JPH0582352B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing expanded graphite in which expanded graphite is obtained by subjecting graphite particles to an expansion chemical treatment and then exothermically expanding a graphite intercalation compound. [Prior art] Expanded graphite is made by exothermic expansion of graphite particles tens to hundreds of times, and is processed into a sheet shape using a rolling mill or a forming press, and is used for parts that require acid resistance and chemical resistance. Used for materials. This expanded graphite is produced by immersing graphite particles in sulfuric acid or nitric acid, then adding an oxidizing agent, thoroughly washing with water, drying, and heating at 800 to 1000℃.
It is obtained by heat treatment for several minutes at a temperature of . Naturally produced graphite powders are mainly used, but various documents include examples of using artificial graphite and graphite. However, few have been put into practical use. For expansion heating, an electric furnace for indirect heating, a gas burner or a heavy oil burner for direct or indirect heating are generally used, but an example using microwave heating as seen in Japanese Patent Application Laid-open No. 74515/1983 There is also. [Problems to be solved by the invention] In general, this type of heating conditions are such that the graphite particles can be heated uniformly, the graphite particles can be rapidly heated to 800 to 1000°C, the temperature can be controlled to a predetermined temperature, and oxidation loss can be prevented. It is required that the structure is such that it does not occur. However, heating methods that use gases and liquids as fuel such as propane, city gas, factory gas, and heavy oil have (a) difficulty in uniformly heating the entire graphite, and (b) difficulty in adjusting the atmosphere, especially the combustion air and flame. (c) Since exhaust gas is generated, exhaust gas treatment equipment is required to treat SO _x , NO _x , dust, etc. (high cost); (d) Incomplete There are disadvantages such as the generation of soot during combustion, which may be mixed with graphite. On the other hand, electric furnaces wrapped with nichrome wire, etc., do not have many of the above disadvantages, but (a) require a large amount of electricity because of indirect heating, (b) the furnace is large, ( c) There are disadvantages such as inability to heat rapidly. In addition, microwave heating allows short-time heating and selective heating, but on the other hand, (a) there is radio wave interference due to leakage radio waves, so sufficient shielding is required; (b) power supply and other equipment. There are disadvantages such as , which is effective. Therefore, an object of the present invention is to provide a method for producing expanded graphite that does not have the above-mentioned drawbacks. [Means for Solving the Problems] In order to achieve the above object, the present invention is characterized in that after graphite particles are treated with an expansion chemical, a graphite intercalation compound is thermally expanded by electromagnetic induction heating. In the present invention, it is desirable that the graphite particles contain some iron content, and examples of substances that meet this requirement include dust and slag obtained during the hot metal pretreatment stage. These dusts and slags contain wood graphite, but the amount is not large. Therefore, physical methods such as flotation and wind selection are used to increase the amount of F.C. F・
A C content of 25 to 80% is sufficient. Further, in order to carry out the present invention effectively, it is desirable that the iron content be 3 to 20%. This iron content is finally removed by acid treatment. The present invention is not limited to the above-mentioned graphite, but natural graphite or artificial graphite may contain some iron. [Operation] Put graphite powder treated with expanding chemicals into a heating container,
When electromagnetic induction heating is performed, eddy currents are generated in the graphite powder and the iron content. Graphite powder and iron have some resistance, so eddy currents generate Joule heat, causing red-hot heating. This red-hot heating causes the graphite intercalation compound to decompose and gasify, and the graphite particles expand under the fluid pressure. Although electromagnetic induction heating uses electrical effects like microwave heating, it does not use high frequencies of several tens to thousands of MHz like microwave heating.
There is no risk of radio wave interference, and equipment costs are low. Furthermore, in electromagnetic induction heating, there is a concern about non-uniform heating due to the skin effect, but this can be resolved by including some iron in the graphite particles.
This iron content is evenly distributed in the graphite particles and induces magnetic lines of force deep inside the heating container, making uniform heating possible. [Example] Hereinafter, an example will be described with reference to the drawings. Figure 1 shows an example in which slag and dust generated during the hot metal pretreatment stage are used as raw materials for expanded graphite.
Recently, when hot metal is tapped from a blast furnace, preliminary treatment of Si, S, and P is performed in the hot metal trough. Since this preliminary treatment generates a large amount of dust and slag, the dust is collected by a wet or dry dust collector, and the slag is discharged from the hot metal trough into a slag trough and collected in one place. These dusts and slags are suitable raw materials for the present invention because they contain wood graphite obtained by changing the raw material coke and also contain iron. However, the graphite contained in the above-mentioned dust and slag is generally only a few percent and contains many other components, so it cannot be used as a raw material for expanded graphite as it is, and it can be purified by physical means such as flotation. The content of Tsushiyu graphite is 25-80
%. Next, the material is subjected to expansion chemical treatment, and conventionally, this type of treatment involves immersion in a strongly oxidizing acid solution. Many acid solutions are based on sulfuric acid or nitric acid, such as fuming sulfuric acid,
Fuming nitric acid, mixed acids of concentrated sulfuric acid and concentrated nitric acid, mixtures of concentrated sulfuric acid and potassium hydrochloride, chromic acid, potassium dichromate, ammonium persulfate, etc., concentrated sulfuric acid and potassium chlorate, phosphoric acid, potassium permanganate, etc. A mixture of is used. In addition, for this process, Japanese Patent Application Laid-Open No. 56-90989
There is also an example in which graphite particles are impregnated with a graphite intercalation compound using an electrolytic method, as in the publication. In the present invention, any of these methods can be adopted, and other methods can also be adopted. After the treatment, the wood graphite is dehydrated and dried in a state containing some iron, and then inserted into a heating furnace 2 equipped with an inductor 1 on the outside. The inductor 1 is a coil that generates a so-called alternating magnetic field, and the heating furnace 2 is generally made of an insulating non-magnetic material. The power supply frequency used for this induction heating ranges from commercial frequency to MHz at most.
Compared to microwave heating, radio wave interference is considerably less of a problem. In general, in induction heating, there is a tendency for heating to become insufficient as you go deeper, although it depends on the power supply frequency. However, this tendency can be reduced by lowering the frequency, and can also be eliminated by the iron content contained in the graphite. Since iron is a ferromagnetic material unlike Kitshu graphite, the lines of magnetic force generated by the inductor 1 concentrate on the iron. Since this iron content is almost uniformly distributed in the wood graphite, and of course is also distributed in the deep part of the heating furnace 2, the iron content first becomes red-hot by induction heating, and the heat is transferred to the surrounding wood graphite. Therefore, non-uniform heating is eliminated by the iron present in the deep part. Conversely, in induction heating, the penetration depth of the eddy current varies depending on the frequency, so
This phenomenon can also be used to perform local heating or selective heating. In order to prevent oxidation loss of Kitshu graphite, the induction heating described above is performed in a non-oxidizing atmosphere (N ₂ ,
Ar). Through this heat treatment, Kitsushigraphite becomes 800~
When the temperature reaches 1000℃, the graphite intercalation compound decomposes and gasifies.
The fluid pressure causes the wood graphite to expand. After expansion, it is placed in a stirring container 3 filled with acid to dissolve the iron contained in the expansion lead, and then dehydrated and dried for finishing. As shown in the figure, this expanded graphite is passed through a rolling mill 4 and processed into a sheet. Furthermore, when natural graphite or artificial graphite is used instead of KITUSHIGHRAPHITE, iron may be added in advance. Next, to explain with specific numerical values, we collected the dust generated in the pig iron receiving pit when desulfurized and dephosphorized hot metal was transferred from the pig iron mixing car to the ladle.
The composition shown in Table A was obtained. Since this dust has a low FC content of 7.2%, it was purified by flotation to increase the content of Kitsushi graphite. As shown in Table 1 B, its components are 57.6% F・C, T・
Fe was 10.7%, and the bulk density was 1.03 g/cc. When this kitshu graphite was induction heated at a power frequency of 3 Hz, the bulk density changed from 1.03 g/cc to 0.007 g/cc.
cc, and an expansion rate of about 150 times was obtained.

[Table] Expanded graphite was further immersed in 36% hydrochloric acid to dissolve and remove iron. The oxidation loss at this time was 5.3%,
The ingredients are as shown in Table 2b.

〔Effect of the invention〕

As explained above, according to the present invention, high temperature maintenance, uniformity, uniform heating, prevention of oxidation loss, rapid heating, local heating, less contamination of the working environment, less waste gas treatment, and radio wave It has many effects such as no disability.

[Brief explanation of the drawing]

FIG. 1 is a flow chart showing one embodiment of the present invention. 1... Dielectric, 2... Heating furnace, 3... Stirring vessel, 4... Rolling mill.

Claims (1)

[Scope of Claims] 1. A method for producing expanded graphite, which comprises treating graphite particles with an expansion chemical and then thermally expanding a graphite intercalation compound by electromagnetic induction heating. 2. In claim 1, the graphite particles are characterized in that the graphite obtained in the hot metal pretreatment stage is made to have an F.C of 25 to 80% by a physical method, and further contains a small amount of iron. Method for producing expanded graphite. 3. The method for producing expanded graphite according to claim 2, characterized in that after the electromagnetic induction heating, acid treatment is performed to remove iron.