JPS5851914B2 - Carbon material manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing carbon materials.

Carbon materials have many open pores (hereinafter referred to as pores) derived from their manufacturing method, and measures have been taken to improve oxidation resistance by filling the pores with various materials.

For example, a method of impregnating with furfuryl alcohol and curing to fill the pores, a method of impregnating with a phosphate, a method of impregnating with a metal salt, a method of impregnating with alumina sol, etc. are known.

Although oxidation resistance can be imparted by these methods, it may be insufficient depending on the application.

On the other hand, there are various sizes of open pores present in carbon materials, ranging from a few micrometers to several hundreds of micrometers.

The method of vacuum impregnation with an aqueous aluminum salt solution is effective for relatively small pores (hereinafter referred to as small pores);
Alumina tends to remain in small pores due to impregnation treatment (hereinafter referred to as a term that includes impregnation and heat treatment steps), but in the case of relatively large pores (hereinafter referred to as large pores), the impregnating liquid tends to leak out due to heat treatment, and the pore size The amount of alumina produced is small compared to the oxidation resistance.

That is, because the amount of impregnating liquid is large, the thermal expansion of the impregnating liquid during heat treatment and the decrease in vapor pressure and viscosity break the balance with the surface tension acting on the inner wall surface of the pores, and it is thought that the blow-out phenomenon occurs.

One way to suppress the bubbling phenomenon is to increase the viscosity of the impregnating liquid by adding methylcellulose, for example, but if the viscosity is too thick, the impregnating liquid cannot penetrate into the small pores.

The present invention solves these problems and provides a carbon product in which both large and small pores are filled with alumina and has excellent oxidation resistance.

The present invention is characterized in that a carbon material is impregnated with an aluminum salt solution and a dispersion of fine alumina powder (including alumina sol) and heat-treated to cover open pores with alumina.
The present invention relates to a method for producing a carbon material with improved oxidation resistance.

The present invention is to improve oxidation resistance by impregnating small pores with an aluminum salt solution and large pores with a dispersion of fine alumina powder or alumina sol, filling both large and small pores with alumina.

There are two methods for filling alumina: one is to impregnate fine alumina powder or alumina sol dispersed in an aluminum salt solution, and the other is to first impregnate with an aluminum salt solution and heat treat it, then impregnate with a dispersion of fine alumina powder and heat treat it. There is a way to do this.

As a result of cutting a carbon material impregnated with only an aluminum salt solution and examining its structure, it was found that alumina was sufficiently found in pores smaller than 10 μm to 50 μm, but larger than this. It has been confirmed that almost no alumina is found in the pores, so the particle size of the alumina fine powder or alumina sol used is 1.
It is desirable that the thickness is 0 μm or less.

The concentration of the aluminum salt solution and the amount of alumina fine powder or alumina sol to be added are not limited as long as the combination is such that after heat treatment, there is little blowing out, a high impregnation rate, and both small and large pores are filled with alumina.

It is within the scope of the present invention to perform the impregnation treatment multiple times, with the first and second impregnation treatments performed with an aluminum salt solution, and the fourth time with an alumina fine powder dispersion.

The method for impregnating the fine alumina powder dispersion is vacuum impregnation or immersion.

Furthermore, there is no limit to the temperature of the impregnating liquid.

The degree of vacuum during vacuum impregnation is 10! It is fine as long as it is less than 11 Hg, and it is preferable to inject the impregnating liquid after reducing the pressure, and after injection, pressurize it to 10 k19/cTL or more using nitrogen gas or compressed air.

The heat treatment conditions are preferably those in which the solvent, dispersion medium, and decomposed volatiles after impregnation are sufficiently volatilized and as much alumina as possible remains, preferably in the range of 400 to 1500°C, and there are no particular restrictions. .

This will be explained below using examples.

Comparative Example 1 A 50% by weight aqueous solution of aluminum nitrate was mixed with an apparent specific gravity of 1.
75 artificial graphite material was vacuum impregnated.

The solution impregnation rate was 13% by weight.

This was placed in a box, filled with powder around the periphery to shut off air, heated to 1200°C at a rate of 50°C per hour, and left to cool. (hereinafter abbreviated as graphite material) was obtained.

Comparative Example 2 The impregnation treatment of Example 1 was carried out twice to obtain a graphite material impregnated with 1.1% by weight of alumina.

Example 1 An artificial graphite material of the same quality as that used in the comparative example was vacuum impregnated with a stirred dispersion of 10% by weight alumina sol in the 50% by weight aqueous solution of aluminum nitrate, and subjected to the same heat treatment as in the comparative example. A graphite material with an impregnation rate of 2.1% by weight was obtained.

Example 2 The impregnated product of Comparative Example 1 was impregnated with the alumina sol dispersion of Example 1 to obtain a graphite material with an impregnation rate of 2.5% by weight.

Example 3 Aluminum hydroxy chloride A72 (OH), CJ' 2-3H on artificial graphite material with apparent specific gravity 1675
A graphite material with an impregnation rate of 3.2% by weight was obtained by impregnation treatment with a solution in which 10% by weight of alumina sol was added to a 20% by weight aqueous solution of No. 20.

Next, in order to compare the oxidation resistance of the alumina-impregnated graphite materials obtained in Comparative Examples and Examples, an oxidation consumption rate test was conducted.

That is, the seven types of samples mentioned above were kept in an electric furnace at 500° C. under natural convection for 20 hours and then cooled, and the weight change rates before and after the test were determined, and the values shown in Table 1 were obtained.

It was difficult for alumina to enter the large pores (large pores), but as in the present invention, by impregnating with a dispersion of fine alumina powder, even the large pores are filled with alumina.
Impregnation rate and oxidation resistance were improved.

Therefore, the present invention is effective when applied to graphite products (graphite heating elements, glass sealing jigs, crucibles, metallurgical, electrical, mechanical sliding parts, etc.) that are used at high temperatures that require oxidation resistance.

For example, in the case of a graphite crucible for aluminum vacuum deposition, molten aluminum penetrates into the pores to produce aluminum carbide.
It is eroded, but if alumina is present on the pore surface,
It is known to prevent penetration of molten aluminum, and the crucible obtained by the impregnation treatment according to the present invention has a lifespan of 100% longer than a crucible that has been simply impregnated with an aluminum salt solution.
．． It has become possible to achieve a five-fold improvement.

Claims (1)

[Claims] 1. A carbon material with improved oxidation resistance characterized by impregnating a carbon material with an aluminum salt solution and a dispersion of fine alumina powder (including alumina sol), heat-treating the material, and coating the open pores with alumina. Manufacturing method.