JP2002105765A - Carbon nanofiber compound and method for producing carbon nanofiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grow carbon nanofibers in a high density on the surface of a substrate. SOLUTION: When a substrate 1 comprising the intermediate phase of nickel oxide and magnesium oxide is disposed in a reducing atmosphere, the nickel oxide is selectively reduced and deposited. Since the nickel deposited from the intermediate phase is uniformly and densely disposed on the surface of the substrate in a fine size, the carbon nanofibers 2 grown from the nickel are also fine, uniform and dense.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon nanofiber composite and a method for producing a carbon nanofiber, and more particularly to a carbon nanofiber composite and a carbon nanofiber in which a plurality of carbon nanofibers are grown at a high density on a substrate. And a method for producing the same.

[0002]

2. Description of the Related Art In recent years, various excellent characteristics have been found in carbon nanofibers represented by carbon nanotubes and the like, and researches have been actively conducted.

For example, it has been reported that it has a hydrogen absorbing / releasing ability (J. Phys. Chem. B, 102 (1998) 4253.) and high methane (natural gas) absorption characteristics. Also, due to the extremely high current density of field emission electrons, attention has been paid to electron emission materials for displays.

[0004] On the other hand, the carbon nanofiber is conventionally obtained by growing one carbon nanofiber on seed element fine particles such as nickel.

[0005] The resulting carbon nanofibers are very fine and are difficult to handle. In addition, simply filling the individually grown carbon nanofibers inevitably makes them bulky.

For this reason, when hydrogen or methane gas is absorbed, the container cannot be filled at a high density, and after filling, the gas is discharged from the container, resulting in a low gas absorption amount per container volume. there were.

There is also known a method of growing carbon nanofibers on the surface of a Ni substrate in a uniform direction. However, since it is necessary to use plasma CVD for growing carbon nanofibers, productivity is low. In addition, the manufacturing cost increases.

[0008]

As described above, conventionally, it has been difficult to easily produce carbon nanofibers as a high-density aggregate.

An object of the present invention is to provide a carbon nanofiber composite in which carbon nanofibers are grown at a high density on a substrate surface and a method for producing carbon nanofibers, which can be produced by a simple method.

[0010]

Means for Solving the Problems The carbon nanofiber composite of the present invention is obtained by growing a substrate having an intermediate phase of an oxide of a transition metal and an oxide of a non-reducible metal, and the seed element deposited on the surface of the substrate. It is characterized by having a carbon nanofiber that has been prepared.

[0011] In the method for producing carbon nanofibers of the present invention, a substrate having an intermediate phase of a transition metal oxide and a hardly reducible metal oxide is reduced in a reducing atmosphere to precipitate a seed element in the intermediate phase. Then, a carbon-containing gas is brought into contact with the deposited seed element to grow carbon nanofibers from the seed element.

Further, the base having the intermediate phase can be formed by heating a mixed powder containing a seed element oxide powder containing a transition metal and a non-reducible metal oxide powder to a reaction temperature.

According to the method for producing carbon nanofibers of the present invention, a mixed powder comprising Fe ₂ O ₃ and Al ₂ O ₃
C. to form a substrate having an intermediate phase composed of FeAlO ₃ by heating at a temperature of not less than 100 ° C., and reducing the substrate in a reducing atmosphere to precipitate Fe in the intermediate phase.
e is brought into contact with a carbon-containing gas to grow carbon nanofibers using Fe as a catalyst.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below.

FIG. 1 is a conceptual diagram showing a cross section of a carbon nanofiber composite of the present invention.

Innumerable carbon nanofibers are grown without gaps on the surface of the substrate 1 composed of an intermediate phase of a transition metal-containing seed element oxide and a hardly reducible oxide.

The substrate 1 has only to have an intermediate phase between a seed element oxide containing a transition metal and a hardly reducible metal oxide. For example, a substrate composed of only an intermediate phase as shown in FIG. A substrate having an intermediate phase formed on a part of the substrate surface may be used.

The “intermediate phase” of the oxide of the seed element and the hardly reducible metal oxide according to the present invention is, as usually used in an alloy system, an oxide of the seed element or a hardly reducible metal oxide. It is not a pure phase of an oxide, but a phase that can be clearly identified. That is, it is a compound obtained by reacting an oxide of a seed element with a hardly reducible metal oxide, and refers to a phase having a crystal structure including a seed element, a hardly reducible metal element, and oxygen.

Oxides of seed elements include, for example, Fe, Co, C
An oxide such as r or Ni may be used, and when these oxides are reduced, a seed element is formed in the intermediate phase. The carbon nanofiber grows using the seed element as a catalyst.

The non-reducible metal oxide refers to an oxide of a metal having a lower reducing property than at least an oxide of a seed element used, and in particular, hydrogen at 15 ° C. to 1000 ° C. or reduced to a metal under plasma conditions. It is preferable to use a metal oxide that is not used. Using hydrogen at 15 ° C. to 500 ° C. or a metal oxide reduced to metal under plasma conditions,
When the seed element is reduced, it may be reduced to a non-reducible metal oxide, and an alloy of the seed element and the non-reducible metal may be precipitated. As a result, the function of the seed element as a catalyst is reduced. .

Further, it is necessary to use the non-reducible metal oxide which forms an intermediate phase with the oxide of the seed element. The intermediate phase differs depending on the combination with the seed element oxide used. For example, when iron oxide is selected as the seed element oxide, Al, Y, Mg, Zn, Ti, Cu, V, or M
oxide of n. Similarly, when nickel oxide is used as the oxide of the seed element, Al, Si or V
If chromium oxide is used, Y or M
g of oxide, Al when cobalt oxide is used,
An oxide of Si, Ti or V can be used.

The intermediate phase obtained by such a combination is:
FeAlO_Three, FeYO_Three, Fe_TwoMgO_Four, Fe_TwoZn
O_Four, Fe_TwoTiO_Five, Fe_TwoCuO_Four, FeVO_Four, FeV
_TwoO₆, FeV_TwoO_Four, Fe_TwoMnO_Four, NiAl_TwoO_Four, Ni
Al₆O_Ten, Ni_TwoAl₁₈O₂₉, Ni_TwoSiO_Four, Ni (V
O_Three)_Two, Ni_Three(VO_Four)_Two, Cr_TwoMgO_Four, CoAl
_TwoO _Four, Co_TwoSiO_Four, Co_TwoTiO_Four, CoTiO_Three, C
oTi_TwoO_FiveOr Co (VO_Three)_Two, Co_Three(VO_Four)_Two,
Co_TwoV_TwoO₇And the like.

The carbon nanofiber according to the present invention is a fiber having a graphite structure and a diameter of 1 μm or less and a length of about 1 μm to 1 mm. For example, the c-plane of graphite is oriented in the fiber length direction. Examples include a laminated shape and a tube shape having a c-plane of graphite as a side wall.

Next, a method for producing the carbon nanofiber composite of the present invention will be described.

First, a method of manufacturing a substrate according to the present invention will be described.

The substrate according to the present invention can be prepared from an oxide of a seed element and a hardly reducible metal oxide.

For example, a mixed powder in which both raw material powders of an oxide powder of a seed element and a non-reducible metal oxide powder are uniformly dispersed is prepared, and the mixed powder is formed into a desired shape under pressure. By sintering at a temperature equal to or higher than the reaction temperature of the powder, it is possible to obtain a substrate composed of an intermediate phase between the oxide of the seed element and the hardly reducible metal oxide.

For example, Fe ₂ O is used as a seed element oxide.
_In the case where an intermediate phase made of FeAlO ₃ is prepared using Al ₂ O ₃ as a raw material as a hardly reducible metal oxide, Fe ₂ O ₃
At a temperature of 1200 ° C. or higher, which is the reaction temperature between Al ₂ O ₃ and
Heating may be performed for 0.5 hour or more.

The seed element and the non-reducible metal, the oxide of the seed element and the non-reducible metal, or the seed element and the non-reducible metal oxide are heated in an oxygen-containing atmosphere under the above-described conditions. By applying, a substrate having an intermediate phase can be prepared.

The intermediate phase thus obtained, for example F
eAlO_ThreeIs Fe_TwoO_ThreeAnd Al _TwoO_ThreeThe base case of
In contrast to the hexagonal (Hexagonal)
It becomes Orthrhombic.

The ratio between the oxide of the seed element and the hardly reducible metal oxide is not particularly limited as long as the composition ratio forms an intermediate phase, but the entire surface in contact with the gas containing carbon is uniform. In consideration of growing carbon nanofibers having a high density, it is preferable that the ratio be approximately the same as the ratio of the seed element of the intermediate phase to be formed and the non-reducible metal (for example, 1: 1 in the case of FeAlO ₃ ).

The average particle size of the raw material powders used is desirably within the range of 100 μm or less.
If the average particle size of the raw material powder is larger than 100 μm, it takes a long time to react the mixed powder, and in some cases, both unreacted raw material powders may remain. On the other hand, raw material powders having an average particle size smaller than 10 nm are difficult to produce and have poor handling properties.
Raw material powder having an average particle size of about 0 μm is used.

Further, a layer comprising an intermediate phase may be formed on an arbitrary substrate surface to form a substrate.

For example, a desired conductive or insulating substrate is prepared, and a seed element oxide and a non-reducible metal oxide are prepared by a PVD method such as vapor deposition, a plating method, or a sol-gel method using an alkoxide. By forming a mixed layer made of and heating the mixed layer to a temperature equal to or higher than the reaction temperature, an intermediate phase can be formed on the substrate surface.

As described above, the intermediate phase obtained by sintering is used as a sputter target or a vapor deposition source,
A layer composed of an intermediate phase can be directly formed on the substrate surface.

When a layer comprising an intermediate phase is formed on the surface of the substrate and then brought into contact with a gas containing carbon, carbon nanofibers are formed only in the region where the intermediate phase exists. Therefore, for example, by forming a layer made of an intermediate phase into a desired shape using a mask pattern or the like, it becomes possible to selectively grow carbon nanofibers only from a desired region of the substrate.

Further, for example, by using a substrate having an intermediate phase formed on the surface of a conductive substrate, the conductive substrate and the oxide of the seed element can be electrically connected. As will be described later, the seed element components in the intermediate phase are reduced and partially precipitated in the intermediate phase. Therefore, if a layer composed of a thin intermediate phase is formed on the surface of the conductive substrate, the conductive substrate and the carbon nanofibers are connected via the seed element, and the base and the carbon nanofibers are electrically connected. A carbon nanofiber composite can be formed.

As described above, in order to electrically connect the base and the oxide of the seed element, the thickness of the layer made of the intermediate phase is desirably 100 μm or less. However, if the thickness of the layer composed of the intermediate phase is too small, the absolute amount of the seed element component becomes small, and the carbon fiber may not grow. Therefore, it is desirable that the thickness of the layer composed of the intermediate phase is 1 μm or more.

Next, a method for growing carbon nanofibers on the substrate surface will be described.

By heating the substrate obtained as described above in a reducing atmosphere, the seed element components in the intermediate phase are reduced and deposited. The deposited seed element functions as a catalyst for decomposing the carbon-containing gas, and has a function of precipitating an oxide of the seed element while decomposing the gas.

The reducing gas is not particularly limited as long as it can reduce the seed element components. For example, a hydrogen gas or a carbon monoxide gas may be used. Further, the seed element component can be reduced by using a gas containing carbon. In this case, the growth of an oxide of the seed element described later can be performed at the same time.

The seed element is precipitated in the intermediate phase reduced by the reducing gas as described above. However, since the seed element is uniformly dispersed in the order of atoms in the intermediate phase, it is innumerable on the surface of the intermediate phase. The seed element deposited at the point (1) has a fine and uniform size and a uniform interval.

As a gas containing carbon to be brought into contact with the deposited seed element, that is, a raw material gas for growing carbon nanofibers, for example, methane gas, ethylene gas or the like can be used.

The heating temperature and heating time for the reduction vary depending on the composition of the intermediate phase. For example, when FeAlO ₃ is used as the intermediate phase, the heating temperature is 400 to 1000.
The heating temperature is preferably in the range of 1 minute to 3 hours. If the heating temperature is lower than 400 ° C., it is difficult to sufficiently reduce and precipitate the seed element components. on the other hand,
When the heating temperature is higher than 1000 ° C., the deposition rate of the seed element is increased, and it is difficult to control the size of the seed element to be deposited. There is a possibility that the distance between the carbon nanofibers may increase. Also,
If the heating time after the reduction start temperature is shorter than 1 minute, the seed element component cannot be sufficiently deposited, and the carbon nanofibers may not be grown. In addition, the heating time is longer than 3 hours. Then, the size of the seed element to be deposited is increased, and the diameter of each obtained carbon nanofiber is increased, and in some cases, the interval between the growing carbon nanofibers is increased.

As described above, since the carbon nanofibers are grown using the base material in which the seed elements are uniformly dispersed in the atomic order, the seed elements functioning as a catalyst for growing the carbon nanofibers are equally spaced. Since the carbon nanofibers are deposited in substantially the same size in this step, nucleation of carbon nanofibers is generated substantially uniformly from this catalyst, and it is possible to grow carbon nanofibers uniformly and densely on the substrate surface.

It is assumed that the hardly reducible metal oxide and the oxide of the seed element are unreacted due to, for example, insufficient heat treatment, and are merely a solid solution composed of the hardly reducible metal oxide and the oxide of the seed element. When is used as the substrate, the timing at which the nuclear embryos exceed the critical nucleus differs depending on the concentration of the seed element. FIG. 4 shows carbon nanofibers when a solid solution of a non-reducible metal oxide and an oxide of a seed element (a substrate in which both oxides did not react and an intermediate phase was not formed) was used as a substrate. 1 shows a conceptual diagram of a complex. As shown in FIG. 4, when a simple solid solution is used for the substrate 101,
Since the seed element to be deposited has a different particle diameter, the resulting seed element oxide has a different diameter, and the carbon nanofiber 1
02 may not grow uniformly on the surface of the substrate or the diameter may be coarsened. Further, a region where the carbon nanofiber does not grow (a region where the seed element does not grow to a size sufficient to function as a catalyst) remains, and a gap may be formed between the carbon nanofibers. For such a reason, there is a possibility that dense and innumerable carbon nanofibers cannot be grown on the substrate surface without gaps.

[0047]

EXAMPLES Example 1 Fe ₂ O ₃ powder having an average particle size of 1.5 μm (oxide of a seed element)
6 g and 4 g of Al ₂ O ₃ powder (reducible metal oxide) having an average particle size of 0.8 μm were prepared as a raw material powder (molar ratio: 1: 1), and both powders were mixed with ethanol using a ball mill. The mixture was wet-mixed for about 5 minutes to obtain a mixed powder. The mixed powder was placed in a mold and formed into a disk-shaped compact having a diameter of 2 cm using a hydraulic press.

[0048] The obtained compact was heated in an air furnace at 1400 ° C for 1 hour.
By performing heat treatment for 0 hour, the mixed powder is reacted and the substrate is formed.
Produced. XRD analysis of the obtained substrate showed that Fe
AlO_ThreeIt was confirmed that it was. Ie hexagonal
(Hexagonal) Fe_TwoO_Three(Oxidation of seed elements
Hexagonal) and Al which is hexagonal_TwoO
_Three(Reducible metal oxide) and FeAlO as an intermediate phase_Three
(Orthorhombic) substrate was confirmed to be obtained.

A sample obtained by processing the substrate into 5 mm square was placed on a quartz boat and inserted into a heat treatment furnace. Thereafter, hydrogen was supplied to the heat treatment furnace at a rate of 1 liter / min, and then the temperature in the furnace was maintained at 600 ° C. for 5 minutes to partially reduce and precipitate Fe in the intermediate phase.

The reason why the substrate was processed into 5 mm square was to make it a size that could be accommodated in the heat treatment furnace. If a large furnace was used, a larger sample could be used.

Then, while supplying hydrogen, ethylene gas was flowed into the heat treatment furnace at a flow rate of 0.1 liter / min to grow carbon nanofibers, thereby producing a carbon nanofiber composite.

FIG. 2 is a photograph showing the obtained carbon nanofiber composite. This photograph is obtained by crushing the obtained carbon nanofiber composite to make the shape of the carbon nanofiber composite easy to understand, and reducing the particle size of the substrate to about 2 μm.

As shown in FIG. 2, innumerable carbon nanofibers grew on the surface of the substrate without gaps and had a diameter of 1 to 2
It can be seen that they are formed in a bundle of about μm. FIG. 3 is a further enlarged photograph of the carbon nanofiber, and each carbon nanofiber had a uniform diameter of about 10 nm.

Reference Example In the same manner as in Example 1, a disk-shaped compact having a diameter of 2 cm and made of a mixed powder of Fe ₂ O ₃ powder and Al ₂ O ₃ powder was prepared.

The obtained molded product was heated at 1000 ° C. for 1 hour in an atmospheric furnace.
Time heat treatment,_TwoO_ThreeAnd Al _TwoO_ThreeFrom a solid solution with
A substrate was prepared.

When the obtained substrate was analyzed by XRD,
A peak of Fe ₂ O _{3 and} a peak of Al ₂ O ₃ are observed,
No FeAlO ₃ peak was observed. That is,
No intermediate phase between Fe ₂ O ₃ and Al ₂ O ₃ was formed.

Thereafter, the substrate is subjected to a reduction treatment in the same manner as in Example 1 to precipitate a seed element on the surface of the substrate, and carbon nanofibers are grown in the same manner as in Example 1 to obtain a carbon nanofiber composite. Was.

FIG. 5 shows a photograph of the obtained carbon nanofiber composite.

As shown, there are gaps between the obtained carbon nanofibers, and the diameters of the carbon nanofibers are different. The diameter of the obtained carbon nanofiber is about 100 nm to 300 nm, which is larger than that obtained in the example.
This is because the particle size of the deposited seed element grew too much,
It seems that the size of each seed element is different.

Examples 2 to 16 A substrate was prepared in the same manner as in Example 1 except that the raw material powders shown in Table 1 were used, and carbon nanofibers were prepared on the surface of the substrate. As in the case shown, carbon nanofibers having a uniform thickness were formed on the substrate surface without any gap.

[Table 1]

[0061]

According to the present invention, a high-density carbon nanofiber composite can be provided by a simple production method.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a carbon nanofiber composite of the present invention.

FIG. 2 is a photograph of a carbon nanofiber composite obtained in an example.

FIG. 3 is an enlarged photograph of the carbon nanofiber obtained in the example.

FIG. 4 is a schematic diagram showing a carbon nanofiber composite obtained using a solid solution phase as a substrate.

FIG. 5 is a photograph showing a carbon nanofiber composite obtained using a solid solution phase as a substrate.

[Explanation of symbols]

 1, 101: substrate 2, 102: carbon nanofiber

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiichi Suenaga 1st office, Toshiba R & D Center, Komukai, Kawasaki, Kanagawa Prefecture (72) Inventor Yasuhiro Gonohe 1-cho, Toshiba R & D Center F-term (reference) 4G046 CA02 CB01 CB08 CB09 CC02 CC06 CC08 4L037 CS03 FA02 FA12 PA04 PA06 PA12

Claims (4)

[Claims] 1. A carbon nanofiber comprising: a base having an intermediate phase of a transition metal oxide and a non-reducible metal oxide; and a carbon nanofiber grown from the transition metal deposited on the surface of the base. Complex. 2. The method according to claim 1, wherein the transition metal in the intermediate phase is precipitated by reducing a substrate having an intermediate phase of a transition metal and a non-reducible metal oxide in a reducing atmosphere. And growing the carbon nanofibers from the deposited transition metal. 3. The method according to claim 1, wherein the mixed powder containing the transition metal-containing seed oxide powder and the non-reducible metal oxide powder is heated to a reaction temperature to form the substrate having the intermediate phase. 3. The method for producing a carbon nanofiber according to item 2. 4. A mixed powder composed of Fe ₂ O ₃ and Al ₂ O ₃ is heated at a temperature of 1200 ° C. or more to form a substrate having an intermediate phase composed of FeAlO ₃ , and the substrate is reduced in a reducing atmosphere. A method for producing carbon nanofibers, comprising: precipitating Fe in the intermediate phase, contacting the precipitated Fe with a carbon-containing gas, and growing carbon nanofibers using Fe as a catalyst.