JP3974604B2 - Surface treatment method of carbon nanomaterial - Google Patents

Description

  The present invention relates to a carbon nanomaterial surface treatment technique and a carbon nanocomposite for the purpose of improving wettability.

  Various fiber reinforced materials called glass fiber reinforced plastic (FRP), carbon fiber reinforced plastic (CFRP), fiber reinforced ceramics (FRC), and carbon fiber reinforced metal (CFRM) have been proposed.

In recent years, special carbon fibers called carbon nanofibers have attracted attention as reinforcing materials, and methods for utilizing them have been proposed (for example, see Patent Document 1).
JP 2003-102343 A (Claim 3)

  Patent Document 1 is characterized in that the overall strength is improved by mixing carbon nanofibers in a resin-based material. Since the resin-based material and the carbon nanofiber can be bonded with an impregnating agent called lysine, there is no difficulty in integration.

  On the other hand, when we tried to use carbon nanofibers as a reinforcing material for metals such as aluminum, there were problems that we had never experienced. The details of carbon nanofibers and their problems will be described next.

  FIG. 8 is a model diagram of a carbon nanofiber. The carbon nanofiber 110 has a configuration in which a sheet of carbon atoms arranged in a hexagonal network is wound in a cylindrical shape, and a diameter D is 1.0 nm (nanometer). Since it is ˜150 nm and at the nano level, it is called carbon nanofiber, carbon nanomaterial or carbon nanotube. The length L is several μm to 100 μm.

  A diamond is a very hard substance in which carbon atoms are arranged in a cubic lattice. Since the carbon nanofiber 110 has a regular crystal structure like diamond, the mechanical strength is large.

FIG. 9 is a diagram for explaining the problems of the carbon nanofiber.
In (a), the container 111 is filled with the medium 112, and the carbon nanofiber 113 is put into the medium 112.

In (b), the agitator 114 is sufficiently stirred. This agitation may be performed with a vibration agitator.
(C) shows a state after being left for a certain period of time, and it can be seen that the carbon nanofiber 113 is deposited on the bottom of the container 111.
In addition, if the specific gravity of the medium 112 is large, the carbon nanofiber 113 is accumulated on the top.

When the medium 112 is a molten metal, the carbon nanofibers 113 cannot be evenly dispersed in the metal if the carbon nanofibers 113 accumulate on the molten metal.
The cause is that the carbon nanofiber 113 has poor wettability with respect to the molten metal.

  This invention makes it a subject to provide the processing method which can improve the wettability of carbon nanomaterial, in order to disperse | distribute carbon nanomaterial uniformly to molten metal.

The surface treatment method for a carbon nanomaterial according to claim 1 is a method of mixing a carbon nanomaterial with a metal powder made of Si or Ti that reacts with carbon to form a compound, and puts the obtained mixture into a vacuum furnace. A vapor deposition process step of evaporating the metal powder under a high temperature vacuum and attaching the vapor to the surface of the carbon nanomaterial, the carbon nanomaterial surface treatment method comprising a vacuum furnace If the metal powder is Si, the furnace temperature is maintained at 1350 to 1400 ° C., and if the metal powder is Ti, the furnace temperature is maintained at 1360 to 1550 ° C., and the furnace pressure is maintained at the saturated vapor pressure state of the metal, The mixture is stirred by a bubbling stirring action accompanying the evaporation of the metal powder to promote contact between the carbon nanomaterial and the metal vapor .

  In the invention according to claim 1, the carbon nanomaterial is mixed with a metal powder containing an element that reacts with carbon to form a compound, and the resulting mixture is placed in a vacuum furnace to evaporate the metal powder under a high temperature vacuum. This vapor is attached to the surface of the carbon nanomaterial. Metal fine particles can be attached to the surface of the carbon nanomaterial in two steps, a mixing step and a vapor deposition step.

The metal fine particles generate carbon and a compound, and this compound exhibits a bonding action, so that the metal fine particles are firmly bonded to the carbon nanomaterial.
When the carbon nanomaterial is mixed in the molten metal, the metal fine particles have high wettability with the molten metal, so that the carbon nanomaterial can be evenly dispersed in the molten metal.

In addition, in the invention according to claim 1 , the metal powder is evaporated in the vapor deposition treatment step, and the mixture is stirred by the bubbling stirring action accompanying this evaporation. Agitation promotes contact between the carbon nanomaterial and the metal vapor. Therefore, the metal fine particles can be evenly dispersed on the surface of the carbon nanomaterial.

Furthermore, in the invention according to claim 1 , the metal is Si or Ti.
Both Si and Ti are metals having a melting point that can be deposited under vacuum, and also have good wettability with molten metal. Since both Si and Ti are easily available, and especially Si is inexpensive, it is suitable for widely spreading the method of the present invention.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is a process explanatory diagram of a carbon nanomaterial surface treatment method according to the present invention.
(A): A carbon nanomaterial 11 is prepared. For example 10g.
(B): Si powder 12 is prepared. For example 1g.

(C): Carbon nanomaterial 11 and Si powder 12 are put in mortar 13 and mixed with pestle 14 for 15 to 30 minutes.
(D): The obtained mixture 15 is put in an alumina container 16 and covered with an alumina lid 17. The lid 17 employs a non-sealing lid, thereby allowing ventilation between the inside and the outside of the container 16.

  (E): A vacuum furnace 20 including a closed furnace body 21, heating means 22 for heating the inside of the furnace body 21, a table 23 on which the container 16 is placed, and a vacuum pump 24 for evacuating the inside of the furnace body 21 is prepared. The container 16 is put in the vacuum furnace 20.

  Although the heating conditions and pressure conditions in the vacuum furnace 20 will be described in the next figure, the Si powder in the mixture 15 evaporates by heating under vacuum. This vapor stirs the space formed by the container 16 and the lid 17 so as to foam. Such an action is called bubbling stirring. The carbon nanomaterial is unwound by this bubbling agitation, and Si vapor comes into contact with the surface of the unraveled carbon nanomaterial to form a compound, which adheres as Si fine particles.

  To summarize FIG. 1, a step of mixing carbon nanomaterial 11 with metal powder 12 containing an element that reacts with carbon to form a compound, and the resulting mixture 15 is placed in a vacuum furnace 20, and metal under high temperature vacuum. A carbon nanomaterial surface treatment method comprising: a vapor deposition treatment step of evaporating the powder 12 and attaching the vapor to the surface of the carbon nanomaterial 11.

FIG. 2 is a graph of furnace temperature and pressure in the furnace corresponding to Si. The horizontal axis represents time, and the vertical axis represents furnace temperature and pressure in the furnace.
Start to 5:00: The furnace temperature is raised from room temperature to 300 ° C. over 5 hours at a vacuum degree of 6 × 10 ⁻³ Pa.

5:00 to 9:00: The furnace temperature is raised from 300 ° C. to 1400 ° C. over 4 hours at a vacuum degree of 5.3 × 10 ^{−3 to} 2.1 × 10 ⁻² Pa.
9 o'clock to 19 o'clock: Hold for 10 hours under conditions of a vacuum degree of 2.1 × 10 ⁻² Pa and 1400 ° C.

Since the melting point of Si is 1427 ° C., the temperature is maintained at a temperature just below the melting point (1350 to 1400 ° C.), and Si is maintained in a saturated vapor pressure state at this temperature. At 1350 ° C., the saturated vapor pressure is about 1.3 × 10 ⁻³ Pa, and at 1400 ° C., the saturated vapor pressure is about 2.1 × 10 ⁻² Pa. Since this degree of vacuum can be easily achieved in a vacuum furnace, the treatment temperature is suitably 1350 to 1400 ° C. However, 1350 ° C. has a low evaporation rate, and 1400 ° C. has a high evaporation rate.

  Next, SiC (silicon carbide) which is a compound of Si and carbon will be described. The standard free energy of formation of SiC is −39.6 kJ / mol at 1400 ° C., and this condition can be satisfied. Therefore, it is considered that Si vapor reacts with carbon of the carbon nanomaterial to become SiC.

Therefore, if the mixture is placed in a semi-sealed container and the Si powder is evaporated, bubbling agitation occurs, and Si fine particles can adhere to the carbon nanomaterial.
The long holding time of 10 hours was aimed at sufficient agitation and reaction. Of course, the holding time may be increased or decreased depending on conditions such as the mixing ratio and the processing amount.

After 19:00: Although the heating means is stopped, furnace cooling is performed while maintaining a vacuum degree of 1.1 × 10 ⁻³ Pa. Furnace cooling is a technique for cooling a product very gradually.

  FIG. 3 is an enlarged view of the carbon nanocomposite material manufactured by the method of the present invention. Si fine particles 31 are included. As described above, these Si fine particles 31 are obtained by crystallizing Si, which is an element that reacts with carbon to form a compound.

  Furthermore, it is important that the Si fine particles 31 are attached to the carbon nanomaterial 11 through SiC which is a carbide. The carbon nanomaterial 11 itself has poor wettability. Therefore, there is a possibility that the bonding strength is insufficient if it is simple Si particles. In this regard, by attaching Si fine particles to the surface of the carbon nanomaterial 11, a SiC reaction layer is formed at the interface, and the Si fine particles 31 can be firmly attached to the carbon nanomaterial 11.

Next, the wettability of the carbon nanocomposite material 30 is examined.
FIG. 4 is a principle diagram of wettability evaluation of the carbon nanocomposite material.
In (a), the carbon nanocomposite material 30 of the present invention is closely bonded to a base material 33 made of steel (for example, SKD61) by a discharge plasma sintering method, a small hole 34 is opened in the center, and the surface is polished.

  (B) is an embodiment diagram, and after putting the carbon nanocomposite material 30 together with the base material 33 into the vacuum chamber 35 and evacuating it with the vacuum pump 36, the argon gas is supplied from the argon gas supply pipe 37, and the vacuum chamber The inside of 35 is made a non-oxidizing atmosphere. Further, the inside of the vacuum chamber 35 is set to the same temperature as the molten magnesium alloy (700 ° C.).

Next, the molten magnesium alloy 39 is pushed up using the cylinder 38. The molten magnesium alloy 39 spread on the carbon nanocomposite material 30 and became a dome shape. Let the wetting angle at this time be θ1.
Members (such as the cylinder 38 and the built-in piston) that come into contact with the molten magnesium alloy are made of an aluminum nitride material to prevent reaction with the molten metal.

  (C) is a comparative example, and when the carbon nanomaterial 11 (see FIG. 1 (a)) is closely bonded to the base material 33 and the molten magnesium alloy 39 is similarly pushed up, the molten magnesium alloy 39 is almost spherical. Became. The wetting angle at this time is θ2.

FIG. 5 is a graph showing the touch angle of Example 1 and the comparative example, and the right vertical axis indicates the wetting angle.
Example 1 showed θ1, and θ1 was 42 °. The comparative example showed θ2, and θ2 was 157 °.
As is well known, wettability is best when the wetting angle is 0 °, and worst when it is 180 °. Thus, the left vertical axis of the graph indicates the wettability. It can be confirmed that Example 1 has much better wettability than the comparative example.

  Returning to FIG. 3, the carbon nanomaterial 11 has poor wettability. On the other hand, the Si fine particles 31 have good wettability. Therefore, the wettability of the carbon nanocomposite material 30 is earned by the Si fine particles 31. The Si fine particles 31 exhibit wettability when mixed with a molten metal such as a magnesium alloy later. For this reason, the carbon nanomaterial can be uniformly dispersed in the molten metal, and if the molten metal is cooled and solidified in this state, a high-quality product (or molded product) can be obtained.

Next, an example in which the metal powder is changed to Ti powder will be described.
The powder 12 in FIG. 1 (b) was changed to Ti powder, other conditions were fit proceeds to FIG. 1 (e) as is. However, the temperature conditions and pressure conditions of the vacuum furnace 20 were as follows.

FIG. 6 is a graph of furnace temperature and furnace pressure corresponding to Ti, with the horizontal axis representing time and the vertical axis representing furnace temperature and pressure in the furnace.
Start to 5:00: The furnace temperature is raised from room temperature to 300 ° C. over 5 hours at a vacuum of 1.4 × 10 ⁻³ Pa.

5:00 to 9:00: The furnace temperature is increased from 300 ° C. to 1450 ° C. over 4 hours at a vacuum degree of 1.5 × 10 ^{−3 to} 1.3 × 10 ⁻² Pa.
9 o'clock to 19 o'clock: Hold for 10 hours under conditions of a vacuum degree of 1.0 × 10 ⁻² Pa and 1450 ° C.

  Since the melting point of Ti is 1680 ° C., the temperature is maintained at a temperature just below the melting point (1360 to 1550 ° C.), and Ti is maintained at a saturated vapor pressure state at this temperature. Since the standard free energy of formation of TiC is about −150 kJ / mol at 1450 ° C. and this condition can be satisfied, it is considered that Ti vapor reacts with carbon of the carbon nanomaterial to become TiC.

After 19:00: Although the heating means is stopped, the furnace is cooled while maintaining the vacuum degree of 1.2 × 10 ⁻³ Pa.

FIG. 7 is a graph showing the touch angle of Example 2 and the comparative example, and the right vertical axis indicates the wetting angle.
Example 2 showed θ1, and θ1 was 119 °. The comparative example showed θ2, and θ2 was 157 °.
The left vertical axis of the graph indicates good or bad wettability, and it was confirmed that Example 2 had better wettability than the comparative example.

In addition, although Si and Ti were illustrated as an element which reacts with carbon and produces | generates a compound, Zr (zirconium) and V (vanadium) are employable as others.
The molten metal as the base material is preferably a magnesium alloy or an aluminum alloy.

  The present invention is suitable for a surface treatment method for a carbon nanomaterial added to a molten magnesium alloy.

It is process explanatory drawing of the surface treatment method of the carbon nanomaterial which concerns on this invention. It is a graph of the furnace temperature and the furnace pressure corresponding to Si. It is an enlarged view of the carbon nanocomposite material manufactured by the method of the present invention. It is a principle figure of wettability evaluation of a carbon nanocomposite material. It is a graph which shows the touch angle of Example 1 and a comparative example. It is a graph of the furnace temperature and furnace pressure corresponding to Ti. It is a graph which shows the touch angle of Example 2 and a comparative example. It is a model figure of a carbon nanofiber. It is a figure explaining the problem of carbon nanofiber.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Carbon nanomaterial, 12 ... Si powder as metal powder, 15 ... Mixture, 20 ... Vacuum furnace, 30 ... Carbon nanocomposite material, 31 ... Si fine particle as metal fine particle.

Claims (1)

A step of mixing a carbon nanomaterial with a metal powder composed of Si or Ti that reacts with carbon to form a compound, and the resulting mixture is placed in a vacuum furnace to evaporate the metal powder under a high temperature vacuum. A vapor deposition process step for attaching the carbon nanomaterial to the surface of the carbon nanomaterial, and a carbon nanomaterial surface treatment method comprising:
In the vapor deposition treatment step, the furnace temperature of the vacuum furnace is maintained at 1350 to 1400 ° C. if the metal powder is Si, 1360 to 1550 ° C. if the metal powder is Ti , and the furnace pressure is set to metal. maintaining the saturated vapor pressure state, the surface of the metal by bubbling stirring effect due to evaporation of the powder, the mixture was stirred carbon nanomaterial, features and to Luke Bon'nano material to the urge contact with the metal vapor Processing method.

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