JP2009155176A - Boron nitride nanofiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high-function, new functional material that can be used industrially qualitatively and quantitatively by directly using an existing process from inexpensive and abundantly available raw materials, and to develop its application A method for producing novel boron nitride nanofibers is provided.
A gas produced by heating and reacting a mixture of boron oxide and boron as a boron source at a temperature of 1000 ° C. or higher in the absence of a catalyst or in the presence of one or more kinds of catalysts selected from metal particles or metal oxides. A method for producing boron nitride nanofibers by further reacting a gaseous boron compound with a gaseous nitrogen compound at 1000 ° C. or higher.
[Selection] Figure 1

Description

  The present invention relates to a method for producing boron nitride nanofibers. The boron nitride nanofibers obtained by the production method of the present invention are useful as insulating and / or highly thermally conductive fillers, gas adsorbents, catalyst carriers, microelectronic components, and optical devices such as photoluminescence and electroluminescence.

Boron nitride is a substance having characteristics such as high thermal conductivity, insulation, and chemical inertness, and its crystal structure mainly has two forms of hexagonal system and cubic system. Further, regarding boron nitride nanostructures, it is known that boron nitride nanotubes having a hollow structure can be produced by chemical vapor deposition using a B ₄ N ₃ O ₂ H compound (Non-patent Document 1). ).

  Boron nitride is expected to be used as various functional materials, and the development of hexagonal, cubic, and novel nanotube structures embodies various long-period layered structures. It is expected to contribute greatly to the realization of highly functional and new functional materials due to physical characteristics. Furthermore, as such a new structure of boron nitride, if it is possible to arbitrarily create not only nanotubes but also fibrous aggregates that have not been known so far, the desired highly functional and new functional materials and their It is thought that it will enable the development of applications, and how to design and prepare a novel boron nitride nanostructure having a long-period structure that has not been known so far has become a concrete issue.

Conventionally, as a method for forming a boron nitride fiber structure, for example, in Patent Document 1, carbon nanotubes formed by CVD using a titanium substrate in which cobalt fine particles are dispersed are nitrided by heating and replacing them in a nitrogen stream with boron oxide. Techniques for producing boron nanofibers are disclosed. Patent Document 2 discloses a method for producing boron nitride nanowires by heating a B ₄ N ₃ O ₂ H compound together with graphite powder in nitrogen gas containing water vapor. These methods can be used as methods for producing boron nitride fiber aggregates of various forms and sizes. However, as long as the precursors are used as starting materials in any method, different elements such as carbon and oxygen that are by-produced in production are used. It is difficult to completely remove impurities formed from this, and there is a problem from the viewpoint of high purity. In addition, it is necessary to prepare expensive carbon nanotubes, special B ₄ N ₃ O ₂ H compounds, etc. as precursor structures, or to form nanofibers of boron nitride, and there is a problem that high cost and mass production are difficult. . Therefore, establishment of a method for manufacturing a large amount of boron nitride nanofibers directly from a starting material which is inexpensive and easily procured industrially has been demanded.

R. Ma, et al., “Advanced Materials (Adv. Mater.)”, 2002, vol. 14, p. 366 JP 2004-190183 A JP-A-2005-75656

  The present invention has been made in view of the above circumstances, and solves the problems of the prior art, and qualitatively and quantitatively industrializes by directly using existing processes from raw materials that can be used in a low cost and in large quantities. It is an object of the present invention to produce a highly functional and new functional material that can be used above and to provide a method for producing a novel boron nitride nanofiber for the purpose of developing its application.

  By using a mixture of boron oxide and boron as a boron source and utilizing a CVD reactor or the like that can set the heating temperature accurately, the present inventors have obtained a novel boron nitride nanofiber having a nano-sized direct structure efficiently. The present invention has been found out that it can be produced. That is, the gist of the present invention is as follows.

1. A gaseous boron compound produced by heating and reacting a mixture of boron oxide and boron as a boron source in the absence of a catalyst or in the presence of one or more kinds of catalysts selected from metal particles or metal oxides at a temperature of 1000 ° C. or higher. Furthermore, the manufacturing method of the boron nitride nanofiber by making it react with gaseous nitrogen compound at 1000 degreeC or more.
2. A part for supplying a gaseous boron compound by heating and reacting the boron source at a temperature of 1000 ° C. or more (a supply part); a part for reacting the boron compound with a gaseous nitrogen compound by heating (reaction part); Supplying the gaseous boron compound at a temperature of 1000 ° C. or higher to the reaction portion heated to a temperature of 1000 ° C. or higher in a reactor equipped with a structure in which the gaseous nitrogen compound does not flow into the supply unit The method for producing boron nitride nanofiber according to the above item 1, wherein the reaction is performed with the gaseous nitrogen compound.
3. Boron nitride nanofibers having a diameter of 50 to 500 nm and a length of 1 to 10 μm produced by the production method of the above item 1 or 2.
4). 4. The boron nitride nanofiber as described in 3 above, which contains a hollow structure comprising continuous cavities having an average diameter of 10 to 50 nm.

  According to the present invention, as an insulating and / or high thermal conductive filler, gas adsorbent, catalyst carrier, microelectronic component, and optical device such as photoluminescence and electroluminescence, etc., using cheap and available starting materials available in large quantities A method for producing useful novel boron nitride nanofibers is provided.

The present invention will be described in detail below.
In the production method of the present invention, boron alone and boron oxide are used as a boron source, and a gaseous boron compound produced by heating and reacting at a temperature of 1000 ° C. or higher in the absence of a catalyst or in the presence of a catalyst is further added with a nitrogen source. It reacts with a certain gaseous nitrogen compound at 1000 ° C. or higher. The present inventors have used gaseous nitrogen as an active (BO) ₂ intermediate (hereinafter sometimes referred to as a boron intermediate) by efficiently using boron and boron oxide as a boron source. It has been found that boron nitride nanofibers can be obtained by reacting with the compound nitrogen and growing in a fibrous form.

  The reaction apparatus that can be used in the production method of the present invention includes a chemical vapor deposition method (hereinafter sometimes abbreviated as a CVD method) used for the production of carbon nanotubes, an arc discharge method, and laser evaporation. The apparatus by CVD method is especially preferable.

  As is well known, boric acid is converted to boron oxide at a high temperature of about 300 ° C. Therefore, in the production method of the present invention, a mixture of boric acid and boron is used as a boron source, and heating is performed in the reaction section. Boron nitride nanofibers can also be obtained by generating a gaseous boron intermediate after conversion to a mixture of boron oxide and boron and further reacting with a gaseous nitrogen compound.

  In the present invention, the desired product can be obtained without a catalyst, but a suitable catalyst can be used to further improve the efficiency of the reaction. Examples of the catalyst used include metal particles or metal oxides such as cobalt, calcium oxide, magnesium oxide, or iron oxide. Among these, magnesium oxide, calcium oxide and the like are particularly preferable from the viewpoints of economy, ease of removal in the post-treatment step of the catalyst, and catalytic activity.

  The gaseous nitrogen compound used as a nitrogen source in the production method of the present invention is inexpensive, has a low risk of explosiveness, etc., has a low content of elements other than nitrogen, and can be easily supplied to the reaction section. A gas at room temperature is preferred. Such compounds include ammonia or methylamines such as monomethylamine, with ammonia being particularly preferred.

  In the present invention, the boron source is heated to react to generate a gaseous boron intermediate and supplied thereto (supply portion), and the boron intermediate and the gaseous nitrogen compound are further heated to react ( Reaction unit) and a structure in which the gaseous nitrogen compound does not flow into the supply unit, the gaseous boron intermediate heated in the supply unit up to a desired reaction temperature, It is preferable to react with the gaseous nitrogen compound while suppressing fluctuations in the reaction temperature by supplying the reaction part heated to the reaction temperature. By doing this, it is possible to avoid the side reactions caused by the destabilization of the reaction part temperature at the time of introduction of the reaction, or impurities generated in the process of raising the reaction part temperature, and to efficiently generate homogeneous boron nitride nanofibers. Can do.

  In the present invention, a reaction apparatus comprising a supply unit, a reaction unit, and a structure in which a gaseous nitrogen compound does not flow into the supply unit is a valve that is only separated during the reaction when the supply unit and the reaction unit are completely separated. For example, the gaseous boron compound and the gaseous nitrogen compound may be brought into contact with each other by opening the gas. For example, the gaseous boron intermediate is supplied from a supply unit provided inside the apparatus having a nested structure. However, the same effect can be obtained by introducing a gaseous nitrogen compound from the outside. This is because the boron intermediate is highly reactive and reacts immediately upon contact with the gaseous nitrogen compound to cause chemical vapor deposition.

  The temperature of the reaction part of the reactor in the present invention is 1000 ° C. or higher. When the temperature of the reaction part is lower than 1000 ° C., amorphous boron nitride is generated, and when the temperature of the reaction part is much higher than 1000 ° C., it is not a boron nitride nanofiber but a rod shape. Alternatively, it is not preferable because particulate boron nitride is generated. The temperature of the reaction part is preferably 1000 ° C to 1500 ° C, more preferably 1000 ° C to 1200 ° C.

  The temperature of the supply unit of the reaction apparatus in the present invention is 1000 ° C. or higher, preferably 1000 ° C. to 1500 ° C., more preferably 1000 ° C. to 1200 ° C., as in the above reaction unit. The temperature of the supply section is particularly preferably the same as the temperature of the reaction section, but the desired boron nitride nanofibers can be obtained within the above preferable or preferable temperature range.

  The heating time in the reaction section can be the consumption time of the gaseous boron compound and gaseous nitrogen compound as reactants, and this can be adjusted according to various production conditions. In particular, from the viewpoint of reaction efficiency and productivity, production with a heating time of about 0.5 to 2 hours is preferably indicated. By cooling the reaction part to room temperature after the heating reaction, boron nitride nanofibers can be obtained as a white powder deposit.

By the method of the present invention described above, boron nitride nanofibers can be easily produced from inexpensive raw materials.
The boron nitride nanofibers of the present invention obtained by the above production method have a length of about 1 to 10 μm and a diameter of about 50 to 500 nm, more preferably about 150 to 500 nm. The diameter of a single fiber may be uniform and constant throughout the fiber, but the diameter continuously changes from one end of the fiber to the other, or the diameter changes discontinuously. Sometimes.

  Further, in the boron nitride nanofibers of the present invention, each boron nitride nanofiber is not only present as a single fiber, but several yarns are bundled together, or a plurality of fibers are bonded together at the end, and the radial or It may take a branched form.

  Moreover, the boron nitride nanofiber of the present invention is characterized by including a hollow structure composed of continuous cavities having an average diameter of about 10 to 50 nm. The hollow structure composed of this continuous structure usually exists in a single fiber, but may exist as a plurality of independent holes and / or continuous holes.

  Hereinafter, the method of the present invention will be described in more detail with reference to examples. However, these examples do not limit the scope of the present invention.

[Example 1]
Boron oxide powder (100 mg) and boron powder (100 mg) were mixed and placed on a 2 cm diameter porcelain tank to form a supply tank. This supply tank was left still in a heating tank composed of a ceramic tube having a diameter of 2.5 cm and a length of 5 cm with one end closed. The whole was placed in a 1-liter quartz tube of a CVD apparatus, and the quartz tube was sealed with a silicon cock provided with piping for supply and exhaust. The inside was evacuated by a pump, and the temperature of the supply tank was raised from room temperature to 1300 ° C. in 120 minutes under an argon stream at a flow rate of 25 ml / min. After confirming that the inside of the supply tank reached 1300 ° C., ammonia gas was introduced into the quartz tube at a flow rate of 500 ml / min. The ammonia gas flowed into the ceramic heating tank, where the gas phase reaction with the boron compound started. This state was maintained for 60 minutes to complete the reaction. After the supply of ammonia gas was completed, the heating was stopped and the system was cooled over 120 minutes. After confirming that the inside of the CVD apparatus had returned to room temperature, the quartz tube was opened. 5 mg of white powder deposited on the inner wall of the ceramic tube was collected (no white powder was deposited in the supply tank). The obtained powder was observed with a transmission electron microscope (TEM) and confirmed to be nanofibers having a diameter of about 200 nm (TEM photograph is shown in FIG. 1). Further, as a result of characteristic peak analysis obtained from EDX (energy dispersive X-ray spectroscopy) spectrum measurement, it was confirmed that this powder composition was composed of nitrogen and boron. From these analysis results, it became clear that the white powder is the target boron nitride nanofiber.

[Example 2]
A mixture of 100 mg boron oxide powder and 100 mg boron powder, 10 mg calcium oxide added thereto, and then placed on a porcelain dish with a diameter of 2 cm. It was left in the tube. The ceramic tube was placed in a 1-liter quartz tube of a CVD apparatus, and the quartz tube was sealed with a silicon cock provided with piping for supply and exhaust. The inside of the CVD apparatus was heated from room temperature to 1300 ° C. for 120 minutes under an argon stream at a flow rate of 25 ml / min. After confirming that the inside of the CVD apparatus reached 1300 ° C., ammonia gas was introduced into the tube at a flow rate of 500 ml / min. This state was maintained for 60 minutes to complete the reaction. After the supply of ammonia gas was completed, the heating was stopped and the system was cooled over 120 minutes. After confirming that the inside of the CVD apparatus had returned to room temperature, the quartz tube was opened. 25 mg of white powder deposited on the inner wall of the ceramic tube was collected. As a result of the characteristic peak analysis obtained from transmission electron microscope (TEM) observation and EDX spectrum measurement, it was confirmed that this white powder was the same boron nitride nanofiber as that of Example 1 and composed of nitrogen and boron. It was.

[Comparative Example 1]
20 mg of white powder deposited on the inner wall of the ceramic tube was collected by performing the same operation as in Example 1 except that only 200 mg of boron oxide powder was used. When the obtained powder was observed with a transmission electron microscope (TEM), it was found to be amorphous particles, and as a result of characteristic peak analysis obtained by EDX spectrum measurement, this powder composition was composed of oxygen and boron. Was confirmed. From these analysis results, it was clarified that the white powder was boron oxide itself and there was no target boron nitride nanofiber.

[Comparative Example 2]
By performing the same operation as in Example 2 except that only 200 mg of boron oxide powder and 10 mg of calcium oxide were used, 30 mg of white powder deposited on the inner wall of the ceramic tube was collected. When the obtained powder was observed with a transmission electron microscope (TEM), it was found to be amorphous particles, and as a result of characteristic peak analysis obtained from EDX spectrum measurement, this powder composition was composed of nitrogen and boron. Was confirmed. From these analysis results, it became clear that the white powder is boron nitride, but there is no target nanofiber.

The TEM observation photograph of the boron nitride nanofiber obtained in Example 1 is shown.

Claims (4)

  A gaseous boron compound produced by heating and reacting a mixture of boron oxide and boron as a boron source in the absence of a catalyst or in the presence of one or more kinds of catalysts selected from metal particles or metal oxides at a temperature of 1000 ° C. or higher. Furthermore, the manufacturing method of the boron nitride nanofiber by making it react with gaseous nitrogen compound at 1000 degreeC or more.   A part for supplying a gaseous boron compound by heating and reacting the boron source at a temperature of 1000 ° C. or more (a supply part); a part for reacting the boron compound with a gaseous nitrogen compound by heating (reaction part); Supplying the gaseous boron compound at a temperature of 1000 ° C. or higher to the reaction portion heated to a temperature of 1000 ° C. or higher in a reactor equipped with a structure in which the gaseous nitrogen compound does not flow into the supply unit The method for producing boron nitride nanofibers according to claim 1, wherein the reaction is performed with the gaseous nitrogen compound.   Boron nitride nanofibers having a diameter of 50 to 500 nm and a length of 1 to 10 μm manufactured by the manufacturing method according to claim 1.   The boron nitride nanofiber according to claim 3, which includes a hollow structure composed of continuous cavities having an average diameter of 10 to 50 nm.