Patent Application
20090220775
The present invention relates to a macroporous carbon material and a mesoporous carbon material starting from a wood material, to a method for producing them, to a porous metal carbon material and to a method for producing it.
A macroporous material is a generic term for a porous material having a mean pore diameter of at least 50 nm, and taking advantage of its structure and the properties of its surface, the material is utilized in various fields as heat-insulating materials, buffer materials, sound absorbent materials, adsorbent materials and catalyst carriers. Above all, a macroporous material formed of a carbon material has characteristics such as high electric conductivity, lightness in weight, heat resistance, chemical resistance and the like, which any other macroporous materials do not have. Accordingly, the macroporous carbon material has wide-range applications for heat-insulating materials, heat exchangers, filters, ceramic sintering tools, glass shaping tools, various electrodes for fuel cells, special adsorbents, various catalyst carriers, filters for vapor filtration, and others (e.g., see Non-Patent References 1, 2).
However, the macroporous carbon material now in practical use is produced in an expensive and complicated production method of heating and carbonizing, as a starting material, a porous material of polyurethane or the like obtained through purification of petroleum, or a material prepared by infiltrating a thermosetting resin or an easily-graphitizing carbon pitch into a fibrous material of cellulose, carbon fibers or the like and curing it therein. As well known, polyurethane, carbon fibers, thermosetting resin and the like are substances produced from a fossil fuel source such as petroleum, and are therefor problematic in that not only their material costs are greatly influenced by the petroleum cost fluctuation but also their production processes are complicated and expensive and that the load for environmental protection is great in treating exhaust gases, organic solvents and others in the process of production and post-treatment.
On the other hand, there are massive resources for wood materials, including domestic wood materials of typically cedar and, as regenerable biomass resources, raw wood materials and waste wood materials. Accordingly, it may be taken into consideration to produce a macroporous carbon material by the use of such wood resources. However, the macroporous carbon material starting from a wood material produced according to a conventional method is only a macroporous carbon material having the cell structure of the starting wood material, and there is known no example of producing a macroporous carbon material of which the porousness such as the mean pore diameter and the porosity thereof is controlled. The macroporous carbon material from a conventional wood material has anisotropy and pore size unevenness resulting from the starting wood material (Non-Patent Reference 3).
As opposed to this, the present applicant has found that the heating condition change in carbonizing a wood material by the use of a small-size furnace attached to a gas chromatograph changes the cell structure of the starting wood powder (Non-Patent Reference 4). In that situation, the inventors of the present application have investigated in detail the density of the starting wood powder, the heating speed, the pressure in, the heating furnace, the shapability and others, and further investigated techniques for producing a macroporous carbon material having the ability of being shaped into desired forms, while controlling the uniform macroporous structure thereof.
The present invention has been made in the above-mentioned background, and its object is to provide a macroporous carbon material, starting from a wood material that exists in large quantities as a regenerable biomass resource and is required to be used effectively, of which the porousness such as the mean pore diameter and the porosity thereof, the bending strength and the compression strength are controlled not limited by the cell structure of the starting wood material; and to provide a novel method capable of producing it at low cost.
The invention is to solve the above-mentioned problems and is characterized by the following:
First: A method for producing a macroporous carbon material by heating and carbonizing a wood powder in an inert gas atmosphere, wherein the mean particle size of the powder is within a range of from 20 to 125 μm, the particle size distribution thereof is within a range of (mean particle size±50 μm), the heating speed is within a range of from 1 to 150° C./sec.
Second: In the above method, the carbonization heating is attained under pressure over atmospheric pressure.
Third: The wood powder is filled in a mold and heated for carbonization thereby giving a molded carbon material.
Fourth: The wood powder is a cedar powder.
Fifth. The wood powder is heated for carbonization and then further heated at a high temperature in an inert gas atmosphere.
Sixth: The macroporous carbon material produced according to any of the above-mentioned methods is further heated in air to give a mesoporous carbon material.
Seventh: The carbon material produced according to any of the above-mentioned methods is, serving as a cathode, electroplated and then this is heated in air to remove the carbon material thereby to give a metal material having a porous structure.
Eighth: A macroporous carbon material having a mean pore diameter of from 1 to 60 μm, a bulk density of from 0.04 to 0.50 g/cm3, a porosity of from 75 to 99%, and having a three-dimensional network structure or a three-dimensional foam structure.
Ninth: The macroporous carbon material has a compression strength falling within a range of from 0.01 to 40.00 MPa.
Tenth: The macroporous carbon material has a bending strength falling within a range of from 0.01 to 40.00 MPa.
Eleventh: The macroporous carbon material has a volume resistivity falling within a range of from 1.0×10−4 to 1.0×10−1Ω·m.
Eleventh: A mesoporous carbon material having a mean pore diameter of from 2 to 50 nm.
Twelfth: A mesoporous carbon material obtained according to the method of the above-mentioned sixth invention.
Thirteenth: A porous metal material having a mean pore diameter of from 1 to 60 μm.
Fourteenth: A porous metal material obtained according to the method of the above-mentioned seventh invention.
According to the present invention as in the above, a macroporous carbon material, a mesoporous carbon material and a porous metal material of which the pore shape and the pore size are controlled according to the purpose of use thereof can be produced inexpensively in a simplified manner. Further, according to the invention, a macroporous carbon material, a mesoporous carbon material and a porous metal material having a three-dimensional network or foam structure of good isotropy can be produced. The materials having such a three-dimensional network structure are expected to have broad-range applications for various filters and catalyst carriers.
The present invention is characterized by the above, and its embodiments are described below.
<1> A wood material is used as the starting material.
A wood material exists in large quantities as a resource, and in consideration of the amount to be generated from it as construction wastes and others, it is inexpensive as compared with the carbon material resourced from fossil fuel and, in addition, since it does not contain substances harmful to the environment such as nitrogen and sulfur, future technical development of using it as a carbon resource is expected.
The invention is characterized in that a wood material having such excellent characteristics is used as the starting material to produce inexpensively a macroporous carbon material. The type of the wood material is not specifically defined, including broadleaf trees, coniferous trees, their processed materials and others.
Of such various wood species, the cedar resource stockpile in Japan is extremely large and its supply cost is low and, in addition, cedar is characterized in that it does not almost contain nitrogen and sulfur atoms, it has a small density and it may be readily powdered; and therefore, it may be favorably taken into consideration to utilize cedar as a starting material. Using a cedar powder, a macroporous carbon material may be produced more inexpensively. In the invention, as a wood material except cedar, also usable is poplar, a type of broadleaf tree. In addition, a powder of lignin and cellulose, main ingredients of a wood material, may also be used to produce a macroporous carbon material.
<2> A wood material is powdered and used as a starting material, and a uniform and isotropic macroporous carbon material is produced.
In general, in case where a macroporous carbon material is produced starting from a wood material, the macroporous carbon material after heating for carbonization keeps the cell texture structure of the wood material directly as it is. Accordingly, the conventional macroporous carbon material has anisotropy and pore size unevenness derived from the starting material.
As a means for solving the problems of the anisotropy and the pore size unevenness, the starting material is powdered and processed in the carbonization step in the invention. In this stage, the shape and the particle size of the powder are previously unified and dressed by sifting or the like, whereby the pores and the pore sizes of the carbon material to be obtained finally may be controlled.
In the invention, the particle size of the wood powder falls within a range of from 20 to 125 μm in terms of the mean particle size thereof, and the particle size distribution thereof falls within a range of plus/minus 50 μm of the mean particle size. Use of the powder having such uniformity is one significant characteristic of the invention. In case where the mean particle size of the starting powder is less than 20 μm, the combustion gas generated in heating could hardly diffuse out of the starting material powder being heated, and therefore the carbon material to be obtained finally may have cracks or bubbles formed inside it. When more than 125 μm, then the voids between the starting wood powder particles may be great and the structure of the carbon material to be finally obtained may be brittle and may be readily broken, and therefore the shapability of the carbon material may worsen.
<3> The filling bulk density of the starting wood powder is controlled, and the bulk density of the macroporous carbon material to be obtained after carbonization is thereby controlled.
When the filling bulk density of the starting wood powder to be filled in a reactor is smaller, then the bulk density of the carbon material to be obtained may be smaller. For example, when a cedar powder (having a mean particle size of 50 μm) is, at a filling bulk density of 0.25 g/cm3, heated at a heating speed of 50° C./sec and kept at 800° C. for 1 hour in an inert gas atmosphere such as a nitrogen gas under atmospheric pressure, and thereafter naturally cooled, then a macroporous carbon material having a bulk density of 0.12 g/cm3 can be produced. As opposed to this, when the same cedar powder is, at a filling bulk density of 0.50 g/cm3, processed under the same condition, then a macroporous carbon material having a bulk density of 0.22 g/cm3 can be produced. When the same cedar powder is, at a filling bulk density of 0.75 g/cm3, processed under the same condition, then a macroporous carbon material having a bulk density of 0.37 g/cm3 can be produced. As in the above, by increasing the filling bulk density of the starting material to be filled in a reactor, the bulk density of the macroporous carbon material to be obtained can be increased and controlled.
<4> The filling bulk density of the starting wood powder is controlled, and the strength of the macroporous carbon material to be obtained after carbonization is thereby controlled.
When the filling bulk density of the starting wood powder to be filled in a reactor is larger, then the bending strength of the carbon material to be obtained may be larger. For example, when a cedar powder (having a mean particle size of 50 μm) is, at a filling bulk density of 0.25 g/cm3, heated at a heating speed of 50° C./sec and kept at 800° C. for 1 hour in an inert gas atmosphere such as a nitrogen gas under atmospheric pressure, and thereafter naturally cooled, then a macroporous carbon material having a bending strength of 0.49 MPa can be produced. As opposed to this, when the same cedar powder is, at a filling bulk density of 0.50 g/cm3, processed under the same condition, then a macroporous carbon material having a bending strength of 5.78 MPa can be produced. When the same cedar powder is, at a filling bulk density of 0.75 g/cm3, processed under the same condition, then a macroporous carbon material having a bending strength of 15.11 MPa can be produced. As in the above, by increasing the filling bulk density of the starting material to be filled in a reactor, the bulk density of the macroporous carbon material to be obtained can be increased and controlled.
<5> In the carbonization step, the heating speed of the reaction system in heating is controlled, and the porous structure such as the porosity and the pore size after carbonization is controlled.
Heretofore, in case where a macroporous carbon material is produced starting from a wood material, the heating speed in the carbonization step is 0.1° C./sec or so and is low. Accordingly, even though the particle size of the wood powder is thinned, a macroporous carbon material still keeping the shape and the micrometer-size structure that the wood powder has is inevitably produced. As opposed to this, in the invention, the heating speed of the reaction system in heating it is set high to fall within a range of from 1 to 150° C./sec. In the invention, this is referred to as a rapid heating method. More preferably, the heating speed is within a range of from 10 to 100° C./sec. Accordingly, the latitude in controlling the porousness such as the porosity, the pore size and the bulk density of the macroporous carbon material to be obtained after carbonization may be broadened, as compared with those produced in conventional methods, whereby a three-dimensional network structure or a three-dimensional foam structure is formed in the material.
Specifically, the heating speed in the rapid heating method has some influences on the number and the size of crosslinks and further on the formation of the three-dimensional network structure or the three-dimensional foam structure.
The heating is continued up to a predetermined carbonization heating temperature, and in this case, the predetermined carbonization heating temperature may vary depending on the type and the particle size of the wood material and others, but in general, it may fall within a range of from 500 to 1200° C., and it may be taken into consideration to keep a constant temperature within 3 hours.
After the heating at the carbonization temperature, the material may be kept naturally cooled.
For example, for obtaining a best macroporous carbon material by the use of a cedar powder, the following may be employed. Concretely, a cedar powder (having a mean particle size of 50 μm) is filled at a filling bulk density of from 0.25 to 1.25 g/cm3, then heated at a heating speed of from 10 to 100° C./sec and kept at 800° C. for 1 hour, and then naturally cooled, whereby a macroporous carbon material having a mean pore diameter (mean pore diameter according to a mercury intrusion method) of from 1 μm to 60 μm, a bulk density of from 0.04 to 0.50 g/cm3 can be produced.
In this, when the heating speed is lower than 1° C./sec, the texture structure of the starting wood powder may partly remain in the macroporous carbon material produced. In case where the macroporous carbon material thus has the texture structure of the starting wood powder, it could not have a three-dimensional network structure or a three-dimensional foam structure therein, and therefore the macroporous structure thereof is brittle and is readily broken and the shapability thereof is poor. On the other hand, when the heating speed is higher than 150° C./sec, then the yield of the macroporous carbon material to be obtained is greatly lowered and the macroporous carbon material has cracks and voids formed inside it and the shapability thereof is thereby lowered. For obtaining a uniform macroporous carbon material of good shapability, the speed is preferably from 10 to 100° C./sec.
<6> In the carbonization step of the starting material powder, the pressure to the reaction system is controlled to thereby control the porous structure after the carbonization.
Further, a finding has been obtained that, when the pressure to the reaction system in heating for carbonization is larger, then the thickness of the crosslinks to form the porous material increases more; and therefore in the invention, it is effective to pressurize the reaction system over the atmospheric pressure.
For example, a cedar powder (having a particle size of about 30 μm and a particle size distribution of from 25 to 32 μm) is heated at a heating speed of 100° C./sec and kept at 800° C. for 1 hour under a varying pressure to the reaction system of from 100 to 300 kPa, and the macroporous carbon material finally obtained is analyzed, whereupon it is confirmed that, when the pressure to the reaction system is larger, then the thickness of the crosslinks is increased from 2 to 10 μm. The reason may be because, increasing the pressure to the reaction system may be effective for keeping the gas generated through thermal decomposition inside the system, whereby the generated gas may be carbonized and solidified on the surface of the crosslink to thereby increase the thickness of the crosslinks. Accordingly, it has been clarified that, by controlling the pressure to the reaction system in the carbonization step, the amount of the gas generated to remain in the system may be controlled and the thickness of each crosslink constituting the porous material may be thereby controlled, and as a result, the overall structure and the shapability of the porous material can be therefore controlled. In case where the pressure to the reaction system is set over 300 kPa, the uniformity of the crosslinked structure of the macroporous carbon material to be produced may lower and the production cost for pressure application may increase, and therefore, in order to obtain a uniform macroporous carbon material of good shapability according to the method of the invention, the pressure to the reaction system is preferably from 100 to 300 kPa.
For the pressurization, it may be favorably taken into consideration to introduce an inert gas, for example, a nitrogen gas or a rare gas.
<7> By controlling the exhaust resistance of the combustion gas generated inside the reactor, the structure of the macroporous carbon material to be obtained after carbonization is controlled.
By controlling the exhaust resistance of the reactor to be filled with a wood powder, the structure of the macroporous carbon material to be finally obtained after carbonization may be controlled. When the exhaust resistance is increased to increase the sealing level inside the reactor, then, as a result, it may be possible to thicken the crosslinks of the three-dimensional network structure. When the heating speed is set high under an increased sealing level, it may be possible to produce even a macroporous carbon material having a foam structure but not a three-dimensional network structure.
<8> By changing the shape of the mold to be filled with a starting material, the shape of the macroporous carbon material to be obtained after carbonization is controlled to be the shape of the mold.
By changing the shape of the mold to be filled with a starting wood material, the shape of the macroporous carbon material of the invention obtained after carbonization may be controlled to have the form of the mold.
<9> Regarding the macroporous carbon material:
In the invention, a macroporous carbon material having a mean pore diameter of from 1 to 60 μm, a bulk density of from 0.04 to 0.50 g/cm3 and a porosity of from 75 to 99% is obtained according to the above-mentioned method. This has a uniform macroporous structure and has a three-dimensional network structure or a three-dimensional foam structure formed therein, and therefore, having a high porosity, this has a high bending strength and a high compression strength. For example, a commercial macroporous carbon material (Tokai Carbon's trade name Porous Carbon PC5060G) has a porosity of 58% and has a bending strength and a compression strength of from 2.5 to 13.0 MPa. As compared with the commercial macroporous carbon material, the macroporous carbon material of the invention has, at the maximum, a porosity of at least about 1.5 times and a bending strength and a compression strength of at least about 3 times.
Further, the macroporous carbon material of the invention has a low electric conductivity and is excellent in point of electroconductivity. For example, its volume resistivity is within a range of from 1.0×10−4 to 1.0×10−1. Preferably, it may be from 1.0×10−4 to 1.0×10−3. For reducing the volume resistivity, for example, in producing a macroporous carbon material in the above-mentioned rapid heating method, the starting material is carbonized and then reheated to attain the intended object. Concretely, as in Example 10 given hereinunder, a wood powder is carbonized by heating it up to 800° C. at a heating speed of 20° C./sec in an inert gas atmosphere of nitrogen gas or the like, and then, not cooled, this is further heated up to a higher temperature of 1600° C. at a heating speed of 20° C./sec. Accordingly, the crystal structure of the macroporous carbon material can be grown further while the three-dimensional network structure thereof is kept as such, and therefore the electroconductivity of the material can be thereby enhanced.
As in the above, the macroporous carbon material of the invention has a macroporous structure and has a three-dimensional network structure or a three-dimensional foam structure formed therein to have a predetermined bending strength and compression strength, and has shapability. The wording “has shapability” as referred to herein means that, as a three-dimensional network structure material or a three-dimensional foam structure material having a macroporous structure and having a predetermined bending strength and compression strength, the macroporous carbon material of the invention may be shaped into blocks of, for example, columnar, tabular or coin-like forms, not using a binder such as resin.
The macroporous carbon material of the invention is expected to have wide-range applications for heat-insulating materials, heat exchangers, filters, ceramic sintering tools, glass shaping tools, various electrodes for fuel cells, special adsorbents, various catalyst carriers, filters for vapor filtration, and others.
<10> Regarding mesoporous carbon material:
In the invention, the macroporous carbon material produced according to the above-mentioned method may be further heated (treated for activation) in air thereby forming, still keeping the macroporous three-dimensional network structure as such, mesopores having a mean pore diameter of from 2 to 50 nm in the surface of the crosslinks constituting the three-dimensional network structure. As a result, the macroporous carbon material of the invention may be a porous carbon material having mesopores falling within the above-mentioned range, in addition to the macropores having a mean pore diameter of from 1 to 60 μm. The porous carbon material thus treated for activation may have a BET specific surface area reaching from 500 to 1200 m2/g, as measured according to a nitrogen gas adsorption method. Accordingly, not only mesopores are additionally formed by the activation treatment but also the BET specific surface area of the material can be increased to from about 1.5 to 4.0 times that of the material before the activation treatment.
<11> Regarding porous metal material:
The invention makes it possible to produce a porous metal material by the use of the above-mentioned macroporous carbon material. For example, the surface of a macroporous carbon material having a mean pore diameter of from 15 to 45 μm is coated with a metal, and then this is heated in air to remove the macroporous carbon material. Accordingly, a macroporous metal material having a mean pore diameter of from 10 to 35 μm can be produced. In consideration of the complicated three-dimensional network structure that the macroporous carbon material has, the metal coating on the surface of the material is, for example, preferably electroplating treatment in which the macroporous carbon material serves as a cathode and a metal material to be applied for plating serves as an anode. The metal material includes, for example, nickel, platinum, palladium, gold, silver, copper, zinc, cadmium, tin, chromium, etc.
As in the above, the invention may readily produce a porous metal material, using the carbon material as a mold.
Examples are shown below for describing the invention in more detail. Needless-to-say, the Invention should not be limited by the following Examples.
From a cedar powder, particles having a particle size of about 30 μm (having a particle size distribution of from 25 to 32 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. After drying, 5 mg of the cedar powder was filled into a stainless cylindrical mold container having a diameter of 5 mm and a height of 7 mm. Next, the container was set in a thermal decomposition unit (PY-2020D, by Frontia Lab.), then the temperature of the furnace for the thermal decomposition unit kept under a pressure of 300 kPa with helium gas kept introduced thereinto was stabilized at 800° C., and the mold container filled with the sample was dropped down and inserted into the furnace of the thermal decomposition unit, and kept heated for 1 hour. Next, the heating was stopped and this was naturally cooled to room temperature. It was previously confirmed that, when the temperature in the thermal decomposition unit is set at 800° C., then the heating speed is 100° C./sec.
The obtained sample was observed for the porous structure thereof, using a scanning electronic microscope (see
Next, the atmospheric pressure in carbonization was set at 100 kPa, and a sample was carbonized according to the same process as above.
The obtained sample was observed for the porous structure thereof, using a scanning electronic microscope (see
Comparing the Examples in which the pressure to the reaction system was varied, it became obvious that in the case where the pressure was high, 300 kPa (
The results in Example 1 show that, according to the rapid heating method, a macroporous carbon material having a three-dimensional network structure was produced. However, the starting material jetted out from the exhaust vent of the sample container, and the shapability was poor. In this Example, tried was producing a macroporous carbon material excellent in shapability and having a three-dimensional network structure by rapid heating in a semi-closed system.
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. After drying, 1 g of the cedar powder was filled into a graphite-made cylindrical mold (φ20: inner diameter 1 cm, outer diameter 2 cm, depth 5 cm) and a rectangular mold (thickness 1.1 cm, width 5.0 cm, height 2.5 cm, wall thickness of mold 0.2 cm) at a filling bulk density of 0.25 g/cm3, as in
The photographic picture of the obtained samples are shown in
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. Next, as in
The photographic picture of the obtained sample having a diameter of 2.4 cm and a thickness of 0.7 mm is shown in
(Case where the Heating Speed is 100° C./Sec)
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. After drying, 1 g of the cedar powder was filled into a graphite-made cylindrical mold (φ20) at a filling bulk density of 0.25 g/cm3, as in
After being collected, the sample was observed with a scanning electronic microscope, and the pore size distribution was determined according to a mercury intrusion method, and the bulk density and the true density were determined. The scanning electromicroscopic photograph is shown in
Porosity(%)=[1−(bulk density)/(true density)]
As a result, the porosity of the sample was 97.1%.
(Case where the Heating Speed is 10° C./Sec)
A sample was produced according to the same process as in Example 4, for which, however, the heating speed in carbonization was set at 10° C./sec. The carbonized sample was observed with a scanning electronic microscope, and the pore size distribution was determined according to a mercury intrusion method, and the bulk density and the true density were determined. The electromicroscopic photograph of the sample is shown in
(Case where the Heating Speed is 1° C./Sec)
A sample was produced according to the same process as in Example 4, for which, however, the heating speed in carbonization was set at 1° C./sec. The carbonized sample was observed with a scanning electronic microscope, and the pore size distribution was determined according to a mercury intrusion method, and the bulk density and the true density were determined. The electromicroscopic photograph of the sample is shown in
(Case where the Heating Speed is 0.1° C./Sec)
A comparative sample was produced according to the same process as in Example 4, for which, however, the heating speed in carbonization was set at 0.1° C./sec. The carbonized sample was observed with a scanning electronic microscope, and the pore size distribution was determined according to a mercury intrusion method, and the bulk density and the true density were determined. The electromicroscopic photograph of the sample is shown in
The experimental results with the heating speed in carbonization as the parameter clarified the following:
(1) The microscopic pictures of the samples confirmed that the microstructure of each sample differs depending on the heating speed in carbonization. In addition, it was confirmed that, when the heating speed in carbonization is lower, the microstructure of the sample after carbonization is more similar to that of the starting cedar powder.
(2) The found data of the bulk density, the porosity and the mean pore diameter of the samples are shown in
The above results confirm that, by controlling the heating speed in carbonization, the macroporous carbon material may be made to have a three-dimensional network structure or a three-dimensional foam structure. Further, it is also confirmed that the mean pore diameter, the bulk density and the porosity of the material can also be controlled.
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. Next, the dried cedar powder was filled into the graphite-made cylindrical mold (φ44) with spacer, shown in
After being collected, the bulk density of the sample was measured according to a mercury intrusion method. As a result, it has become obvious that, when the filling bulk density of the starting cedar powder is larger, then the bulk density of the obtained macroporous carbon material is larger. For example, when a cedar powder was processed at a filling bulk density of 0.25 g/cm3, then a macroporous carbon material having a bulk density of 0.12 g/cm3 was produced. Similarly, at a filling bulk density of 0.50 g/cm3, a macroporous carbon material having a bulk density of 0.22 g/cm3 was produced. Further, at an increased filling bulk density of 0.75 g/cm3, a macroporous carbon material having a bulk density of 0.37 g/cm3 was produced. Accordingly, by increasing the filling bulk density of the starting material, the bulk density of the macroporous carbon material to be obtained finally can be increased.
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. Next, the dried cedar powder was filled into the graphite-made cylindrical mold (φ44) with spacer, shown in
Test pieces having a length of 25 mm and a width of 4 mm were cut out of the thus-collected, coin-like shaped sample. The thickness of each test piece was measured. Using a universal strength tester (Instron), each test piece was tested for the bending strength according to a three-point bending test under the condition of a span of 20 mm and a loading rate of 0.5 mm/min. As a result, it was clarified that, when the filling bulk density in filling the starting cedar powder into the mold is higher, then the bending strength of the carbon material obtained finally is higher. For example, in the case where the cedar powder was filled at a filling bulk density of 0.25 g/cm3, the macroporous carbon material produced had a bending strength of 0.49 MPa. In the case where the same cedar powder was filled at a filling bulk density of 0.50 g/cm3, the macroporous carbon material produced had a bending strength of 5.78 MPa. Further, in the case where the cedar powder was filled at a filling bulk density of 0.75 g/cm3, the macroporous carbon material produced had a bending strength of 15.11 MPa. Accordingly, by increasing the filling bulk density of the starting material, the bending strength of the macroporous carbon material to be obtained finally was increased.
A poplar was selected as a typical wood species of a broadleaf tree. From a poplar powder, particles having a particle size of 50 μm were sifted. The selected poplar powder was dried at 105° C. for 12 hours under atmospheric pressure. After drying, 1 g of the poplar powder was filled into a graphite-made cylindrical mold (φ20: inner diameter 1 cm, outer diameter 2 cm, depth 5 cm) at a filling bulk density of 0.25 g/cm3, as in
A scanning electromicroscopic photograph of the thus-collected, columnar shaped sample is shown in
A waste wood material was powdered and dipped in diluted sulfuric acid having a concentration of 0.5 mol/L, whereby the preservative components, copper, arsenic and chromium were completely removed to give a western hemlock powder, and this was used as a starting material. Western hemlock is a type of preservative-processed wood for construction materials, and there are large quantities of its wastes all over the world. The preservative-removed, western hemlock powder was dried at 105° C. for 12 hours under atmospheric pressure. After drying, 1 g of the western hemlock powder was filled into a graphite-made cylindrical mold (φ20) at a filling bulk density of 0.25 g/cm3, as in
A scanning electromicroscopic photograph of the thus-collected, columnar shaped sample is shown in
A lignin powder (Tokyo Chemical Industry's alkali-removed lignin) and a cellulose powder (Asahi Kasei's Avicel PH101) each were dried at 105° C. for 12 hours under atmospheric pressure. After drying, the lignin and the cellulose were mixed in a ratio of 1/1, near to the weight ratio of lignin/cellulose in main wood, and this was used as a starting material. After drying, 2 g of the starting material was filled into a graphite-made cylindrical mold (φ20) at a filling bulk density of 0.51 g/cm3, as in
A scanning electromicroscopic photograph of the thus-collected, columnar shaped sample is shown in
(Case where the Heating Speed is 100° C./Sec)
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. After drying, 1 g of the cedar powder was filled into a graphite-made cylindrical mold (φ20) at a filling bulk density of 0.25 g/cm3, as in
Using a universal strength tester, the thus-collected, columnar shaped sample was tested for the compression strength. The compression strength of the sample was 0.490 MPa.
(Case where the Heating Speed is 10° C./Sec)
A carbonized sample was produced according to the same process as in the above where the heating speed was 100° C./sec, for which, however, the heating speed in carbonization was set at 10° C./sec. Using a universal strength tester, the collected columnar shaped sample was tested for the compression strength. The compression strength of the sample was 0.308 MPa.
(Case where the Heating Speed is 1° C./Sec)
A carbonized sample was produced according to the same process as in the above where the heating speed was 100° C./sec, for which, however, the heating speed in carbonization was set at 1° C./sec. Using a universal strength tester, the collected columnar shaped sample was tested for the compression strength. The compression strength of the sample was 0.052 MPa.
(Case where the Heating Speed is 0.1° C./Sec)
A comparative sample was produced according to the same process as in the above where the heating speed was 100° C./sec, for which, however, the heating speed in carbonization was set at 0.1° C./sec. Using a universal strength tester, the collected columnar shaped sample was tested for the compression strength. However, under compression, the sample was thickened and its accurate compression strength could not be measured.
The above-mentioned experimental results based on the heating speed in carbonization as a parameter confirm that the samples carbonized at a higher heating speed could have a higher compression strength.
In this Example, a macroporous carbon material produced according to a rapid heating method is again heated at a high temperature in a nitrogen gas atmosphere to thereby increase the electroconductivity of the material. Concretely, by the reheating, a graphite phase having a high electric conductivity is grown in the crystal of the macroporous carbon material, thereby reducing the electric resistance of the material and increasing the electroconductivity thereof. From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. After drying, 1 g of the cedar powder was filled into a graphite-made cylindrical mold (φ20) at a filling bulk density of 0.25 g/cm3, as in
In this Reference Example, a starting material was carbonized according to the same process as in Example 10. In this, however, the sample was not reheated, and the electrification was stopped. After being naturally cooled to room temperature, the carbonized sample was collected.
The microstructure of the thus-collected sample was observed with a scanning electronic microscope, and the crystal structure thereof was analyzed according to a powder X-ray diffractiometric method. Further, according to a 4-probe resistivity measuring method, the volume resistivity of the sample heated up to 800° C. was measured.
The scanning electromicroscopic photograph of the sample is shown in
The above experimental results clarified the following:
1) From the result of microstructure observation, it was confirmed that the reheated sample has the same three-dimensional network structure as that of the non-reheated sample, or that is, the reheated sample kept the three-dimensional network structure therefore before reheating.
2) From the crystal structure analysis according to the powdery X-ray diffractiometric method, it is known that the reheated sample had a peak nearer to the graphite (002) peak (spacing d002=0.3544 nm) (see
3) From the result of the volume resistivity measurement, it is known that the volume resistivity of the reheated sample was lowered to about ⅕ of that of the non-reheated sample; and this indicates that the reheating treatment may enhance the electroconductivity of the treated sample.
These verify that, when the macroporous carbon material produced according to a rapid heating method is reheated at a high temperature, then the crystal structure of the material may be grown further while the three-dimensional network structure thereof is kept as such, and the electroconductivity of the material may be thereby enhanced.
In this Example, the macroporous carbon material produced according to a rapid heating method is reheated in air to thereby increase the specific surface area thereof. Also described is a method of forming mesopores (pores having a mean pore diameter of from 2 to 50 nm and characteristic of a mesoporous material), which do not almost exist in ordinary charcoal, in the macroporous carbon material. Concretely, the macroporous carbon material was reheated in air to thereby increase the specific surface area thereof and to form mesopores therein.
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. Next, the dried cedar powder was filled into the graphite-made cylindrical mold (φ44) with spacer shown in
The reheated sample was observed with a scanning electronic microscope, and the pore diameter distribution and the specific surface area thereof were determined according to a mercury intrusion method and a nitrogen gas adsorption method. The scanning electromicroscopic photograph is shown in
The results show that mesopores having a pore diameter of from 25 to 50 nm, which did not exist before the reheating treatment, remarkably increased as a result of the reheating in this Example. On the other hand, the non-reheated sample had few mesopores. Accordingly, it is known that mesopores were newly formed by the reheating treatment.
The BET relative surface area of the reheated sample was 677.74 m2/g. On the other hand, the BET relative surface area of the non-reheated sample was 372.10 m2/g. Taking this into consideration, it is known that the relative surface area of the sample increased by 1.82 times as a result of the reheating treatment.
Many metals such as typically nickel are applicable to electroplating. Accordingly, in the fields of batteries, filters, heat-insulating materials and others, production of porous metals by electroplating by the use of a porous material serving as a mold is carried out flourishingly.
In this Example, porous nickel was produced, using the macroporous carbon material produced according to a rapid heating method, as a mold. Concretely, the macroporous carbon material produced according to a rapid heating method is plated with nickel, and after the plating, the macroporous carbon material serving as a mold is burnt away and removed thereby producing porous nickel.
From a cedar powder, particles having a particle size of about 50 μm (having a particle size distribution of from 32 to 63 μm) were sifted. The selected cedar powder was dried at 105° C. for 12 hours under atmospheric pressure. Next, the dried cedar powder was filled into the graphite-made cylindrical mold (φ44) with spacer shown in
The surface and the cross section of the sample thus heated in air were observed with a scanning electronic microscope. The scanning electromicroscopic photograph of the surface is shown in
As a result, it is known that, by heating in air at 450° C. for 1 hour, the mold carbon was almost entirely removed and the ingredient of nickel alone was obtained. It is also known that NiO was formed by heating. From the analytical data of the pore size distribution according to a mercury intrusion method, the mean pore diameter of the sample was 33.99 μm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-128605 | May 2006 | JP | national |
| 2007-039613 | Feb 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/059395 | 5/2/2007 | WO | 00 | 2/11/2009 |
