Long carbonaceous molding, long carbonaceous product, and method of production thereof

Abstract

Long carbonaceous moldings and long carbonaceous products as well as methods of production thereof are provided by which carbonaceous products can be obtained without allowing twisting or curving and with less frequent occurrence of cracking etc., even when subjected to heat treatment, and which are excellent in mass productivity. The long carbonaceous moldings have an aspect ratio of 3 to 20 and show fluctuations in the density thereof of not more than 0.05 Mg/m3 throughout the whole moldings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional representation of the main parts of a dry CIP apparatus for molding the long carbonaceous molding according to the invention.

FIG. 2 is a representation of each of the long carbonaceous moldings produced in Examples 1 to 6 according to the invention.

FIG. 3 is an illustration of the sectional regions of sampling for evaluating fluctuations in bulk density as employed for the moldings of Examples 1 to 6 according to the invention.

FIG. 4( a) is a graphic representation of the results of bulk density fluctuation evaluation in Examples 1 to 3. FIG. 4(b) is a graphic representation of the results of bulk density fluctuation evaluation in Examples 4 to 6 (after heat treatment).

FIG. 5 is an illustration of each of the long carbonaceous moldings obtained in Comparative Examples 1 to 7.

FIG. 6 is an illustration of the sectional regions of sampling for evaluating fluctuations in bulk density as employed for the moldings of Comparative Examples 1 to 7.

FIG. 7( a) is a graphic representation of the results of bulk density fluctuation evaluation in Comparative Examples 1 to 4. FIG. 7(b) is a graphic representation of the results of bulk density fluctuation evaluation in Comparative Examples 5 to 7 (after heat treatment).

FIG. 8 is an illustration of the long carbonaceous molding of Example 7 according to the invention.

FIG. 9 is an illustration of the long carbonaceous molding of Comparative Example 8.

FIG. 10 is an illustration of the regions of sampling for evaluating fluctuations in bulk density as employed for the molding of Example 7 according to the invention.

FIG. 11 is a graphic representation of the results of bulk density fluctuation evaluation in Example 7 and Comparative Example 8.

FIG. 12 is a graphic representation of the results of bulk density fluctuation evaluation in Example 8 and Comparative Example 9.

FIG. 13 is a graphic representation of the relationship between pore radius and cumulative pore volume as found in Example 8.

FIG. 14 is an illustration of the sites of cutting samples for leakage resistance testing from the long carbonaceous molding shown in FIG. 8 after resin impregnation.

FIG. 15 is a schematic representation of the apparatus used in leakage resistance testing of the samples cut out as shown in FIG. 14.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the accompanying drawings, an example of the embodiment of the long carbonaceous molding of the invention is described below.

FIG. 1 is a sectional representation of the main parts of a dry CIP apparatus for molding the long carbonaceous molding according to the invention. The molding apparatus 1 shown in FIG. 1 is mainly composed of a cylindrical pressure vessel 3 having an opening for introducing and discharging a hydraulic medium, such as water, an oil, an emulsion containing a rust preventive lubricant, ethylene glycol, a ring-shaped upper lid 4 and a ring-shaped lower lid 5 respectively inserted into and fixed to an upper opening and a lower opening of the pressure vessel 3, an upper punch 6 and a lower punch 7 detachably inserted into the upper lid 4 and lower lid 5, respectively, a double cylindrical pressurizing rubber mold 8 and a rubber mold for molding 9, hereinafter referred to as a “rubber mold 9”, both fitted in the pressure vessel 3, and press frames 11, 12 capable of coming into contact with the end faces of the upper and lower punches 6, 7 and resisting the axial force in the step of isotropic pressing by means of the hydraulic medium. Furthermore, a dry apparatus for molding the long carbonaceous molding according to the invention contains a metal insert 15. The metal insert 15 spans the length of the processing chamber 14. A cross-section of the metal insert 15 can be triangular, square, pentagonal, hexagonal, or any regularly shaped polygon. Moreover, a cross-section of the metal insert 15 can be circular. The composition makeup of the metal insert 15 can be any material that is compatible with the disclosed process. Metal materials suitable for use as metal insert 15 include aluminum, copper and steel. It is a matter of course that the opening 2 for introducing and discharging the hydraulic medium is fitted with a decompression mechanism or the like including a pressure generating device (a combination of a piston, a cylinder and a nonreturn valve; not shown).

Now, the working of the apparatus is described, but it should be understood that the presently claimed invention should by no means be limited to the description thereof. The press frames 11, 12 are removed, the upper punch 6 is withdrawn and, in that condition, the metal insert 15 is introduced into the processing chamber and subsequently, a raw material powder 10 is filled into the processing chamber 14 from above. The metal insert 15 preferably extends through the middle of (e.g., along the axis of) the raw material powder 10, but can be offset from the middle of the raw material powder 10. After completion of this charging operation, the upper punch 6 is inserted into the upper lid 4, and the press frames 11, 12 are brought into contact with the end faces of the upper and lower punches 6, 7. The preparation for pressing is now completed.

The hydraulic medium from the pressure generating device is introduced into the pressure vessel 3 through the introduction/discharge opening 2, whereupon the raw material powder 10 filled in the processing chamber 14 through the rubber mold 9 is molded by isotropic pressing, i.e., compression molded. On that occasion, the axial force is resisted by the press frames 11, 12. After completion of press molding under a predetermined isotropic pressure, the pressure is reduced to thereby allow the rubber mold 9 to return to its original state, i.e., with a concomitant increase in diameter and, at the same time, the press frames 11, 12 are removed, and the lower punch 7 is drawn out by means of a lifter device or the like. In this manner, a long carbonaceous molding can be shaped.

After the long carbonaceous molding is shaped, the metal insert 15 can be removed and separated from the long carbonaceous molding. Before or after the metal insert 15 is removed from the long carbonaceous molding, the long carbonaceous molding can be heated. When the metal insert 15 is removed from the long carbonaceous molding prior to heating, the cracking observed in conventional carbonaceous moldings when heated with a decomposable thermoplastic core does not occur.

When, in the step of molding, elastic spacers 13, 13 made of a rubber or the like are fitted, as cushioning members, to the upper and lower contacting portions of the raw material powder 10, it becomes possible to inhibit the so-called elephant foot phenomenon from occurring at these end portions, hence it becomes unnecessary to perform post-treatment after molding and the efficiency of product production can be further increased. Further, when the rubber mold 9 is vibrated from the surroundings on the occasion of charging of the raw material powder 10 into the rubber mold 9, it becomes possible to uniformly charge the raw material powder 10 into the rubber mold 9, with the result that the fluctuations in bulk density after molding can be further reduced.

Even when a carbon powder with a not very good flowability is used as the raw material powder, molding thereof in the above-mentioned manner can give a long carbonaceous molding having an axial length of at least 600 mm and an aspect ratio of 3 to 20 and showing fluctuations in density of not more than 0.05 Mg/m³, preferably not more than 0.03 Mg/m³, throughout the whole molding, making it possible to prevent the occurrence of curving or twisting, among others, after heat treatment, whereby the product yield can be markedly improved.

Preferably used as the raw material powder is a powder prepared by kneading a carbon or graphite powder with an average particle size of 5 to 50 μm and a binding agent together and grinding the mixture resulting from kneading to an average particle size of 1 to 150 μm, preferably 5 to 100 μm, more preferably 10 to 50 μm. Pitch or a resin binder such as a thermosetting resin can be used as the binding agent.

A powder prepared by kneading a carbonaceous filler and a binding agent together, grinding the resulting mixture, mixing the powder resulting from grinding with any of metal powders, metal compound powders or ceramic powders and, after kneading, grinding the mixture to an average particle size of 10 to 100 μm, preferably 10 to 50 μm may also be used as an alternative raw material powder. The metal powder, metal compound powder or ceramic powder preferably has an average particle size of 5 to 100 μm, preferably 5 to 50 μm, and the mixing ratio between the carbonaceous filler and the metal powder, metal compound powder and/or ceramic powder (carbonaceous filler/metal powder, metal compound powder and/or ceramic powder) in the raw material powder is preferably 0.01 to 1, preferably 0.2 to 0.5. The metal powder is preferably a powder of Cu, Fe, Ni, Cr, Mo, Sn, Al, Si or W, the metal compound powder is preferably a powder of MoS₂, WS₂ or a phosphate salt, and the ceramic powder is preferably a powder of the oxide, nitride or carbide of Al, Si, B or Zr.

When a carbonaceous molding having such characteristics as mentioned above is heat-treated within the temperature range of 500 to 3,000° C., a long carbonaceous product with an average pore radius of not greater than 10 μm, preferably not greater than 1 μm, can be obtained.

Further, this long carbonaceous product can be impregnated and/or coated with at least one material selected from among metals, ceramics, carbon and resins. The metals which can be used for impregnation include, but are not limited to, Cu, Al, Sb, white metal and Sn, among others. An appropriate metal species can be selected according to the intended use of the product and can be used for impregnation by any of the impregnation methods known in the art. As examples of the ceramics which can be used for impregnation and/or coating, there may be mentioned SiC and BN. An appropriate ceramics can also be selected according to the intended use of the product. In impregnating and/or coating with such ceramics, methods known in the art, for example the method comprising impregnating the carbonaceous product with a slurry containing a ceramic precursor, followed by heat treatment for ceramic formation, the CVI (chemical vapor infiltration) method, and the CVD (chemical vapor deposition) method, can be employed. Further, thermosetting resins, such as phenol resins, may be mentioned as examples of the resins for impregnation and/or coating. Pyrolytic carbon can also be used for impregnation and/or coating.

The long carbonaceous moldings of the invention and the long carbonaceous products of the invention which are derived from the moldings by heat treatment can be produced by one step of molding without causing curving or twisting in spite of their being long and having a length of at least 600 mm with an aspect ratio of 3 to 20. Unlike the case of the conventional long carbonaceous moldings, the carbon formed has no azimuth or bearings and the so-called isotropic materials with an anisotropy ratio of 1.05 to 1.5 can be obtained. The process of molding thereof can be carried out semiautomatically, and the production cost can be markedly reduced.

EXAMPLES

The following examples illustrate the present invention more specifically.

Examples 1 to 6

First, the production of a long carbonaceous molding using a dry CIP apparatus is described. A raw material powder was prepared by kneading a carbon powder with pitch as a binding agent, grinding the mixture resulting from kneading to an average particle size of 15 μm and further kneading the resulting powder with a copper powder having an average particle size of 5 μm. The mixing ratio between the carbon powder and copper powder was 2:3.

Then, a molding was produced from the above raw material powder using the dry CIP apparatus described hereinabove referring to an embodiment of the invention. More specifically, a long carbonaceous molding, as shown in FIG. 2, with a molding size of 48×38×652 (unit: mm) and a molding weight of 3,099 g was produced at a molding pressure of 343 MPa in the dry CIP apparatus.

This long carbonaceous molding was cut into segments with the sizes shown in FIG. 2 at the sites shown in FIG. 2. More specifically, a 70-mm-long molding segment 18 was cut out from the left end of the long carbonaceous molding shown in FIG. 2, then a 10-mm-long molding segment 15, a 200-mm-long molding segment, a 10-mm-long molding segment 16, a 70-mm-long molding segment 19, a 150-mm-long molding segment, a 10-mm-long molding segment 17, and a 140-mm-long molding segment 20 were cut out. Among these molding segments, the segments 15, 16 and 17 were used as the samples of Examples 1 to 3.

Then, out of the molding segments cut out in the above manner, the segments 18, 19 and 20 were heat-treated in a calcining oven at 950° C. The heat-treated molding segments 18, 19 and 20 were used as the samples of Examples 4 to 6.

Comparative Examples 1 to 7

Using coke as the raw material powder and using a 750 ton press, a long carbonaceous molding, as shown in FIG. 5, with a molding size of 50×30×335 (unit: mm) and a molding weight of 1,350 g was produced by metal mold molding at a molding pressure of 343 MPa.

This long carbonaceous molding was cut into segments with the sizes shown in FIG. 5 at the sites shown in FIG. 5. More specifically, a 10-mm-long molding segment 21 was cut out from the left end of the long carbonaceous molding shown in FIG. 5, then a 80-mm-long molding segment 25, a 10-mm-long molding segment 22, a 55-mm-long molding segment 26, a 10-mm-long molding segment 23, a 160-mm-long molding segment 27, and a 10-mm-long molding segment 24 were cut out. Among these molding segments, the segments 21 to 24 were used as the samples of Comparative Examples 1 to 4.

Then, out of the molding segments cut out in the above manner, the segments 25, 26 and 27 were heat-treated in a calcining oven at 950° C. The heat-treated molding segments 25, 26 and 27 were used as the samples of Comparative Examples 5 to 7.

Then, for bulk density fluctuation evaluation in each example, specimens were taken from the respective sectional regions i to viii of each molding, as shown in FIG. 3. For bulk density fluctuation evaluation in each comparative example, specimens were taken from the respective sectional regions a to j of each molding, as shown in FIG. 6. Bulk density measurements were carried out by the Archimedean method (method of determining the density of a specimen based on the law of nature that a solid body in a liquid is given a buoyancy equal to the weight of the liquid it displaces) using an electronic specific gravimeter (model ED-120T, product of Mirage Boeki). In the following examples and comparative examples, the bulk density measurements were performed in the same manner. The results of the above bulk density fluctuation evaluation are shown in FIG. 4. FIG. 4(a) is a graphic representation of the measurement results in Examples 1 to 3, and FIG. 4(b) is a graphic representation of the measurement results in Examples 4 to 6. FIG. 7(a) is a graphic representation of the measurement results in Comparative Examples 1 to 4, and FIG. 7(b) is a graphic representation of the measurement results in Comparative Examples 5 to 7. In each graph, the abscissa denotes the distance from the left end of the long carbonaceous molding and the ordinate denotes the bulk density.

As shown in FIG. 4(a), the bulk densities of the specimens of Examples 1 to 3 were 2.84 to 2.87 Mg/m³, while the bulk densities of the specimens of Comparative Examples 1 to 4 were 2.79 to 2.86 Mg/m³, as shown in FIG. 7(a). From these results, it could be confirmed that the bulk density fluctuations after molding are smaller in dry CIP molding than in metal mold molding. Therefore, based on the results of Examples 1 to 3, it could be established that long carbonaceous moldings showing uniform bulk density fluctuations throughout the whole moldings in spite of their being long moldings can be produced by dry CIP molding.

As shown in FIG. 4(b), the bulk densities of the specimens of Examples 4 to 6 were 3.20 to 3.30 Mg/m³, while the bulk densities of the specimens of Comparative Examples 5 to 7 were 3.18 to 3.28 Mg/m³, as shown in FIG. 7(b). In these cases, the middle portions after heat treatment showed higher values as compared with the terminal portions. However, since the dry CIP molding product was 652 mm long and the metal mold molding product was 335 mm long, the bulk density fluctuations were smaller in dry CIP molding upon comparison on the same length basis. Thus, based on the results of Examples 4 to 6, it could be established that long carbonaceous moldings showing uniform bulk density fluctuations throughout the whole moldings in spite of their being long moldings can be produced by dry CIP molding.

Example 7

A raw material powder was prepared by kneading a carbon powder with pitch as a binding agent and grinding the mixture after kneading to an average particle size of 30 μm. Then, using the dry CIP apparatus described hereinabove referring to an embodiment of the invention, a molding was produced from the raw material powder. More specifically, a long carbonaceous molding 28, as shown in FIG. 8, with a molding size of ø 50×650 (unit: mm) and a molding weight of 2,050 g was produced at a molding pressure of 100 MPa in the dry CIP apparatus and then it was heat-treated in a calcining oven at 1,200° C. This heat-treated molding 28 was used as the sample of Example 7.

Comparative Example 8

Using a powder prepared by kneading a raw material powder with pitch as a binding agent and grinding the mixture after kneading to an average particle size of 30 μm, an ordinary metal mold molding 29, as shown in FIG. 9, with a molding size of ø60×85 (unit: mm) and a molding weight of 400 g was produced on a 100 ton press and then it was heat-treated in a calcining oven at 1,200° C. This heat-treated metal mold molding 29 was used as the sample of Comparative Example 8.

Then, for evaluating the bulk density fluctuations in the sample of Example 7, a plurality of cubic specimens (each edge being 10 mm long) were cut out from the peripheral portion and central portion of the molding, and each specimen was measured for bulk density. For evaluating the bulk density fluctuations in the sample of Comparative Example 8, a plurality of cubic specimens (each edge being 10 mm long) were cut out only from the peripheral portion of the molding, and each specimen was measured for bulk density. The results of these bulk density fluctuation measurements are shown in FIG. 11. In FIG. 11, the abscissa of the graph denotes the distance from the left end of the long carbonaceous molding and the ordinate denotes the bulk density. The indications “peripheral portion” and “central portion” are for the specimens of Example 7, and the indication “metal mold” is for the specimens of Comparative Example 8.

As shown in FIG. 11, the bulk densities of the specimens of Example 7 were 1.82 to 1.84 Mg/m³, and the bulk densities of the specimens of Comparative Example 8 were 1.79 to 1.84 Mg/m³. From these results, it could be confirmed that the bulk density fluctuations after molding were smaller in dry CIP molding than in metal mold molding. Thus, based on the results of Example 7, it could be established that long carbonaceous molding showing uniform bulk density fluctuations throughout the whole moldings in spite of their being long moldings can be produced by dry CIP molding.

Example 8

The sample of Example 7 was subjected to resin impregnation and used as the sample of Example 8.

Comparative Example 9

The sample of Comparative Example 8 was subjected to resin impregnation and used as the sample of Comparative Example 9.

Then, for evaluating the bulk density fluctuations in the sample of Example 8, a plurality of cubic specimens (each edge being 10 mm long) were cut out from the peripheral portion and central portion of the molding in the same manner as shown in FIG. 10, and each specimen was measured for bulk density. For evaluating the bulk density fluctuations in the sample of Comparative Example 9, a plurality of cubic specimens (each edge being 10 mm long) were cut out only from the peripheral portion of the molding, and each specimen was measured for bulk density. The results of these bulk density fluctuation measurements are shown in FIG. 12. In FIG. 12, the abscissa of the graph denotes the distance from the left end of the long carbonaceous molding and the ordinate denotes the bulk density. The indications “peripheral portion” and “central portion” are for the specimens of Example 8, and the indication “metal mold” is for the specimens of Comparative Example 9.

Further, the relationship between pore radius and cumulative pore volume was examined for the sample of Example 8. The results are shown in FIG. 13.

Further, for leakage resistance testing of the sample of Example 8, moldings 30 with a size of ø40/ø30×50 (unit: mm) were cut out of the molding 28 with a size of ø 50×650 (unit: mm). As shown in FIG. 15, one end and the other end of each molding 30 cut out were tightly closed with plates 31, 32 so as to inhibit gas passage through between the molding 30 and each of the plate 31, 32. The outside surface of the molding 30 was sprayed with soapy water, and nitrogen was sent to the inside space through a vent 31a disposed in one end plate 31 under a pressure of 0.5 MPa for 20 minutes or under a pressure of 0.7 MPa for 20 minutes for leakage resistance evaluation. The reason why soapy water was sprayed on the outside surface of the molding 30 on that occasion is that when nitrogen leakage occurred, foaming occurred, indicating the leakage.

As shown in FIG. 12, the bulk densities of the specimens of Example 8 were 1.92 to 1.94 Mg/m³, and the bulk densities of the specimens of Comparative Example 9 were 1.88 to 1.93 Mg/m³. From these results, it could be confirmed that the bulk density fluctuations after molding and resin impregnation were smaller in dry CIP molding than in metal mold molding. Thus, based on the results of Example 8, it could be established that long carbonaceous moldings showing uniform bulk density fluctuations throughout the whole moldings in spite of their being long moldings can be produced by dry CIP molding.

From the data shown in FIG. 13, it is evident that a sufficient extent of resin impregnation can be attained until the central portion of the molding on the occasion of resin impregnation and that the difference in pore volume between the molding surface and the central portion of the molding is not great.

Furthermore, no nitrogen leakage was observed everywhere in the inside space formed by the molding 30 and the plates 31, 32 under the pressure of 0.5 MPa or 0.7 MPa.

Since various design changes can be made in carrying out the present invention without departing from the scopes of the claims, the above-described modes of embodiment and examples are by no means limitative of the scope of the invention.

Claims

1. A method of producing a carbonaceous molding, the method comprising providing a dry isostatic press molding apparatus comprising a processing chamber and a metal insert in the processing chamber;adding to the processing chamber around the metal insert a raw material powder prepared by kneading a carbonaceous filler with a binding agent to produce a mixture andgrinding the mixture to an average particle size of 1 to 150 μm; anddry isostatic press molding the raw material powder added to the processing chamber to produce the carbonaceous molding, whereinthe carbonaceous molding has a density that fluctuates over the entire carbonaceous molding by not more than 0.05 Mg/m3; andthe carbonaceous molding has an aspect ratio of 3 to 20.

2. The method according to claim 1, further comprising, after the dry isostatic press molding, separating the metal insert from the carbonaceous molding.

3. The method according the claim 1, wherein the dry isostatic press molding apparatus further comprises at least one cushioning member; andthe at least one cushioning member comes into contact with the raw material powder during the dry isostatic press molding.

4. The method according to claim 1, wherein at the beginning of the dry isostatic press molding the metal insert is in contact with the raw material powder.

5. The method according to claim 1, further comprising heating the carbonaceous molding.

6. The method according to claim 5, wherein the heating is at a temperature in a range of from 900° C. to 3000° C.

7. A method of producing a carbonaceous molding, the method comprising providing a dry isostatic press molding apparatus comprising a processing chamber and a metal insert in the processing chamber;adding to the processing chamber around the metal insert a raw material powder prepared by kneading a carbonaceous filler with a binding agent to produce a mixture,grinding the mixture to a ground powder having an average particle size of 1 to 150 μm andblending the ground powder with at least one other powder having an average particle size of 5 to 100 μm selected from the group consisting of a metal powder, a metal compound powder and a ceramic powder, where a mixing ratio between the carbonaceous filler and the at least one other powder is 0.01 to 1 by mass; anddry isostatic press molding the raw material powder added to the processing chamber to produce the carbonaceous molding, whereinthe carbonaceous molding has a density that fluctuates over the entire carbonaceous molding by not more than 0.05 Mg/m3; andthe carbonaceous molding has an aspect ratio of 3 to 20.

8. The method according to claim 7, further comprising, after the dry isostatic press molding, separating the metal insert from the carbonaceous molding.

9. The method according the claim 7, wherein the dry isostatic press molding apparatus further comprises at least one cushioning member; andthe at least one cushioning member comes into contact with the raw material powder during the dry isostatic press molding.

10. The method according to claim 7, wherein at the beginning of the dry isostatic press molding the metal insert is in contact with the raw material powder.

11. The method according to claim 7, further comprising heating the carbonaceous molding.

12. The method according to claim 11, wherein the heating is at a temperature of 500° C. or above.

13. The method according to claim 7, wherein the at least one other powder comprises the metal powder; andthe metal powder comprises at least one selected from the group consisting of Cu, Fe, Ni, Cr, Mo, Sn, Al, Si and W.

14. The method according to claim 7, wherein the at least one other powder comprises the metal compound powder; andthe metal compound powder comprises at least one selected from the group consisting of MoS2, WS2 and a phosphate salt.

15. The method according to claim 7, wherein the at least one other powder comprises the ceramic powder; andthe ceramic powder comprises at least one selected from the group consisting of oxides, nitrides and carbides of at least one of Al, Si, B and Zr.