JP7002170B2 - Graphite powder manufacturing method - Google Patents

Description

The present invention relates to a method for producing graphite powder using a furnace in which the vertical upper end surface is open to the atmosphere and an electrode is provided on the inner wall surface.

The high-purity graphite powder is used as a powder such as a secondary battery negative electrode material and a mechanical sealant, or as a member used for semiconductor production. In particular, products used in a semiconductor manufacturing process having an ash content on the order of several tens to several ppm are expensive because they are manufactured by highly removing impurities by high-temperature and long-term treatment. Conventionally, a method for producing a high-purity graphite powder using a halogen gas or a halide has been known.

Patent Document 1 describes an apparatus for continuously purifying by placing a cylindrical heating container made of graphite in a heating furnace filled with a heat insulating material and energizing and heating while supplying graphite. Patent Document 2 describes a method of polymerizing condensed polycyclic hydrocarbons to obtain a mesophase pitch, and then heat-treating and pulverizing to obtain a crystalline graphite powder having an average particle size of 10 μm. Patent Document 3 describes a method of obtaining a high-purity graphite member by firing a carbon raw material powder together with a binder, impregnating it with an organic substance containing halogen, and heat-treating the impregnated body.

In all of the methods described in Patent Documents 1 to 3, a halide is used, and the metal oxide in the graphite is reduced to the metal halide to lower the boiling point and volatilize. Similar to these, it is also common to reduce the ash content by applying heat in the presence of halogen gas or halide after installing it in the heating device by firing it together with the binder or burying it in carbon. It is done in. However, if it is attempted to produce high-purity graphite powder having an ash content of several tens of ppm or less using halogen gas or a halide, it is necessary to provide gas leakage prevention measures and exhaust gas treatment equipment, resulting in high cost.

On the other hand, a method for producing graphite using an Athison furnace (see Non-Patent Document 1 and Patent Document 4) is known. In the method described in Patent Document 5, graphite is simply produced by filling a container in a furnace with a raw material to be graphitized and passing an electric current through a thin carbon rod. In the method described in Patent Document 6, a mixture of coke and silica stone is filled in a furnace, a carbon material is energized to generate silicon carbide, and silicon atoms are thermally dissociated by heating to produce graphite.

Japanese Unexamined Patent Publication No. 8-198612 Japanese Unexamined Patent Publication No. 10-121054 Japanese Unexamined Patent Publication No. 2006-232565 Japanese Unexamined Patent Publication No. 2015-157737 1945 Patent Application Publication No. 525 Japanese Unexamined Patent Publication No. 9-157022

New Edition Industrial Reactor Handbook, published by Energy Conservation Center, Japan, November 28, 1997, P485-488

As described above, conventionally, when graphite powder is produced by a simple method, high-purity graphite powder having an ash content of several tens of ppm or less cannot be produced. On the other hand, if it is attempted to produce high-purity graphite powder, expensive equipment or the like is required and the production cost increases.

The present invention has been made in view of such circumstances, and is a method for producing graphite powder, which can obtain high-purity graphite powder at low cost by efficiently discharging impurities in the graphite powder raw material with simple equipment. The purpose is to provide.

(1) In order to achieve the above object, the method for producing graphite powder of the present invention is a method for producing graphite powder using a furnace in which the vertical upper end surface is open to the atmosphere and an electrode is provided on the inner wall surface, and is an inorganic silicic acid. It includes a step of arranging a graphite powder raw material which is embedded inside a filler in which quality particles and carbonaceous particles are mixed and connects the electrodes in the furnace, and a step of energizing and heating the graphite powder raw material. The bulk density of the filler is 0.50 × 10 ³ kg / m ³ or more and 1.2 × 10 ³ kg / m ³ or less.

By heating with the above-mentioned bulk density filler, the SiO gas generated from the filler is rapidly diffused inside the filler while maintaining the shape of the graphite powder raw material to reduce the metal oxide and reduce it with high efficiency. Metal can be discharged into the filler. As a result, impurities in the graphite powder raw material can be discharged with high efficiency by simple equipment, and high-purity graphite powder can be obtained at low cost. Further, in addition to directly heating the graphite powder raw material by passing an electric current, the filler is a mixture of inorganic silicic acid particles and carbonaceous particles, and an extra electric current is unlikely to be generated in the surroundings, so that energy efficiency can be improved. ..

(2) Further, in the method for producing graphite powder of the present invention, the graphite powder raw material is representative of the graphite powder raw material on both the inner wall surface and the vertical upper end surface where the electrodes of the furnace are not installed. It is characterized in that it is embedded inside the filler at intervals of 2 times or more and 10 times or less of the graphite. This makes it possible to improve the yield of high-purity graphite powder while maintaining SiO gas in the furnace and efficiently removing metal impurities.

(3) Further, the method for producing graphite powder of the present invention is characterized in that the representative thickness of the graphite powder raw material is in the range of 50 mm or more and 500 mm or less. As a result, metal impurities can be removed to the center of the graphite powder raw material while maintaining sufficient energization for heating.

(4) Further, the method for producing graphite powder of the present invention is characterized in that the ash content of the filler excluding Si is 1000 ppm or less by weight with respect to the filler. As a result, impurities flowing from the filler to the graphite powder raw material can be reduced, and the graphite powder raw material can be highly purified.

(5) Further, in the method for producing graphite powder of the present invention, the weight fraction of the carbonic particles contained in the filler is 30 wt% or more and 60 wt% with respect to the total weight of the carbonic particles and the inorganic silicic acid particles. It is characterized by the following. This makes it possible to generate SiO gas with high efficiency.

According to the present invention, impurities in the graphite powder raw material can be discharged with high efficiency by simple equipment, and high-purity graphite powder can be obtained at low cost.

(A) and (b) are side sectional views and normal sectional views showing a furnace, a filler, and a graphite powder raw material, respectively. It is a table which shows the experimental conditions of each Example and a comparative example, and the measurement result of the ash content after firing for 16 hours. It is a graph which shows the relationship between the firing time and the amount of ash.

As a result of diligent research, the present inventors have filled a filler containing an inorganic siliceous raw material and a carbonaceous raw material into a filler, and the graphite powder raw material is energized and heated, so that no halide is used and the cost is low. Invented a method capable of producing high-purity graphite. Hereinafter, embodiments of the present invention will be described.

[Principle for obtaining high-purity graphite]
Generally, graphite is highly purified by heat treatment. This is because the volatile substance is volatilized and the oxide of the metal contained in graphite is reduced to form a simple substance of metal and evaporated. The reducing atmosphere can be maintained by placing the graphite to be highly purified in a place kept with halogen gas or by burying it in carbon.

The method of heating in halogen gas results in indirect heating via gas, resulting in poor energy efficiency. In addition, it is necessary to use a large amount of highly reactive halogen gas, and it is necessary to take safety measures against the gas. There is a direct heating method in which a voltage is applied to carbon in which an object is buried and heated by Joule heat. However, the current also flows to other carbons, and the current efficiency is inferior. Further, since there is no flow of particles in the furnace, even if the metal becomes a simple substance, it is difficult to be excluded from the carbon raw material and impurities are likely to remain.

On the other hand, if the graphite powder raw material is embedded in a filler composed of an inorganic silicic acid raw material and a carbonaceous raw material and heated by energization, the graphite powder raw material can be directly heated, and the energy efficiency is higher than that in the case of heating in gas. high. Further, since the filler is a mixture of an inorganic siliceous raw material and a carbonaceous raw material, it is difficult for an extra current to flow to the surroundings as compared with the case where carbon is used as the filler.

Further, when the temperature inside the furnace becomes high, the inorganic silicic acid raw material and the carbonaceous raw material react with each other to generate highly active SiO gas. A part of this SiO gas enters between the graphite powder raw materials, but the SiO gas has strong reducing property and can reduce the metal oxide contained in the graphite powder raw material. By heating, the graphite powder raw material is heated to 2500 ° C. or higher, and at this temperature, at least a part of the metal is vaporized. The vaporized metal moves from the graphite powder raw material into the filler by the flow of SiO gas.

At low temperatures, metals become oxides and carbides again. Since the reducing atmosphere is weaker and the temperature is lower in the filler than in the graphite powder raw material, impurities move to the filler side. Similar transfer of impurities occurs even when graphite is purified in carbon. In the above manufacturing method, by generating a reducing SiO gas, the impurity element contained in the graphite powder raw material can be quickly reduced and eliminated to the filler side. As a result, highly purified graphite powder can be obtained from the graphite powder raw material.

[Method for manufacturing graphite powder]
Next, a method for producing graphite powder based on the above principle will be described.

(Composition of furnace)
First, the configuration of the furnace used in the manufacturing method will be described. 1 (a) and 1 (b) are a side sectional view and a normal sectional view showing a furnace 10, a filler 20, and a graphite powder raw material 30, respectively. The method for producing graphite powder of the present invention is carried out using a furnace 10 which is a reaction vessel with electrodes 15a and 15b. The furnace 10 has a vertical upper end surface open to the atmosphere and has electrodes on the inner wall surface.

The shape of the container forming the furnace body 11 is not particularly limited, but it is necessary to have electrodes 15a and 15b for energizing the graphite powder raw material 30. The electrodes 15a and 15b are preferably provided on opposite end surfaces inside the container, and the furnace body 11 preferably has two parallel facing surfaces. It is convenient and preferable to use a rectangular container for the furnace body 11. The furnace body 11 may have a slit as a gap for venting gas to maintain an appropriate concentration when the reaction gas is excessively generated.

The material of the furnace body 11 is not particularly limited, but since the wall surface becomes hot due to heat transfer from the graphite powder raw material when energized, it is desirable to use a material having high fire resistance for the portion in contact with the filler. For example, high alumina refractory bricks, calcium silicate boards and the like are suitable.

As the electrodes 15a and 15b to be held in the furnace body 11, metal-free materials are preferable from the viewpoint of high purity. Since the electrodes 15a and 15b are affected by heat transfer from the graphite powder raw material, a graphite molded body that is resistant to high temperatures is suitable.

(Procedure of the whole method)
The graphite powder raw material 30 is embedded so as to connect the electrodes 15a and 15b in the furnace 10 inside the filler 20 in which the inorganic silicic acid particles and the carbonic acid particles are mixed.

As the inorganic silicic acid raw material, a substance generally represented by the chemical formula SiO ₂ can be used. Examples of the substance represented by SiO ₂ include silica gel, quartz powder, crystalline silica powder, amorphous silica powder, silica gel and the like. Amorphous silica powder and silica gel are particularly suitable because the generation of SiO gas is more likely to occur when amorphous SiO ₂ is used.

As the carbonaceous raw material, both crystalline graphite and amorphous carbon black can be used. Both may be in any form, for example, soil-like, scale-like, or the like. Amorphous carbon black powder with low conductivity is particularly suitable as a carbonaceous raw material because it is desirable to pass a large amount of current through graphite, which is the target of high purification, in terms of energy cost.

After the graphite powder raw material 30 is embedded in the filler 20, the electrodes 15a and 15b are energized. As a result, the filled graphite powder raw material 30 generates heat when energized. Heat is gradually transferred from the graphite powder raw material 30 to the surrounding filler 20 by heat transfer, and SiO gas is gradually generated, and the graphite becomes highly purified.

As the reaction progresses, the carbonaceous raw material around the graphite powder raw material 30 and the inorganic silicic acid raw material gradually melt or react to form a vitreous structure and silicon carbide crystals generated by the reaction. In this way, highly purified graphite powder can be obtained from the graphite powder raw material 30. In addition to directly heating the graphite powder raw material by passing an electric current, the filler is a mixture of inorganic silicic acid particles and carbonaceous particles, and an extra electric current is unlikely to be generated in the surroundings, so that energy efficiency can be improved.

For energization, it is preferable to adjust the current or the like so that the temperature around the graphite powder raw material 30 becomes 1500 ° C. or higher. This produces SiO gas. In order to facilitate the isolation described later, it is particularly preferable to set the temperature to 2200 ° C. or higher at which hard silicon carbide crystals are likely to occur.

After energization for a predetermined time, the obtained graphite powder is taken out from the furnace body 11 after waiting for cooling. The graphite powder is in a state of being wrapped in a glassy structure or a shell of silicon carbide crystals generated during the above reaction, and can be easily separated from the filler and the above shell. For example, the whole shell can be taken out, the shell can be crushed with a hammer or the like, the graphite powder inside can be scraped out, and the mixed shell can be removed by sieving.

In this way, the graphite powder containing about 0.1% of ash can be purified at low cost, and the ash can be reduced to 50 ppm or less. The produced high-purity graphite powder can be used for high-purity graphite crucibles, semiconductor manufacturing members, and the like.

(Details of filler in the furnace body and raw material for graphite powder)
The bulk density of the filler filled in the furnace body is adjusted to 0.50 × 10 ³ kg / m ³ or more and 1.2 × 10 ³ kg / m ³ or less. By setting the bulk density to 1.2 × 10 ³ kg / m ³ or less, the diffusion rate of the SiO gas generated in the filler can be maintained, and the reduction reaction of the impurity metal can be promoted. Further, by setting the bulk density to 0.50 × 10 ³ kg / m ³ or more, a part of the filler reacts to form silicon carbide (true density 3.21 × 10 ³ kg / m ³ ). It is possible to suppress the progress, maintain the volume of the filler, and prevent the collapse of the graphite powder raw material packed in columns. The bulk density of the filler is more preferably 0.55 × 10 ³ kg / m ³ or more and 1.15 × 10 ³ kg / m ³ or less. As a result, the effect of discharging the impurity metal is enhanced, and the handling becomes easier.

The ash content of the filler excluding Si is preferably 1000 ppm or less by weight with respect to the filler. As a result, impurities flowing from the filler to the graphite powder raw material can be reduced, and the graphite powder raw material can be highly purified. Since the ash content is 1000 ppm or less, the transfer of impurities from the filler to the graphite powder raw material is suppressed. As a result, high purity can be effectively achieved and an ash content of 50 ppm or less can be achieved.

The weight fraction of the carbonic particles contained in the filler is preferably 30 wt% or more and 60 wt% or less with respect to the total weight of the carbonic particles and the inorganic silicic acid particles. This makes it possible to generate SiO gas with high efficiency. Since the weight fraction of the carbonaceous particles is 30 wt% or more, the reduction reaction of SiO ₂ as an inorganic siliceous raw material is likely to occur, and the amount of SiO gas generated can be secured. Further, since the weight fraction of the carbonaceous particles is 60 wt% or less, the abundance of SiO ₂ can be secured and a sufficient amount of SiO gas generated can be maintained.

The graphite powder raw material may be electrically connected between the electrodes, but is preferably formed in a columnar shape. Then, as shown in FIG. 1A, the thickness X of the graphite powder raw material 30 is twice or more and 10 times or less with respect to both the inner wall surface and the vertical upper end surface where the electrodes of the furnace 10 are not installed. It is preferable that the filler 20 is embedded inside the filler 20 at intervals. This makes it possible to improve the yield of high-purity graphite powder while maintaining SiO gas in the furnace and efficiently removing metal impurities.

That is, the filler 20 is filled on both the inner wall surface and the vertical upper end surface where the electrodes of the furnace 10 are not installed at intervals of at least twice the typical thickness of the graphite powder raw material 30, so that the filling material 20 is high. It is possible to prevent the SiO gas, which is the key to purification, from diffusing out of the furnace, and the efficiency of removing metal impurities is improved. In addition, heat transfer from the graphite powder is buffered and damage to the furnace wall can be reduced. It is possible to prevent contamination of graphite powder by metal impurities eluted from the furnace wall.

On the other hand, since the filler 20 is filled on both the inner wall surface and the vertical upper end surface where the electrodes of the furnace 10 are not installed at intervals of 10 times or less the typical thickness of the graphite powder raw material 30, the filling material 20 is filled. The amount of material 20 used can be reduced. Further, since the pillar of the graphite powder raw material 30 does not become too thin, sufficient energization can be ensured during the high purification treatment.

Here, the representative thickness X is a representative thickness of the graphite powder raw material 30 formed in a columnar shape, and when the cross section of the column is square, it refers to the length of one side thereof. Further, when the length of each side is a rectangle of A and B, it means X = (A + B) / 2, and when it is a cylinder, it means the diameter thereof. In other cases, it refers to the diameter of a circle having the same outer peripheral length (that is, X = L / π), where L is the outer peripheral length of the cross section. When the representative thickness X of the graphite powder raw material 30 changes in the furnace, X is adopted at the position where the cross-sectional area of the pillar of the graphite powder raw material 30 is the smallest.

Further, the representative thickness X of the graphite powder raw material 30 is preferably in the range of 50 mm or more and 500 mm or less. Since the representative thickness X of the graphite powder raw material 30 is 50 mm or more, sufficient energization can be ensured during the high purification treatment. On the other hand, since it is 500 mm or less, SiO gas can be sufficiently diffused into the graphite powder raw material 30 and metal impurities can be removed to the inside.

[Experimental conditions of Examples and Comparative Examples]
Graphite powder was produced as Examples 1 to 10 and Comparative Examples 1 to 8, and an experiment was conducted to measure the purity.

(Example 1)
Using high-alumina refractory bricks, a rectangular parallelepiped furnace body having internal dimensions of 1050 mm in width, 2530 mm in length, and 1020 mm in height was prepared. Then, holes are made in the bricks at equal positions from the walls on both sides of the short length 480 mm on the two sides of the furnace body in the long direction, and a columnar graphite molded body having a diameter of 100 mm and a length of 320 mm is used as an electrode. Was inserted.

Carbon black (ash content 550 ppm, bulk density 0.74 × 10 ³ kg / m ³ ) as a carbonaceous raw material, and amorphous silica (ash content 670 ppm, bulk density 0.53 × 10 ³ kg / m ³ ) as an inorganic siliceous raw material. Was mixed at a mass ratio of 4: 6 to prepare a filler having an ash content of 622 ppm and a bulk density of 0.66 × 10 ³ kg / m ³ . The bulk density of the raw material is described in "JIS K 1474 Activated Carbon Test Method Filling Density" for carbonaceous raw materials and in "JIS K 1150 Silica Gel Test Method Bulk Density" for inorganic silicic acid raw materials. Measured by method.

In addition, a graphite powder raw material having an ash content of 420 ppm and a bulk density of 0.35 × 10 ³ kg / m ³ was prepared. However, when calculated from the volume and weight at the time of filling, the bulk density of the graphite powder raw material at the time of filling is 0.65 × 10 ³ kg / m ³ . The bulk density of the raw material was measured by the method described in "JIS K 1474 Activated Carbon Test Method Filling Density".

The furnace body was filled with 1610 kg of a filler and 23.7 kg of a graphite powder raw material. At this time, the graphite powder raw material was filled in a rectangular parallelepiped shape having a width of 120 mm, a height of 120 mm, and a length of 2530 mm so as to connect the electrodes at both ends. The filling height was 960 mm. After filling the filler and the graphite powder raw material, the graphite powder raw material was energized through the electrodes at both ends.

After firing at 2400 ° C. for 16 hours by energization heating, the mixture was air-cooled to room temperature, and the graphite powder contained in the vitreous and silicon carbide crystals was taken out from the furnace body. The entire recovered graphite powder was sufficiently mixed before sampling, and the ash content of the graphite powder was measured according to the ash content calculation method described later. Similarly, the ash content of the graphite powder after firing for 8 hours and 24 hours was also measured. The firing for 8 hours and 24 hours was performed only for Example 1, Comparative Examples 1 and 3.

(Example 2)
The filling shape of the graphite powder raw material was a rectangular parallelepiped having a width of 180 mm, a height of 180 mm, and a length of 2530 mm, and the other conditions were the same as in Example 1.

(Example 3)
The filling shape of the graphite powder raw material was a rectangular parallelepiped having a width of 80 mm, a height of 80 mm, and a length of 2530 mm, and the other conditions were the same as in Example 1.

(Example 4)
As the inorganic siliceous material, silica gel having a bulk density of 1.40 × 10 ³ kg / m ³ and an ash content of 1070 ppm was used, and the other conditions were the same as in Example 1.

(Example 5)
As the inorganic siliceous material, an amorphous silica powder having a bulk density of 0.38 × 10 ³ kg / m ³ and an ash content of 540 ppm was used, and the other conditions were the same as in Example 1.

(Example 6)
The shape of the graphite powder raw material of Example 2 and the inorganic silicic acid raw material of Example 4 were adopted, and the steps were carried out in the same manner as in Example 1 under other conditions.

(Example 7)
The mixing ratio of the carbonaceous material and the inorganic silicic acid raw material was 5: 5, and the other conditions were the same as in Example 1.

(Example 8)
The mixing ratio of the carbonaceous material and the inorganic silicic acid raw material was 6: 4, and the other conditions were the same as in Example 1.

(Example 9)
The furnace body was configured with internal dimensions of 2100 mm in length, 2530 mm in width, and 2040 mm in height (filling height 2000 mm), and the electrodes were arranged at a height of 960 mm from the bottom surface. The filling shape of the graphite powder raw material was a rectangular parallelepiped having a width of 240 mm, a height of 240 mm, and a length of 2530 mm. The process was carried out in the same manner as in Example 1 under other conditions.

(Example 10)
The furnace body was configured with the same dimensions as in Example 9, and the filling shape of the graphite powder raw material was a rectangular parallelepiped having a width of 360 mm, a height of 360 mm, and a length of 2530 mm. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 1)
The filling shape of the graphite powder raw material was a rectangular parallelepiped having a width of 240 mm, a height of 240 mm, and a length of 2530 mm. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 2)
The filling shape of the graphite powder raw material was a rectangular parallelepiped having a width of 40 mm, a height of 40 mm, and a length of 2530 mm. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 3)
As the inorganic siliceous raw material, silica sand having a bulk density of 1.66 × 10 ³ kg / m ³ and an ash content of 430 ppm was used. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 4)
As the inorganic siliceous raw material, amorphous silica having a bulk density of 0.16 × 10 ³ kg / m ³ and an ash content of 250 ppm was used. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 5)
Silica gel with a bulk density of 1.40 × 10 ³ kg / m ³ and an ash content of 1070 ppm is used as an inorganic siliceous material, and carbon black with a bulk density of 0.91 × 10 ³ kg / m ³ and an ash content of 380 ppm is used as a carbonaceous raw material. It was used. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 6)
The mixing ratio of the carbonaceous material and the inorganic silicic acid raw material was set to 7: 3. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 7)
The dimensions of the furnace body were the same as in Example 9, and the filling shape of the graphite powder raw material was a rectangular parallelepiped having a width of 480 mm, a height of 480 mm, and a length of 2530 mm. The process was carried out in the same manner as in Example 1 under other conditions.

(Comparative Example 8)
As a carbonaceous raw material, carbon black having a bulk density of 0.68 × 10 ³ kg / m ³ and an ash content of 4200 ppm was used. The process was carried out in the same manner as in Example 1 under other conditions.

(Calculation method of ash content)
The ash content of the carbonaceous raw material in the graphite powder and the filler can be analyzed according to the ash content analysis method described in "JIS M 8511 Industrial Analysis and Test Method of Natural Graphite". The same analysis method is used when an amorphous carbonaceous raw material such as carbon black is used.

For the ash content of the inorganic silicic acid raw material, the method for analyzing silica sand described in "JIS R 2212-2: 2006 Chemical Analysis Method for Refractory Products-Part 2: Silica Stone Refractory" can be used. That is, aluminum oxide, iron oxide (III), titanium oxide (IV), manganese oxide (II), calcium oxide, magnesium oxide, phosphorus oxide (V), and boron oxide (III) are quantified (calculated as mass fraction). And calculate the sum. The same analysis method is used when an amorphous inorganic siliceous raw material such as amorphous silica is used. The ash content of the entire filler can be calculated by measuring the ash content of each raw material constituting the filler and taking a weighted average according to the mixing ratio.

[Experimental results of Examples and Comparative Examples]
(Amount of ash after firing for 16 hours)
FIG. 2 is a table showing the experimental conditions of each Example and Comparative Example and the measurement results of the ash content after firing for 16 hours. In Examples 1 to 10, the ash content was less than 50 ppm in each of the examples. In Comparative Examples 1 to 8, the ash content greatly exceeded 50 ppm.

In Comparative Examples 2 and 4, a rapid increase in the resistance value was observed during energization, and electric power could not be applied. In Comparative Example 2, power could not be applied 1 hour after the start of energization, and in Comparative Example 4 3 hours after the start of energization. This is considered to be due to the disconnection of the graphite powder raw material, and indicates that the columns of the graphite powder raw material are likely to collapse if the columns of the graphite powder raw material to be treated are too thin or the bulk density of the filler is too small.

The reason why the ash content was not reduced in Comparative Examples 1, 3, 5, and 7 is considered to be that the SiO gas did not permeate into the graphite powder raw material to be treated. Further, it is considered that the reason why the ash content was not reduced in Comparative Example 6 is that the carbonaceous raw material was excessive and the amount of SiO gas generated was small (or immediately changed to silicon carbide). In Comparative Example 8, it is considered that the purity of the carbon black was low and the ash content of the graphite powder raw material was relatively high because some of the impurities in the carbon black were diffused into the graphite powder raw material.

No experiment was conducted in which the mixing ratio of the carbonaceous material and the inorganic silicic acid raw material was 3: 7. This is because it was predicted that when this experiment was performed, the reduction of the siliceous raw material did not proceed, the amount of SiO gas generated decreased, and it became difficult to separate the filler and the graphite powder after firing due to the absence of silicon carbide. ..

(Relationship between firing time and ash content)
For Example 1, Comparative Examples 1 and 3, the amount of ash in the graphite powder was confirmed according to the firing time. FIG. 3 is a graph showing the relationship between the firing time and the amount of ash. In each case, the values became almost constant 16 hours after firing. It is considered that this is because the reaction of the filler progressed and the production of SiC became active, so that the SiO was not supplied to the graphite powder raw material. In Comparative Example 1 in which the amount of the graphite powder raw material is large and Comparative Example 3 in which the bulk density of the filler is large, the reaction is completed without sufficiently supplying SiO gas to the graphite powder raw material.

From the above, when the graphite powder raw material is embedded in the filler composed of carbonaceous and inorganic silicic acid, the bulk density of the filler and the size ratio between the graphite powder raw material and the filler are set to an appropriate range and energized. , It was demonstrated that the graphite powder can be sufficiently purified.

10 Reactor 11 Reactor body 15a, 15b Electrode 20 Filler 30 Graphite powder raw material

Claims (1)

A method for producing graphite powder using a furnace in which the vertical upper end surface is open to the atmosphere and an electrode is provided on the inner wall surface.
A process of arranging a graphite powder raw material that is embedded inside a filler in which inorganic silicic acid particles and carbonaceous particles are mixed and connects the electrodes in the furnace, and
Including the step of energizing and heating the graphite powder raw material.
The bulk density of the filler is 0.50 × 10 ³ kg / m ³ or more and 1.2 × 10 ³ kg / m ³ or less .
The graphite powder raw material is filled in the inner wall surface and the vertical upper end surface where the electrodes of the furnace are not installed at intervals of 2 times or more and 10 times or less the typical thickness of the graphite powder raw material. Buried inside the material,
The representative thickness of the graphite powder raw material is in the range of 50 mm or more and 500 mm or less.
The ash content of the filler excluding Si is 1000 ppm or less by weight with respect to the filler.
A method for producing graphite powder , wherein the weight fraction of the carbonic particles contained in the filler is 30 wt% or more and 60 wt% or less with respect to the total weight of the carbonic particles and the inorganic silicic acid particles .

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