JPH11131072A - Compound carbide sintered by electrosintering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound sintered carbide having high electrically conductive rating, by simultaneously both sintering at a higher temperature and molding into a product of a preferred shape in a short time calcined carbide powder from biomass as starting raw materials along with metal powder or metal oxide powder. SOLUTION: This compound sintered carbide is obtained by blending carbide powder obtained through calcining such biomass as woods (e.g. a Japanese cedar), coffee bean leavings and beer cake at about 700 deg.C with powder of metal (e.g. Fe) or metal oxide (e.g. Fe2 O3 ), by filling the resultant powder mixture as a raw material (preferably as an only raw material) into a mold and by both sintering and molding simultaneously it according to an electrosintering method where turning on the electricity among powdered grains under an application of pressure is conducted. Consequently, the compound sintered carbide having extraordinarily low volume resistivity and high electrical conductivity is obtained and enables utilization and mass-production of it as a graphite electrode material having a high-quality graphitized structure, an electrically conductive material or an electromagnetic shielding material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a carbon material having excellent electrical conductivity which is sintered by a current sintering method using a mixture of biomass, which is a biological organic resource, and a metal or metal oxide as a starting material. Composite sintered coal.

[0002]

2. Description of the Related Art It is generally known to obtain wood charcoal, a calcined carbide, by subjecting a woody raw material, which is a type of biomass, to heat treatment. In recent years, attempts have been made to further improve the quality of this charcoal and to effectively use it as a carbon material. As one of the attempts, it has been considered that the carbon material is used as a raw material to be formed into a molded article having a predetermined shape and used for applications such as a conductive material or an electromagnetic shielding material. Here, in order to obtain a high-quality carbon material from a woody raw material, first, 300 ° C to 800 ° C.
To produce charcoal. Then, the charcoal is calcined in a high temperature range of 800 ° C. to 3000 ° C. to produce a high-grade carbon material. Two-stage firing is conceivable. Then, it is conceivable to obtain the above-mentioned molded body by mixing the obtained carbon material powder with a binder and pressing the mixture into a predetermined shape while heating.
In order to burn the charcoal in the above-mentioned high temperature range, it is general to use an external heating type electric furnace.

[0003] Conventionally, as a method for obtaining a carbon material, for example, when obtaining a carbon fiber, polyacrylonitrile (PAN), pitch, or benzene, methane or the like is used as a starting material, and these starting materials are treated at a high temperature. It is known that they are manufactured by performing It is also known that when a carbon material for an electrode material is obtained, coke is made into fine powder, a hitch binder is added to the fine powder, and the powder is pressed at a high temperature.

[0004]

However, in the production of the above-mentioned molded article, the above-mentioned electric furnace requires several hours to elevate the temperature in the furnace. It is necessary to wait for cooling before removing the carbon material,
It takes a considerable amount of time and effort to form a compact from a carbon material. Furthermore, even in the molding of the above-mentioned molded body, it is necessary to use a binder because the carbon material powder cannot be molded by itself, and furthermore,
Pressing or heating is required for the molding. As described above, a great deal of labor and time are required, and there is a disadvantage that the efficiency of the production becomes extremely low and the mass productivity is lacking. In addition, the volume resistivity of the compact obtained even after firing at a firing temperature of 1000 ° C. or more is as high as about 10 ⁻¹ Ω · cm (Journal of the Society of Materials, 43, 485, 156, 1993). There is a demand for higher conductivity as a material used as a conductive material or an electromagnetic shielding material.

On the other hand, an electric current sintering method is known as a method for producing a sintered body from a powder raw material (JP-B-56-49).
In this case, it is considered that a sintering aid is required as a binder.

The present invention has been made in view of such circumstances, and an object of the present invention is to easily perform sintering by simultaneously performing high-temperature firing and forming into a predetermined shape in a short time. An object of the present invention is to obtain a composite sintered coal as a carbon material having high conductivity and a high density by using a substance containing biomass as a starting material while obtaining a body.

[0007]

In order to achieve the above object, the invention according to claims 1 to 5 is directed to a method in which a metal powder or a metal oxide is added to a carbonized powder obtained by firing a material containing biomass. The mixed powder obtained by mixing the powders of the products is used as a raw material, and the raw material is filled in a mold and pressurized while applying electricity between the powder particles to sinter to obtain a composite sintered carbon.

[0008] Here, the above-mentioned biomass is a biological organic resource and is a substance containing plant residues such as wood, bamboo, grass, and coffee bean shells, and paper or cellulose such as pulp. . Further, such a substance containing biomass is, for example, a composite material of the above-mentioned paper, virgin pulp or waste paper, and a phenol-based resin, an olefin-based resin, a starch-based biodegradable resin, or the like. From the viewpoint of effective utilization of resources,
For example, thinned wood, sawdust, unused wood, waste wood such as house demolition material, cut grass, coconut shell, palm tree, or beer lees, juice scum, shochu lees, coffee grounds, okara,
It is preferable to use waste materials such as plant residues such as fir hulls, millet husks, and bran. Further, as a calcined carbide obtained by calcining a substance containing biomass, a temperature of approximately 300 ° C. to approximately 80 ° C.
It is preferable that the powder is fired in a temperature range up to 0 ° C., and the metal powder or the metal oxide powder is Cu, A
1, Ag, Ti, Ni, Li, Si, Fe, Pt, V,
Cr, Mn, Co, Zr, Mo, Pd, K, Sn, Au
It is preferable to use a powder of one or more metals selected from the above, or a powder of each metal oxide of one or more metals. Furthermore, it is preferable to use only the above-mentioned mixed powder without using a binder to fill the mold by the electric current sintering method. In addition, it is preferable that the above-mentioned composite sintered charcoal has been subjected to electric sintering under reduced pressure.

In the case of the above structure, the calcined carbide obtained by calcining a substance containing biomass is an amorphous carbon material having a disordered crystal arrangement and a non-graphitizable carbon material. The composite sintered charcoal sintered by the electric current sintering is densified and has a high-quality graphitized structure.
In addition, since the composite sintered charcoal is formed by sintering a mixed powder obtained by mixing a metal powder or a metal oxide powder with the above-mentioned calcined carbide powder, only the calcined carbide powder alone is used. Thus, it exhibits significantly higher conductivity than sintered coal formed by sintering as a raw material. Therefore, this composite sintered charcoal can be used as a conductive material, an electromagnetic shielding material, an electric discharge machining electrode, a negative electrode such as a lithium battery or a cadmium battery, an electrode such as a positive / negative electrode for temperature difference or concentration difference power generation, a member for sputtering, a susceptor, It can be used for applications such as members for semiconductor processing such as crucibles and boards.

[0010] In the above electric current sintering, a mixed powder of charcoal powder, which is a calcined carbide, and a powder of metal or metal oxide is directly applied with a pulse voltage while being pressed in a mold, so that powder particles are interposed between the powder particles. A micro-discharge occurs, which generates a plasma on the surface of the powder particles to clean and activate the surface. At the same time, Joule heat is generated between the powder particles, and the powder particles are thermally bonded to form a composite, thereby producing a composite sintered body in a state of being formed into a predetermined shape corresponding to the mold. That is, the raw material of the mixed powder is heated from the inside by the energization, and the contact between the heated powder particles is promoted by pressure and joined to each other, that is,
Sintering is performed to graphitize (crystallize). For this reason, sintering and molding are performed simultaneously and special equipment for molding is not required as compared with the case where firing is performed in a high temperature range using a conventional electric furnace, and the furnace is placed in an electric furnace. And the time and effort to get out of the electric furnace is eliminated. In addition, compared to the case where the temperature is raised in an electric furnace, firing and sintering can be completed in a much shorter time (several minutes), and the above-described graphitization occurs at a lower temperature. This makes it possible to easily obtain a composite sintered body used for applications such as a conductive material from a substance containing biomass. Further, by filling only the mixed powder into a composite sintered body without mixing the binder with the mold, a sintering aid such as a binder is not required, and troublesome uniformity with the binder is eliminated. Work such as mixing is not required, and a composite sintered body can be more easily obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 shows an apparatus for producing a composite sintered body of the present invention by an electric current sintering method.
Reference numerals 2 and 2 denote an electrode / pressing punch, and reference numeral 3 denotes a mixed powder of raw materials.

The mold 1 has a columnar hole 1a which is opened up and down inside. An electrode / pressing punch 2, 2 having an outer diameter substantially the same as the inner diameter of the hole 1a is formed vertically from each side. It is adapted to be fitted inside so as to be relatively movable. And
In a state where the mixed powder 3 is filled between the two-electrode / pressing punches 2 and 2 in the mold 1, the two-electrode / pressing punches 2 and 2 are pressed in the direction of the arrow in FIG. Pressing punches 2 and 2 for both electrodes
An electric current is supplied between them to form a mixed powder 3 between the two 2 and 2 and to be sintered.

The mixed powder 3 is obtained by mixing a powder of a calcined carbide obtained by calcining biomass with a metal powder or a metal oxide powder. The powder of the above-mentioned calcined carbide is obtained by calcining charcoal (charcoal) obtained by performing a heat treatment at a low temperature range of about 300 ° C. to about 800 ° C. in a carbonizing furnace (not shown) using cut wood or thinned wood as biomass as a raw material. The powder is adjusted to have a predetermined diameter. The metal powder or metal oxide powder may be Cu, Al,
Ag, Ti, Ni, Li, Si, Fe, Pt, V, C
powder of one or more metals selected from r, Mn, Co, Zr, Mo, Pd, K, Sn, and Au;
Alternatively, a metal oxide powder of one or more of the above metals is used. The mixing ratio of the calcined carbide powder and the metal powder or metal oxide powder is 100 parts by weight of the calcined carbide powder to 1 metal powder or metal oxide powder.
It is preferably set to 50. Of course, the weight ratio of the metal powder or the metal oxide powder may be 50 or more, but a mixed ratio of about 50 by weight can provide a composite sintered body having sufficiently high conductivity. On the other hand, from the viewpoint of saving and reducing the metal powder or the metal oxide powder, it is preferable to reduce the mixing ratio, and the weight ratio is 1 to 1.
It is preferable to set the value in the range of 25, 25 to 50, specifically 1 to 10, 11 to 25.

The mixed powder 3 is filled between the punches 2 and 2 for both electrodes in the mold 1 and the filled powder 3 is sandwiched between the punches 2 and 2 for both electrodes. A predetermined current is applied for several minutes while applying pressure.
By this energization, first, micro-discharge is caused between the particles of the mixed powder 3 to generate plasma on the surface of the particles, whereby the surface of the particles is cleaned and activated. Continuing with this, Joule heat is generated between the particles of the mixed powder 3 by the above-mentioned energization, and the particles are thermally bonded while firing the particles. As a result, a composite sintered body formed into a predetermined cylindrical shape by the inner peripheral surface of the mold 1 and the tip surfaces of both electrodes and the press punches 2 and 2 is obtained.

It is preferable that the above-mentioned filling into the mold 1 is performed using only the above-mentioned mixed powder 3, but the sintering aid containing 50% or more of fixed carbon is added to the mixed powder 3.
You may make it mix in the range of about weight% or less. Further, another inorganic powder, ceramic powder, or the like may be mixed with the mixed powder 3 to obtain a composite sintered body including charcoal powder, metal powder, metal oxide powder, inorganic powder, ceramic powder, and the like. . In addition, the obtained sintered body whose concentration distribution changes in the thickness direction (functionally graded material)
In order to achieve this, the mixing ratio of the charcoal powder and the other metal powder or the like may be changed in the thickness direction to fill the mold 1 and then be subjected to current sintering while pressing. Further, a mold 1 for carrying out the above-mentioned electric current sintering method, a double electrode / pressing punch 2, 2
May be performed at a predetermined negative pressure or a vacuum state in the space in which is installed. Further, it may be carried out in an inert gas such as Ar, N2, He or in air.

<Second Embodiment> FIG. 2 shows an apparatus for producing a composite sintered carbon according to the present invention by an electric current sintering method.
1 is a frame, 12 is a graphite die as a mold, 13
a and 13b are upper and lower punches fitted into the die 12, 14a and 14b are upper and lower electrodes sandwiching the upper and lower punches 13a and 13b, and 15 is upper and lower electrodes 14a and 14b.
, A hydraulic cylinder 16 for pressing the upper electrode 14b, 17 a die 12 and upper and lower punches 13
a, 13b and upper and lower electrodes 14a, 14b are disposed inside; a vacuum pump 18 for evacuating the vacuum chamber 17; and 19, both punches 13a, 13
This is a radiation thermometer that measures the temperature inside the die 12 sandwiched between the b.

As shown in detail in FIG. 3, the die 12 is formed with a cylindrical hole 12a which is open in the vertical direction, and each punch 1 having an outer diameter substantially equal to the inner diameter of the hole 12a.
3a and 13b are internally fitted so as to be relatively movable in the vertical direction from the upper and lower sides. And the vacuum pump 18
The vacuum chamber 17 is evacuated to a predetermined vacuum state by operating the hydraulic cylinder 16 and the upper punch 13a is pressed via the upper electrode 14a to thereby sinter the powder 20 between the upper and lower punches 13a and 13b (see FIG. 4), and a power supply 15 is applied to the upper and lower electrodes 14a and 14b.
And then sintering. The sintering temperature at this time is set to a predetermined temperature while being measured by the radiation thermometer 19.

Next, a process for obtaining sintered coal using the above-described biomass-containing substance as a starting material will be described with reference to FIG. Basically, the same woody material as in the case of the first embodiment is applied at a temperature of about 300 ° C. to 800 ° C. in a carbonization furnace (not shown).
A low-temperature baking to obtain a calcined carbide (charcoal) by heat treatment and carbonization in a low temperature range of ℃, and the same metal powder or metal oxide as in the first embodiment into a powder obtained by pulverizing the charcoal to a predetermined diameter. Raw material preparation to obtain a mixed powder by mixing a predetermined amount of the material powder in the same manner as in the first embodiment, and sintering in a high temperature range of 800 ° C. to 3000 ° C. by electric current sintering (discharge sintering) to form a composite sintered carbon And firing at a high temperature. In the low-temperature firing, smoke generated by the heat treatment in the carbonization furnace is burned by an afterburner to make it pollution-free, and then exhausted. In the high-temperature firing, the charcoal is pulverized into powder having a predetermined diameter, and the charcoal powder and the metal powder or metal oxide powder are respectively weighed and uniformly mixed, and a predetermined amount of the mixed powder is diced. 12 upper and lower punches 13a, 13b
The mold is packed in the gap, and then, under a predetermined vacuum state in the vacuum chamber 17, the above-mentioned hydraulic cylinder 16 applies a predetermined high pressure to discharge sintering, and the resultant is cooled to obtain a composite sintered carbon.

[0020]

The present invention will be described below in more detail with reference to examples.

<Example 1> A cedar material is heat-treated at a temperature of approximately 700 ° C to produce a calcined carbide, which is made into a powder of 20 to 40 mesh to obtain a charcoal powder. On the other hand, Fe was similarly converted into powder of 20 to 40 mesh as metal powder,
Prepare powder. Then, 0.10619 g of Fe powder was uniformly mixed with 0.3053 g of charcoal powder, and the charcoal /
A mixed powder of Fe is prepared. Only the raw material of the mixed powder is filled in the mold 1 and 1 to 0.1 Torr for protection of the mold 1.
In a vacuum atmosphere of 500 kg / cm 2, a current value of 750 A and a voltage of 3.3 V for 5 minutes to produce a charcoal / Fe composite sintered body (see sample No. 1 in Table 1). ). And the bulk density (g / c) of the obtained composite sintered body
m3) and the volume resistivity (Ω · cm) were measured.

The first embodiment and the following embodiments 2 to 4
Then, a graphite sheet is interposed between the mixed powder and the electrode / pressing punches 2 to prevent carbon from adhering to the punches 2.

<Embodiment 2> The charcoal powder of the above-described embodiment 1 was used.
To 3081 g, 0.1670 g of Al powder of 20 to 40 mesh as a metal powder is uniformly mixed, and the charcoal / Al
A mixed powder of is prepared. Using only the raw material of this mixed powder in mold 1
In a vacuum atmosphere of 1 to 0.1 Torr, a pressure of 500 kg / cm @ 2, a current of 500 A, and a voltage of 3.
By sintering at 1 V for 5 minutes, a charcoal / Al composite sintered body was prepared (see Sample No. 2 in Table 1). Then, the bulk density (g / cm 3) and the volume specific resistivity (Ω · cm) of the obtained composite sintered body were measured.

<Embodiment 3> The charcoal powder of the above-mentioned embodiment 1 was used.
To 3032 g, 0.1618 g of a 20-40 mesh Fe2 O3 powder as a metal oxide powder is uniformly mixed to prepare a mixed powder of charcoal / Fe2 O3. Only the raw material of this mixed powder was filled in a mold 1 and sintered in a vacuum atmosphere of 1 to 0.1 Torr at a pressure of 500 kg / cm @ 2, a current value of 900 A and a voltage of 4.0 V for 5 minutes. /
A composite sintered body of Fe2 O3 was prepared (Sample No. 1 in Table 1).
3). And the bulk density (g
/ Cm3) and volume resistivity (Ω · cm).

<Embodiment 4> The charcoal powder of the above-mentioned embodiment 1 was used.
To 3000 g, 0.1500 g of 20 to 40 mesh Cu powder is uniformly mixed as a metal powder, and charcoal / Cu
A mixed powder of is prepared. Using only the raw material of this mixed powder in mold 1
And in a vacuum atmosphere of 1 to 0.1 Torr, a pressure of 500 kg / cm @ 2, a current value of 550 A, and a voltage of 2.
By sintering at 7V for 5 minutes, a charcoal / Cu composite sintered body was prepared (see Sample No. 4 in Table 1). Then, the bulk density (g / cm 3) and the volume specific resistivity (Ω · cm) of the obtained composite sintered body were measured.

<Embodiment 5> As in the case of Embodiment 3, in the case of a combination of charcoal powder and Fe2 O3 powder, the mixing ratio of charcoal powder and Fe2 O3 powder
Weight ratio of Fe2 O3 powder 50 to 0, charcoal powder 100
The sintering temperature (internal temperature) was changed variously between approximately 1000 ° C. and 2000 ° C. by using two types of mixed powders each set to the weight ratio of the Fe 2 O 3 powder 25, and
A composite sintered body of Fe2 O3 was prepared, and the volume specific resistivity (Ω · cm) was measured. The sintering conditions in this case were as follows: the pressure was 500 kg / cm 2, the sintering time was 5 minutes, and the current value and voltage were changed so that the internal temperature was approximately 1000 ° C. to 2000 ° C.

<Test Results 1> Table 1 shows the composition, sintering conditions, and measurement results of Examples 1 to 4 described above.

[0028]

[Table 1]

(Volume resistivity) According to the test results shown in Table 1, the volume resistivity of Example 3 in which Fe 2 O 3 was mixed and the volume resistivity of Example 1 in which Fe was mixed were 3.916 × 10 3 respectively.
⁻⁴ Ω · cm and 4.125 × 10 ⁻⁴ Ω · cm, which are extremely low values, and the volume resistivity of Example 4 was 3.980 × 1.
0 ⁻³ Ω · cm, and the specific volume resistivity of Example 2 is 2.468.
It was a very low value of × 10 ^-2 Ω · cm. In the composite sintered body obtained by mixing the metal powder or the metal oxide powder with the charcoal powder, even in Example 2, which exhibited the highest volume resistivity, the volume resistivity when the charcoal was fired at 1000 ° C. or more. Even when compared with a rate of 10 ^-1 Ω · cm (see the above-mentioned journal of the Society of Materials), a material exhibiting excellent conductivity was obtained. Therefore, a material that can be suitably used as a conductive material or an electromagnetic shielding material has been obtained.

(Bulk Density) Regarding the bulk density, Example 3 in which Fe 2 O 3 was mixed and Example 1 in which Fe was mixed were 2.45 g / cm ³ and 2.29 g / cm ³ , respectively.
³ and shows an extremely high value, Example 2 and Example 4 also respectively 1.60 g / cm ^3, exhibited a significantly higher value than when sintering only 1.75 g / cm ³ and charcoal powder.

(Sintering time and sintering temperature) The sintering time was 5 minutes in each of Examples 1 to 4, but high-temperature sintering with an internal temperature of 1300 ° C to 1700 ° C can be performed. Such high-temperature sintering could be performed in an extremely short time as compared with the case of using an electric furnace.

<Test Result 2> FIG. 5 shows the measurement results of Example 5 described above.

According to FIG. 5, when the mixing ratio of charcoal / Fe 2 O 3 is 100/50 by weight, the volume resistivity (see the dotted line in FIG. 5) is obtained when the sintering temperature is in the range of 1000 ° C. to 2000 ° C. It shows a value of about 4 × 10 ⁻⁴ Ω · cm, and the volume resistivity (see the solid line in the figure) when the mixing ratio is 100/25 in weight ratio, when the sintering temperature is in the range of 1000 ° C. to 2000 ° C. The value tended to decrease as the sintering temperature increased from 5 × 10 ⁻³ Ω · cm to 9 × 10 ⁻⁴ Ω · cm. Therefore, even when the mixing ratio of the metal oxide powder is reduced to 100/25, the volume resistivity of charcoal fired at 1000 ° C. or higher is 10 ⁻¹ Ω · cm (the Journal of Materials Society, supra). (See Reference Example 1), and a material exhibiting excellent conductivity was obtained. From the tendency of the measurement results of the specific volume resistivity, the mixing amount of the above Fe2 O3 powder is
Even if the mixing ratio of charcoal / Fe2 O3 is eventually reduced to 100/1 by weight ratio even more than in the case of 00/25, the volume specificity is lower than in the case where the above charcoal is calcined at 1000 ° C. or more. It is believed that resistivity can be achieved.
Further, if the mixing amount of the Fe2 O3 powder is set to about 100/50 as described above, a low volume resistivity equal to or higher than that of graphite can be realized, and high conductivity can be realized.

[0034]

As described above, according to the composite sintered charcoal sintered by the electric current sintering method according to any one of claims 1 to 5, the material containing biomass is obtained by firing. Although the calcined carbide is a non-graphitizable carbon material,
A carbon material having a high-density graphitized structure by a composite sintered charcoal sintered by current sintering using a mixed powder obtained by mixing a metal powder or a metal oxide powder with the powder of the calcined carbide; In addition to providing a graphite material, a carbon material having extremely low electric resistance (high conductivity) can be provided. Further, the above-described composite sintered coal can be easily obtained by an electric current sintering method.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a mold and an electrode / punch used in a first embodiment and an example of the present invention.

FIG. 2 is a schematic diagram of an electric current sintering apparatus used in a second embodiment.

FIG. 3 is a partially cutaway perspective view of a mold and a punch used in the electric current sintering apparatus of FIG. 2;

FIG. 4 is a process chart showing a manufacturing process in a second embodiment.

FIG. 5 is a diagram showing the relationship between sintering temperature and specific volume resistivity for charcoal / Fe2 O3.

[Explanation of symbols]

 1 type 3 mixed powder (raw material) 12 die (type) 20 mixed powder (raw material)

Claims (5)

[Claims] 1. A mixed powder in which a metal powder or a metal oxide powder is mixed with a calcined carbide powder obtained by calcining a substance containing biomass, and the raw material is filled in a mold. A composite sintered charcoal sintered by an electric current sintering method, characterized in that it is sintered by being energized between powder particles while being pressurized. 2. The composite sintered coal according to claim 1, wherein the biomass-containing substance is a cellulose-containing substance. 3. The method according to claim 1, wherein the metal powder or the metal oxide powder comprises Cu, Al,
Ag, Ti, Ni, Li, Si, Fe, Pt, V, C
a powder of one or more metals selected from r, Mn, Co, Zr, Mo, Pd, K, Sn, and Au, or a powder of a metal oxide of one or more of the above metals A composite sintered charcoal sintered by an electric current sintering method. 4. The composite sintered carbon according to claim 1, wherein the calcined carbide is calcined in a temperature range from about 300 ° C. to about 800 ° C. . 5. The method according to claim 1, wherein the powder raw material filled in the mold is pressurized and energized in a reduced pressure state and sintered. Composite sintered charcoal.