JPH0645505B2 - Manufacturing method of isotropic graphite material with high resistivity - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an isotropic graphite material capable of adjusting its specific resistance to a high level.

[Conventional technology]

The isotropic graphite material has a high degree of isotropic property in addition to the material characteristics peculiar to graphite, and therefore, isotropic materials such as structural materials for nuclear reactors, electrodes for electrical discharge machining, crucibles for pulling semiconductor single crystals and heaters are used. It is used as various members.

Among them, in applying to a precision electric heating member such as a heater for quoting a semiconductor single crystal, it is necessary to match the total specific resistance value with the power supply capacity of equipment. As a means for this, measures such as adjusting the specific resistance of the material, changing the thickness of the heater and the number of slits to be processed and installed have been taken.

The most common method for changing the specific resistance of the isotropic graphite material is to control the processing temperature during the graphitization process, and to impart a high specific resistance suitable as a heater. Can be achieved by lowering the treatment temperature and keeping the graphitization degree of the material low.

[Problems to be Solved by the Invention]

However, since isotropic graphite having a reduced degree of graphitization is easily reactive due to its material structure, when it is used as a heater for pulling a silicon single crystal, for example, it becomes fragile silicon carbide in contact with vaporized silicon. Easily converted to cause functional deterioration. Therefore, in reality, the high-order adjustment of the specific resistance is performed mainly by thinning the heater member and shaping the number of slits, which is the main cause of the deformation and damage of the hitter and the shortening of the service life.

The present invention solves these problems and provides a method for producing an isotropic graphite material capable of adjusting the specific resistance of the material to a high level without lowering the degree of graphitization.

[Means for Solving the Problems]

That is, the method for producing an isotropic graphite material with high specific resistance according to the present invention comprises kneading a raw material filler prepared by mixing 20 to 50% (inner ratio) of graphite powder in a coke powder with a tar pitch binder, In the kneading process, dinitronaphthalene is added and subjected to a kneading treatment, and then the kneaded material is crushed and rubber press-molded, and then the molded body is subjected to firing carbonization and graphitization treatment. .

As the coke powder, a conventional coal-based or petroleum-based calcined coke having an average particle size of 30 μm or less is pulverized by a pulverizer.
It is preferable to use a finely pulverized product having a size of about 10 μm. On the other hand, as the graphite powder, artificial graphite such as a processing residual material of isotropic graphite is finely pulverized by a pulverizer to have an average particle diameter of 30 μm or less, preferably about 10 μm.

The coke powder and the graphite powder are mixed to form a raw material filler, and the blending ratio in this case is preferably set in the range of 20 to 50% (inner ratio) as the weight ratio of the graphite powder to the coke powder. The reason for this is that if the compounding ratio of the graphite powder is less than 20% by weight, the specific resistance does not effectively increase, and if it exceeds 50% by weight, the specific resistance increases, but the material strength tends to decline. Because.

Raw material filler that is a mixture of coke powder and graphite powder,
Then, knead with the tar pitch binder. For the kneading, for example, a kneading device having a strong shearing force such as a double-arm kneader or a pressure kneader is used, and it takes 5 to 8 hours until the volatile content reaches a predetermined content in a temperature range around 250 ° C. Knead enough.

In the above kneading process, the addition of dinitronaphthalene further promotes the increase in resistivity. The amount of dinitronaphthalene added is 5 to 7% by weight based on the raw material filler.
The degree is sufficient, and in this case, it is preferable to knead at a temperature of about 200 ° C.

The kneaded product is cooled and then pulverized into a molding powder. The particle size of the molding powder is preferably finely pulverized so that the average particle diameter is 100 μm or less.

The molding powder is continuously filled in a molding rubber case having a desired shape, and the stored gas (mainly air) is deaerated under reduced pressure and sealed, and then pressure-molded by a hydrostatic press at about 1000 kg / cm ² .

The molded body having an isotropic structure thus obtained is packed in a firing furnace, subjected to firing carbonization treatment up to 1000 ° C., further transferred to a graphitization furnace, and subjected to graphitization treatment at a temperature of 2500 ° C. or higher.

[Work]

The specific resistance of the isotropic graphite material manufactured by the conventional manufacturing method is generally in the range of 10 to 15 × 10 ⁻⁴ Ωcm. On the other hand, in the case of the present invention, by controlling the mixing ratio of the coke powder and the graphite powder, 12 to 20 × 10 ⁻⁴ Ωcm can be obtained.
Can be freely adjusted to a desired specific resistance value in the high range of.

Moreover, since it is not necessary to reduce the degree of graphitization of the material, the function is not deteriorated such that the structure becomes easily reactive.
Therefore, when it is applied to a heater member for pulling a silicon single crystal, it is possible to give a specific resistance that matches the power supply capacity of equipment without performing shape processing such as thinning the material or increasing the number of slits. It will be possible.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

Examples 1 to 3 and Comparative Example 1 Raw material filler in which various proportions of calcined Pitch Coke powder finely pulverized to an average particle diameter of 10 μm and artificial graphite powder finely pulverized to an average particle diameter of 10 μm, a softening point of 90 ° C., and fixed A coal tar pitch binder having a carbon content of 56% was put into a double-arm type kneader in an appropriate weight% with respect to the raw material filler and kneaded at a temperature of 250 ° C. During the kneading, dinitronaphthalene was added in the range of 5.5 to 7.0% by weight with respect to the raw material filler, and the kneading was continued for 6 hours. After cooling the kneaded product, it was pulverized to a particle size of 80 μm in average particle size,
It was packed in a rubber press having a length of 50 mm and a length of 500 mm, and the inside was evacuated to remove air and other gas components contained therein.

After sealing the rubber case, the rubber case was placed in a cold isostatic press and pressed at a pressure of 100 kg / cm ² for 5 minutes to obtain a molded body. Then, the molded body was fired to 1000 ° C. in a non-oxidizing atmosphere, further transferred to a graphitizing furnace and graphitized at a temperature of 2800 ° C.

The component composition of each example is shown in Table 1, and the physical properties of the resulting isotropic graphite material are shown in Table 2. In addition, a correlation graph between the blending ratio of the raw material filler and the specific resistance for the examples is shown in the figure.

From the results of Tables 1 and 2 and the figures, it is recognized that the isotropic graphite materials of Examples 1 to 3 have increased specific resistance as the graphite powder ratio of the raw material filler increases. However, in Comparative Example 1 in which the blending ratio of the graphite powder exceeds 50% by weight, the physical properties were deteriorated, and especially the bending strength was significantly reduced.

Comparative Examples 2 to 5 An isotropic graphite material was manufactured under the same conditions as those of the examples except that the binder content was slightly changed and dinitronaphthalene was not added during kneading.

Table 3 shows the composition of ingredients and the physical properties of each of the obtained isotropic graphite materials. Incidentally, as Comparative Example 5, an example produced without adding graphite powder is also shown. Moreover, the correlation graph of the blending ratio of the raw material filler and the specific resistance in Comparative Examples 2 to 4 is also shown in the figure.

From Tables 3 and 4 and the results shown in the drawings, it is clearly recognized that Comparative Examples 2 to 4 to which no dinitronaphthalene is added have somewhat better strength characteristics than the Examples, but are inferior in the effect of increasing the specific resistance. . In Comparative Example 5, no graphite powder was blended, so the specific resistance was remarkably low.

〔The invention's effect〕

According to the present invention, a mixture of coke powder and graphite powder is used as a raw material filler, and the addition of dinitronaphthalene in the binder kneading process of the isotropic graphite material without the need to reduce the graphitization degree of the material. The resistivity can be adjusted as high as desired. Therefore, particularly when applied to a heater member used for pulling up a silicon semiconductor, weakening of the material due to reaction with silicon is slightly suppressed, and processing such as thinning or increase in the number of slits that causes deterioration of material strength is also performed. Since it is possible to give a proper specific resistance according to the installed capacity without performing the above, a practical effect that the durability life is significantly improved is brought about.

[Brief description of drawings]

The figure is a graph showing the correlation between the blending ratio of the raw material filler and the specific resistance in Examples and Comparative Examples.

Claims (1)

[Claims] 1. A coke powder having a weight ratio of 20 to 50%.
A raw material filler containing (internal) graphite powder was kneaded with a tar pitch binder, and kneaded by adding dinitronaphthalene in the kneading process. Then, the kneaded product was crushed by rubber press molding, and then a molded body was formed. A method for producing an isotropic graphite material having a high specific resistance, which is characterized by firing carbonization and graphitization.