JPH0526752B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Fields> The present invention is applicable to metallurgical, mechanical, electrical, chemical,
Or it is effective in application fields such as nuclear reactors.
In particular, the present invention relates to graphite materials that require high strength, high hardness, and oxidation resistance, such as metal refining crucibles, carbon jigs, rolls for silicon steel sheet heat treatment, and methods for producing the same. <Prior art and its problems> Currently, graphite materials are widely used for mechanical and electrical applications due to their unique properties. However, conventional graphite materials cannot be used in an oxidizing atmosphere.
Oxidative consumption begins at around 500°C, so when used at high frequencies, a neutral or reducing atmosphere is required, which greatly limits the range of use. Therefore, in order to improve the oxidation resistance of carbon materials at high temperatures, methods have been used to impregnate carbon materials with phosphate and/or phosphoric acid aqueous solutions, and fine silica sol or alumina sol. This method is effective for carbon materials having a bulk specific gravity of less than 1.85 and a relatively large pore size. In this case, the pores of the carbon material are sufficiently filled with the impregnating agent, so that an oxidation-resistant effect can be obtained.
However, in the case of high-density carbon materials having a bulk specific gravity of 1.85 or more, even if high-pressure impregnation is performed using the above method, the impregnating agent will penetrate only to a depth of 2 to 3 mm from the surface at most. For this reason, in the above-mentioned high-density carbon material, due to mechanical wear etc. that occurs during use, the
When broken by ~3 mm, a region substantially unfilled with oxidizing agent is exposed, causing severe oxidative consumption and significantly shortening the life of the carbon product. This is because fine silica particles coagulate under the phosphoric acid region during impregnation, causing bridging and gathering within the pores of the carbon material. This phenomenon is particularly noticeable in dense carbon materials with a bulk specific gravity of 1.85 or more. The effectiveness of fine silica sol, phosphate and/or phosphoric acid as an oxidation-resistant impregnating agent has already been demonstrated in many documents and patents, such as JP-A 1989-1999-1.
No. 92427. However, conventionally,
Excellent properties as a material (bending strength of 500 kg/cm ² or more,
It has been difficult to fill a high-density, high-strength graphite material with a bulk specific gravity of 1.85 or higher and a Shore hardness of 80 or higher) with the above-mentioned impregnating agent uniformly and to a sufficient depth. For this reason, when used as a heat treatment roll that requires wear resistance, for example, the graphite material has lubricity, is dense and has no pores of several μm that can cause pick-up, and has high shore hardness. Despite these advantages, it has been difficult to use high-density carbon materials due to problems with oxidation resistance. <Object of the Invention> An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a high-density, high-strength graphite material having oxidation resistance and a method for producing the same. <Structure of the Invention> When the present inventors simultaneously impregnate a high-density graphite material with silica sol and phosphate and/or phosphoric acid as an oxidation-resistant impregnation agent, the oxidation-resistant impregnation agent is However, if ultrafine silica sol with a particle size of 4 to 10 nm is impregnated alone, even high-density graphite material with a bulk specific gravity of 1.85 or more can be impregnated in a sufficient amount. The inventors have discovered that a graphite material can be easily impregnated with a phosphate and/or an aqueous phosphoric acid solution, leading to the present invention. The present invention has a bulk specific gravity of 1.85 or more and a bending strength of 500.
Oxidation resistance characterized by impregnating graphite material with Kg/cm ² or more and Shore hardness of 80 or more with fine silica with a primary particle size of 4 to 10 nm and phosphate and/or phosphoric acid. The object of the present invention is to provide a high-density, high-strength graphite material having a high density and high strength. In addition, the present invention has a bulk specific gravity of 1.85 or more and a bending strength of
A graphite material of 500 kg/cm ² or more and a Shore hardness of 80 or more is impregnated with fine silica sol with a primary particle size of 4 to 10 nm, dried, and then impregnated with an aqueous solution of phosphate and/or phosphoric acid and dried. The present invention provides a method for producing a high-density, high-strength graphite material having characteristic oxidation resistance. The present invention will be explained in more detail below. The graphite material used in the present invention may be a high-density graphite material having a bulk specific gravity of 1.85 or more, a bending strength of 500 Kg/cm ² or more, and a Shore hardness of 80 or more, but it is more preferably graphite obtained using mesophase small spheres as a raw material. material is preferred. The reason for this is that the mesophase small spheres are spherical in shape and have high chemical reactivity, which strengthens the bonds between the particles and provides an extremely superior isotropic, high-density, high-strength graphite material. be. Even graphite materials with a bulk specific gravity of less than 1.85, a bending strength of less than 500 Kg/cm ² or a Shore hardness of less than 80 can be treated with oxidation-resistant impregnation agents such as fine silica and phosphates and/or phosphoric acids (hereinafter referred to as "phosphates"). It can be easily impregnated by a one-step impregnation method in which both are simultaneously impregnated. However, if the graphite material exceeds the above-mentioned characteristic range, it is not possible to impregnate the inside with the oxidation-resistant impregnating agent. The fine-grained silica used in the present invention as an oxidation-resistant impregnation agent preferably has a primary particle size of 4 to 10 nm.
The reason for this is that it is difficult to manufacture silica with a particle size of less than 4 nm, and if the particle size exceeds 10 nm, the secondary particle size, which is slightly agglomerated, becomes large, making it difficult to fill the small pores of the high-density graphite material. This is because the impregnating property is poor, which is not preferable. In addition, the primary particle size means the diameter of a unit particle, and the secondary particle size means the particle size in a state in which primary particles are associated. Typical examples of the phosphates used as the oxidation-resistant impregnation agent in the present invention include phosphoric acid, magnesium phosphate, aluminum phosphate, calcium phosphate, and zinc phosphate. The method for manufacturing the oxidation-resistant high-density graphite material of the present invention will be described below. The method of the present invention is a two-stage impregnation method consisting of a first stage in which a high-density, high-strength graphite material is impregnated with ultrafine silica, and a second stage in which a silica-impregnated graphite material is impregnated with phosphates. In the first stage of the method of the present invention, a high-density, high-strength graphite material with a bulk specific gravity of 1.85 or more, a bending strength of 500 Kg/cm ² or more, and a Shore hardness of 80 or more, which has been degassed under reduced pressure, has a primary particle size of 4 to 10 nm. It is preferable to inject a silica sol containing 3 to 30% by weight of fine silica particles. The reason for this is that a silica sol with a concentration of less than 3% by weight cannot sufficiently fill the pores of the graphite material, and a silica sol with a concentration of more than 30% by weight tends to cause fine particles of silica to aggregate.
This is because the particle size of the secondary particles becomes large, resulting in poor impregnating properties, which is not preferable. Impregnation of the graphite material with the silica sol is carried out according to a conventional method. For example, after injecting the silica sol into the graphite material,
It is degassed, then pressurized to uniformly impregnate a sufficient amount of the above-mentioned fine silica sol, and then dried. In the second step of the method of the present invention, the silica-filled graphite material is impregnated with phosphates in a conventional manner and dried to produce a high-density, high-strength graphite material with oxidation resistance. For example, after the silica-filled graphite material is degassed under reduced pressure, an aqueous solution of phosphates is injected into the graphite material, degassed under reduced pressure, impregnated under pressure, and dried. Thereafter, if necessary, excess phosphorus can be volatilized by heat treatment at the operating temperature in an atmosphere containing H ₂ as a main component. The reason why the two-stage impregnation method of the present invention is adopted is that the one-stage impregnation method, in which silica sol and phosphate salts are impregnated at the same time, penetrates only to a depth of 2 to 3 mm from the surface. The next particle size is 4
If ultrafine silica sol of ~10 nm is impregnated alone, the small pores of the graphite material will be sufficiently filled with the fine silica, so the graphite material should be impregnated with the silica uniformly and to a sufficient depth. This is because it can be done. Further, when dried after being impregnated with ultrafine silica, the silica-filled graphite material still has pores large enough to allow liquid to penetrate, so it can be easily impregnated with an aqueous phosphate solution. On the other hand, when the high-density, high-strength graphite material with a bulk specific gravity of 1.85 or more used in the present invention is simultaneously impregnated with silica sol and phosphates, the silica sol is in a metastable region in acidity and is stable for a short period of time. Although the silica sol is dispersed, it is slightly aggregated, so even if it is an ultrafine silica sol with a particle size of 4 to 10 nm, the apparent particle size, that is, the secondary particle size becomes large, making impregnation difficult. It is. The high-density, high-strength graphite material with oxidation resistance obtained by the above method has uniformly excellent oxidation resistance deep down, and has a mechanical strength of over 500 kg/cm ² in bending strength and over 80 in Shore hardness. Because of its excellent properties, it is ideal for a variety of industrial fields, especially for heat treatment rolls for silicon steel sheets, which are used at high temperatures and in oxidizing atmospheres. Moreover, the two-stage impregnation method of the present invention can produce a high-density, high-strength graphite material having oxidation resistance and having oxidation resistance impregnated with an oxidation-resistant agent uniformly and to a sufficient depth, compared to the conventional one-stage impregnation method. <Examples> Next, the present invention will be specifically described with reference to Examples and Comparative Examples. The high-density, high-strength graphite material is manufactured using mesophase small spheres as a raw material, and has a bulk specific gravity of 1.88, a bending strength of 930 Kg/cm ² , a shore hardness of 84, and an average pore diameter.
A 20×20×20 mm cubic test piece was cut out from the graphite material and used as a test piece. Further, as the siligasol, one having a primary particle diameter of 4 nm or more and 6 nm or less, and a 7% concentration solution of silica having a primary particle diameter of more than 10 nm and 20 nm or less were used. Further, as the phosphate aqueous solution, phosphoric acid and a magnesium phosphate aqueous solution were used. After impregnating with phosphates and drying, each sample was held at 1100° C. for 5 hours in an H ₂ atmosphere to volatilize excess phosphorus. This is a necessary treatment to prevent confusion with weight loss due to oxidation in later oxidation tests. As a result, a piece of high-density, high-strength graphite material having oxidation resistance and having pores filled with silica particles, phosphoric acid, and magnesium phosphate was obtained. Conditions for Examples and Comparative Examples are shown below. Example 1 The above unimpregnated cubic specimen was placed in a vacuum container for 2 to 3 times.
After maintaining mmHg for 2 hours, silica sol with a primary particle size of 4 to 6 nm and a concentration of 7% was injected, and degassed for an additional hour. Next, this test piece was heated to 5 kg/cm ² in a pressure vessel.
After holding for 2 hours, it was dried in air at 150°C for 5 hours. The silica-impregnated test piece obtained in this way was again
After degassing at 3 mmHg for 2 hours, a 20% by weight aqueous solution of phosphoric acid and magnesium phosphate adjusted to a molar ratio of 2:1 was injected into the specimen, and after degassing for an additional 1 hour, 5 in a pressure vessel
kg/cm ² for 2 hours, and then the test piece was taken out and dried in air at 300°C for 5 hours. after that,
Excess phosphorus was volatilized by the above method to obtain a piece of graphite material subjected to two-stage impregnation treatment. Comparative Example 1 A 20% aqueous solution of silica gel, phosphoric acid, and magnesium phosphate with the same particle size (4 to 6 nm) as in the example, adjusted to a molar ratio of 3:2:4, was added to the unimpregnated cubic test piece. After simultaneous impregnation under the same conditions as in the example, excess phosphorus was volatilized by the method described above to obtain a piece of graphite material obtained by the conventional one-step impregnation method. Comparative Example 2 The above unimpregnated cubic specimen had a primary particle size of more than 10 nm.
Silica sol of 20 nm or less was adjusted to a concentration of 7%, impregnated and dried under the same conditions as in the example, and then treated in the same manner as in the example to obtain a piece of graphite material obtained by two-stage impregnation treatment using silica with a large particle size. . Comparative Example 3 The unimpregnated cubic test piece described above was used as it was without any processing. The oxidation resistance of each graphite material piece described above was examined using the following method. That is, in both Examples and Comparative Examples, in order to examine the internal oxidation property and the surface oxidation property, each 20 x 20 x 20 mm
An as-is sample (A) and a sample cut in half (10 x 20 x 20 mm) (B) were prepared, and their oxidation resistance against water vapor under an iron catalyst was investigated. That is, 0.05 g of reagent electrolyzed iron powder was applied to one side of sample A, and
Place it on the cut surface and heat it to 1100℃, dew point 50.
It was oxidized for 1 hour under H ₂ atmosphere at ℃, and the amount of weight loss was measured. This is a suitability test for a roll for heat treatment of silicon steel sheets. Table 1 shows the oxidation test results of Examples and Comparative Examples. As shown in Table 1, even when ultrafine silica sol is used, one-stage impregnation is performed by the conventional method (Comparative Example 1), and even when two-stage impregnation is used, the silica particle size is large (Comparative Example 2). ) are both surface parts (A)
The oxidation resistance of the interior (B) is extremely inferior compared to that of the graphite material, but the graphite material subjected to the two-step impregnation treatment using the ultrafine silica sol according to the present invention has the same oxidation resistance on the inside as on the surface. It is recognized that the person has a sexual nature. Furthermore, the mechanical strength after the impregnation treatment was comparable to that before the treatment. That is, as described above, a high-strength, high-density graphite material having excellent oxidation resistance has been obtained according to the present invention, and this material is especially suitable as a roll for heat treating silicon steel sheets.

[Table] <Effects of the Invention> As detailed above, according to the present invention, a high-density, high-strength graphite material impregnated with ultrafine silica and phosphates can be obtained by using an oxidation-resistant impregnation agent (the above-mentioned ultrafine silica and Because the graphite material is impregnated with phosphate and/or phosphoric acid to a sufficient depth evenly, there is almost no weight loss due to oxidation even when used at high temperatures and in an oxidizing atmosphere. , it is possible to prevent the deterioration of graphite materials due to oxidation, which is the biggest weakness of graphite materials. For this reason, high-density, high-strength graphite materials with oxidation resistance are used as materials for metallurgical, electrical, mechanical, and nuclear reactor applications that have poor usage conditions, especially silicon steel sheets used at high temperatures and in oxidizing atmospheres. Ideal as a roll for heat treatment. Furthermore, according to the method of the present invention, ultrafine silica is first applied to the high-density, high-strength graphite material, which was difficult to sufficiently impregnate with an oxidation-resistant agent using the conventional one-stage impregnation method. Alternatively, phosphoric acid can be impregnated uniformly and to a sufficient depth according to a conventional method, so that not only the surface of the graphite material but also the pores of a sufficient depth can be sufficiently filled. When impregnating with the oxidation resistant agent, the conventional method is used.
Since no special equipment is required, the manufacturing cost of high-density, high-strength graphite material with oxidation resistance can be significantly reduced.

Claims (1)

[Claims] 1. A graphite material having a bulk specific gravity of 1.85 or more, a bending strength of 500 Kg/cm ² or more, and a Shore hardness of 80 or more, containing fine silica with a primary particle size of 4 to 10 nm, phosphate and/or phosphoric acid. A high-density, high-strength graphite material with oxidation resistance characterized by being impregnated with. 2 A graphite material with a bulk specific gravity of 1.85 or more, a bending strength of 500 Kg/cm ² or more, and a Shore hardness of 80 or more is impregnated with fine silica sol with a primary particle size of 4 to 10 nm, dried, and then treated with phosphate and/or phosphoric acid. A method for producing a high-density, high-strength graphite material having oxidation resistance, the method comprising impregnating and drying an aqueous solution of.