JPH0692269B2 - Impermeable carbon material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas-impermeable carbon material having excellent thermal conductivity, electrical conductivity and chemical resistance, and high mechanical strength. .

<Background Art> In recent years, a carbon molding material has been attracting attention as a material excellent in dimensional stability, heat resistance, electrical conductivity, thermal conductivity, and chemical resistance in addition to being lightweight, semiconductor jigs, Its use is promoted in various fields such as nuclear reactor materials and electrodes.

Among them, especially "gas impermeable carbon material" shows low electrical resistance and good chemical resistance in addition to gas permeation barrier properties, so its application as "separating plate for phosphoric acid fuel cell" attracts attention. I am collecting. Because the separation plate of the phosphoric acid fuel cell serves as a partition between hydrogen and natural gas supplied as fuel and air for combustion, it is necessary to have a function of preventing the mixture of both. In addition, it was required to be a good conductor of generated electricity and heat, and to have excellent corrosion resistance to phosphoric acid at approximately 200 ° C, but the physical properties of gas impermeable carbon materials are very close to these required characteristics. This is because the.

Therefore, various proposals have hitherto been made to realize a gas-impermeable carbon material having sufficiently satisfactory characteristics as a “separator for a phosphoric acid fuel cell” and the like.

For example, Japanese Patent Publication No. 56-22836 discloses a carbon material obtained by molding and curing a mixture of a curable resin and a cured phenolic resin fiber, and then firing the mixture at a temperature of 800 ° C. or higher. There is. However, in addition to the problem that the carbon material disclosed in the publication is inferior in electrical and thermal conductivity and phosphoric acid resistance as compared with the graphite carbon material because it is an amorphous carbonaceous material, workability (for example, It was not completely satisfactory in terms of groove workability when processed into a ribbed separation plate.

Therefore, as a carbon material having improved electrical conductivity, thermal conductivity, phosphoric acid resistance, and workability, there has been proposed a carbon material obtained by firing a raw material obtained by mixing graphite powder with a thermosetting resin (Japanese Patent Laid-Open No. Sho 61-206).
57-72273, JP-A-59-195514, JP-A-59-232906
Etc.). In addition, these carbon materials are obtained by dispersing graphite powder having good phosphoric acid resistance and good processability in an amorphous carbonaceous (so-called "glassy carbonaceous") matrix, which is a good conductor of electricity and heat. Therefore, it certainly had the characteristics of superior electrical conductivity, thermal conductivity, phosphoric acid resistance, and processability as compared with the case of using the amorphous carbon alone.

However, the above-mentioned carbon material made of a thermosetting resin as a raw material shows that "the thermosetting resin contracts remarkably while the graphite does not contract at all in the carbonization and firing process, and therefore, due to the difference in contraction rate, both It cannot prevent the occurrence of cracks at the interface of the "." Therefore, the reliability of gas impermeability was poor.

<Means for Solving the Problems> From the above viewpoints, the present inventors are of course excellent in gas shielding property, and also have satisfactory electrical conductivity, thermal conductivity,
A study was conducted to provide an impermeable carbon material that has phosphoric acidity and processability and is sufficiently satisfactory even when applied to a separator for a phosphoric acid fuel cell. Is strongly contracted during the carbonization and firing process. ”When a mesophase powder is mixed with a thermosetting resin that shows a significant shrinkage during the carbonization and firing process, the mesophase powder is cured by heat. Since it shrinks at the time of carbonization and firing like a thermosetting resin, the generation of cracks at the interface with the thermosetting resin of the matrix should be suppressed. As a result of further research on a carbon material having a mixture of a resin and a mesophase powder as a starting material, as a result, "a mixture obtained by carbonizing and firing the mixture is a" carbide derived from mesophase powder "and a" thermosetting substance-derived carbonaceous material ". Carbide " No cracks were observed at the interface between the two, and it is a carbon material with excellent impermeability, and it is also fully satisfactory in terms of electrical conductivity, thermal conductivity, phosphoric acid resistance, and workability. " It came to the knowledge of.

The present invention was made based on the above findings, and the impermeable carbon material is composed of a mixed / fired product of 5 to 70% by weight of mesophase powder and 30 to 95% by weight of a thermosetting resin. It has excellent gas shielding property, electrical conductivity, thermal conductivity, phosphoric acid resistance, strength and workability.

The thermosetting resin to which the present invention is applied is a resin that can give a carbide by carbonizing and firing, and examples thereof include phenol resin, furan resin, xylene resin, and epoxy resin. It is preferable to use a phenol resin or furan resin having a high carbon content, and if possible, it is preferable to select a resin having a carbonization yield of 50% by weight or more. If such a resin is a starting material, a sufficiently excellent impermeable carbon material can be obtained.

The mesophase powder may be produced from any pitch such as petroleum-based or coal-based pitch. However, since carbon materials containing few impurities are required from the viewpoint of phosphoric acid corrosion resistance and stability of battery reaction, in the case of coal-based mesophase powder, it is preferable to purify the raw material for mesophase production.

Usually, heavy oil or pitch of petroleum or coal is 350 to 5
When heat-treated at 00 ° C, optically anisotropic spheres called spherulites are formed in the matrix phase of the pitch at the beginning of the heat treatment, and when heat treatment is continued, spherulites repeat coalescence / growth The whole becomes an optically anisotropic substance, a so-called “bulk mesophase”. The spherulites and bulk mesophases do not generally show a softening point, although they differ depending on heat treatment conditions. In other words, it is a carbon precursor that has a coke-like property called infusibility but also has a pitch-like property that contains a few% by weight of volatile matter.

The mesophase powder targeted by the present invention is “a bulk mesophase pulverized”.

For example, "a bulk mesophase having a carbon content of 92% by weight or more, a volatile content up to 900 ° C of 7 to 20% by weight, and a linear shrinkage rate of 1% or more when heated to 500 ° C has an average particle size of 40 µm.
"Mesophase powder pulverized to m or less" is a preferable target.

Here, when the carbon content is less than 92%, the elements other than carbon decompose and gasify during the firing process to increase the weight reduction amount, and the atoms other than carbon inhibit the graphitization property, resulting in thermal conductivity,
The electrical conductivity and phosphoric acid resistance may not be improved.

If the volatile content up to 900 ° C is less than 7% by weight, the wettability of the matrix with the thermosetting resin is poor during the combustion process,
Gaps (cracks) may occur at the interface between the mesophase powder and the matrix, which may reduce the impermeability.
When it exceeds 13% by weight, there is a concern that a large amount of volatile components generated from the inside of the mesophase powder may cause foaming or porosity to reduce impermeability.

The linear shrinkage when heated to 500 ° C. is a value measured by pressure-molding the mesophase powder alone at a pressure of ² t / cm ² or more and collecting a sample from the obtained molded body. . When the linear shrinkage is less than 1%, a gap is generated at the interface between the carbon particles derived from the mesophase powder after carbonization and firing and the matrix carbon derived from the thermosetting resin, and the impermeability tends to decrease. It is not preferable.

Next, the manufacturing conditions of the impermeable carbon material using the mesophase powder and the thermosetting resin having such properties will be described.

The mesophase powder is 5 in the mixture with the thermosetting resin.
It is blended so as to have a ratio in the range of up to 70% by weight.

If the blending ratio is less than 5% by weight, the mesophase powder cannot be blended and hardened, and the thermal conductivity, electrical conductivity, phosphoric acid resistance, and processability deteriorate. On the other hand, if the content exceeds 70% by weight, the surface area of the mesophase powder increases and the thermosetting resin cannot uniformly bind the mesophase powder, resulting in a decrease in strength.

In order to produce an impermeable carbon material, the mixture blended as described above is charged into a mold, and usually 5 to 5 at a temperature of 130 to 200 ° C.
Press molding at a pressure of 150 kg / cm ² . The shaped body is then optionally "post-cured" by heating at 130-200 ° C for 10-30 hours. The post-cured molded body has a temperature rising rate of 0.5 to 50 in a non-oxidizing atmosphere (for example, under the flow of N ₂ gas or Ar gas).
It is carbonized and baked at a temperature of at least 800 ° C at a temperature of 800 ° C / hr, and further graphitized as necessary to obtain an impermeable carbon material.

Hereinafter, the present invention will be described more specifically by way of examples.

<Example> Example 1 Carbon content: 93.3% by weight, volatile matter up to 900 ° C:
First, a mesophase powder with a linear shrinkage of 10.3% by weight and a linear shrinkage up to 500 ° C of 3%, an average particle diameter of 15 μm, and a phenol / novolak resin powder with a carbonization yield of 52% by weight at 1000 ° C.
After mixing at the compounding ratio shown in the table (Table 1 shows only the compounding ratio of mesophase powder, the rest is compounded resin), 1m
Charged in a mold with a flat area of × 1m, temperature: 180 ℃, pressure: 8
Heat and pressure molding at kg / cm ² for 30 minutes to obtain a molded body with a thickness of 1 mm, then heat this molded body to 200 ° C over 20 hours, and then hold at 200 ° C for 20 hours. "Cured".

Next, the post-cured compact was heated in a "container filled with powdered coke" at a rate of 4 ° C / hr to 1000 ° C to carbonize it, and then in an argon atmosphere at a rate of 4 ° C / min. The temperature was raised to 2500 ° C. to obtain a graphitized product having a thickness of 0.8 mm.

The physical properties of the obtained graphitized product were measured.
Shown in the table.

Incidentally, "air permeability" in Table 1, the differential pressure 1kg / cm _² N ²
Measuring the amount of gas passing at room temperature Sought by.

"Phosphoric acid resistance" is 1000% in 100% phosphoric acid solution at 200 ℃.
It is the weight loss rate with respect to the initial weight after immersion for a period of time.

Example 2 Carbon content: 93.3% by weight, volatile matter up to 900 ° C .: 9.8% by weight,
Linear shrinkage up to 500 ℃ is 2%, average particle size 3 is 30μm
50 parts by weight of the mesophase powder of Example 2 was mixed with 25 parts by weight of the phenol / nozole resin solution, and then dried at 80 ° C. for 10 minutes. A graphitized product was produced in the same manner as in Example 1 except that 25 parts by weight of phenol / novolak resin powder was added to the dry powder thus obtained to prepare a starting mixture.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Comparative Example 1 Fixed carbon: 97.0% by weight, ash: 2% by weight, volatile: 1% by weight
Then, a graphitized product was produced by the same method as in Example 1 except that natural graphite having an average particle size of 10 μm was used instead of the mesophase powder.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Comparative Example 2 A graphitized product was produced in the same manner as in Example 1, except that the same raw material as that used in Example 1 was used and only the mixing ratio was changed.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

Comparative Example 3 Phenol-novolak resin: 50 parts by weight and a 10 mm long chop of cured phenolic resin fiber [Kynol KF1010: Gunei Kagaku KK]: 50 parts by weight were mixed, and the same method as in Example 1 was followed. Was molded, post-cured, carbonized and graphitized.

The physical properties of the obtained graphitized product were measured, and the results are also shown in Table 1.

In addition, it was very difficult to process both the obtained 1000 ° C. baked product and 2500 ° C. baked product.

<Summary of Effects> As described above, according to the present invention, the gas shielding property,
It has excellent electrical conductivity, thermal conductivity, acid resistance to phosphoric acid, strength and processability, and can provide an impervious carbon material that is sufficiently satisfactory even when applied to a separator for phosphoric acid fuel cells. It has a great effect.

Claims (1)

[Claims] 1. An impervious carbon material comprising a mixed and fired product of 5 to 70% by weight of mesophase powder and 30 to 95% by weight of a thermosetting resin.