JPS605523B2 - Manufacturing method of graphite base material for oxidation-resistant coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a graphite substrate which has been subjected to an oxidation-resistant coating.

Graphite material is considered to be an extremely unique high-temperature material due to its thermal stability and high high-temperature strength. However, in the presence of oxygen when used at high temperatures,
It has a fatal flaw: it oxidizes at relatively low temperatures. For this reason, the surface of graphite material is coated with an oxidation-resistant film such as SIC or NOC. At this time, a difficult situation arises because the graphite crystal constituting the graphite material has an anisotropic structure in which hexagonal mesh planes are stacked in layers.

One of them is that the coefficient of thermal expansion in the direction of the layer plane of graphite crystal is ~0×10-6/℃, whereas in the direction perpendicular to this, the coefficient of thermal expansion is as high as 28×10-6/℃. It is to have. Another reason is that such anisotropic expansion or contraction creates unavoidable fine pores during cooling from the graphitization process, which absorbs a significant portion of the thermal expansion coefficient and changes the thermal expansion coefficient of the graphite material. It is to lower the Therefore, the average thermal expansion coefficient of graphite crystal is theoretically ~9.4×10-6/
Therefore, the graphite materials that will be produced in the future should have a fairly high coefficient of thermal expansion, but commercially available graphite materials have a much lower coefficient of thermal expansion of about 2 to 3 × 10-6/℃. It only shows. For this reason, for example, 4.5 to 5 x 10-
When a graphite material is coated with SIC, which has a coefficient of thermal expansion of 6/° C., the coating breaks down during heating cycles due to the thermal expansion coefficient mismatch and the thermal expansion coefficient, and it no longer serves as a protective coating.

Therefore, as a graphite base material for applying an oxidation-resistant film,
It is necessary that the material is isomerophilic and that the coefficient of thermal expansion can be adjusted within a considerable range. To achieve this, the optically anisotropic region in which fine pores act to absorb thermal expansion must be surrounded by carbon with a homogeneous structure, and the particle as a whole should not exhibit any thermal expansion absorption effect. , it appears to be an essential requirement to use aggregate with a crystalline structure. Furthermore, since such a crystalline aggregate is isotropic in structure, it is desirable for obtaining an isotropic graphite material. Examples of materials that meet these conditions include crystalline petroleum coke, crystalline pitch coke, phenanthrene coke, naphthalene coke, coumarin coke, and even polystyrene coke, each of which has a fine mosaic structural unit of less than ten French. Conceivable.

For example, phenanthrene coke consists of several small mosaic structural units, and if a compact is made from this as a skeleton, an isotropic graphite material with a coefficient of thermal expansion of 7.2 x 10-6/°C can be obtained. be able to. Therefore, by appropriately mixing the above-mentioned coke with commercially available petroleum coke or pitch coke having a low coefficient of thermal expansion, a graphite base material having a coefficient of thermal expansion and cough matching the respective protective coatings should be obtained. And the coefficient of thermal expansion is 1.0 to 8.0×10-6/
It can be freely changed within the range of °C. Example 1 Fenance reso coke and commercially available regular grade petroleum coke were pulverized to -200 mesh, thoroughly mixed in various proportions, coal coal pitch was added as a binder, and the mixture was boiled to produce a powder of 800 kg/ground. Mold with molding pressure.

After the molded product was fired, it was graphitized at 2600°C, and the relationship between its coefficient of thermal expansion and the mixing ratio of coke changed as shown below, indicating that it could be freely adjusted within a considerable range. Fenancere Commercial regular Coke with thermal expansion coefficient of graphite material - grade coke Number (350℃, 450℃
)100 0 6.9xlo-6
〆C80 20 5.860
40 5.250 5
0 4.940 60
4.620 80 3.60
100 3.4 Example 2 5 anchor parts of the above-mentioned finanthrene coke and 5 anchor parts of regular coke were mixed and the surface of graphite material used as aggregate was coated with SIC by chemical vapor deposition method and maintained at 1000 qo. The experiment was repeated in which the sample was oxidized for 30 minutes in an electric furnace.

The weight change of the product of the present invention was 1.2% after 20 trials, whereas the weight change of the product coated on a commercially available graphite material was 10.8% after 5 trials. Example A graphite material was prepared in the same manner as in Example 1 by mixing 9 anchors of trimorphic pitch coke and 1 base of commercially available regular grade pitch coke to form an aggregate.

The elongation rate during heating was compared with that of niobium carbide, and the results were as follows. Niobium carbide Commercially available graphite material Invention product 200℃ 0.12% 0.05 grandchild 0.1
0 shot 400℃ 0.24 0.12
0.23600℃ 0.37 0.20
0.36800℃U. 53 0.2
8 0.50 Compared to commercially available graphite, the product of the present invention has a much higher expansion rate and is well suited to coating materials that exhibit a high expansion rate such as niobium carbide. I understand that.

Example 4 20% of phenanthrene coke and commercially available pitch coke
The mixture is ground to a particle size that passes through 0 mesh, and 5 parts by weight of both are mixed together. Coal tar pitch is added as a graphite material to this, mixed and molded at a molding pressure of 800k9/carp.

After the molded product was fired, it was graphitized at 2600 oo. This graphitized material was coated with SIC by chemical vapor deposition. I did a spalling test on this one. This sports ring test was conducted to determine how many times it would break if 100,000 pieces were taken out of a furnace and brought to room temperature.
For comparison, a case where only commercially available pitch coke was used instead of the above mixture of phenanthrene coke and commercially available pitch coke, and the same treatment was carried out thereafter, and a case where carbon black was used instead of the above phenanthrene coke. A spalling test was conducted in the same manner for each case in which the sample was used and treated in the same manner.

Claims (1)

[Claims] 1. By appropriately mixing coke with an isotropic, microcrystalline structure with mosaic structural units of less than 10 microns, such as microcrystalline pitch coke and phenanthrene, with commercially available low-expansion coke to form aggregate. , a method for obtaining isotropic graphite material that matches the thermal expansion properties of various coating materials.