately 2% slurry. After that, a small amount of aluminum sulfate and a polymer flocculant are added to fix the boron nitride powder on the fiber surface.
After dehydration molding, heat dry at 120℃ for 5 hours,
A fibrous molded body was obtained by firing at ℃ for 10 hours. Table 1 below shows the raw materials and conditions of Examples 2 and 3, Experimental Examples 1 and 2, and Comparative Examples 1 and 2, and summarizes their physical properties. In addition, in Experimental Examples 1 and 2, the amount of BN was outside the scope of this invention,
Comparative Examples 1 and 2 have binders that are outside the scope of the present invention.

【table】

[Table] Effects of the Invention As described above, according to the present invention, a borosilicate glass layer is formed by heating on the surface of a siliceous fiber that has been treated with an acid to dealkalize the surface layer to form a siliceous layer. In the method of fusing the contact points between fibers, BN, B ₄ C,
Because it uses a finely powdered insoluble boron compound that undergoes oxidative decomposition when heated in an oxidizing atmosphere such as B ₂ O ₃ , leaving only boron oxide without volatilization, it has outstanding strength at room and high temperatures. A fibrous molded article is obtained, and the fibrous molded article has good heat shrinkage at high temperatures, as small as the original fibers remaining as a skeleton, and the fiber surface becomes borosilicate glass. This suppresses crystallization of the fiber skeleton during high-temperature heating, prevents embrittlement of the molded product, and reduces strength loss after heating.
In addition to having good thermal shock resistance, from a manufacturing perspective, boric acid raw materials are attached to the fiber surface by a fixing method, so the amount of attachment can be maintained at a constant level without adjusting the moisture content during dehydration molding. Moreover, since migration does not occur, there is no need for special drying treatment such as high frequency drying, and water treatment is easy, so the effects are extremely large.

Claims (1)

[Scope of Claims] 1. A borosilicate glass coating is formed on the fiber surface by dispersing silicic acid fibers in water together with a finely powdered insoluble boron compound having an average particle size of 1 μm or less, dehydrating, molding, and drying and firing. A highly heat-resistant and high-strength fibrous molded article characterized in that the contact points between the fibers are fused. 2. The boron oxide (B ₂ O ₃ ) source for forming the borosilicate glassy coating is in the form of a fine powder that oxidizes and decomposes when heated in an oxidizing atmosphere, leaving only boron oxide without volatilization. The highly heat-resistant and high-strength fibrous molded article according to claim 1, which is an insoluble boron compound. 3. Claim 2, wherein the finely powdered insoluble boron compound is fine particles of boron nitride (BN), boron carbide (B ₄ C), or boron oxide (B ₂ O ₃ ) coated with a water-insoluble organic thin film. High heat resistance and high strength fibrous molded article. 4 The amount of boron nitride (BN), boron carbide (B ₄ C), and boron oxide (B ₂ O ₃ ) added to the fiber is
The highly heat-resistant and high-strength fibrous molded article according to claim 3, which contains 0.5 to 20% by weight in terms of B ₂ O ₃ . 5 The average particle size of the boron nitride (BN), boron carbide (B ₄ C), and boron oxide (B ₂ O ₃ ) and the amount added to the fibers are each 1 μm or less and 1 to 8% by weight in terms of B ₂ O ₃ A highly heat-resistant and high-strength fibrous molded article according to claim 4. 6. A step of treating the siliceous fiber with acid to dealkalize the surface layer thereof to form a siliceous layer;
These fibers are dispersed in water together with a finely powdered insoluble boron compound with an average particle size of 1 μm or less, which serves as a source of boron oxide (B ₂ O ₃ ) for forming a borosilicate glass coating, and the insoluble boron compound is fixed uniformly on the fiber surface. A borosilicate glass film is formed on the surface of the silicic acid fibers, and the contact points between the fibers are melted by the steps of dehydrating the obtained molded product, drying and baking the dehydrated molded product, and melting the contact points between the fibers. A method for producing a highly heat-resistant and high-strength fibrous molded article, which is characterized in that it is coated with a fibrous material. 7 The boron oxide (B ₂ O ₃ ) source for forming the borosilicate glassy coating is in the form of a fine powder that oxidizes and decomposes when heated in an oxidizing atmosphere, leaving only boron oxide without volatilization. The method for producing a highly heat-resistant and high-strength fibrous molded article according to claim 6, which is an insoluble boron compound. 8. Claim 7, wherein the fine powder insoluble boron compound is fine particles of boron nitride (BN), boron carbide (B ₄ C), or boron oxide (B ₂ O ₃ ) coated with a water-insoluble organic thin film. The method for producing the highly heat resistant and high strength fibrous molded article. 9 The amount of boron nitride (BN), boron carbide (B ₄ C), and boron oxide (B ₂ O ₃ ) added to the fiber is
The method for producing a highly heat-resistant and high-strength fibrous molded article according to claim 8, wherein the content is 0.5 to 20% by weight in terms of B ₂ O ₃ . 10 the boron nitride (BN), boron carbide (B ₄ C),
High heat resistance and high heat resistance according to claim _{9 ,} wherein the average particle size of boron oxide ( _B2O3 ) and the amount added to the fiber are 1 μm or less and 1 to 8% by weight in terms of _B2O3 , respectively. A method for producing a strong fibrous molded article.