JP6756115B2 - Graphitization treatment method of amorphous carbon material and products and graphite produced when graphitating - Google Patents

Description

The present invention relates to products and graphite produced during the recovery of graphitization processing method and graphite amorphous carbon material.

Graphite is a layered crystal of carbon, and there is an increasing demand for crystalline graphite raw materials as refractory raw materials and lithium secondary battery electrode materials. However, naturally occurring scaly graphite tends to be depleted. In addition, natural graphite inevitably contains silica. Therefore, attempts have been made to synthesize crystalline graphite based on non-crystalline amorphous carbon, resin, and carbon raw materials. Here, since carbon is a substance having a high sublimation point (3642 ° C.) and is a substance that finally melts under high temperature and high pressure (4327 ° C., 10.8 MPa), amorphous carbon or the like is crystallized to be crystalline. In order to synthesize a certain graphite, it is necessary to convert the amorphous structure into a crystalline structure by high temperature and high pressure, and it is very difficult to develop a method for crystallization. Therefore, since the 1980s, research on a graphitization (crystallization) catalyst that realizes a reaction of crystallizing and graphitizing carbon having an amorphous structure under relatively low temperature conditions and normal pressure has been promoted.

The following method has been proposed for the graphitization reaction process using the above-mentioned graphitization catalyst. In Patent Document 1, compounds such as Si, Fe, Ti, and B are used as a graphitization catalyst, the binder portion of the material is graphitized at 2000 ° C. or higher, and the negative electrode of a lithium secondary battery having a low average charge / discharge voltage and high durability. A method of providing the material is disclosed. In Patent Document 2, petroleum-based or coal-based tars or pitches, resin graphite precursors, water-soluble transition metal compounds, and alkalis are brought into contact with each other in water, and at 1500 ° C. or higher through a catalytic reaction of transition metal oxides. A method for graphitization is disclosed. Further, Non-Patent Document 1 reports a method of adding a graphitizing catalyst such as Fe or B to a phenol resin to graphitize at 1300 ° C. or higher. Further, Non-Patent Document 2 summarizes general catalytic graphitization reactions. In order to confirm that the amorphous carbon is actually graphitized, for example, as in Patent Document 3, powder X-ray diffraction and Raman spectroscopic analysis are used.

On the other hand, some processes for graphitizing carbon powder using microwaves have also been proposed. In Patent Document 4, microwave heating is used as an auxiliary for heating the electric furnace, and graphitization is performed by raising the temperature of the carbon powder to 3200 ° C. or higher. In Patent Document 5, microwave resonance is applied to 3000. A method of graphitizing by heating carbon powder to ° C. is disclosed.

In the conventional graphitization process as described above, the graphitization reaction is carried out at a lower temperature of about 2000 ° C. using a graphitization catalyst, or the carbon powder temperature in the electric furnace is raised to a high temperature of 3000 ° C. by applying microwave heating. It is said that it was possible to crystallize amorphous carbon into graphite by a method of heating efficiently.

Further, in Patent Document 6, when the carbon raw material is dispersed in the conductive resin, the metal oxides and metal sulfides remaining in the carbon raw material obtained by firing at 2800 ° C. reduce the molecular weight of the resin, and the conductive resin. A method of halogenating these residues and vaporizing them at a predetermined temperature to remove them has been proposed.

International Publication No. 2002/059040 JP-A-2009-263160 Japanese Unexamined Patent Publication No. 2014-89975 Japanese Unexamined Patent Publication No. 2000-16807 Japanese Unexamined Patent Publication No. 2000-86222 International Publication No. 2015/20130

Refractory magazine vol. 65 No. 3 pp. 122 (2013) Carbon vol. 1980 No. 102 pp. 118-131 (1980)

However, the graphite produced by the above method does not have a perfect graphite structure, and contains amorphous carbon and carbon having a multi-layer structure. Amorphous carbon or carbon having a multi-layer structure is not preferable because the oxidation resistance is inferior. In particular, Non-Patent Document 1 uses a graphite crystallization process using a graphitization catalyst, and has a temperature of 1000 ° C to 2000 ° C, which is much lower than the carbon sublimation point (3642 ° C) and triple point (4327 ° C). It has also been reported that graphite crystallization is possible under conditions. However, in the graphite produced by this method, the XRD peak 2θ is deviated from 26.5 ° showing the graphite crystal, and the crystallinity is insufficient. In addition, as a heating method, it is necessary to raise the temperature of the entire material to a high temperature because it is heated from the outside using heat conduction and heat radiation, which is also an incomplete method in terms of improving the yield of graphite crystals. ..

On the other hand, in the example of Patent Document 4 of microwave heating aimed at improving the heating efficiency, it is necessary to use a carbon powder raw material that does not adhere to the reaction vessel as the starting material, and there is a high possibility that the yield will decrease and the productivity will be poor. Further, in the example of Patent Document 5, when resonance is used, there is a problem that the microwave density distribution is not stable and an error is large in heating up to 3000 ° C.

Further, as an applied technique of graphite, it is used as a carbon raw material used for a conductive resin or the like. In order to apply graphite produced by the prior art to such an application, metal oxides and metal sulfides have been removed by halogenation or the like. However, it has been difficult to completely remove impurities that are harmful to the characteristics of the carbon raw material used for the conductive resin and the like.

In any case, the above-mentioned prior art is insufficient to completely crystallize graphite, contains graphite other than crystallized graphite, and raises the temperature of the entire raw material, so that the graphitized sample is brought to room temperature. There are problems such as the time required for cooling and the fact that carbon and graphitized carbon can easily ignite by reacting with residual oxygen in the furnace, sample container, and heat insulating material.

(1) A graphitization treatment method in which a graphitization catalyst is added to an amorphous carbon material and dispersed, and the amorphous carbon material in which the graphitization catalyst is dispersed is irradiated with microwaves and heated. ,
The graphitizing catalyst is a simple substance of a metal containing at least one element selected from Fe, Ni, and Co.
The average particle size of the graphitizing catalyst is 200 [μm] or less.
The addition ratio of the graphitizing catalyst to the amorphous carbon material is 5% or more and 15% or less in terms of mass ratio.
The amorphous carbon material, thereby graphitized reaction by heating of 1000 ° C. or higher 1620 ° C. or less,
A method for graphitizing an amorphous carbon material, which is characterized by the above.
(2) In the graphitization reaction, the amorphous carbon material in which the graphitization catalyst is dispersed is not heated to a temperature higher than the temperature at which the metal constituting the graphitization catalyst is melted, according to (1). The method for graphitizing an amorphous carbon material according to the above method.
(3) The method for graphitizing an amorphous carbon material according to (1) or (2), wherein the graphitizing catalyst is metal Fe.
(4) After the completion of the graphitization reaction, the amorphous carbon material in which the graphitization catalyst is dispersed is heated to a temperature higher than the temperature at which the metal elements constituting the graphitization catalyst are melted, and the metal is melt-aggregated. The method for graphitizing an amorphous carbon material according to any one of (1) to (3), which comprises separating and recovering 95% or more of the amount of metal.
(5) A graphitizing catalyst was added to the amorphous carbon material at a ratio of 5% or more and 15% or less in terms of mass ratio, the catalyst was dispersed in the amorphous carbon material, and the catalyst was dispersed. When recovering graphite in a method of irradiating a crystalline carbon material with microwaves , heating it at 1000 ° C. or higher, and performing a graphitization treatment without heating it above a temperature at which the metal constituting the graphite catalyst melts. The product to be produced
The graphitizing catalyst is a simple substance of a metal containing at least one element selected from Fe, Ni, and Co.
The product is a mixture having a structure formed by separating the graphite produced by the graphitization reaction and the metal into different phases.
A product produced when graphite is recovered, characterized in that the metal has a particle size of 1 μm or less.
(6) Graphite in which the graphite phase and the metal phase are separated from the graphite phase into separate phases.
In the graphite phase, the maximum peak obtained by structural analysis by XRD is 2θ = 26.5 ± 0.02 °, and the half-value width of the maximum peak is 0.2 ° or less.
The metal phase contains at least one element selected from Fe, Ni, and Co, and has a particle size of 1 μm or less.
Graphite characterized by that.
(7) A graphitization treatment method in which a graphitization catalyst is added to an amorphous carbon material and dispersed, and the amorphous carbon material in which the graphitization catalyst is dispersed is irradiated with microwaves and heated. ,
The graphitizing catalyst is a simple substance or compound of a metal containing at least one element selected from Fe, Ni, and Co.
The average particle size of the graphitizing catalyst is 200 [μm] or less.
The addition ratio of the graphitizing catalyst to the amorphous carbon material is 5% or more and 15% or less in terms of mass ratio.
The amorphous carbon material is heated to 1000 ° C. or higher to cause a graphitization reaction.
After completion of the graphitization reaction, the amorphous carbon material in which the graphitization catalyst is dispersed is heated to a temperature higher than the temperature at which the metal elements constituting the graphitization catalyst are melted, and the metal is melt-aggregated to obtain the amount of the metal. A method for graphitizing an amorphous carbon material, which comprises separating and recovering 95% or more.
(8) In the graphitization reaction, the amorphous carbon material in which the graphitization catalyst is dispersed is heated to a temperature lower than the temperature at which the metal constituting the graphitization catalyst is melted, according to (7). The method for graphitizing an amorphous carbon material according to the above method.
(9) The method for graphitizing an amorphous carbon material according to (7) or (8), wherein the graphitizing catalyst is metallic Fe or iron oxide.

According to the present invention, since graphite can be produced by an artificial method that does not contain impurities in the raw material, it is graphitized without containing silica or the like like natural graphite and without leaving amorphous carbon or carbon having a disordered layer structure. Artificial graphite can be provided. In addition, by selectively heating the graphitization catalyst with microwaves and setting the temperature near the surface of the catalyst where the catalytic reaction occurs to the temperature required for the graphitization reaction, graphitization can be performed in a short time by heating at a low temperature as a whole. Can be done. Further, since the material can be heated uniformly, the graphitization reaction can be carried out with good yield without leaving unreacted substances inside the material. Further, even if the graphitization catalyst is a metal compound, it is metallized during the reaction, so that the metallized graphitization catalyst can be separated and recovered after heating by raising the temperature to a temperature equal to or higher than the melting point of the metal. In addition, treatment is possible at temperatures below the temperature at which amorphous carbon and graphitized carbon ignite.

Microwave heating device Sample installation diagram XRD peak analysis diagram Sample internal temperature, microwave incident / reflected energy measurement results in Invention Example 1 Invention Example 1 XRD evaluation result Sample internal temperature, microwave incident / reflected energy measurement results in Invention Example 4 Sample internal temperature, microwave incident / reflected energy measurement results in Invention Example 6 Invention Example 8 XRD evaluation result Comparative Example 1 XRD evaluation result Comparative Example 2 XRD evaluation result Comparative Example 3 XRD evaluation result Comparative Example 4 XRD evaluation result Comparative Example 5 XRD evaluation result Sample internal temperature and microwave incident / reflected energy measurement results in Comparative Example 6 Comparative Example 6 Sample Photograph Comparative Example 7 Sample Photograph Sample internal temperature, microwave incident / reflected energy measurement results in an example of invention using glassy carbon as an amorphous carbon raw material Example of invention using glassy carbon as an amorphous carbon raw material XRD evaluation result

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the present invention, a graphitization treatment is performed by adding a graphitization catalyst to an amorphous carbon material, dispersing it, irradiating it with microwaves, and heating it.
In the present invention, it is important that the graphitized catalyst is heated preferentially over the amorphous carbon material by using microwaves. When the graphitizing catalyst is selectively and preferentially strongly heated by microwaves, even if the graphitizing catalyst itself becomes high in temperature, the entire amorphous carbon material becomes as high as 2000 to 3000 ° C. as in the past. It will never be. Then, when the graphitizing catalyst itself is heated to the graphitization temperature or higher, the amorphous carbon material at the interface portion in contact with the surface of the graphitizing catalyst is heated by heat conduction from the graphitizing catalyst and the effect of the catalyst. It can be graphitized. The calorific value of the graphitizing catalyst, which is reduced by heat conduction from the graphitizing catalyst to the amorphous carbon material, can always be replenished as long as microwave heating is continued. That is, the vicinity of the contact interface between the graphitization catalyst and the amorphous carbon material, which is the reaction field of the graphitization reaction, can always be heated to the temperature required for graphitization.
In addition, since the graphitizing catalyst is uniformly dispersed in the amorphous carbon material, when microwave heating is performed, the particles dispersed inside the amorphous carbon material are also dispersed in the vicinity of the surface. As for the particles, each graphitization catalyst particle is heated evenly. That is, since the internal graphitization catalyst also acts as each heat source, it can be uniformly heated from the inside to uniformly graphitize the entire amorphous carbon material.

In the present invention, the amorphous carbon material refers to a raw material having a carbon source other than graphite. Typically, it is preferable to use a carbon-containing resin such as glassy carbon, pitch, tar or phenol resin.

Dispersion of the catalyst in the amorphous carbon material is performed by dissolving the catalyst in a solvent when the amorphous carbon material is a resin, dispersing it in a solvent when the amorphous carbon material is glassy carbon or the like, and further mixing the catalyst. Do. As the solvent, ethylene glycol, ethanol, water or the like can be used. The amount of the amorphous carbon material added to the solvent is not particularly specified, but about 15 to 45% by mass is recommended.

The graphitization catalyst of the present invention is required to be a simple substance composed of a metal containing at least one element selected from Fe, Ni, and Co, or a compound thereof. These elements have excellent microwave absorption characteristics and can efficiently heat the graphitization catalyst itself. And it is more easily heated by microwaves than the amorphous carbon material.

As one of the indexes showing the microwave absorption characteristics, there is a skin depth δ represented by the following formula 1.
δ = (2ρ / ωμ) ^0.5 (Equation 1)
Here, ρ: electrical resistivity [Ω · m], ω: 2πf [f (Hz)], μ: magnetic permeability [H / m], f: microwave frequency [Hz].

Table 1 shows the skin depth of the metal when the microwave frequency f = 2.45 [GHz] actually used. In order for microwaves to be absorbed, the skin depth δ should be small. Further, it is preferable that the melting point is low for processing at a low temperature. From the above, among the elements having the above-mentioned graphitization catalytic reaction characteristics, Fe, Ni, and Co having a small skin depth and a relatively low melting point were used in the graphitization reaction by microwave heating of the present invention. A graphitization catalyst is used. It can also be used with these alloys.

The metal compound can also be applied as a catalyst, and the graphitization catalyst can be selectively heated by microwaves. For example, carbides, sulfides, oxides, borides and nitrides of Fe, Ni and Co can be used. The temperature of the catalyst selectively rises, C, S, O, B, and N are desorbed, and finally the catalyst becomes a simple substance and graphitization proceeds. Therefore, for any of the metal compounds, a catalytic reaction occurs by selective heating with microwaves through a state composed of only metal elements. Therefore, C, S, O, etc. are used as the graphitization catalysts added before the start of the reaction. It may be a compound containing any of the elements B and N, or a compound composed only of a metal.

Further, among them, it is more preferable to use metal Fe or iron oxide as the metal element having graphitization catalytic ability. Fe has the best affinity for C and has high C solubility, and is therefore preferable. Iron oxide is easily heated by dielectric heating by microwaves. In addition, iron oxide is decomposed by heating to produce metallic iron. When metallic iron is produced, metallic iron acts as a catalyst as described above, which is preferable as in the case where Fe is added as a catalyst.

The average particle size of the graphitized catalyst particles used in the present invention is 200 μm or less. The average particle size is the volume-based cumulative particle size distribution D50 value measured by the laser microtrack method. At this time, a particle size distribution in which D10 / D50> 0.5 and D50 / D90> 0.5 is preferable. As a result of diligent studies by the inventors, when the average particle size exceeds 200 μm, metal particles are melt-aggregated before the graphitization reaction, the microwave absorption capacity is reduced, and the sample is heated to a temperature at which the graphitization reaction occurs. Can not.

The amount of the catalyst added in the present invention is 5 to 15% by mass with respect to the amorphous carbon material. If it is less than 5%, the amount of dispersion in the amorphous carbon material is small, and the amorphous carbon material cannot be sufficiently graphitized. If it exceeds 15%, the catalyst melts and aggregates, the microwave absorption capacity decreases, and the sample cannot be heated to a temperature at which a graphitization reaction occurs.

The present invention is carried out by raising the temperature of the amorphous carbon material to 1000 ° C. or higher by microwave irradiation. If the temperature is lower than 1000 ° C., the graphitization reaction does not proceed sufficiently, so that the graphite crystallinity is poor and graphite having good characteristics cannot be obtained. If the temperature is 1000 ° C. or higher, graphitization proceeds sufficiently, and graphite having good graphite crystallinity and good characteristics can be obtained.
The inventor found that when the heating temperature of the amorphous carbon material was set to 1000 ° C. or higher, at least a part of the metal constituting the graphitization catalyst was melted, and a liquid preferable as a graphitization reaction field could survive. , Found that graphitization is promoted more. Therefore, when the graphitizing catalyst is a simple substance or a compound composed of a metal containing at least one element selected from Fe, Ni, and Co, 1000 ° C. or higher is required.

Here, the temperature of the amorphous carbon material is thick, for example, with an inner diameter of 5 to 10 mm, because the temperature of the catalyst surface or the place where the reaction is occurring cannot be directly measured when the catalyst is locally heated by microwave heating. The protective tube is brought into contact with the sample, and the radiant light from the inside of the protective tube is measured by a radiation thermometer.

When the graphitization reaction is allowed to proceed by the production method of the present invention, the product becomes a structure in which completely graphitized graphite and the metal constituting the graphitization catalyst are separated into separate phases. At this time, it was found that the graphitizing catalyst added in a size of 200 μm or less on the order of microns was a metal refined to a size on the order of submicrons in the structure after completion of the reaction. This was observed when the entire amorphous carbon material was cooled without heating to a temperature higher than the melting temperature of the metal constituting the graphitization catalyst after the graphitization reaction. Then, when the heating was controlled in this way, graphite having very good crystallinity was obtained.
The reason for the miniaturization is not always clear, but the metals that make up the graphitization catalyst melt (in the case of compounds, they melt after metallization), and the melted metal volatilizes and diffuses into the amorphous carbon material. However, it is conceivable that the metal is finely dispersed by condensing at the diffusion destination during cooling. At this time, it is considered that carbon is dissolved in the diffused molten metal, and the metal carbide is generated and then precipitated as graphite, so that the amorphous carbon material is uniformly and efficiently graphitized.
Such a peculiar phenomenon cannot be obtained by the prior art, and the graphitizing catalyst is miniaturized to the submicron order of about 1 μm or less in particle size and uniformly dispersed in the entire amorphous carbon material. It is presumed that graphitization has progressed sufficiently over the period.

The particle size of the fine particles is the particle size when the metal portion is approximately spherically approximated by image analysis after observation with an optical microscope, and the distribution has an average of 1 μm or less and a standard deviation of less than 0.5 μm. In the reaction product of the present invention, at the end of the graphitization reaction, the graphitized graphite phase and the metal phase containing at least one element selected from Fe, Ni, and Co are the size of the metal phase. Is obtained as a finely dispersed mixed structure of 1 μm or less. When only the graphite phase is taken out, the graphite phase and the metal phase may be mechanically separated as described later. The product before separating the metal and graphite produced by the graphitization of the present invention will be referred to as a graphitization product.

By the way, when a graphitization catalyst is added to a solvent in which an amorphous carbon material is dispersed, if these catalysts are precipitated and become non-uniformly dispersed in the solvent, the sample is heated non-uniformly. There is a risk of However, in the present invention, regardless of the initial dispersion state of the catalyst, the metal of the catalyst becomes finer in the heating process and is uniformly dispersed in the amorphous carbon material. Therefore, after the graphitization reaction, the metal is dispersed in the sample site. Regardless, it is possible to uniformly graphitize. In the conventional electric furnace heating or the like, the non-homogeneous addition of the catalyst is directly reflected in the heterogeneity of the produced graphite. Therefore, the graphite synthesis by microwave heating of the present invention has a much higher yield than the case of electric furnace heating, and can be synthesized almost 100%.

However, if the entire amorphous carbon material is heated to a temperature higher than the melting temperature of the metal constituting the graphitization catalyst at the stage of the graphitization treatment, the metal melts and aggregates, and a sufficient graphitization reaction cannot be carried out. In some cases.

Therefore, in the present invention, the upper limit of the graphitization treatment temperature of the amorphous carbon material is preferably lower than the temperature at which the metal elements constituting the graphitization catalyst are melted. Here, the graphitization catalyst of the present invention contains at least one element selected from Fe, Ni, and Co, and the melting points of each metal are shown in Table 1, but various metals are used in the graphitization reaction process. Since the metal does not necessarily start melting at the melting point of the pure element in order to dissolve the components, the upper limit of the graphitization treatment temperature of the present invention is set to be lower than the temperature at which the metal becomes liquid (melting point). Further, when the heating temperature is increased, the amount of heat input increases, the energy cost such as electric power increases, the device needs to be made highly heat resistant, and the equipment cost increases. Therefore, the lower the temperature is preferable.

In radiant heating from the outside such as heating in an electric furnace, the graphitization catalyst is heated through the amorphous carbon material, so the graphitization temperature is located near the interface between the graphitization catalyst and the amorphous carbon material, which is the reaction field. If it is heated to the above level, the entire amorphous carbon material must be heated to a high temperature more than necessary, resulting in poor thermal efficiency and production efficiency. Further, at a temperature at which the graphitization reaction proceeds for the entire material, there is a concern that the graphitization catalysts may aggregate with each other. When the graphitizing catalyst aggregates, the contact interface area between the catalyst and the material decreases, and the part where the catalytic effect can be obtained decreases. On the other hand, in the method of the present invention, the temperature of the reaction field can be raised to a temperature at which graphitization proceeds sufficiently while maintaining the heating temperature of the amorphous carbon material at a temperature at which the graphitization catalyst does not aggregate.
That is, while the graphitization catalyst is selectively heated by microwave heating and the graphitization reaction proceeds, if the temperature of the material is kept below the melting point of the metal contained in the graphitization catalyst, the graphitization catalyst is discrete. The particles do not aggregate with each other.

In the present invention, after the graphitization reaction has sufficiently proceeded, the catalyst metal is heated by heating the temperature of the entire amorphous carbon material in which the graphitization catalyst is dispersed to a temperature higher than the temperature at which the metal elements constituting the catalyst are melted. Is melt-aggregated, and after the reaction is completed, it is cooled and solidified so that the metal contained in the catalyst can be easily separated and recovered. As a result, 95% or more of the amount of metal contained in the added catalyst can be separated and recovered.

In the present invention, the compound used for the graphitization catalyst remains as a metal after the graphitization reaction as described above. Therefore, by heating the entire material temperature to a temperature equal to or higher than the melting temperature of the metal elements constituting the graphitization catalyst, it is possible to agglomerate and recover these metals after the graphitization reaction. As a result of diligent studies by the inventors, it is difficult to completely reaggregate by high-temperature heating, and although some of them remain dispersed on the submicron order, most of them have a particle size that can be sieved. It can be reaggregated. By this method, it has been confirmed that at least 95% of the added metal amount / mass ratio can be recovered. The metal recovery method is as follows, for example. The obtained graphitized material is put into a container filled with zirconia balls or alumina balls having a diameter of 10 to 20 mm, pulverized by a ball mill at 100 rpm, and the obtained sample is separated by a sieve of 106 [μm] and recovered. At this time, the metal can be separated by remaining on the sieve.

In the present invention, it is preferable to perform heating while exhausting volatile substances. When a resin or the like is used as the amorphous carbon material and a metal compound is used as the catalyst, metal oxides and metal sulfides are generated during heating. By heating while exhausting the volatile substances, the graphitization reaction can be carried out with good yield without leaving metal oxides, metal sulfides and the like inside the generated graphite. Further, volatile matter generated from the sample such as ethylene glycol having a boiling point higher than the temperature inside the heating device adheres to the inner wall of the heat insulating layer of the device, and the volatile matter adhering portion absorbs microwaves and hinders the heating of the sample. By heating while exhausting the volatile substance, it is possible to prevent the volatile matter from adhering to the inner wall, so that the heating of the sample is not hindered and the microwave heating can be efficiently performed. Exhaust is not particularly important if the amorphous carbon material does not contain volatiles whose boiling point is higher than the temperature inside the heating device. Exhaust is not particularly important as long as the volatile material can be heated without blocking the exposure of microwaves to the amorphous carbon material.

Next, the microwave heating method will be described.
The microwave used in the present invention has a frequency of 2.45 GHz. The frequency is suitable for heating and drying the amorphous carbon material and solvent of the present invention, and for heating metal catalyst particles. However, the frequency is not limited as long as the surface of the metal catalyst can be melted and heated to a temperature at which the graphitization reaction can be carried out.

FIG. 1 shows an example of an apparatus used in the method for producing graphite by microwave heating of the present invention. The microwave is irradiated from the microwave oscillator 11 into the applicator 14 via the waveguide 12. The applicator, N _2, an inert gas such as Ar (15) an inert gas stream atmosphere. The shape of the waveguide 12 conforms to the EIAJ standard, and in the case of 2.45 GHz band microwave, WRJ-2, WRI-22 or WRI-26 is selected. The shape of the applicator 14 is preferably an internal dimension of 400 mm or more in order to uniformly disperse microwaves in the applicator. Microwave incident energy and reflected energy are measured by a power monitor (13). By using microwaves, only the sample can be heated efficiently, but in the open state, the heat removed from the sample surface is large and the heating efficiency is lowered. In the present invention, by installing the heat insulating layer 17 on the outer periphery of the sample container 16, heat removal from the sample is suppressed and the heating efficiency is improved.

FIG. 2 shows a sample installation diagram. In order to efficiently heat the amorphous carbon material in which the graphitization catalyst of the present invention is dispersed, it is preferable to set the gas inflow rate in the applicator 14 (see FIG. 1) to be equal to or higher than the volatile matter generation rate. Therefore, the sample weight is set according to the volatile content. Assuming that the temperature inside the applicator is about 300 K, in the case of a sample containing 60% of the solvent ethylene glycol, about 30 L of volatile matter is generated in 100 g of the sample. Under the sample heating conditions shown below, the sample temperature reaches the boiling point of ethylene glycol in about 20 to 30 minutes, so that the volatile matter generation rate is at least 1.0 to 1.5 [L / min]. The gas inflow speed in the applicator needs to be set to a value higher than this speed, that is, 1.5 [L / min]. The sample 201 is filled in the sample container 202 and further stored in the external crucible 203. A heat insulating layer 204 is provided between the sample container 202 and the outer crucible 203 by filling fine powder of an oxide composed of Al ₂ O ₃ , SiO ₂ , MgO, CaO or a compound thereof, and further outside the outer crucible 203. Is provided with a ceramic fiber-like heat insulating layer 205. The oxide fine powder heat insulating layer 204 and the outer crucible 203 may be a ceramic fiber-like heat insulating layer.

The microwave heat treatment of the present invention is performed by monitoring the sample temperature and controlling the microwave irradiation output. As shown in FIG. 2, the sample temperature is determined by inserting a ceramic protective tube 206 into the sample 201 and radiating heat from the inside of the protective tube heated by heat transfer from the sample heated by the microwave. Detect with and measure the temperature. If the average temperature of the sample can be measured, the method is not limited to this method.

In order to raise the temperature of the sample stably, the initial output is recommended to be a value that can supply energy of (incident output)-(reflection output) of 3 [W / g] or more based on the study by the inventors.

In the microwave heating of the present invention, the irradiation output is controlled while monitoring the sample temperature. Regarding the heating control at the start of the graphitization treatment, it is possible to increase the rate of temperature rise of the sample temperature by increasing the irradiation output, but according to the study by the inventors, the sample is rapidly raised in the presence of a solvent. Since there is a risk of explosion when warmed, it is recommended that the upper limit of microwave output be (irradiation output) / (sample weight) = 10 [W / g] when the sample temperature is 500 ° C or less. ..

In the microwave irradiation of the present invention, while monitoring the sample temperature, the generation of volatile components from the amorphous carbon is completed, and the temperature is 1000 ° C. or higher, up to a temperature at which the amorphous carbon is sufficiently crystallized. Amorphous carbon is sufficiently crystallized when the temperature rise is observed again without increasing the microwave irradiation output after the stagnation phenomenon of the temperature rise rate is observed due to the volatilization of the solvent and the graphitization reaction. It is in a state of being.
In the process in which only the graphitization catalyst is selectively heated and the temperature of the surrounding amorphous carbon material or the like is raised by the heat, volatilization of the solvent or the like and decomposition of impurities also occur. At this time, if the microwave irradiation output is constant, the heating rate becomes slower or stagnant than at the start. The temperature range in which this phenomenon occurs varies depending on the starting material, but is generally up to 800 ° C. After such a phenomenon is completed, it is possible to continue heating at a constant output, or it is possible to increase the output to increase the heating rate. In any case, the temperature reaches 1000 ° C. or higher. If the temperature is raised, the graphitization treatment can be completed.

Even when volatile components are generated and impurities are decomposed, the irradiated microwave energy is consumed by those reaction energies, so that the rate of temperature rise of the sample is significantly reduced. The evaporation / decomposition temperature of impurities varies depending on the starting material, but when the temperature rise rate of the sample drops once in the temperature range of 200 to 300 ° C. and the temperature rise is started again without increasing the microwave irradiation output. It is determined that the decomposition from the starting material at that temperature is completed. When increasing the microwave irradiation output in order to increase the heating rate and the reached temperature, the temperature is equal to or higher than the graphitization reaction temperature and the impurity decomposition temperature.

If the generation of volatile components and the decomposition of impurities are completed and the temperature can be raised to about 900 to 950 ° C, then the sample temperature can be reached to a higher temperature of 1000 ° C or higher by increasing the irradiation output. Preferably, while monitoring the sample temperature, the temperature is controlled so that the metal constituting the catalyst is at most below the melting temperature. If the sample temperature is raised above the melting temperature of the metal in a state of insufficient graphitization, the subsequent graphitization reaction will not proceed sufficiently due to the aggregation of the metal. The higher the sample temperature, the more the crystallinity can be improved as long as the temperature is not raised above the melting temperature of the metal.

On the other hand, after the graphitization reaction has sufficiently proceeded, the catalyst metal is melted by heating the temperature of the entire amorphous carbon material in which the graphitization catalyst is dispersed to a temperature higher than the melting temperature of the metal elements constituting the catalyst. The metal contained in the catalyst can be easily separated and recovered by aggregating and cooling and solidifying after the reaction is completed. As a result, 95% or more of the amount of metal contained in the added catalyst can be separated and recovered. In order to carry out the graphitization reaction so that the graphitization reaction proceeds sufficiently, the heating conditions are determined by appropriately confirming graphitization by XRD from the conditions determined with reference to the heating temperature and time of the examples of the present invention. Can be carried out.

By the above-mentioned graphitization method of the present invention, at the end of the graphitization reaction, the size of the metal phase of the graphitized graphite phase and the metal phase containing at least one element selected from Fe, Ni, and Co is 1 μm or less. It is obtained as a finely dispersed mixed structure of graphite. When only the graphite phase is taken out, the graphite phase and the metal phase may be mechanically separated as described later. Further, in the graphitized graphite phase, the peak position of the maximum peak obtained by structural analysis by XRD is 2θ = 26.5 ± 0.02 °, and the half-value width of the maximum peak is 0.2 ° or less. The maximum peak position and the half price range of the maximum peak will be described in detail below.

Unlike natural graphite, the artificial graphite of the present invention does not contain Si in the raw material, so that it can be substantially free of silica which is inevitably contained in natural graphite. Further, where complete graphitization was not possible with conventional artificial graphite, the peak position of the maximum peak obtained by structural analysis by XRD does not deviate from 2θ = 26.5 ± 0.02 °. It was possible to obtain graphite having extremely high crystallinity, in which the half-value range of the maximum peak was 0.2 or less. The crystallinity indicates that the sharper the peak of XRD, the less turbulence of X-rays and the more crystals having a predetermined structure. On the contrary, the broad peak indicates that a mixture other than the specific crystal structure is mixed. In the present invention, the half price range is defined as 0.2 or less as an index of the degree of crystallinity. The half-value width is a numerical value obtained by measuring the width of the waveform at the intensity position where the peak height is halved.

The crystallinity of graphite in the present invention is evaluated by using powder X-ray diffraction (hereinafter, XRD) using Kα rays of Cu. FIG. 3 shows an XRD peak analysis diagram. According to Non-Patent Document 2, the interlayer peaks of graphite have 2θ = 26 ° and 26.5 °, but the crystal peak corresponding to the phase called ORDER STATE with high crystallinity is the peak of 2θ = 26.5 °. Therefore, for the crystallinity after the graphitization reaction, the peak half width (hereinafter, FWHM) 33 of the peak in the graphite [002] direction near 2θ = 26.5 ° was measured.
According to the study by the inventors, it was confirmed that the graphite crystal had excellent oxidation resistance when the half-value width was 0.2 ° or less, and it was judged that the amorphous carbon was graphitized.

Table 2 lists the graphitization treatment conditions of Invention Examples 1 to 8 and Comparative Examples 1 to 7 of the present invention.
Phenolic resin was used as the amorphous carbon. Among the amorphous carbon materials, the phenol resin is more difficult to graphitize than the material such as glassy carbon. Therefore, if the phenol resin can be graphitized, it can be said that the amorphous carbon material can be graphitized. In Invention Example 1, after mixing ethylene glycol with a phenol resin, 150 g of a sample in which Fe having an average particle size of 100 μm was added and dispersed (amorphous carbon: ethylene glycol: metal Fe = 45: 55: by mass ratio%). 5) was used as a starting material. The graphitization catalyst used in Invention Example 1 is a ferrite (α-phase) single-phase metal Fe. The temperature measurement method and graphitization evaluation method are as described above. Inventive Examples 2 to 8 and Comparative Examples 1 to 7 were carried out under the conditions shown in Table 2.

For the graphitization treatment, microwave (2.45 GHz) irradiation was performed using the apparatus shown in FIGS. 1 and 2.
FIG. 4 shows the measurement results of the sample internal temperature 51, the microwave incident energy 52, and the microwave reflected energy 53 during microwave irradiation in the first invention example. When the microwave irradiation output was initially constant at 0.8 kW, the sample temperature rose again after the solvent volatile substance volatilized (54) and then stagnated due to the graphitization reaction (55). The temperature reached 900 ° C. about 90 minutes after the start of wave irradiation. Next, the irradiation output was increased to 1.5 [kW], and after 150 [min] from the start of irradiation, when the sample temperature reached 1500 ° C., microwave irradiation was stopped. The sample was cooled to room temperature in an inert gas stream and recovered, and the crystallinity was evaluated by XRD.

FIG. 5 shows the XRD evaluation results in Invention Example 1. The formation of the Fe phase and the graphite phase used as the metal catalyst was confirmed. The half-value width of graphite was calculated to be 0.18, and sufficient crystallinity was confirmed. In addition, from the XRD evaluation results collected from 5 points on the sample inside the crucible, it was confirmed that the half-value range was 0.2 or less at any of the collection points, and the half-value range was confirmed by the method of Example 1 of the present invention. It was confirmed that the graphite crystals having a value of 0.2 or less were almost 100%. It was also confirmed by observing the surface with an electron microscope that all of the measuring parts were graphitized. In an electron microscope, graphite can be identified by its brightness. The brightness is highest for catalyst-derived metals and lowest for other non-graphitized parts. Graphite exhibits an intermediate brightness.

In Invention Example 2, the starting material was adjusted under the same conditions as in Invention Example 1 except that the amount of Fe, which is a graphitization catalyst, was set to 5%, and graphitization was performed under the same heating conditions as in Invention Example 1. This is an example. The XRD evaluation result of the obtained sample was the same as that in FIG. Similar to Invention Example 1, a sharp graphite 002 peak was observed at 2θ = 26.5 °, and it was confirmed that a graphite sample having a half value width of 0.2 and good crystallinity was obtained.

Inventive Example 3 is the same as Invention Example 1 except that the starting material was adjusted under the same conditions as in Invention Example 1 except that the amount of Fe, which is a graphitization catalyst, was added to 15%, and the ultimate temperature was 1600 ° C. This is an example of graphitization under the same heating conditions. The XRD evaluation result of the obtained sample was almost the same as that in FIG. A sharp graphite 002 peak was observed at 2θ = 26.5 °, and it was confirmed that a graphite sample having a half value width of 0.15 and good crystallinity was obtained.

In Invention Example 4, the starting material is adjusted under the same conditions as in Invention Example 1, and the heating condition is 1600 ° C. after irradiating the microwave irradiation condition with 800 [W] × 90 [min] and then gradually increasing the output. In this example, the output was adjusted so that the sample temperature was maintained in the range of 1600 ± 20 ° C., and the treatment was performed for 128 minutes. The sample temperature history at this time is shown in FIG. The XRD evaluation result of the obtained sample was almost the same as that in FIG. A sharp graphite 002 peak was observed at 2θ = 26.5 °, and it was confirmed that a graphite sample having good crystallinity with a half-value width of 0.1 was obtained.

Further, in Invention Example 3 and Invention Example 4, as a result of heating to 1000 ° C. or higher to accelerate the graphitization reaction and then raising the temperature to the melting point (1538 ° C.) or higher of the metal Fe, aggregation of the metal Fe was observed. .. The aggregated metal Fe was separated and recovered. The method for recovering the metal Fe was as follows. That is, the obtained graphitized material was put into a container having a diameter of 150 × 200 mm, pulverized by a ball mill at 100 rpm using an alumina ball having a diameter of 20 mm, and then the obtained sample was separated by a sieve of 106 [μm] and recovered. .. Table 3 shows the results of comparing the metal Fe recovery rate with that of Invention Example 1. The recovery rate of Invention Example 3 was 98%, and it was confirmed that the metal Fe could be recovered as a result of heating above the melting point of Fe. Further, in Invention Example 4, as a result of heating and holding the sample temperature above the melting point of Fe, the recovery rate was 99% or more. On the other hand, in Invention Example 1, since the temperature was 1500 ° C., which was lower than the melting point of iron, iron was dispersed as fine particles, and the recovery rate was low.

In Invention Example 5, the starting material was adjusted under the same conditions as in Invention Example 1 except that the average particle size of Fe, which is a graphitization catalyst, was set to 200 μm, and the heating condition was a constant microwave irradiation condition of 800 [W]. This is an example of graphitization under the condition of reaching temperature of 1200 [° C.]. The XRD evaluation result of the obtained sample was the same as that in FIG. A sharp graphite 002 peak was observed at 26.48 ° near 2θ = 26.5 °, and it was confirmed that a graphite sample with a half-value width of 0.2 and good crystallinity was obtained. Fe of the catalyst was dispersed as fine particles of 1 μm or less.

In Invention Example 6, the starting material was adjusted under the same conditions as in Invention Example 1, and the heating conditions were treated at an ultimate temperature of 1050 [° C.] with the microwave irradiation condition being constant at 800 [W]. FIG. 7 shows the sample temperature history. The XRD evaluation result of the obtained sample was the same as that in FIG. A sharp graphite 002 peak was observed at 26.48 ° near 2θ = 26.5 °, and it was confirmed that a graphite sample with a half-value width of 0.2 and good crystallinity was obtained. In this example, no stagnation period was observed, but sufficient graphitization is possible if the ultimate temperature is 1000 ° C. or higher.

In Invention Example 7, the starting material was adjusted under the same conditions as in Invention Example 1 except that the average particle size of Fe, which is a graphitization catalyst, was 4 [μm], and the heating condition was 800 [microwave irradiation condition. W] This is an example in which graphitization is performed while keeping the value constant. The reached temperature was 1000 [° C.], and the XRD evaluation result of the obtained sample was the same as that in FIG. A sharp graphite 002 peak was observed at 26.48 ° near 2θ = 26.5 °, and it was confirmed that a graphite sample with a half-value width of 0.2 and good crystallinity was obtained.

In Invention Example 8, the starting material was adjusted under the same conditions as in Invention Example 1 except that the graphitizing catalyst was Fe ₂ O ₃ having a particle size of 0.07 [μm], and the heating condition was microwave heating condition 800. This is an example of graphitization under [W] × 90 [min] + 1500 [W] × 60 [min]. The ultimate temperature is 1460 [° C.], and the XRD evaluation results of the obtained sample are shown in FIG. The added Fe ₂ O ₃ phase was not confirmed, and all Fe sources were detected as ferrite phases (αFe). A sharp graphite 002 peak was observed at 26.49 ° near 2θ = 26.5 °, and it was confirmed that a graphite sample with a half-value width of 0.16 and good crystallinity was obtained. It is presumed that Fe ₂ O ₃ was selectively heated by dielectric heating with microwaves, oxygen was separated, and the graphitization catalytic reaction with metallic iron proceeded.

In Comparative Example 1, microwave heat treatment was performed under the same conditions as in Invention Example 6 without adding a graphitization catalyst. The maximum temperature reached for the sample was 800 ° C. The XRD evaluation result of the obtained sample is shown in FIG. No graphite 002 peak was detected near 2θ = 26.5 °, and graphitization was not confirmed.

In Comparative Example 2-4, using an electric furnace instead of microwave as a heating source, 800 ° C. respectively samples the maximum temperature, 1000 ° C., and 1500 ° C., by heating holding time 10 hours under _{N 2} gas atmosphere, Graphitization treatment was performed. Others are the same conditions as in Invention Example 6. The temperature rising rate at this time was 600 [K / hr]. The XRD evaluation results of the obtained sample are shown in FIGS. 10, 11 and 12, respectively. The peaks observed near 2θ = 26.5 ° had poor crystallinity, 2θ = 26.0 °, 2θ = 26.0 °, and 2θ = 26.1 °, respectively. In addition, the half-value range of the above peaks was 2.5, 2.1, and 2.2, respectively, and it was confirmed that they were hardly graphitized.

In addition, in all the samples treated in the electric furnace, hybrid peaks of 2θ = 26 ° and 2θ = 26.5 ° were observed, and a mixed layer structure (2θ = 26 °) and graphite crystals (2θ = 26.5 °) were observed. Was confirmed to be mixed. On the other hand, the graphite 002 peak of Invention Example 1 was a graphite crystal containing no disordered layer structure. Therefore, as compared with the conventional electric furnace treatment, the microwave heat treatment of the present invention can obtain graphite having high crystallinity which has not been conventionally obtained in a short period of time.

Comparative Example 5 is an example in which microwave irradiation was performed under the same conditions as in Invention Example 6 and the microwave irradiation was stopped after reaching 800 [° C.]. The XRD evaluation result of the obtained sample is shown in FIG. A graphite 002 peak was observed at 26.4 ° near 2θ = 26.5 °, but the half-value width was 2.5, and sufficient crystallinity was not obtained. Further the invention Examples 1 and 2 were not observed, the peak of cementite (Fe 3 _C) phase was detected. When the cementite phase remained, it was confirmed that the graphitization reaction by microwave heating did not proceed sufficiently.

In Comparative Example 6, a metal Fe having an average particle size of 250 μm was used, and microwave heat treatment was performed under the same conditions as in Invention Example 6. FIG. 14 shows the sample internal temperature and microwave incident / reflected energy measurement results in Comparative Example 6. In this treatment, the microwave reflection energy became stronger during the treatment, the temperature could not be raised to 1000 ° C. or higher, and the graphitization treatment could not be performed. The appearance of the recovered sample is shown in FIG. 15, and it was confirmed that the Fe particles were melt-aggregated. It is considered that the microwave was reflected by the melt aggregation of the metal Fe, and the sample could not be heated.

In Comparative Example 7, the amount of the metal Fe added was 20% by mass, and the microwave heat treatment was performed under the same conditions as in Invention Example 6. The appearance of the obtained sample is shown in FIG. It was confirmed that the Fe particles were melt-aggregated, and when microwave heating was performed under the conditions, the microwave reflection energy after the melt-aggregation of Fe was strengthened, and the temperature rise stopped before the volatile components in the starting material were completely volatilized. It was confirmed that the conversion did not occur.

Further, when glassy carbon was used as an amorphous carbon material and the graphitization reaction was carried out based on the heating temperature history shown in FIG. 17, it was confirmed that graphite having good crystallinity was produced as shown in FIG. It was.

Further, as a result of component analysis of Invention Example 4, as shown in Table 4, it was confirmed that graphite containing no impurities could be produced as compared with natural graphite and pyrolyzed graphite.

* 1: Z-5F manufactured by Ito Graphite Industry Co., Ltd.
* 2: See JP-A-2001-240404, Japan Matex.

According to the present invention, graphite having good crystallinity without impurities can be provided. In addition, since we were able to provide a graphitization treatment method for amorphous carbon materials that has a short treatment time and a low equipment temperature, it has high thermal efficiency and energy efficiency, and is industrially usable because it can produce graphite with less equipment burden. Has.

11: Microwave oscillator waveguide 12: Waveguide 13: Power monitor 14: Applicator 15: Inflow inert gas 16: Sample 17: Insulation material 18: Exhaust port 201: Sample 202: Sample container 203: External crucible 204: Oxide fine powder heat insulating layer 205: Ceramic fiber heat insulating layer 206: Ceramic protective tube 207: Radiation waveguide 208: Container 209: Void 31: Peak height 32: Peak half price 33: Peak half price width (FWHM)
51: Sample internal temperature 52: Microwave incident energy 53: Microwave reflected energy 54: Temperature change during volatilization of volatile substances 55: Temperature stagnation due to graphitization reaction

Claims (9)

A graphitization treatment method in which a graphitization catalyst is added to an amorphous carbon material and dispersed, and the amorphous carbon material in which the graphitization catalyst is dispersed is heated by irradiating microwaves.
The graphitizing catalyst is a simple substance of a metal containing at least one element selected from Fe, Ni, and Co.
The average particle size of the graphitizing catalyst is 200 [μm] or less.
The addition ratio of the graphitizing catalyst to the amorphous carbon material is 5% or more and 15% or less in terms of mass ratio.
The amorphous carbon material, thereby graphitized reaction by heating of 1000 ° C. or higher 1620 ° C. or less,
A method for graphitizing an amorphous carbon material, which is characterized by the above. In the graphitization reaction, the amorphous carbon material obtained by dispersing a pre-Symbol graphitization catalyst, metal constituting the graphitization catalyst is characterized by not heated above a temperature at which melting, according to claim 1 A method for graphitizing an amorphous carbon material. The method for graphitizing an amorphous carbon material according to claim 1 or 2, wherein the graphitizing catalyst is metal Fe. After completion of the graphitization reaction, the amorphous carbon material in which the graphitization catalyst is dispersed is heated to a temperature higher than the temperature at which the metal elements constituting the graphitization catalyst are melted, and the metal is melt-aggregated to obtain the amount of the metal. The method for graphitizing an amorphous carbon material according to any one of claims 1 to 3, wherein 95% or more is separated and recovered. A graphitizing catalyst was added to the amorphous carbon material at a ratio of 5% or more and 15% or less in terms of mass ratio, the catalyst was dispersed in the amorphous carbon material, and the catalyst was dispersed in the amorphous carbon. material is irradiated with microwaves to, and heated to above 1000 ° C., and a method of metal constituting the graphitization catalyst is graphitized without heating above the temperature of melting, produced during the recovery of graphite It ’s a product,
The graphitizing catalyst is a simple substance of a metal containing at least one element selected from Fe, Ni, and Co.
The product is a mixture having a structure formed by separating the graphite produced by the graphitization reaction and the metal into different phases.
A product produced when graphite is recovered, characterized in that the metal has a particle size of 1 μm or less. Graphite in which the graphite phase and the metal phase are separated from the graphite phase into separate phases.
In the graphite phase, the maximum peak obtained by structural analysis by XRD is 2θ = 26.5 ± 0.02 °, and the half-value width of the maximum peak is 0.2 ° or less.
The metal phase contains at least one element selected from Fe, Ni, and Co, and has a particle size of 1 μm or less.
Graphite characterized by that. A graphitization treatment method in which a graphitization catalyst is added to an amorphous carbon material and dispersed, and the amorphous carbon material in which the graphitization catalyst is dispersed is heated by irradiating microwaves.
The graphitizing catalyst is a simple substance or compound of a metal containing at least one element selected from Fe, Ni, and Co.
The average particle size of the graphitizing catalyst is 200 [μm] or less.
The addition ratio of the graphitizing catalyst to the amorphous carbon material is 5% or more and 15% or less in terms of mass ratio.
The amorphous carbon material is heated to 1000 ° C. or higher to cause a graphitization reaction.
After completion of the graphitization reaction, the amorphous carbon material in which the graphitization catalyst is dispersed is heated to a temperature higher than the temperature at which the metal elements constituting the graphitization catalyst are melted, and the metal is melt-aggregated to obtain the amount of the metal. A method for graphitizing an amorphous carbon material, which comprises separating and recovering 95% or more. The non-graphite according to claim 7, wherein in the graphitization reaction, the amorphous carbon material in which the graphitization catalyst is dispersed is heated to a temperature lower than the temperature at which the metal constituting the graphitization catalyst melts. A method for graphitizing a crystalline carbon material. The method for graphitizing an amorphous carbon material according to claim 7 or 8, wherein the graphitizing catalyst is metallic Fe or iron oxide.