NANOCARBON/ALUMINUM COMPOSITE MATERIAL, PROCESS FOR PRODUCING THE SAME, AND PLATING LIQUID FOR USE IN SAID PROCESS

Abstract

 [Object] To provide a nanocarbon/aluminum composite material having high strength and electrical conductivity for suitable use in a lead wire, a heat exchanger and an automotive part and a process for producing the nanocarbon/aluminum composite material.
[Solution] There is provided a plating liquid for nanocarbon/aluminum composite production, comprising an aluminum halide, nanocarbon and 1,3-dialkylimidazolium halide and/or the like, wherein the molar ratio of the aluminum halide to the 1,3-dialkylimidazolium halide and/or the like is in the range of 20:80 to 80:20 and the 1,3-dialkylimidazolium halide and/or the like has an alkyl group with a carbon number of 1 to 12. There are also provided a nanocarbon/aluminum composite production process comprising forming a plating film on a substrate surface by electrolysis of the plating liquid in a dry, oxygen-free atmosphere with the passage of a direct current etc. under the electrolysis conditions of a bath temperature of 0 to 300°C and a current density of 0.01 to 50 A/dm² and a nanocarbon/aluminum composite material produced by this production process.

Description

TECHNICAL FIELD

[0001] The present invention relates to a nanocarbon/aluminum composite material, particularly suitable for use in electric conductors such as power cables and lead wires, heat exchangers such as radiators, condensers and evaporators and automotive parts, a process for production of the nanocarbon/aluminum composite material and a plating liquid for use in the nanocarbon/aluminum composite production process.

BACKGROUND ART

[0002] In general, power cable and lead wire materials such as aluminum alloys and heat exchanger materials are required to have high electrical conductivity and high thermal conductivity.
From the recent viewpoint of global environmental conservation, there is a growing need for weight and size reductions of power cables, lead wires, heat exchangers and automotive parts. It is thus desired that the materials of the power cables, lead wires, heat exchangers and automotive parts have high strength while being shaped in thinner forms.

[0003] The largest number of studies has so far been made on carbon-fiber reinforced aluminum alloys as high-strength light-weight composite materials. (Refer to Patent Documents 1 and 2.)

[0004] Also, attention has recently been given to carbon nanotube (hereinafter referred to as "CNT") as carbon fiber. The applicability of CNT is being examined in expectation of further performance improvements because of excellent CNT properties e.g. toughness, electrical conductivity and thermal conductivity.
Various metals such as copper, nickel and aluminum are used as matrices for production of CNT composite materials. (Refer to Patent Documents 3 and 4.) In particular, it is reported that CNT/aluminum composite materials increase in strength and attain high thermal conductivity. (Refer to Non-Patent Document 1.)

[0005] On the other hand, various aluminum material production processes such as three-layer electrolysis, fractional crystallization and electrodeposition are known. Among others, the electrodeposition can be carried out in a single process step and thus regarded as most attractive. However, the electrodeposition of aluminum from a water system is impractical under the influence of competitive hydrogen generation reaction due to the fact that aluminum has a negative standard electrode potential of-1.68 V vs. SHE (standard hydrogen electrode). The electrodeposition of aluminum from an organic solvent system is feasible, but is difficult to put into industrially practical use due to the danger of flashing.

Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-008989

Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-048206

Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-156074

Patent Document 4: Japanese Laid-Open Patent Publication No. 2004-315297 Non-Patent Document 1: Journal of Materials Research, T. Kuzamaki et al., 1998, Vol. 13, P.2445

DISCLOSURE OF THE INVENTION

Problems to be solved by the Invention

[0006] Each of the nanocarbon/aluminum composite material production processes of Patent Documents 1-4 and Non-Patent Document 1 includes a complicated series of process steps, e.g., placing an aluminum powder and CNT into an aluminum case, followed by heating at 600°C for 1.5 hour under a reduced pressure of 5.3·10^-1 Pa, pressurizing at 100 MPa for 60 minutes, and then, extruding at 10 MPa/min and 600°C. In these production processes, the nanocarbon is added and mixed by stirring into the molten metal. There thus arises a problem that it is difficult to disperse the nanocarbon uniformly in the molten metal because of the large difference in specific gravity between the metal and the nanocarbon.

[0007] The carbon-fiber/aluminum composite material shows no sign of strength deterioration when heated at 500°C or lower in a non-oxidizing atmosphere. However, there arises a problem in the carbon-fiber/aluminum composite material that the interface reaction between the matrix and the carbon fiber occurs to form aluminum carbide (Al₄C₃) and thereby decrease not only the cross section of the carbon fiber but also the strength of the carbon fiber due to the occurrence of a notch effect at the carbide end when the heating retention time becomes higher than or equal to 550°C.
It has also been shown by previous researches that the carbon fiber gets oxidized by heating in the air and faces a serious problem of deterioration.

[0008] In view of the above prior art problems, the present invention has been made to provide a nanocarbon/aluminum composite material having high strength and electrical conductivity for suitable use in electric conductors such as power cables and lead wires, heat exchangers such as radiators, condensers and evaporators and automotive parts, a process for production of the nanocarbon/aluminum composite material and a plating liquid for use in the nanocarbon/aluminum composite production process.

Means for solving the problems

[0009] As a result of extensive researches, the present inventors have produced a technical finding that an room-temperature molten salt (also called "cold molten salt", "ambient-temperature molten salt" or "ionic liquid") is expected to be especially useful for various alloy electrodeposition baths and cell electrolytes in terms of the following advantages (1)-(3).

(1) The room-temperature molten salt allows easy plating of any metal or alloy e.g. aluminum having a negative standard electrode potential.

(2) The room-temperature molten salt is usable at room temperature and easy to handle.

(3) The room-temperature molten salt shows non-volatility and non-flammability and has no danger of flashing.

[0010] Based on such a technical finding, the present inventors have proceeded with further researches and found that the above object of the present invention can be accomplished by preparing and using a specific plating liquid.

[0011] Namely, there is provided a plating liquid for nanocarbon/aluminum composite production according to the present invention, comprising an aluminum halide, nanocarbon and 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, wherein the molar ratio of the aluminum halide to the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide is in the range of 20 : 80 to 80 : 20; the 1,3-dialkylimidazolium halide has an alkyl group with a carbon number of 1 to 12; and the monoalkylpyridinium halide has an alkyl group with a carbon number 1 to 12

[0012] There is provided a first process for preparing the plating liquid for nanocarbon/aluminum composite production according to the present invention, comprising: mixing aluminum halide and nanocarbon together, mixing the mixture of the aluminum halide and the nanocarbon with 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, and then, melting the mixture of the aluminum halide, the nanocarbon and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide; or mixing nanocarbon with 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, mixing the mixture of the nanocarbon and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide with aluminum halide, and then, melting the mixture of the aluminum halide, the nanocarbon and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide.

[0013] There is provided a second process for preparing the plating liquid for nanocarbon/aluminum composite production according to the present invention, comprising: mixing aluminum halide and nanocarbon together or mixing nanocarbon with 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, and then, mixing the nanocarbon mixture with a molten salt of aluminum halide and 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide.

[0014] There is also provided a process for producing a nanocarbon/aluminum composite material by using the plating liquid for nanocarbon/aluminum composite production according to the present invention, comprising: forming a plating film on a substrate surface by electrolysis of the plating liquid in a dry, oxygen-free atmosphere with the passage of a direct current and/or a pulsed current under the electrolysis conditions of a bath temperature of 0 to 300°C and a current density of 0.01 to 50 A/dm².

[0015] There is further provided a nanocarbon/aluminum composite material produced by the nanocarbon/aluminum composite production process according to the present invention.

Effect of the Invention

[0016] It is possible in the present invention to provide a nanocarbon/aluminum composite material having high strength and electrical conductivity for suitable use in electric conductors such power cables and lead wires, heat exchangers such as radiators, condensers and evaporators and automotive parts and a process for production of the nanocarbon/aluminum composite material by the preparation and use of a specific plating liquid.

Best mode for carrying out the Invention

[0017] Hereinafter, the plating liquid for nanocarbon/aluminum composite production according to the present invention will be described below in detail. In the following description, all percentages (%) are by mass unless otherwise specified.

[0018] The plating liquid for nanocarbon/aluminum composite production according to the present invention contains an aluminum halide, nanocarbon and either one or both of 1,3-dialkylimidazolium halide and monoalkylpyridinium halide, wherein the molar ratio of the aluminum halide to the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide is in the range of 20 : 80 to 80 : 20; the 1,3-dialkylimidazolium halide has an alkyl group or groups with a carbon number of 1 to 12; and the monoalkylpyridinium halide has an alkyl group with a carbon number of 1 to 12 as mentioned above.

[0019] In the present invention, it is essential that the molar ratio of the aluminum halide to the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide is in the range of 20 : 80 to 80 : 20.
If the above molar ratio is not satisfied, the resulting liquid does not get molten at room temperature and thus cannot be used as the plating liquid. Even when molten at higher temperature, the resulting liquid is too high in viscosity and not suitable as the plating liquid for production of the nanocarbon/aluminum composite material with high strength and electrical conductivity.
Herein, the 1,3-dialkylimidazolium halide and the monoalkylpyridinium halide can be used alone or in combination thereof as long as the above mole ratio condition is satisfied.

[0020] It is also essential in the present invention that the 1,3-dialkylimidazolium halide has an alkyl group with a carbon number of 1 to 12; and the monoalkylpyridinium halide has an alkyl group with a carbon number of 1 to 12.
If the alkyl group does not have the above carbon number, the resulting liquid does not get molten at room temperature and thus cannot be used as the plating liquid. Even when molten at higher temperature, the resulting liquid is too high in viscosity and not suitable as the plating liquid for production of the nanocarbon/aluminum composite material with high strength and electrical conductivity.

[0021] With the above composition, however, the plating liquid is capable of being used to produce the nanocarbon/aluminum composite material with high strength and electrical conductivity.

[0022] It is preferable in the present invention that the nanocarbon is contained in an amount of 0.01 to 50 g/L, more preferably 0.01 to 20 g/L, with respect to the total volume of the aluminum halide and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide.
If the nanocarbon content amount is less than 0.01 g/L, the amount of nanocarbon particles in aluminum plating is so small that it may become difficult for the plating to obtain desired properties. If the nanocarbon content amount exceeds 50 g/L, the concentration of nanocarbon particles in the electrolytic bath is so high that the nanocarbon particles may get aggregated and precipitated and, at the time of raising the product from the electrolytic bath upon completion of the electrolysis, adhered excessively to the product.

[0023] The respective liquid components will be described in more detail below.
An explanation of the aluminum halide will be first given below.
There is no particular restriction on the aluminum halide as long as the aluminum halide is capable of being used in the above plating liquid for production of the nanocarbon/aluminum composite material. For example, aluminum chloride (AlCl₃) is preferably usable. It is particularly preferable to use anhydrous AlCl₃.

[0024] Next, an explanation of the 1,3-dialkylimidazolium halide will be given below.
There is no particular restriction on the 1,3-dialkylimidazolium halide as long as the 1,3-dialkylimidazolium halide has at least one alkyl group with a carbon number of 1 to 12 and is capable of being used in the above plating liquid for production of the nanocarbon/aluminum composite material. It is preferable that the 1,3-dialkylimidazolium halide has one alkyl group with a carbon number of 1 to 5, more preferably two alkyl groups with a carbon number of 1 to 5. More specifically, 1-ethyl-3-methylimidazolium chloride (hereinafter referred to as "EMIC") is preferably usable. These two alkyl groups may be the same or different.

[0025] An explanation of the monoalkylpyridinium halide will be given below.
There is no particular restriction on the monoalkylpyridinium halide as long as the monoalkylpyridinium halide has an alkyl group with a carbon number of 1 to 12 and is capable of being used in the above plating liquid for production of the nanocarbon/aluminum composite material. It is preferable that the monoalkylpyridinium halide has one alkyl group with a carbon number of 1 to 5.
More specifically, 1-butylpyridinium halide (hereinafter referred to as "BPC") is preferably usable.

[0026] In terms of the physical properties, notably electrical conductivity, viscosity and melting point, of the plating liquid, it is preferable to use the EMIC having a low melting point of about 84°C.

[0027] An explanation of the nanocarbon will be given below.
There is no particular restriction on the nanocarbon. As the nanocarbon, there can be used carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, carbon black, acetylene black, ketjen black or any mixture thereof.

[0028] It is preferable in the present invention to use, as one kind of nanocarbon, carbon nanotube with a diameter of 1 to 100 nm, a length of 1 to 100 µm and an aspect ratio of 10 to 100.
If the carbon nanotube diameter is smaller than 1 nm, it is likely that the carbon nanotube will get aggregated and precipitated so that it is difficult to incorporate a sufficient amount of carbon nanotube in aluminum plating. If the carbon nanotube diameter exceeds 100 nm, it is also likely that the carbon nanotube will get precipitated so that it is difficult to incorporate a sufficient amount of carbon nanotube in aluminum plating. If the carbon nanotube length is less than 1 µm, it is likely that the carbon nanotube will get aggregated and precipitated so that it is difficult to incorporate a sufficient amount of carbon nanotube in aluminum plating as in the case where the carbon nanotube diameter is smaller than 1 nm. If the carbon nanotube length exceeds 100 µm, it is also likely that the carbon nanotube will get precipitated so that it is difficult to incorporate a sufficient amount of carbon nanotube in aluminum plating as in the case where the carbon nanotube diameter exceeds 100 nm.
Herein, the carbon nanotube may have either a single-wall structure, a multi-wall structure or any composite structure thereof.

[0029] Next, the preparation of the plating liquid for nanocarbon/aluminum composite production according to the present invention will be explained below.
A first process of preparing the plating liquid for nanocarbon/aluminum composite production according to the present invention includes mixing an aluminum halide and nanocarbon together, mixing the resulting mixture with either one or both of 1,3-dialkylimidazolium halide and monoalkylpyridinium halide and melting the mixture, or mixing a nanocarbon with either one or both of 1,3-dialkylimidazolium halide and monoalkylpyridinium halide, mixing the resulting mixture with an aluminum halide and melting the mixture.

[0030] A second process of preparing the plating liquid for nanocarbon/aluminum composite production according to the present invention includes mixing an aluminum halide and nanocarbon together, or mixing nanocarbon with either one or both of 1,3-dialkylimidazolium halide and monoalkylpyridinium halide, and then, mixing the resulting mixture with a molten salt of the aluminum halide and either one or both of 1,3-dialkylimidazolium halide and monoalkylpyridinium halide.

[0031] In the first and second preparation processes, both of the 1,3-dialkylimidazolium halide and the monoalkylpyridinium halide have alkyl groups with a carbon number of 1 to 12, which may be the same or different.
There are no particular restrictions on the aluminum halide and the nanocarbon. Any of the above-mentioned aluminum halide and nanocarbon materials are usable.

[0032] The plating liquid for nanocarbon/aluminum composite production according to the present invention is not limited to those prepared by the above first and second preparation processes and can be prepared by any process as long as the plating liquid has a specific composition of aluminum halide, nanocarbon and either one or both of 1,3-dialkylimidazolium halide and monoalkylpyridinium halide. In the case of preparing the plating liquid for nanocarbon/aluminum composite production by the first preparation process, the nanocarbon is mixed in advance with the salt. This makes the nanocarbon unlikely to get aggregated and thus desirably leads to a uniform dispersion of the nanocarbon in the plating liquid. In the case of preparing the plating liquid for nanocarbon/aluminum composite production by the second preparation process, the nanocarbon mixture is directly added into the molten salt of the aluminum halide and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide. This promotes a desirably more uniform dispersion of the nanocarbon in the plating liquid.

[0033] By way of more specific example, the plating liquid can be prepared by e.g. mixing AlCl₃ as one kind of aluminum halide and EMIC as one kind of 1,3-dialkylimidazolium halide at a given molar ratio to obtain a room-temperature molten salt as a base, followed by adding thereto CNT as one kind of nanocarbon appropriately.
For ease of handling, it is preferable to disperse the CNT into AlCl₃ or EMIC before adding the CNT to the molten salt.
When the room-temperature molten salt is not in a completely molten state, it is preferable to melt the salt completely by heating.
It is further preferable to immerse an Al wire in the completely molten salt before adding the CNT to the molten salt in order to remove impurities from the AlCl₃-EMIC room-temperature molten salt.
There is no particular restriction on the technique for dispersing the CNT in the AlCl₃-EMIC room-temperature molten salt. For example, ultrasonic irradiation or stirring can be used.

[0034] The production of the nanocarbon/aluminum composite material will be next explained below.
A process for producing the nanocarbon/aluminum composite material by using the plating liquid for nanocarbon/aluminum composite production according to the present invention includes forming a plating film on a substrate surface by electrolysis of the plating liquid in a dry, oxygen-free atmosphere with the passage of either a direct current, a pulsed current or an appropriate combination thereof under the electrolysis conditions of a bath temperature of 0 to 300°C and a current density of 0.01 to 50 A/dm².

[0035] If the bath temperature is lower than 0°C, the plating liquid gets solidified.
If the bath temperature exceeds 300°C, the plating liquid gets decomposed by heat. In either case, it is difficult to accomplish the electrolysis.
If the current density is less than 0.01 A/dm², the electrolysis time becomes too long for practical use. If the current density exceeds 50 A/dm², the plating liquid reaches a decomposition voltage level so that it is difficult to accomplish the plating.
Herein, the "dry, oxygen-free atmosphere" means an atmosphere with a moisture content of 2 ppm or lower and an oxygen content of 1 ppm or lower in the present invention. An argon (Ar) or nitrogen (N₂) atmosphere is generally usable as the dry, oxygen-free atmosphere.

[0036] By the above process, it is possible to produce the nanocarbon/aluminum composite material (plating film) with high strength and electrical conductivity on the substrate surface.
It is also possible by means of electroplating in the above process to form the plating film of the nanocarbon/aluminum composite material easily in a single process step. Further, the plating film of the nanocarbon/aluminum composite material can be formed into a desired shape.

[0037] There is no particular restriction on the electrolytic technique in the production of the nanocarbon/aluminum composite material. For example, the electrolysis can be accomplished by using any known two-electrode cell.
One example of the electrolysis is to apply a voltage to the plating liquid, in which the CNT is dispersed in the AlCl₃-EMIC room-temperature molten salt, with a cathode and an anode immersed in the plating liquid and connected to a direct-current power source to feed a constant current, a pulsed current or a combination thereof between these two electrodes.
The intensity of the applied voltage may be changed at each period.
The electrolysis may be done intermittently for about 0.1 to 600 seconds.
The electrolysis may be done by repeated cycles of voltage application and stop as necessary at intervals of about 0.1 to 1 second.

[0038] The plating amount of the nanocarbon/aluminum composite material can be controlled by adjusting the nanocarbon dispersion amount, the current density, the electrolysis time and the like as appropriate.
For example, the plating amount of the nanocarbon/aluminum composite material can be increased by increasing the nanocarbon dispersion amount, raising the electrolysis voltage to increase the current density, increasing the electrolysis time or any combination thereof.
In the case of continuous production of the nanocarbon/aluminum composite material, it is desirable to replenish the nanocarbon and the AlCl₃-EMIC room-temperature molten salt sequentially so as to complement a decrease in the nanocarbon dispersion amount.

[0039] There is no particular restriction on the material and form of the cathode (negative electrode). The cathode can be an electric conductor of any material and form as long as it is chemically and electrochemically stable toward the plating liquid.
As the cathode material, there can be used e.g. copper, brass, nickel, stainless, tungsten, molybdenum and the like. Copper and brass are preferred in terms of the electrochemical stability, drawability and cost efficiency, but are not limited thereto.
As the cathode form, the surface configuration, thickness and size are not particularly restricted. The cathode can be a porous metal substrate of foil form, plate form, spiral wire form, foam form, nonwoven form, mesh form, felt form or expanded form. Among others, foil form and plate form are preferred.
By the above electrolystic technique, the plating film is formed to cover a surface of the cathode as the substrate.

[0040] As the anode (positive electrode), any known conductive substrate can be used with no particular restriction. The anode material can be preferably selected from platinum and graphite that are chemically and electrochemically stable toward the plating liquid, and aluminum that does not cause contamination of the plating liquid by dissolution.
There is no particular restriction on the form of the anode. The anode can be of e.g. plate form or spiral form.

[0041] Next, the nanocarbon/aluminum composite material according to the present invention will be explained below.
In the present invention, the nanocarbon/aluminum composite material is produced by the above nanocarbon/aluminum composite production process.
The thus-produced nanocarbon/aluminum composite material is capable of not only attaining high electrical and thermal conductivity but also being provided in thinner form for weight and size reduction and thus is suitable as a high-strength lightweight composite material for use in power cables, lead wires, heat exchangers such as radiators, condensers and evaporators, automotive parts and the like.

[0042] For example, the plating film of the nanocarbon/aluminum composite material can be formed by the above electrolystic technique.
In the present invention, the nanocarbon content of the nanocarbon/aluminum composite material is preferably in the range of 0.1 to 50%, more preferably 0.1 to 20%.
If the nanocarbon content is less than 0.1%, the material cannot obtain desired properties with almost none of nanocarbon characteristic features reflected therein. If the nanocarbon content exceeds 50%, the aluminum content is too low to function as a matrix for establishing a bonding between the nanocarbon particles so that the nanocarbon-to-nanocarbon bonding may become weakened to cause a sudden deterioration of material strength.

Examples

[0043] The present invention will be described in more detail with reference to the following examples. It should be however noted that the following examples are only illustrative and not intended to limit the invention thereto.

(Example 1)

[0044] First, AlCl₃ and EMIC were weighed out at a molar ratio of 66.7 : 33.3 and mixed together with stirring. The resulting mixture was completely melted and purified by substitution through the immersion of Al wire in the mixture for 1 week or more.
A plating liquid for MWCNT/aluminum composite production was prepared by adding 0.1 to 30.0 g/L of multi-wall carbon nanotube (MWCNT with a tube diameter of 1.2 to 2.0 nm and a tube length of 2 to 5 µm) into the above mixture.
A NWCNT/aluminum composite material was then produced by constant current electrolysis of the plating liquid with sufficient stirring.

[0045] Herein, the preparation and electrolysis of the plating liquid were carried out in a dry nitrogen atmosphere. In the constant current electrolysis, a two-electrode cell with a cathode of Cu plate (99.96%) and an anode of Al plate (99.99%) was used. The cathode had been pretreated by grinding with an emery paper (No. 2000), electrolytic degreasing with 10% aqueous solution of sodium orthosilicate and then acid treatment with 10 vol% HCl. The electrolysis conditions were set to a bath temperature of 30°C, a current density of 5,10, 20, 30 mA/cm² and an electrolysis charge amount of 50 C/cm².

[0046] A surface state of the NWCNT/aluminum composite material was monitored by means of a scanning electron microscope (SEM "JSM-6500F" available from JEOL Ltd.) so as to observe the incorporation of NWCNT into the Al deposit in a practical manner. The observation showed that the NWCNT was first adsorbed onto deposit surfaces, then captured by initial Al deposit nucleus (about 1 to 100,000 atoms), totally incorporated into the grown Al deposit nucleus and then almost completely embedded in the Al deposit. It has been found out by the observation that the NWCNT was eutectic with Al and present in monodisperse form.

[0047] Further, the MWCNT content of the MWCNT/aluminum composite material was determined to be 0.1 to 20% by means of a total organic carbon meter ("TOC-5000A" available from SHIMADZU Corporation).
The relationship between the MNCNT addition amount of the plating liquid and the Vickers hardness of the composite material was analyzed as follows. (Refer to FIG. 1.) The analysis was made semiquantitatively on the assumptions that an increase in the MWCNT eutectic amount could allow an increase in the composite material hardness and that the hardness of an Al plating film with an MWCNT addition amount of 0 g/L was adopted as a comparative example. In the present example, the hardness of the Al plating film was 50 Hv when the current density was set to any of 50, 10, 20 and 30 mA/cm². As shown in FIG. 1, the hardness of the composite material became higher than that of the Al plating film at each current density as the MWCNT addition amount of the plating bath increased. In view of the fact that a metal generally increases in hardness when nanoparticles exist in the metal, the eutectic of the MWCNT was supported by the increased hardness of the composite material in the present example. Herein, a Vickers hardness tester ("HM-124" available from AKASHI Co. Ltd.) was used in the hardness measurement.

[0048] The specific resistance of the composite material was further determined by four-terminal measurement according to JIS C 2525 and found to be lower than that of the Al plating film.
Based on the above results, analyses were also made on other kinds of nanocarbon particles. The same effect was obtained by the use of any of single-wall carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, carbon black, acetylene black and ketjen black.
The usability of the nanocarbon/aluminum composite material, composite production method and plating liquid according to the present invention have thus been proved as above.

(Example 2)

[0049] A predetermined amount of EMIC and MWCNT (with a tube diameter of 1.2 to 2.0 nm and a tube length of 2 to 5 µm) was mixed together, followed by adding AlCl₃ and melting the resulting mixture to yield a plating liquid for MWCNT/aluminum composite production. The molar ratio of AlCl₃ and EMIC in the plating liquid was set to 66.7 : 33.3. The MWCNT addition amount was set to 0.1 to 30.0 g/L.
ANWCNT/aluminum composite material was then produced by constant current electrolysis of the plating liquid with sufficient stirring as is the case with Example 1.
The preparation and electrolysis of the plating liquid were herein carried out in a dry nitrogen atmosphere. Further, the two-electrode electrolysis cell, the cathode pretreatment process and the electrolysis conditions were the same as in Example 1.

[0050] A surface state of the NWCNT/aluminum composite material was observed by means of SEM. It has been found out by the observation that the NWCNT was eutectic with Al and present in monodisperse form as is the case with Example 1.

[0051] Further, the MWCNT content of the MWCNT/aluminum composite material was determined to be 0.1 to 20% by means of a total organic carbon meter ("TOC-5000A" available from SHIMADZU Corporation).
The relationship between the MNCNT addition amount of the plating liquid and the Vickers hardness of the composite material was analyzed as follows. (Refer to FIG. 2.) As is the case with Example 1, the analysis was made on the assumption that the hardness of an Al plating film with an MWCNT addition amount of 0 g/L was adopted as a comparative example. The hardness of the composite material became higher than that of the Al plating film at each current density as the MWCNT addition amount of the plating bath increased As shown in FIG. 2. In view of the fact that a metal generally increases in hardness when nanoparticles exist in the metal, the eutectic of the MWCNT was supported by the increased hardness of the composite material in the present example. Herein, a Vickers hardness tester ("HM-124" available from AKASHI Co. Ltd.) was used in the hardness measurement.

[0052] The specific resistance of the composite material was further determined by four-terminal measurement and found to be lower than that of the Al plating film.
Based on the above results, analyses were also made on other kinds of nanocarbon particles. The same effect was obtained by the use of any of single-wall carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, carbon black, acetylene black and ketjen black.
The usability of the nanocarbon/aluminum composite material, composite production method and plating liquid according to the present invention have thus been proved as above.

(Example 3)

[0053] A predetermined amount of EMIC and MWCNT (with a tube diameter of 1.2 to 2.0 nm and a tube length of 2 to 5 µm) was mixed together and added to an AlCl₃-EMIC molten salt to yield a plating liquid for MWCNT/aluminum composite production. The molar ratio of AlCl₃ and EMIC in the plating liquid was set to 66.7 : 33.3. The MWCNT addition amount was set to 0.1 to 30.0 g/L.
A NWCNT/aluminum composite material was then produced by constant current electrolysis of the plating liquid with sufficient stirring as is the case with Example 1.
The preparation and electrolysis of the plating liquid were herein carried out in a dry nitrogen atmosphere. Further, the two-electrode electrolysis cell, the cathode pretreatment process and the electrolysis conditions were the same as in Example 1.

[0054] A surface state of the NWCNT/aluminum composite material was observed by means of SEM. It has been found out by the observation that the NWCNT was eutectic with Al and present in monodisperse form as is the case with Example 1.

[0055] The MWCNT content of the MWCNT/aluminum composite material was determined to be 0.1 to 20% by means of a total organic carbon meter ("TOC-5000A" available from SHIMADZU Corporation).
The relationship between the MNCNT addition amount of the plating liquid and the Vickers hardness of the composite material was analyzed as follows. (Refer to FIG. 3.) As is the case with Example 1, the analysis was made on the assumption that the hardness of an Al plating film with an MWCNT addition amount of 0 g/L was adopted as a comparative example. The hardness of the composite material became higher than that of the Al plating film at each current density as the MWCNT addition amount of the plating bath increased As shown in FIG. 3. In view of the fact that a metal generally increases in hardness when nanoparticles exist in the metal, the eutectic of the MWCNT was supported by the increased hardness of the composite material in the present example. Herein, a Vickers hardness tester ("HM-124" available from AKASHI Co. Ltd.) was used in the hardness measurement.

[0056] The specific resistance of the composite material was further determined by four-terminal measurement and found to be lower than that of the Al plating film.
Based on the above results, analyses were also made on other kinds of nanocarbon particles. The same effect was obtained by the use of any of single-wall carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, carbon black, acetylene black and ketjen black.
The usability of the nanocarbon/aluminum composite material, composite production method and plating liquid according to the present invention have thus been proved as above.

Brief Description of the Drawings

[0057] 

FIG. 1 is a graph showing a relationship between NWCNT addition amount and material hardness in Example 1 and Comparative Example.

FIG. 2 is a graph showing a relationship between NWCNT addition amount and material hardness in Example 2 and Comparative Example.

FIG. 3 is a graph showing a relationship between NWCNT addition amount and material hardness in Example 3 and Comparative Example.

Claims

1. A plating liquid for nanocarbon/aluminum composite production, comprising an aluminum halide, nanocarbon and 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, wherein the molar ratio of the aluminum halide to the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide is in the range of 20 : 80 to 80 : 20; the 1,3-dialkylimidazolium halide has an alkyl group with a carbon number of 1 to 12; and the monoalkylpyridinium halide has an alkyl group with a carbon number of 1 to 12.

2. The plating liquid for nanocarbon/aluminum composite production according to claim 1, wherein the nanocarbon is contained in an amount of 0.01 to 50 g/L with respect to the total volume of the aluminum halide and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide.

3. The plating liquid for nanocarbon/aluminum composite production according to claim 1, wherein the nanocarbon is at least one selected from the group consisting of carbon nanotube, carbon nanofiber, carbon nanohorn, fullerene, carbon black, acetylene black and ketjen black.

4. The plating liquid for nanocarbon/aluminum composite production according to claim 3, wherein the nanocarbon tube has a diameter of 1 to 100 nm, a length of 1 to 100 µm and an aspect ratio of 10 to 100.

5. A process for preparing the plating liquid for nanocarbon/aluminum composite production according to claim 1, comprising: mixing aluminum halide and nanocarbon together, mixing the mixture of the aluminum halide and the nanocarbon with 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, and then, melting the mixture of the aluminum halide, the nanocarbon and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide; or mixing nanocarbon with 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, mixing the mixture of the nanocarbon and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide with aluminum halide, and then, melting the mixture of the aluminum halide, the nanocarbon and the 1,3-dialkylimidazolium halide and/or the monoalkylpyridinium halide.

6. A process for preparing the plating liquid for nanocarbon/aluminum composite production according to claim 1, comprising: mixing aluminum halide and nanocarbon together or mixing nanocarbon with 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide, and then, mixing the nanocarbon mixture with a molten salt of aluminum halide and 1,3-dialkylimidazolium halide and/or monoalkylpyridinium halide.

7. A process for producing a nanocarbon/aluminum composite material by using the plating liquid for nanocarbon/aluminum composite production according to claim 1, comprising: forming a plating film on a substrate surface by electrolysis of the plating liquid in a dry, oxygen-free atmosphere with the passage of a direct current and/or a pulsed current under the electrolysis conditions of a bath temperature of 0 to 300°C and a current density of 0.01 to 50 A/dm².

8. A nanocarbon/aluminum composite material produced by the nanocarbon/aluminum composite material production process according to claim 7.

9. The nanocarbon/aluminum composite material according to claim 8, wherein the nanocarbon content of the nanocarbon/aluminum composite material is in the range of 0.1 to 50%.

Drawing