Patent Publication Number: US-8110288-B2

Title: Carbon nanocomposite material comprising a SiC film coating, and method of manufacturing the same

Description:
FIELD OF THE INVENTION 
     The present invention relates to a carbon nanocomposite material with improved wettability and a method of manufacturing the same. 
     BAKGROUND OF THE INVENTION 
     In recent years, special carbon fibers referred to as carbon nanofibers have received attention as a reinforcing material, and methods of using the material have been proposed. 
       FIG. 10  hereof is a schematic view showing a model of a carbon nanofiber. The carbon nanofiber  110  has a configuration in which a sheet composed of carbon atoms arranged in a hexagonal reticulated shape is cylindrically wrapped in a diameter D of 1.0 nm (nanometer) to 150 nm. The fiber is structured on a nanolevel, and is therefore referred to as a carbon nanofiber, a carbon nanomaterial, or a carbon nanotube. A length L ranges from a few micrometers to 100 μm. 
     A material in which carbon atoms are aligned in a cubic lattice pattern is diamond, and diamond is a very hard material. The carbon nanofiber  110  has considerable mechanical strength because it possesses an ordered crystal structure visibly similar to diamond. 
       FIGS. 11(   a ) to ( c ) are views illustrating a problem of a carbon nanofiber. 
     In  FIG. 11(   a ), a container  111  is filled with a medium  112 , and a carbon nanofiber  113  is added to the medium  112  in  FIG. 11(   a ). 
     In  FIG. 11(   b ), the system is thoroughly agitated using a mixer  114 . This agitation can also be performed by an oscillating mixer. 
     Shown in  FIG. 11(   c ) is the state of the system after being left to stand for a fixed interval of time. It is apparent that the carbon nanofiber  113  has precipitated on the bottom of the container  111 . 
     The carbon nanofiber  113  accumulates on the top if the specific gravity of the media  112  is high. 
     When the media  112  is a molten metal, the carbon nanofiber  113  cannot be uniformly dispersed in the metal because the carbon nanofiber  113  accumulates on the top of the molten metal. This is the reason that the carbon nanofiber  113  has poor wettability in relation to molten metal. 
     In view of the above, a surface treatment aimed at improving wettability has been proposed, as disclosed in Japanese Patent Application Laid-Open Publication No. 2006-44970 (JP 2006-44970 A). 
     Shown in  FIG. 12  is a carbon nanocomposite material manufactured using the method disclosed in JP 2006-44970 A. 
     A carbon nanocomposite material  120  is composed of a disaggregated carbon nanomaterial  121  and a plurality of Si microparticles  122  that are uniformly deposited on the surface of the carbon nanomaterial  121 . The Si microparticles  122  are a substance in which Si, which is an element that reacts with carbon and forms a compound, has been crystallized. The Si microparticles  122  are deposited on the surface of the carbon nanomaterial  121 , whereby a reaction layer of SiC forms at the interface, and the Si microparticles  122  are securely deposited on the carbon nanomaterial. 
     Deposition is carried out in conditions in which the temperature of a vacuum furnace is 1400° C. and the furnace pressure is 6×10 −3  to 2.1×10 −1  Pa. 
     However, there are several portions  123  in which the carbon nanomaterial  121  is exposed. The exposed portions  123  remain in a state of poor wettability. 
     For this reason, when the carbon nanomaterial  121  has been mixed with molten resin or molten metal, the bonding of the exposed portions  123  to the resin or metal cannot be expected. As a result, it was made apparent that the expected improvement in strength could not be obtained. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a treatment method that can further improve the wettability of a carbon nanomaterial in order to uniformly disperse the carbon nanomaterial in molten metal or the like. 
     The present inventors investigated the reasons that expected improvement in strength is not obtained in a conventional carbon nanocomposite material. In this investigation, one of the defect factors was found to be that the furnace temperature of a vacuum furnace was set to 1400° C. and the furnace pressure was set to 6×10 −3  to 1×10 −1  Pa. In view of the above, the relationship between the furnace temperature and furnace pressure of the vacuum furnace and the mechanical characteristics of the resulting carbon nanocomposite material were studied in detail. As a result, the appropriate furnace temperature and furnace pressure were identified. A summary of the results is as noted below. 
     According to an aspect of the present invention, there is provided a carbon nanocomposite material comprising: a carbon nanomaterial, and a film formed on the surface of the carbon nanomaterial, wherein the film contains an element Si, and an average film thickness thereof is 10 to 50 nm. 
     A composite metal in which a carbon nanocomposite material having an average film thickness of 10 to 50 nm is added to molten metal reduces the depth of abrasion marks. In other words, a dramatic improvement in hardness and other mechanical properties is observed. The film contains Si. Si is a metal having a melting point at which evaporation is possible under a vacuum, and has good wettability with molten metal. Si is inexpensive and simple to procure, and is therefore advantageous in terms of widely disseminating the present invention. 
     The film is preferably deposited on the entire surface of the carbon nanomaterial. Therefore, the bond between the metal and the carbon nanomaterial is strengthened. 
     According to another aspect of the present invention, there is provided a method for manufacturing a carbon nanocomposite material comprising: a step for mixing a carbon nanomaterial and microparticles that include an element Si; and an evaporation treatment step for placing the resulting mixed substance in a vacuum furnace, evaporating the microparticles under a high-temperature vacuum, and depositing the vapor on a surface of the carbon nanomaterial, wherein the furnace temperature of the vacuum furnace in the evaporation treatment step is set to from 1100 to 1250° C. and the furnace pressure of the vacuum furnace is set to a higher vacuum than the saturated vapor pressure of the microparticles at the temperature thus set. 
     A composite metal in which a carbon nanocomposite material manufactured at a furnace temperature setting of 1100 to 1250° C. is added to molten metal reduces the depth of abrasion marks. In other words, a dramatic improvement in hardness and other mechanical properties is observed. The microparticles are Si. Si is a metal having a melting point at which evaporation is possible under a vacuum, and has good wettability with molten metal. Si is inexpensive and simple to procure, and is therefore advantageous in terms of widely disseminating the present invention. 
     The mixing ratio of the microparticles and the carbon nanomaterial is 1:1. Consequently, a mixing ratio between the microparticles and the carbon nanomaterial of 10:10, that is, 1:1, showed a dramatic improvement in the hardness and other mechanical properties in comparison with a mixing ratio of 5:10 or 1:10. 
     The average particle diameter of the microparticles is preferably 10 μm or less. Unreacted Si is generated when the average particle diameter of the Si microparticles exceeds 20 μm, and there is no such concern at 10 μm or less. Therefore, the average particle diameter of the microparticles is set to 10 μm or less. The average particle diameter is more preferably 1 μm or less. When the average particle diameter is set to 1 μm or less, the microparticles are more readily vaporized, and a carbon nanocomposite material in which the microparticles are thinly and uniformly deposited can be obtained even if the furnace temperature is reduced. 
     In the mixing step, an organic solvent is mixed with the carbon nanomaterial and the microparticles, and the resulting mixture is dried. Carbon nanomaterial readily aggregates, but aggregation can be avoided and uniform mixing can be achieved by mixing the microparticles in an organic solvent. As a result, the carbon nanomaterial can be fully coated by the microparticles. 
     The organic solvent is preferably ethanol. An organic solvent leaves a solvent behind after treatment, and removal of the left solvent therefore becomes a problem. Concerning this point, ethanol is preferred because it can be removed by drying, and post-processing is therefore facilitated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a view showing steps in a method of surface treatment of a carbon nanomaterial according to the present invention; 
         FIGS. 2(   a ) to ( c ) are views showing essential points of measuring the depth of abrasion marks; 
         FIG. 3  is a graph showing a vapor of Si; 
         FIGS. 4(   a ) and ( b ) are enlarged views of a carbon nanocomposite material in embodiment 2; 
         FIGS. 5(   a ) and ( b ) are enlarged views of a carbon nanocomposite material in comparative example 2; 
         FIG. 6  is a graph showing a relationship between the furnace temperature and the depth of abrasion marks; 
         FIG. 7  is a graph showing a relationship between the average film thickness and the depth of abrasion marks; 
         FIG. 8  is a graph in which embodiment 6 is added to the graph shown in  FIG. 6  and in which the relationship is shown between the furnace temperature and the depth of abrasion marks; 
         FIG. 9  is a graph in which embodiment 6 is added to the graph of  FIG. 7  and in which a relationship is shown between the average film thickness and the depth of abrasion marks; 
         FIG. 10  is a schematic view showing a model of a conventional carbon nanofiber; 
         FIGS. 11(   a ) to ( c ) are views showing a problem of conventional carbon nanofiber; and 
         FIG. 12  is an enlarged view of a carbon nanocomposite material manufactured using a conventional method. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is now made to  FIGS. 1A to 1E  showing steps in a method of surface treatment of a carbon nanomaterial according to the present invention. 
     In (a) of  FIG. 1 , a carbon nanomaterial  11  is prepared in an amount of  10  g, for example. A Si powder  12  composed of microparticles containing an element that reacts with carbon and forms a compound is prepared at the same time in an amount of 10 g, for example. 
     In (b) of  FIG. 1 , a container  13  is filled with ethanol  14  as an organic solvent, and the carbon nanomaterial  11  and the Si powder  12  are added. The materials are then agitated and mixed using a mixer  15 . The rotational speed of the mixer  15  is 750 rpm. The materials are sufficiently mixed with about 2 hours of agitation. 
     In (c) of  FIG. 1 , the resulting mixture  16  is filtered and dried. 
     In (d) of  FIG. 1 , the resulting mixture  16  is placed in a zirconium container  17  and covered with a zirconium lid  18 . A non-airtight lid is used as the lid  18  to allow for ventilation between the interior and the exterior of the container  17 . 
     In (e) of  FIG. 1 , a vacuum furnace  20  is provided having an airtight furnace  21 , heating means  22  for heating the interior of the furnace  21 , a stand  23  on which the container  17  is placed, and a vacuum pump  24  for forming a vacuum inside the interior of furnace  21 . The container  17  is placed inside the vacuum furnace  20 . The Si powder  12  in the mixture  16  is vaporized by being heated in the vacuum. The vaporized Si makes contact with the surface of the nearby carbon nanomaterial, forms a compound, and is deposited as a film of SiC. 
     A carbon nanocomposite material  25  in which a film composed of SiC microparticles is deposited on a carbon nanomaterial can be obtained by the method described above. 
     The method of manufacturing a carbon nanocomposite material according to the present invention comprises: step (a) for preparing a carbon nanomaterial  11  and microparticles  12  containing an element that reacts with carbon to form a compound; a mixing step (b) for mixing the carbon nanomaterial  11 , the microparticles  12 , and ethanol  14 ; a drying step (c) for drying the resulting mixture  16 ; and an evaporation treatment step (e) for placing the dried mixture  16  in a vacuum furnace  20 , evaporating the microparticles under a high-temperature vacuum, and depositing the vapor on a surface of the carbon nanomaterial. 
     (a) to (c) of  FIG. 2  are views illustrating essential points of measuring the depth of abrasion marks. A test piece is necessary in order to measure the abrasion marks. In view of the above, a high-temperature container  26  is filled with molten Mg (magnesium)  27 , a 20 mass % equivalent of the carbon nanocomposite material  25  is introduced into the container, and the materials are thoroughly agitated with a stirring rod  28 , as shown in  FIG. 2(   a ). The molten Mg  27  is cooled, and a test piece  29  shown in  FIG. 2(   b ) is produced. The test piece  29  is a flat plate having a thickness of 2 mm, a height of 33 mm, and a width of 30 mm. 
     A test rod  31  shown in  FIG. 2(   c ) by an imaginary line is rubbed against the test piece  29 . The test rod  31  is made of an SUS material and is provided with a spherical surface having a diameter of 10 mm at the distal end (the lower end in the drawing). Contact is made under a pressing force of 200 g (about 3 N), and the test rod is reciprocated 100 times at a distance of 30 mm and a velocity of 600 mm per minute. The depth of the abrasion marks that occur on the surface are measured using a laser microscope. Shallower abrasion marks are preferred. 
     The quality of the carbon nanocomposite material  25  is affected by the furnace temperature and furnace pressure of the vacuum furnace in the evaporation treatment step conducted in the vacuum furnace  20  shown in  FIG. 1(   e ). The system is also affected by the mixture ratio of the carbon nanomaterial  11  and the Si powder  12 , and by the particle diameter (average particle diameter) of the Si powder  12 . The experiment discussed in the next section was performed in order to quantitatively confirm these effects. 
     EXPERIMENTAL EXAMPLES 
     Experimental examples according to the present invention are described below. The present invention is not limited to the experimental examples below. 
     Embodiments 1 to 3 and Comparative Examples 1 to 3 
     A test was carried out in order to establish a suitable value for the furnace temperature in the evaporation treatment step. The experiment conditions and results are summarized in TABLE 1. The asterisks appended to TABLE 1 indicate remarks (the same applies to TABLES 2 to 4). 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                   
                 Embodiment 1 
                 Embodiment 2 
                 Embodiment 3 
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Carbon nanomaterial 
                 10 g 
               
               
                 Si powder 
                 10 g 
               
               
                 Average particle diameter of Si 
                 4 μm 
               
               
                 Mixed liquid 
                 Ethanol 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 * Evaporation 
                 Furnace 
                 1150° C. 
                 1200° C. 
                 1250° C. 
                 1300° C. 
                 1350° C. 
                 1450° C. 
               
               
                 treatment 
                 temperature 
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Furnace 
                 1 × 10 −5  Pa 
               
               
                   
                 pressure 
                   
               
               
                   
                 Time 
                 20 hours 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Carbon 
                 Appearance 
                 — 
                 FIG. 4 
                 — 
                 — 
                 FIG. 5 
                 — 
               
               
                 nanocomposite 
                   
                   
                   
                   
                   
                   
                   
               
               
                 material 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                 Film 
                 Average 
                 Average 
                 Average 
                 Average 
                 Average 
                 Average 
               
               
                   
                 thickness 
                 25 nm 
                 40 nm 
                 50 nm 
                 70 nm 
                 100 nm 
                 120 nm 
               
            
           
           
               
               
            
               
                 Test piece composition 
                 20 mass % carbon nanocomposite material + 80 mass % Mg 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Depth of the abrasion marks 
                 7 μm 
                 6.2 μm 
                 6.5 μm 
                 7.4 μm 
                 7.8 μm 
                 12 μm 
               
            
           
           
               
               
            
               
                 Determination criterion 
                 ½ or less of the depth (14.2 μm) of the abrasion marks in pure Mg 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Determination 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
                 X 
               
               
                   
               
            
           
         
       
     
     In other words, the furnace temperature was changed from 1150° C. to 1450° C. in 50° C. (and 100° C.) increments. Additionally, the furnace pressure was set to 1×10 −5  Pa for the following reasons. 
       FIG. 3  shows a vapor diagram of Si. Si evaporates in the area below the Si vapor line  32  (high-vacuum area). In embodiment (abbreviated to EMB.) 1, the furnace temperature was set at 1150° C. The vapor pressure at 1150° C. was about 3×10 −4  Pa. The pressure was set to 1×10 −5  Pa to allow for this vapor pressure. The Si could be adequately vaporized when the furnace pressure was 1×10 −5  Pa. Embodiments 2 and 3 produced similar results. 
     The evaporation treatment step was completed, and the resulting carbon nanocomposite material  25  was observed under an electron microscope (SEM). Embodiment 2 and comparative example 2 are described with reference to  FIGS. 4 and 5  as a typical example. 
       FIGS. 4(   a ) and ( b ) are enlarged views of a carbon nanocomposite material of embodiment 2 (also referred to as EMB. 2). Compactness was observed in the SiC film  19  formed on the surface of the carbon nanomaterial  11 , as shown in  FIG. 4(   a ). When a cross-section was then observed, the SiC film  19  having a uniform thickness was deposited on the carbon nanomaterial  11 , as shown in  FIG. 4(   b ). The average thickness of the film  19  was about 40 nm. 
       FIGS. 5(   a ) and ( b ) are enlarged views of the carbon nanocomposite material of comparative example (abbreviated to COMP. EX.) 2. The external appearance was observed to have large convexities and concavities in a SiC film  19 ′ formed on the surface of the carbon nanomaterial  11 , as shown in  FIG. 5(   a ). When a cross-section was then observed, the SiC film  19 ′ was rough, variability was observed in the thickness, and the average film thickness was about 100 nm, as shown in  FIG. 5(   b ). 
     Such a carbon nanocomposite material  25  was added to Mg, a test piece was produced, and a test was performed to measure the abrasion marks on the test piece. 
     Prior to this measurement test, criteria for evaluating the depth of the abrasion marks were established using the following procedure. 
     The test piece  29  of  FIG. 2(   c ) was replaced by a pure Mg plate. The pure Mg plate was then rubbed by a test rod  31 , abrasion marks were produced, and the depth of the abrasion marks was measured and found to be 14.2 μm. 
     In the present embodiment, the depth of the abrasion marks can be expected to be less than 14.2 μm because the carbon nanocomposite material was added to Mg to provide reinforcement. In view of the above, the addition of carbon nanomaterial was determined to have an effect at half (½) the value of 14.2 μm or less. 
     Next, a test was performed to measure the abrasion marks on the test pieces of embodiments 1 to 3 and comparative examples 1 to 3, as shown in TABLE 1. 
     The depth of the abrasion marks in embodiment 1 having a furnace temperature of 1,150° C. was 7 μm. 
     The depth of the abrasion marks in embodiment 2 having a furnace temperature of 1,200° C. was 6.2 μm. 
     The depth of the abrasion marks in embodiment 3 having a furnace temperature of 1,250° C. was 6.5 μm. 
     The depth of the abrasion marks in comparative example 1 having a furnace temperature of 1300° C. was 7.4 μm. 
     The depth of the abrasion marks in comparative example 2 having a furnace temperature of 1350° C. was 7.8 μm. 
     The depth of the abrasion marks in comparative example 3 having a furnace temperature of 1400° C. was 12 μm. 
       FIG. 6  is a graph showing the relationship between the furnace temperature and the depth of the abrasion marks. A dramatic effect of the carbon nanomaterial was observed by setting the furnace temperature to a temperature of 1150° C. to 1250° C. Particularly, embodiment 2 exhibited the best effect. In the graph, E1 to E3 represent embodiments 1 to 3. Represented by CE1 to CE3 are comparative examples 1 to 3. 
       FIG. 7  is a graph showing the relationship between the average film thickness and the depth of the abrasion marks. A dramatic effect of the carbon nanomaterial was observed in an average film thickness range of 25 to 50 nm. 
     Comparative Examples (CE) 4 and 5 
     Since embodiment 2 exhibited the best results, embodiment 2 was used as a reference and only the quantity of Si powder was changed. In other words, the quantity of Si powder was 10 g in embodiment 2, but was changed to 5 g in comparative example 4, and 1 g in comparative example 5. The quantity of carbon nanomaterial was kept at 10 g. The result is shown in TABLE 2 below. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Comparative 
                 Comparative 
               
               
                   
                 Embodiment 2 
                 Example 4 
                 Example 5 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Carbon nanomaterial 
                 10 g 
               
            
           
           
               
               
               
               
            
               
                 * Si powder 
                 10 g 
                 5 g 
                 1 g 
               
            
           
           
               
               
            
               
                 Average particle diameter 
                 4 μm 
               
               
                 of Si 
                   
               
               
                 Mixing liquid 
                 Ethanol 
               
            
           
           
               
               
               
            
               
                 Evaporation 
                 Furnace 
                 1200° C. 
               
               
                 processing 
                 temperature 
                   
               
               
                   
                 Furnace 
                 1 × 10 −5  Pa 
               
               
                   
                 pressure 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Time 
                 20 hours 
                 5 hours 
                 5 hours 
               
            
           
           
               
               
            
               
                 Test piece composition 
                 20 mass % carbon nanocomposite  
               
               
                   
                 material + 80 mass % Mg 
               
            
           
           
               
               
               
               
            
               
                 Depth of the abrasion 
                 6.2 μm 
                 7.8 μm 
                 9.1 μm 
               
               
                 marks 
                   
                   
                   
               
            
           
           
               
               
            
               
                 Determination criterion 
                 ½ or less of the depth (14.2 μm) 
               
               
                   
                 of the abrasion marks in pure Mg 
               
            
           
           
               
               
               
               
            
               
                 Determination 
                 ◯ 
                 X 
                 X 
               
               
                 Wettability 
                 35° 
                 40° 
                 42° 
               
               
                   
               
            
           
         
       
     
     In accordance with TABLE 2, the depth of the abrasion marks was 7.8 μm in comparative example 4 in which the carbon nanomaterial was 10 g and the Si powder was 5 g. 
     The depth of the abrasion marks was 9.1 μm in comparative example 5 in which the carbon nanomaterial was 10 g and the Si powder was 1 g. 
     Wettability was also studied. A detailed description will be omitted because the measurement method is the same as the method disclosed in Japanese Laid-open Patent Publication No. 2006-44970. 
     A lower level of wettability is preferred. The wettability results were 35° in embodiment 2, 40° in comparative example 4, and 42° in comparative example 5. Comparative examples 4 and 5 had poorer wettability than Embodiment 2. 
     It was confirmed from embodiment 2 and comparative examples 4 and 5 that it is best to mix 10 g of Si powder with 10 g of carbon nanomaterial. 
     Comparative Examples 6 and 7 
     Si powder having an average particle diameter of 4 μm was used in TABLES 1 and 2 described above. Time is required when the particle diameter of the Si is increased, and an unfinished reaction is expected in an evaporation treatment time of 20 hours. 
     In view of the above, an experiment was performed in which the average particle diameter of the Si powder was changed to 10 μm and 20 μm. The results are shown in TABLE 3 below. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Comparative 
                 Comparative 
               
               
                   
                 Embodiment 2 
                 Embodiment 3 
                 Embodiment 4 
                 Embodiment 5 
                 Example 6 
                 Example 7 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Carbon nanomaterial 
                 10 g 
               
               
                 Si powder 
                 10 g 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Average particle diameter 
                 4 μm 
                 4 μm 
                 10 μm 
                 10 μm 
                 20 μm 
                 20 μm 
               
               
                 of Si 
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
            
               
                 Mixed liquid 
                 Ethanol 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Evaporation 
                 Furnace 
                 1200° C. 
                 1250° C. 
                 1200° C. 
                 1250° C. 
                 1200° C. 
                 1250° C. 
               
               
                 processing 
                 temperature 
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Furnace 
                 1 × 10 −5  Pa 
               
               
                   
                 pressure 
                   
               
               
                   
                 Time 
                 20 hours 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Unreacted Si 
                 None 
                 None 
                 Trace 
                 None 
                 Large 
                 Large 
               
               
                   
                   
                   
                   
                   
                 amount 
                 amount 
               
            
           
           
               
               
            
               
                 Determination criterion 
                 Trace amounts of or no unreacted Si 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Determination 
                 ◯ 
                 ◯ 
                 ◯ 
                 ◯ 
                 X 
                 X 
               
               
                   
               
            
           
         
       
     
     When the resulting carbon nanocomposite material was measured using a particle size distribution measuring apparatus (Horiba LA-920 laser diffraction particle size distribution analyzer), unreacted Si powder could not be detected in embodiments 2 and 3 in which the average particle diameter of the Si was 4 μm. 
     Trace amounts of the unreacted Si powder were detected in embodiment 4 (furnace temperature: 1200° C.) in which the average particle diameter of the Si was 10 μm. However, the amount was within acceptable limits. 
     Unreacted Si powder could not be detected in embodiment 5 (furnace temperature: 1250° C.) in which the average particle diameter of the Si was 10 μm. 
     A large amount of the unreacted Si powder was detected in embodiment 6 (furnace temperature: 1200° C.) in which the average particle diameter of the Si was 20 μm. 
     A large amount of the unreacted Si powder was detected in embodiment 7 (furnace temperature: 1250° C.) in which the average particle diameter of the Si was 20 μm. 
     Consequently, it is desirable to use Si powder having an average particle diameter of 10 μm or greater. 
     An additional experiment was subsequently performed in relation to the embodiment shown in TABLE 1 described above. The content and results are described below. 
     Embodiment 6 
     The experiment conditions of embodiment 6 are as shown in TABLE 4. Embodiment 1 described in TABLE 1 is included for reference. 
     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Embodiment 6 
                 Embodiment 1 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Carbon nanomaterial 
                 10 g 
               
               
                 Si powder 
                 10 g 
               
            
           
           
               
               
               
            
               
                 Average particle diameter of Si 
                 1 μm 
                 4 μm 
               
            
           
           
               
               
            
               
                 Mixed liquid 
                 Ethanol 
               
            
           
           
               
               
               
               
            
               
                 Evaporation treatment 
                 Furnace 
                 1100° C. 
                 1150° C. 
               
               
                   
                 temperature 
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Furnace 
                 1 × 10 −5  Pa 
               
               
                   
                 pressure 
                   
               
               
                   
                 Time 
                 20 hours 
               
            
           
           
               
               
               
               
            
               
                 Carbon nanocomposite 
                 Appearance 
                 — 
                 — 
               
               
                 material 
                 Film thickness 
                 Average 10 nm 
                 Average 25 nm 
               
            
           
           
               
               
            
               
                 Test piece composition 
                 20 mass % carbon 
               
               
                   
                 nanocomposite material + 
               
               
                   
                 80 mass % Mg 
               
            
           
           
               
               
               
            
               
                 Depth of the abrasion marks 
                 7.1 μm 
                 7 μm 
               
            
           
           
               
               
            
               
                 Determination criterion 
                 ½ or less of the depth 
               
               
                   
                 (14.2 μm) of the abrasion 
               
               
                   
                 marks in pure Mg 
               
            
           
           
               
               
               
            
               
                 Determination 
                 ◯ 
                 ◯ 
               
               
                   
               
            
           
         
       
     
     In other words, 10 g of the carbon nanomaterial and 10 g of Si powder were mixed in the same manner as embodiment 1 (TABLE 1). The average particle diameter of the Si was 1 μm (4 μm, in embodiment 1). Ethanol was used for the mixed liquid in the same manner as in embodiment 1. 
     The furnace temperature in the evaporation treatment was 1100° C. (1150° C., in embodiment 1). The furnace pressure was 1×10 −5  Pa in the same manner as in embodiment 1, and the evaporation time was 20 hours in the same manner as in embodiment 1. 
     In accordance with the vapor diagram of  FIG. 3 , Si can be evaporated because the intersection point between the horizontal axis at 1100° C. and the vertical axis at 1×10 −5  Pa is in the area below the Si vapor line  32  (high vacuum area). Although evaporation is possible, the rate of evaporation is reduced. 
     The average particle diameter of the Si, which was 4 μm in embodiment 1, was set to 1 μm in embodiment 6 as a countermeasure. The microparticles could be readily vaporized by setting the average particle diameter to 1 μm, and a carbon nanocomposite material in which the microparticles were thinly and uniformly deposited could be obtained even when the furnace temperature was reduced. 
     The results shown in TABLE 4 above were obtained after an experiment was performed using the conditions noted above. 
     In other words, the average thickness of the carbon nanocomposite material was 10 nm, and the depth of the abrasion marks was 7.1 μm. 
       FIG. 8  is a graph in which the results of embodiment 6 have been added to  FIG. 6 . 
       FIG. 8  is a graph to which embodiment 6 is added, and the graph shows the correlation between the furnace temperature and the depth of the abrasion marks. A dramatic effect of the carbon nanomaterial was observed by setting the furnace temperature to from 1100 to 1250° C. In particular, embodiment 2 provided the best results. 
       FIG. 9  shows a graph in which the results of embodiment 6 have been added to  FIG. 7 . 
       FIG. 9  is a graph to which embodiment 6 is added, and the graph shows the correlation between the furnace temperature and the depth of the abrasion marks. A dramatic effect of the carbon nanomaterial was observed when the average film thickness was from 10 to 50 nm. 
     In addition to ethanol, the organic solvent may be methanol or another alcohol; acetone, methyl ethyl ketone, or another ketone; or other ethanols. An aqueous solution that includes these may also be used.