JPWO2006085479A1 - Method for producing silicon carbide nanofiber - Google Patents

Abstract

Disclosed is a method for producing silicon carbide nanofibers, which can easily and reliably produce extremely thin and long silicon carbide nanofibers. A mixing step of mixing a silicon carbide precursor polymer and a carbon precursor polymer, a melt spinning step of melt spinning the polymer mixture obtained in this step, and a silicon carbide precursor polymer in the fibrous material obtained in this step And a carbon precursor polymer, an infusifying step for infusifying the fiber, a heat treatment step for heat-treating the fiber infusible in this step, and an acid treatment step for acid-treating the heat-treated fiber. A method for producing silicon-based nanofibers.

Description

  The present invention relates to a method for producing silicon carbide-based nanofibers, and more particularly to a method for producing silicon carbide-based nanofibers suitable for producing extremely thin and long fibers.

  In recent years, there is an increasing need for high-strength materials that can be used in high-temperature regions such as turbine parts for improving the efficiency of engines, airframes, energy plants, and the like for aerospace and transportation equipment. Silicon carbide (SiC) fiber has mechanical properties such as no change in tensile strength and elastic modulus up to a high temperature of 1300 ° C, and is characterized by being stable in an oxidizing atmosphere and extremely low in reactivity with metals. It is also used as a ceramic composite material because of its excellent chemical resistance and wear resistance.

  However, silicon carbide fibers that have been developed so far have high strength but are rigid, and the average particle diameter of the fibers is as thick as about 14 μm, which makes it difficult to handle and slightly in terms of workability. The problem remains. In order to improve processability, it is necessary to prepare thinner silicon carbide fibers. Even if the fiber is rigid, if the fiber diameter is reduced, the flexibility of the fiber is improved. Therefore, since the characteristics of the composite material strongly depend on the properties of the reinforcing fiber, it is extremely important to prepare a high-strength and ultrafine silicon carbide-based fiber in producing a high-performance composite material.

A method for producing silicon carbide-based nanofibers has already been proposed. (See Patent Document 1)
In this method, polycarbosilane as a silicon carbide precursor is mixed with a thermally decomposable resin, then melt-spun, and then heat-treated. In this method, silicon carbide precursor (polycarbosilane) fine particles are dispersed in a polymer that disappears by heating, and then drawn by melt spinning, then infusible, and finally carbonized to obtain silicon carbide fibers. Yes.
JP, 2004-360115, A However, silicon carbide nanofibers are recognized in the silicon carbide fibers that have been drawn, infusible, and finally carbonized by melt spinning obtained in this production process. A phenomenon in which the fibers are slightly fused is observed, and a phenomenon in which a sheath-like portion is formed around the nanofiber is observed. As a result, it was difficult to separate and separate the silicon carbide nanofibers, and it was difficult to produce extremely thin and long silicon carbide nanofibers.

  An object of the present invention is to solve the above-mentioned problems and to provide a method for producing silicon carbide nanofibers that can easily and reliably produce extremely thin and long silicon carbide nanofibers.

The above problems are solved by the invention having the following configuration.
(1) A mixing step of mixing a silicon carbide precursor polymer and a carbon precursor polymer, a melt spinning step of melt spinning the polymer mixture obtained in this step, and silicon carbide in the fibrous material obtained in this step It comprises an infusibilization step for infusifying the precursor polymer and the carbon precursor polymer, a heat treatment step for heat-treating the fiber infusible in this step, and an acid treatment step for acid-treating the heat-treated fiber. A method for producing silicon carbide nanofibers.
(2) The method for producing silicon carbide-based nanofiber according to (1), wherein the silicon carbide precursor polymer is polycarbosilane.
(3) The method for producing silicon carbide nanofibers according to (2), wherein the polycarbosilane is represented by the following general formula (1).

(In the general formula (1), R ¹ and R ² each represent a hydrogen atom or a hydrocarbon group, and at least one of R ¹ and R ² is a hydrogen atom. N represents the number of polymerizable units. )
(4) The carbonization according to any one of (1) to (3), wherein the infusibilization step holds the fibrous material obtained by melt spinning in a solution for curing the carbon precursor polymer. A method for producing silicon-based nanofibers.
(5) The infusibilization step is characterized in that the fibrous material obtained by melt spinning is held in a solution for curing the carbon precursor polymer and then heated in an oxygen atmosphere (1) to (3) ) The method for producing a silicon carbide nanofiber according to any one of the above.
(6) The method for producing silicon carbide nanofiber according to any one of (1) to (5), wherein the heat treatment step is performed in an inert gas atmosphere.
(7) The method for producing silicon carbide-based nanofiber according to any one of (1) to (6), wherein the acid treatment step uses a mixed acid of nitric acid and sulfuric acid or concentrated sulfuric acid.

  According to the present invention, extremely thin and long silicon carbide nanofibers can be produced easily and reliably.

It is a SEM photograph of the silicon carbide nanofiber obtained with the manufacturing method of the present invention. It is a SEM enlarged photograph of the principal part of FIG.

The method for producing silicon carbide-based nanofibers of the present invention includes a mixing step of mixing a silicon carbide precursor polymer and a carbon precursor polymer, a melt spinning step of melt spinning the polymer mixture obtained in this step, and this step The infusibilization step for infusifying the silicon carbide precursor polymer and the carbon precursor polymer in the fibrous material obtained in Step 1, the heat treatment step for heat treating the infusible fiber in this step, and the acid treatment for the heat treated fiber And an acid treatment step.
<Mixing step of mixing silicon carbide precursor polymer and carbon precursor polymer>
The silicon carbide precursor polymer refers to an organic silicon polymer compound that can be converted into silicon carbide in the production process of the present invention, and examples thereof include polycarbosilane, polysilazane, polysiloxane, polydimethylsilylvinylacetylene, and the like. Such an organosilicon polymer compound may be a polymer compound containing a metal element such as boron, titanium, zirconium, or aluminum in addition to carbon, silicon, oxygen, and nitrogen. Of these organosilicon polymer compounds, polycarbosilane is most preferred.

  The polycarbosilane (PCS) can be selected from those having various molecular structures and polymerization degrees, and those having the following general formula (1) are preferred.

(In the general formula (1), R ¹ and R ² each represent a hydrogen atom or a hydrocarbon group, and at least one of R ¹ and R ² is a hydrogen atom. N represents the number of polymerizable units. )
Examples of the hydrocarbon group include a methyl group, an ethyl group, and propyl. Among these, a methyl group is particularly preferable. More preferably, polycarbosilane consisting of the following general formula is preferable, and the average molecular weight is preferably 500 to 2,000.

The carbon precursor polymer means a polymer in which carbon remains even when heat-treated in an inert gas atmosphere, and is different from the thermally decomposable disappearing polymer used in JP-A-2004-360115. That is, the thermally decomposable disappearing polymer is a polymer that decomposes and disappears up to 450 ° C. even at a maximum temperature of, for example, 400 ° C. or lower when heated in an inert gas atmosphere such as a nitrogen atmosphere. The body polymer is a polymer in which carbon remains without being decomposed and lost even when heat-treated in an inert gas atmosphere.

  The carbon precursor polymer can be treated at a high temperature of about 1000 ° C. in order to obtain carbon in which carbon remains after the heat treatment in an inert gas atmosphere and most of the elements other than carbon are removed from the polymer. It is necessary, and the crystallinity improves as the processing temperature rises, and carbon remains even after high temperature processing at about 3,000 ° C.

  Specific examples of the carbon precursor polymer in the present invention include polyacrylonitrile (PAN), a phenol resin, a furan resin, and an epoxy resin that are used as raw materials for carbon fibers. In addition, polymethyl acrylate (PMA) ), Polyvinyl chloride, polyvinyl alcohol, polyimide, polyamide, polyoxadiazole, poly p-phenylene vinylene, polyvinylidene chloride, liquid crystalline polymer and other polymers containing carbon atoms. Among these, resins such as polyacrylonitrile, polyvinyl chloride, and polyvinyl alcohol are preferable because they can promote crystal development. In the case of a polymer that is graphitized by heat treatment, it is difficult to remove carbon by oxidation treatment. In particular, it is difficult to separate and separate individual silicon carbide fibers, and therefore polymers with low crystallinity are preferred. From this point, for example, phenol resins, especially novolac phenol resins, polyacrylonitrile, poly Vinyl chloride and the like are preferable.

  The carbon precursor polymer may be a copolymer of a monomer constituting the carbon precursor polymer and a monomer constituting the heat dissipation polymer (for example, a copolymer of PMA and PSt, a copolymer of PAN and PMA, PAN and PMMA, And the like) can also be used.

  When mixing the silicon carbide precursor polymer and the carbon precursor polymer, it is preferable to mix the silicon carbide precursor polymer and the carbon precursor polymer in a solvent. In this case, it is preferable to select a solvent in consideration of solubility in both polymers. As a result, the silicon carbide precursor polymer and the carbon precursor polymer are uniformly dispersed. Thereafter, the solvent is removed, and a polymer blend of the silicon carbide precursor polymer and the carbon precursor polymer is obtained. Further, a method of mechanically kneading silicon carbide precursor polymer powder and carbon precursor polymer powder without using a solvent may be used.

  When mixing the silicon carbide precursor polymer and the carbon precursor polymer, select the mixing ratio of the particles of both polymers so that the carbon precursor polymer is the sea and the silicon carbide precursor polymer is the island. If the mixing amount of the silicon carbide precursor polymer is too large, it is likely to become a sea, so it is difficult to produce silicon carbide nanofibers, while if the mixing amount of the carbon silicon precursor polymer is too small, the silicon carbide Since the yield of the nanofibers tends to be low, the mixing ratio (mass ratio) of silicon carbide precursor polymer: carbon precursor polymer is preferably 2: 8 to 6: 4.

<Melt spinning process>
The polymer blend obtained in the above step is melt-spun by a melt spinning machine, but is preferably spun in an inert atmosphere. Although the melting temperature at the time of melt spinning is arbitrarily selected depending on the type of polymer used, for example, when the carbon precursor polymer is a novolak phenol resin, 105 to 110 ° C. is preferable.

<Infusibilization process>
The infusibilization step includes a step of infusibilizing the carbon precursor polymer and a step of infusibilizing the silicon carbide precursor polymer.

  This infusibilization process prevents the carbon silicon precursor polymer from fusing during the heat treatment after this process, and maintains the fibrous form by melt spinning of the silicon carbide precursor polymer in the matrix structure composed of the carbon precursor polymer. In addition, it is effective to easily peel and separate individual fibers. The means for infusibilizing the carbon precursor polymer can be arbitrarily selected depending on the type of the carbon precursor polymer. For example, a compound capable of curing the carbon precursor polymer by a chemical reaction, for example, an acidic curable liquid (hydrochloric acid / formalin). ), A method using air oxidation, a method using ozone, and the like.

  The step of infusibilizing the silicon carbide precursor polymer includes a method using a chemical reaction with oxygen, oxide, unsaturated hydrocarbon compound, etc., and a method of causing a crosslinking reaction using various radiations such as electron beams and ultraviolet rays. A known method such as the above can be used. The conditions for infusibilization are appropriately selected according to the infusibilization method employed, for example, the atmosphere, temperature, time, and specific method.

  In the infusibilization step, the above-described methods can be used in combination. For example, infusibilization with an acidic curable solution and oxygen can be performed.

<Heat treatment process>
Next, the thermal decomposition reaction and decarbonization reaction of the silicon carbide precursor polymer infusibilized by the heat treatment proceeds, and the chemical composition of the resulting silicon carbide fiber is controlled, that is, the amount of surplus carbon is suppressed, and the infusible carbon is controlled. The precursor polymer is carbonized.

  The heat treatment conditions are desirably performed in a non-oxidizing atmosphere, preferably in an inert gas atmosphere. Examples of the inert gas include nitrogen gas, argon gas, helium gas, and practically, nitrogen gas is preferable.

The heat treatment temperature is preferably 1000 to 1350 ° C, more preferably 1100 to 1250 ° C. When the heat treatment temperature is lower than 1000 ° C., silicon carbide (SiC) may become silica (SiO ₂ ), and the resulting silicon carbide nanofiber is mixed with silicon carbide (SiC) and silica (SiO ₂ ) It may be difficult to maintain the mechanical strength and the like of the silicon carbide nanofibers at a desired value, and the physical properties of the silicon carbide nanofibers obtained even when the heat treatment temperature exceeds 1350 ° C. are mostly. It cannot be expected to improve. The heat treatment time varies depending on the heat treatment temperature, but is preferably 5 minutes to 1 hour in a temperature range of 1100 to 1250 ° C.
<Acid treatment process>
The heat-treated fiber is then subjected to acid treatment to remove the produced carbon. The acid used for the acid treatment is not particularly limited as long as it can dissolve carbon. For example, a mixed acid of nitric acid and sulfuric acid, concentrated sulfuric acid, concentrated nitric acid and the like can be mentioned. A mixed acid with sulfuric acid, concentrated sulfuric acid, and concentrated nitric acid are preferred. In the acid treatment, it is desirable to hold the heat-treated fiber for a predetermined time while stirring in an acid heated to a temperature near the boiling point of these acids.
<Other processes>
The carbonized component of the carbon precursor polymer is removed by acid treatment, and the infusible silicon carbide nanofibers are recovered. As this recovery means, means such as ultrasonic sieving, filtration, and centrifugation can be employed.
<Industrial applicability>
The silicon carbide nanofibers obtained in the present invention are a high-strength material that can be used in a high-temperature region such as a turbine portion for improving the efficiency of engines, aircraft, energy plants, etc. for aerospace and transportation equipment, under an oxidizing atmosphere. In addition, it has the characteristics of being stable and extremely low in reactivity with metals, and is excellent in chemical resistance and wear resistance, so it is useful for ceramic composite materials and the like.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Example 1)
<Raw material>
Polycarbosilane (PCS; manufactured by Nippon Carbon Co., Ltd.) was used as the silicon carbide precursor resin, and novolak resin (PF; manufactured by Gunei Chemical Co., Ltd.) having a softening point of 100 ° C. was used as the carbon precursor resin.
<Sample preparation>
Weighing was performed so that the mass ratio of PCS and PF was 3: 7, and both resins were dissolved and mixed in a tetrahydrofuran (THF) solvent using a sonicator. Subsequently, the solvent of this mixed solution was removed using a rotary evaporator, and then dried for one day with a 60 ° C. heat true dryer to obtain a mixed resin.
<Melt spinning>
The prepared polymer blend was melt-spun at a temperature of 105 to 110 ° C. in an inert gas (argon gas) atmosphere using a spinning apparatus.
<Infusibilization>
-PF infusibilization treatment-
The PCS-PF mixed resin obtained by melt spinning was heated to 105 ° C. at 0.5 ° C./min in a phenol curing solution [(hydrochloric acid / formalin) manufactured by Gunei Chemical Co., Ltd.] for 24 hours. Retained.
-PCS infusibilization treatment-
After infusibility treatment of PF, the temperature was raised to 130 ° C. at 5 ° C./h in an oxygen atmosphere, and held for 1 hour.
<Heat treatment>
The infusible polymer blend fiber was placed in an alumina board and heat treated up to 1000 ° C. at 100 ° C./h in an inert gas atmosphere (nitrogen gas) using a horizontal tubular furnace (manufactured by Ishizuka Electric Co., Ltd.). . Further, this fiber was heated to 1000 ° C. at 50 ° C./h using an infrared gold image furnace (manufactured by ULVAC-RIKO, Inc.), then heated to 1200 ° C. at 10 ° C./h and held for 10 minutes.
<Acid treatment>
The heat-treated sample was held in 60% nitric acid at 170 to 180 ° C. for 12 hours with stirring to remove PF as a matrix.
<Silicon carbide nanofiber>
An SEM photograph of the obtained silicon carbide nanofiber is shown in FIG. 1, and an enlarged SEM photograph of an essential part thereof is shown in FIG.

As shown in FIGS. 1 and 2, the silicon carbide nanofibers obtained by this example are extremely thin, long nanofibers of about 100 to 200 nm, and are almost recognized as a fusion part or a sheath shape between the fibers. I was not.
(Comparative Example 1)
<Raw material>
As a silicon carbide precursor resin, two types of polycarbosilanes (PCS; manufactured by Nippon Carbon Co., Ltd.) having a softening point of 240 ° C. and a softening point of 80 ° C. were mixed at 4: 6. The softening point of this mixed polycarbosilane was 180 ° C. On the other hand, polystyrene particles of about 1 to 5 microns were prepared by spray drying of a toluene solution of polystyrene (softening point 190 ° C.) as a thermally decomposable polymer. Polystyrene having a mass ratio of 7 was added to the mixed polycarbosilane 3 and mechanically kneaded using a mini-extruder to obtain a polymer blend. The polymer blend was continuously melt spun at 180-190 ° C. The polymer blend fiber and iodine were put in a glass container and kept at 100 ° C. for 12 hours. By this operation, iodine extracts hydrogen in the polymer blend to become hydrogen iodide, and insolubilization proceeds. Finally, heat treatment was performed at 1000 ° C. for 1 hour in a nitrogen stream. An elementary fiber having a diameter of about 50 nm could be confirmed by a TEM photograph. According to X-ray diffraction, the fiber is amorphous.
When treated at 1,500 ° C., formation of β-type silicon carbide was observed.

However, a fused portion between the silicon carbide fibers, a sheath shape, and the like were recognized.

[0002]
Although iodine nanofibers are observed, a phenomenon in which these nanofibers are slightly fused is observed, and a phenomenon in which a sheath-like portion is formed around the nanofiber is observed. As a result, it was difficult to separate and separate the silicon carbide nanofibers, and it was difficult to produce extremely thin and long silicon carbide nanofibers.
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
[0005]
An object of the present invention is to solve the above-mentioned problems and to provide a method for producing silicon carbide nanofibers that can easily and reliably produce extremely thin and long silicon carbide nanofibers.
[Means for Solving the Problems]
[0006]
The above problems are solved by the invention having the following configuration.
(1) A mixing step of mixing a silicon carbide precursor polymer with a carbon precursor polymer in which carbon remains without being decomposed and lost even when heat-treated in an inert gas at a temperature of at least 1000 ° C., and in this step The melt spinning step of melt spinning the obtained polymer mixture, the infusibilization step of infusifying the silicon carbide precursor polymer and the carbon precursor polymer in the fibrous material obtained in this step, and the infusible step in this step A method for producing silicon carbide-based nanofibers, comprising: a heat treatment step for heat treating a fiber; and an acid treatment step for acid-treating the heat-treated fiber.
(2) The method for producing silicon carbide-based nanofiber according to (1), wherein the silicon carbide precursor polymer is polycarbosilane.
(3) The method for producing silicon carbide nanofibers according to (2), wherein the polycarbosilane is represented by the following general formula (1).
[0007]
[Chemical 1]

[0002]
Although iodine nanofibers are observed, a phenomenon in which these nanofibers are slightly fused is observed, and a phenomenon in which a sheath-like portion is formed around the nanofiber is observed. As a result, it was difficult to separate and separate the silicon carbide nanofibers, and it was difficult to produce extremely thin and long silicon carbide nanofibers.
[Disclosure of the Invention]
[Problems to be solved by the invention]
[0005]
An object of the present invention is to solve the above-mentioned problems and to provide a method for producing silicon carbide nanofibers that can easily and reliably produce extremely thin and long silicon carbide nanofibers.
[Means for solving problems]
[0006]
The above problems are solved by the invention having the following configuration.
(1) A mixing step of mixing a silicon carbide precursor polymer with a carbon precursor polymer in which carbon remains without being decomposed and lost even when heat-treated in an inert gas at a temperature of at least 1000 ° C., and in this step The melt spinning step of melt spinning the obtained polymer mixture, the infusibilization step of infusifying the silicon carbide precursor polymer and the carbon precursor polymer in the fibrous material obtained in this step, and the infusible step in this step A method for producing silicon carbide-based nanofibers, comprising: a heat treatment step for heat-treating the fibers; and an acid treatment step for acid-treating the heat-treated fibers.
(2) The method for producing silicon carbide-based nanofiber according to (1), wherein the silicon carbide precursor polymer is polycarbosilane.
(3) The method for producing silicon carbide nanofibers according to (2), wherein the polycarbosilane is represented by the following general formula (1).
[0007]
[Chemical 1]

Claims (7)

  A mixing step of mixing a silicon carbide precursor polymer and a carbon precursor polymer, a melt spinning step of melt spinning the polymer mixture obtained in this step, and a silicon carbide precursor polymer in the fibrous material obtained in this step And a carbon precursor polymer, an infusifying step for infusifying the fiber, a heat treatment step for heat-treating the fiber infusible in this step, and an acid treatment step for acid-treating the heat-treated fiber. A method for producing silicon-based nanofibers.   2. The method for producing silicon carbide-based nanofibers according to claim 1, wherein the silicon carbide precursor polymer is polycarbosilane. The method for producing silicon carbide-based nanofiber according to claim 2, wherein the polycarbosilane is represented by the following general formula (1).
(In the general formula (1), R ¹ and R ² each represent a hydrogen atom or a hydrocarbon group, and at least one of R ¹ and R ² is a hydrogen atom. N represents the number of polymerizable units. )   The silicon carbide according to any one of claims 1 to 3, wherein the infusibilizing step holds the fibrous material obtained by melt spinning in a solution for curing the carbon precursor polymer. Of producing nanofibers   4. The infusibilization step, wherein the fibrous material obtained by melt spinning is held in a solution for curing the carbon precursor polymer, and then heated in an oxygen atmosphere. A method for producing the silicon carbide-based nanofiber according to claim 1.   The method for producing a silicon carbide-based nanofiber according to any one of claims 1 to 5, wherein the heat treatment step is performed in an inert gas atmosphere. The acid treatment step uses any one of a mixed acid of nitric acid and sulfuric acid, concentrated sulfuric acid, or concentrated nitric acid, and manufacturing the silicon carbide-based nanofiber according to any one of claims 1 to 6. Method.