JPH0313196B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a high temperature structural member and a method for manufacturing the same. (Prior art) Currently, sintered bodies such as high-purity silicon carbide with a purity of 95% or higher are being used in the field of application as structural members for high temperatures, taking advantage of their properties such as strength at high temperatures and thermal shock resistance. . However, when such structural members are used in a high-temperature oxidizing atmosphere, the crystals in the high-purity silicon carbide sintered body react with oxygen and change to silicon oxide according to the reaction formula: SiC + 3/20 ₂ → SiO ₂ + CO. . At this time, volumetric expansion occurs within the sintered body, causing a decrease in strength of the sintered body. Therefore, it is extremely important to improve oxidation resistance in high-purity silicon carbide sintered bodies. As a means to deal with this, there are two methods: adding sintering aids such as boric acid to fine powder of high-purity silicon carbide in advance to make the structure of the sintered body denser, and open pores in the silicon carbide sintered body. A method of press-fitting silicon into the material to achieve densification is known. Also, JP-A-56-
As shown in Japanese Patent No. 52869, a method of forming a mullite film on the surface of carbon silicon particles is known. (Problems to be Solved by the Invention) By the way, in the above-mentioned first means, a sintering aid such as boric acid is added to fine silicon carbide powder and mixed,
By shaping and firing in a high-temperature reducing atmosphere, a high-strength, dense sintered body with excellent oxidation resistance is obtained. However, the sintered body undergoes large shrinkage during firing, making it large and complicated There is a problem that a sintered body having a specific shape cannot be obtained. In addition, in the second method described above, a high-strength, dense high-temperature structural member with excellent oxidation resistance is obtained by press-fitting silicon into the open pores of the sintered body. Since it is press-fitted in a molten state at high temperatures, there is a problem in that equipment and processing costs are extremely high. Furthermore, in the third means described above,
Although a high-temperature structural member with excellent acid resistance can be obtained, it is still not satisfactory. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a high-temperature structural member that does not have the above-mentioned problems, and a method for producing the same. (Means for Solving the Problems) Accordingly, the first aspect of the present invention is that at least the inner surface of the open pores of a sintered porous body made of high-purity silicon carbide is coated with an oxide coating made of a metal acid compound and silicon oxide. In the high-temperature structural member covered with The amount of adhesion to the sintered porous body is 0.1 to 0.8% by weight in terms of oxide. The sintered body constituting the high temperature structural member is a porous body with an open porosity of 5 to 30%, generally less than 20%,
The oxide film is a glass film, and the glass film forming agent includes a compound of an alkaline earth metal such as magnesium or calcium, or a vanadium compound, an aluminum compound, or a silicon compound.
Preferred compounds as the film forming agent include magnesium sulfate, magnesium chloride, magnesium acetate, magnesium carbonate, magnesium oxide, calcium chloride, calcium acetate, calcium sulfate, calcium hydroxide, calcium carbonate, vanadium sulfate oxide, vanadium chloride, vanadium oxide, Examples include aluminum hydroxide, aluminum phosphate, and colloidal silica. The amount of glass film forming agent deposited is 0.1 to 0.6% by weight based on the sintered body when it contains an alkaline earth metal, and 0.1 to 0.6% by weight based on the sintered body when it contains only a vanadium compound. 0.1 in terms of oxide
Preferably it is ~0.8% by weight. The mixing ratio of the aluminum compound is preferably 80 to 30% by weight in terms of oxide for the alkaline earth metal compound, and 20 to 80% by weight in terms of oxide for the vanadium compound. A second invention of the present invention is a method for manufacturing the above-described high-temperature structural member, in which the inner surface of at least the open pores of the sintered porous body is made of an aluminum compound and an alkaline earth metal compound or a vanadium compound. a step of applying a liquid film forming agent;
The sintered porous body is fired to form the oxide film, and the viscosity of the film forming agent is
It is characterized by a poise of 0.5 to 3.0. As oxide film forming agents such as glass film forming agents, the various compounds mentioned above are used alone or in combination, but when these compounds are soluble in water or other solvents, they are used as a solution, and when they are poorly soluble, they are used as a solution. Use as a suspension. In this case, the compound
It is preferable to use it as an ultrafine powder of 1 μm or less and around 0.5 μm. The method for press-fitting the film-forming agent is to place the sintered body and a solution or suspension of the film-forming agent in the same container and highly reduce the pressure in the container, so that the solution or suspension is released into the sintered body. It is easily pressed into the pores. There is a risk that the press-fitted glass film forming agent may move within the sintered body due to differences in gravity and drying speed, resulting in uneven distribution. As a countermeasure against this, the following measures are taken. The first method is to gel the film-forming agent prior to drying, by leaving it at a predetermined temperature for a predetermined period of time, for example, 10 hours, or by adjusting the pH of the film-forming agent to a predetermined value, for example, PH6 or higher. This results in gelation. The second method is to dry the press-fitted film forming agent while rotating the sintered body, which is highly effective for cylindrical sintered bodies.The sintered body is then fired. A glass film consisting of a silicon compound, an aluminum compound, and an alkaline earth metal compound or a vanadium compound is formed on the surface of the silicon carbide crystal by the injected film forming agent. It is preferable to carry out in an oxidizing atmosphere with a concentration of 2% or more. (Operations and Effects of the Invention) In the high-temperature structural member according to the present invention, a glass film such as an oxide film is formed on the surface of the silicon carbide crystal in the open pores, so that it cannot be used in a high-temperature oxidizing atmosphere. Also, oxygen to the silicon carbide crystals is blocked, and the silicon carbide is not oxidized. Therefore, such high-temperature structural members have high oxidation resistance,
Even when used in a high-temperature oxidizing atmosphere, there is no reduction in strength due to volumetric expansion. Therefore, the amount of oxide film-forming agents such as glass film-forming agents deposited on the high-temperature structural member is 0.1 to 0.6% by weight in terms of oxides if the film-forming agent contains an alkaline earth metal compound. When the film-forming agent contains a vanadium compound, it is preferably 0.1 to 0.8% by weight in terms of oxide. If the amount of the film forming agent deposited is less than 0.1% by weight, the oxide film will not be sufficient to completely cover the surface of the silicon carbide crystal;
If it exceeds 0.8% by weight, the amount of the oxide film is too large and the oxide film forming agent may melt onto the surface of the structural member when used at high temperatures. Further, according to the manufacturing method of the present invention, it is possible to obtain the above-mentioned high-temperature structural member. It is necessary to press fit into the open pores of the sintered body. The viscosity of the film forming agent
If the viscosity is less than 0.5 poise, movement due to gravity will occur before the film-forming agent gels after press-fitting, causing uneven distribution of the film-forming agent, and conversely, the viscosity will be 3.0
If the poise is exceeded, the viscosity of the film forming agent is so high that it does not fully penetrate into the open pores of the sintered body. The sintered body after press-fitting the oxide film forming agent such as the glass film forming agent is preferably fired at a temperature of 1200 to 1500° C. in an oxidizing atmosphere with an oxygen concentration of 2% or more. If the firing temperature is less than 1200°C, there is a risk that silicon oxide will not be sufficiently produced from the sintered body and an oxide film will not be formed sufficiently.
If the temperature exceeds 1500°C, too much silicon oxide is produced from the sintered body, causing melting of the oxide film and shortening the life of the high-temperature structural member. Regarding the oxygen concentration in the atmosphere, if it is less than 2%, silicon oxide will not be generated from the sintered body and it will be difficult to form an oxide film. Example 1 Coarse particles (average particle size 210 μm) and fine particles (average particle size 0.6 μm) of silicon carbide were mixed in a 1:1 ratio and water was added.
15% by weight was added and mixed in a pot mill to prepare a slurry. This slurry was cast into a plaster mold, and the molded body was fired at a temperature of 2100°C in a nitrogen atmosphere to obtain a flat plate-shaped high-purity silicon carbide sintered body. Aqueous solutions of various concentrations containing a 1:1 mixture of magnesium sulfate and alumina sol, which are glass film forming agents, were injected into the open pores of the obtained sintered body using a vacuum treatment method, and after drying, the sintered body was was recalcined in air at a temperature of 1300°C. The characteristics of the obtained sintered body were
Shown in the table. In addition, % in Table 1 is weight %,
The injected amount is expressed as % by weight in terms of oxide, and the oxidation resistance value is expressed as the weight increase rate per hour ( ^10-3
%).

[Table] Example 2 Samples were obtained in the same manner as in Example 1, except that a 5% by weight suspension (in terms of oxide) of various combinations (by weight) of calcium carbonate and fine alumina powder was used as the glass film forming agent. Table 2 shows the properties of the high temperature structural members. Note that the acid resistance test was also the same as in Example 1.

[Table] Example 3 In the open pores of the uninjected sintered body obtained in Example 1,
A 5% by weight aqueous solution of a 1:1 mixture of magnesium sulfate and alumina sol, which are glass film forming agents, was injected by a vacuum treatment method, dried, and then refired under various conditions. Table 3 shows the properties of the obtained high-temperature structural members corresponding to Examples 1 and 2. The amount of film forming agent injected into the sintered body is 0.2% by weight in terms of oxide.
It is.

[Table] Example 4 Vanadium oxide sulfate and alumina sol 1:1
Using a 5% by weight suspension (calculated as oxide) with a viscosity of 1.8 poise (by weight) as a glass film forming agent,
A high-temperature structural member was obtained in the same manner as in Example 1 except that the injection amount was 0.3% by weight. The oxidation resistance (10 ^-3 %) of the obtained high-temperature structural member was 0.14, and there were no problems with the degree of glass melting. Example 5 A tube-shaped high-purity silicon carbide sintered body with an outer diameter of 30 mm, an inner diameter of 20 mm, and a length of 2000 mm was formed in the same manner as in Example 1, and magnesium sulfate and aluminum phosphate, which are glass film forming agents, were added to the tube-shaped sintered body. Aqueous solutions of various viscosities in a 1:1 ratio were injected. Table 4 shows the variation in the amount of press-fitting in this case. Note that the value of the variation is determined by measuring the amount of press-in (wt%) at five locations in the length direction of the sintered body, and is shown as the difference between the maximum value and the minimum value of the amount of press-in.

[Table] Example 6 Three tube-shaped sintered bodies obtained in Example 5 were used, and sintered body A was treated with a 1:1 mixture of magnesium sulfate and aluminum phosphate, which are glass film forming agents. A weight % aqueous solution was injected into the sintered body A, and the sintered body A was placed horizontally on a drying table and dried at a temperature of 80° C. for 12 hours. In the same way, sintered body B is also press-fitted, and the same sintered body B is
At a temperature of 80°C while rotating at a speed of 5 revolutions per minute.
Dry for 12 hours. A 5% by weight aqueous solution of a 1:1 mixture of magnesium sulfate and alumina sol, which are glass film forming agents, was injected into the sintered body C, and the sintered body C was heated to 80°C to gel. Dry at temperature for 12 hours. Table 5 shows the variation in the amount of press-fit in each of these sintered bodies A to C. Note that the value of variation was measured and calculated in the same manner as in Example 5.

【table】

Claims (1)

[Scope of Claims] 1. A high-temperature structural member in which at least the inner surface of open pores of a sintered porous body made of high-purity silicon carbide is covered with an oxide film made of a metal oxide and silicon oxide, The coating is composed of a glass coating consisting of a silicon compound, an aluminum compound, and an alkaline earth metal compound or a vanadium compound, and the amount of the oxide coating attached to the sintered porous body is expressed in terms of oxide. 0.1-0.8% by weight
A high temperature structural member characterized by: 2 The inner surface of at least the open pores of the sintered porous body made of high-purity silicon carbide is covered with an oxide film made of a metal oxide and silicon oxide, and the oxide film is covered with a silicon compound, an aluminum compound, and an alkaline earth compound. A structural member for high temperature use, which is composed of a glass coating made of a three-component compound of a metal compound or a vanadium compound, and the amount of the oxide coating attached to the sintered porous body is 0.1 to 0.8% by weight in terms of oxide. The manufacturing method includes a step of attaching a liquid film forming agent consisting of an aluminum compound and an alkaline earth metal compound or a vanadium compound to the inner surface of at least the open pores of the sintered porous body, and firing the sintered porous body. forming the oxide film,
A method for producing a high temperature structural member, characterized in that the film forming agent has a viscosity of 0.5 to 3.0 poise.