JP7302123B2 - Fibrous boron carbide and method for producing the same - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act September 26, 2018 Published by the Ceramic Society of Japan, Kanto Branch 34th Research Presentation Meeting of the Ceramic Society of Japan, Kanto Branch Released at 1B14 September 26, 2018 Published at the 34th Ceramic Society of Japan Kanto Branch Research Presentation September 26, 2018 Published by The Chemical Society of Japan Published in the 8th CSJ Chemistry Festa 2018 Lecture Proceedings P5-110 October 24, 2018 Published at the 8th CSJ Chemistry Festa 2018 March 1, 2019 Public Interest Incorporated Association Japan Ceramic Society Issued by The Ceramic Society of Japan 2019 Annual Meeting Lecture Proceedings Published in 3D10 March 26, 2019 Public Interest Incorporated Association Japan Published at the Ceramic Society 2019 Annual Meeting March 29, 2019 https://kaken. nii. ac. jp/ja/file/KAKENHI-PROJECT-16K21067/16K21067seika. Published in pdf July 9, 2019 https://www. science direct. Published at com/journal/materials-letters/vol/254/suppl/C September 3, 2019 Published by the Ceramic Society of Japan Kanto Branch In the 35th Research Presentation of the Ceramic Society of Japan Kanto Branch Lecture Proceedings September 3, 2019 Published at the 35th Research Presentation Meeting of the Ceramic Society of Japan, Kanto Branch August 28, 2019 https://smic-2019. events. gunma-u. ac. Published at jp/ September 6, 2019 Published at S-Membrane International Conference 2019

The present invention relates to fibrous boron carbide and its production method.

Boron carbide ( _B4C ), which is a carbide of boron, is a non-oxide ceramic with excellent physical properties (high melting point: melting point 2430°C, low density, high hardness, wear resistance) and functionality (neutron absorption capacity). . Due to its high hardness and low specific gravity, B ₄ C is mainly used as abrasives and structural materials. In addition, since it exhibits high wear resistance even under high temperature conditions, it is used for wear-resistant materials and cutting tools. Furthermore, B ₄ C exhibits a high neutron absorption capacity and has high chemical and thermal stability, so it is used as a neutron absorber and shielding material in the field of nuclear power industry.

As an industrial production method of B ₄ C, the thermal carbon reduction method of boric oxide (B ₂ O ₃ ) (2B ₂ O ₃ +7C→B ₄ C + 6CO) is most often used, but this method requires a synthesis temperature of about The temperature is as high as 2000°C. Also, pulverization requires post-grinding and washing steps.
In recent years, a low-temperature synthesis method (about 1500°C) using a condensate of boric acid and an organic compound (polyol) having multiple hydroxy groups, a saccharide that is an oxidation product of polyol, etc. has been studied (Patent Document 1). . This condensate or the like becomes a composite of B ₂ O ₃ and carbon by heat treatment, and the production of B ₄ C proceeds based on the thermal carbon reduction reaction. However, there is a problem that free carbon derived from organic compounds remains in the product.

The present inventor disperses the boron source and the carbon source at the molecular level by forming a borate ester (B—O—C) bond through dehydration condensation of boric acid and an organic compound (polyol) having a plurality of hydroxy groups. In addition, by introducing a thermal decomposition operation in air before firing under an inert atmosphere to the boric acid-polyol condensate, excess carbon in the reaction was removed and residual free carbon was suppressed. In addition, by controlling the nanostructure of an active precursor (B ₂ O ₃ -carbon structure) composed of B ₂ O ₃ and carbon obtained by thermally decomposing a boric acid-polyol condensate in the atmosphere, 1200 We have succeeded in synthesizing a B ₄ C powder containing almost no residual free carbon at a low temperature of 10° C. (Non-Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2003-277039

M. Kakiage et al., J. Ceram. Soc. Jpn., 119, 422 (2011). M. Kakiage et al., J. Ceram. Soc. Jpn., 121, 40 (2013).

Boron carbide obtained by a conventional hot carbon reduction method is an ingot, and is used by pulverizing into powder. A powder is also obtained when an organic compound (polyol) is used as the carbon source and a B ₂ O ₃ -carbon structure is prepared to produce boron carbide. Thus, boron carbide is conventionally used as a powder. Since boron carbide has a high melting point and high hardness, boron carbide obtained as a powder must be used as a powder or as a sintered body. I had a problem.
As a result of intensive studies on methods for producing boron carbide, which is obtained as powder by conventional methods, the present inventors have found a new method for obtaining a novel boron carbide body having a fibrous form.

An object of the present invention is to provide fibrous boron carbide, which is a novel boron carbide body in which grains of boron carbide are linked to form a fibrous form, and a suitable method for producing the same.

The method for producing fibrous boron carbide according to the present invention includes the steps of preparing a solution of boric acid and an organic compound, and using the solution of boric acid and an organic compound to produce condensate fibers of boric acid and an organic compound. spinning, pyrolyzing the condensate fiber in the air to produce a B ₂ O ₃ -carbon structure fiber, and exposing the B ₂ O ₃ -carbon structure fiber to a vacuum or an inert gas. sintering in an atmosphere to produce fibrous boron carbide in which granular boron carbide is linked.
As a means for suitably spinning the condensate fiber, an electrospinning method is used in the step of adjusting the viscosity of the solution of the boric acid and the organic compound using an acid and spinning the condensate fiber. adjusting the viscosity of the solution of the boric acid and the organic compound using the plasticizer of the organic compound, and applying electrospinning in the step of spinning the condensate fiber, etc. .
The acid used to adjust the viscosity of the solution of the boric acid and the organic compound is preferably an inorganic acid such as hydrochloric acid, and the plasticizer for the organic compound is preferably a low-molecular-weight polyol such as glycols, glycerin, or sugar alcohol. .
Moreover, a polyol can be used as the organic compound used for preparing the solution containing the boric acid and the organic compound. As the polyol, for example, polyvinyl alcohol (hereinafter sometimes referred to as PVA) can be used, and as the solvent used for preparing the solution, for example, dimethyl sulfoxide (hereinafter sometimes referred to as DMSO) ) can be used.

The fibrous boron carbide according to the present invention is fibrous boron carbide in which granular boron carbide is connected, and the fibrous boron carbide has a plurality of granular boron carbide particles having a particle size of 1 μm to 5 μm. It is connected and configured in a fibrous form.
Here, it is preferable that each of the granular boron carbide contains secondary particles each of which is formed by gathering a plurality of fine particles of boron carbide having a particle diameter of 1 μm or less.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide fibrous boron carbide, which is a novel boron carbide body in which grains of boron carbide are linked to form a fibrous form, and a suitable method for producing the same.

FIG. 2 is a flow diagram showing a method for producing fibrous boron carbide; Field-emission scanning electron microscope (FE-SEM) photographs of boric acid-PVA condensate fibers obtained by electrospinning boric acid-PVA/DMSO solutions prepared with different amounts of hydrochloric acid added, and a graph showing the fiber diameter distribution. is. FIG. 2 shows an FE-SEM photograph and an appearance photograph of a B ₂ O ₃ -carbon structure fiber obtained by pyrolyzing a boric acid-PVA condensate fiber in the air. FIG. 4 is a graph showing an FE-SEM photograph and a pore size distribution of the pyrolyzate after washing the pyrolyzate with warm water to remove B ₂ O ₃ ; FIG. (a) XRD pattern and (b) Scanning Electron Microscope (SEM) photograph of the fired product obtained by firing the B ₂ O ₃ -carbon structure fiber under Ar gas flow. be. 1 is a graph showing SEM photographs of boric acid-PVA-glycerin condensate fibers obtained by electrospinning boric acid-PVA-glycerin/DMSO solutions prepared by varying the amount of glycerin added, and the fiber diameter distribution thereof. (a) Appearance photograph, (b) digital microscope photograph, and (c) of fibrous B ₂ O ₃ -carbon structure obtained by pyrolyzing boric acid-PVA-glycerin condensate fiber in air. It is an FE-SEM photograph. SEM photographs of a fired product obtained by firing a fibrous B ₂ O ₃ -carbon structure, (a) is an SEM photo of a fired product at a firing temperature of 1300°C, and (b) is a firing temperature of 1400°C. is a SEM photograph of the baked product. Fig. 2 shows a powder X-ray diffraction (XDR) pattern of a fired product obtained by firing a fibrous B ₂ O ₃ -carbon structure at a firing temperature of 1400°C.

Hereinafter, the method for producing fibrous boron carbide and the fibrous boron carbide of the present invention will be described with specific examples.
However, the following specific example shows one aspect of the present invention, and the present invention is not limited to the following description, and it goes without saying that various modifications are possible.

In the present disclosure, a numerical range described using "-" represents a numerical range including the numerical values before and after "-" as lower and upper limits.
In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are multiple substances corresponding to each component in the composition, unless otherwise specified. .
In the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.
In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described step by step. Moreover, in the numerical ranges described in the present disclosure, the upper limit value or lower limit value described in a certain numerical range may be replaced with the values shown in the examples.
Moreover, in the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.

<<Method for producing fibrous boron carbide>>
A method for producing fibrous boron carbide according to the present invention is shown in FIG. 1 as a process chart (flow chart).

[Step of preparing a solution containing boric acid and an organic compound (Step I)],
In the production method of the present invention, first, boric acid and a polyol (polyvinyl alcohol (PVA) in this example) are prepared as an organic compound, and a solution of the boric acid and the polyol is prepared.
As a solution of boric acid and polyol, a boric acid-PVA aqueous solution or a dimethylsulfoxide (DMSO) solution can be used. As the solvent used for the solution of boric acid and the organic compound, a solvent that can be easily prepared into fibrous form in the subsequent spinning process may be used.
In this example, DMSO is used as a solvent, but it is not limited to this, and can be used by appropriately selecting from water, 1,1,1,3,3,3-hexafluoro-2-propanol, etc. can be done.

[Step of spinning a condensate fiber of boric acid and an organic compound using a solution containing boric acid and an organic compound (step II)]
The boric acid-polyol solution obtained in Step I is then used to make condensate fibers of boric acid and polyol by dry spinning or electrospinning. FIG. 1 shows an example of producing condensate fibers of boric acid and PVA.
When spinning the condensate fiber, it is preferable to adjust the viscosity of the solution to a viscosity that facilitates spinning into a fibrous form.
Inorganic acids such as hydrochloric acid, plasticizers for the above organic compounds, and the like can be used to adjust the viscosity. These may use only 1 type and may use 2 or more types together.
In one aspect of the present invention, PVA is used as the organic compound for preparing the solution, and glycerin, which is a known polyol as a plasticizer for PVA, is used as the plasticizer for the organic compound for adjusting the viscosity of the solution. However, the combination of the organic compound and the viscosity-adjusting compound is not limited to the above. For example, even when PVA is used as the organic compound, it is possible to adjust the viscosity of the solution using only hydrochloric acid.

[Step of pyrolyzing the condensate fiber in the air to produce a B ₂ O ₃ -carbon structure fiber [step III]
Next, the condensate fiber of boric acid and an organic compound produced in step II above is thermally decomposed in the atmosphere to produce a B ₂ O ₃ -carbon structure fiber. The temperature at which the condensate fiber is thermally decomposed in the air can be, for example, 400°C to 900°C, preferably 400°C to 700°C. The heating time for maintaining the above temperature for thermal decomposition can be about 0.5 to 5 hours.
The heating temperature, heating time, and the like in step III are preferably appropriately selected depending on the raw material, spinning method, and spinning conditions.

[Step of sintering B ₂ O ₃ -carbon structure fibers in vacuum or in an inert gas atmosphere to produce fibrous boron carbide in which granular boron carbide is linked (step IV)]
Next, fibrous boron carbide can be obtained by firing the B ₂ O ₃ -carbon structure fibers obtained in Step III above in a vacuum or in an inert gas atmosphere.
By firing in a vacuum or in an inert gas atmosphere, fibrous boron carbide can be efficiently obtained under conditions in which the influence of oxygen is reduced.
In the present disclosure, "in a vacuum" refers to a condition in which the pressure is reduced below atmospheric pressure, and does not necessarily refer to a state in which no air exists. For example, the pressure range is preferably 100 Pa or less.
Examples of inert gas include Ar gas.
The firing temperature is not particularly limited as long as it can convert the B ₂ O ₃ -carbon structure fibers into fibrous boron carbide, and is appropriately adjusted depending on the physical properties, size, etc. of the desired fibrous boron carbide.
The firing temperature can be set to, for example, 1100°C to 2450°C, preferably 1200°C to 1850°C.

According to the method for producing fibrous boron carbide according to the present invention, it is possible to easily obtain fibrous boron carbide in which particles of boron carbide are linked in a fibrous form.
In addition, since the fibrous boron carbide according to the present invention, which will be described later, is provided as fibrous boron carbide, it can be used for new uses of boron carbide.

<<Fibrous Boron Carbide>>
The fibrous boron carbide of the present invention is a fibrous boron carbide in which granular boron carbide is connected, and the fibrous boron carbide has a plurality of granular boron carbides having a particle size of 1 μm to 5 μm connected. It is made into a fibrous form.

It is preferable that each of the granular boron carbide contained in the fibrous boron carbide contains a secondary particle composed of a plurality of aggregated fine particles of boron carbide having a particle diameter of 1 μm or less. The average particle size of secondary particles is preferably in the range of 1 μm to 5 μm. The granular boron carbide contained in the fibrous boron carbide may contain primary particles having a particle size of 1 μm to 5 μm.
Although the method for producing the fibrous boron carbide of the present invention is not particularly limited, it is preferable from the viewpoint of productivity to obtain the fibrous boron carbide by the above-described method for producing the fibrous boron carbide of the present invention.

<Production Example 1 of Fibrous Boron Carbide Body>
Experimental examples in which B ₂ O ₃ -carbon structure fibers were produced and fibrous boron carbide (hereinafter, boron carbide may be abbreviated as B ₄ C hereinafter) are explained below according to the production method of the present invention. do.
In this experiment, PVA, which is a polyol, was used as the organic compound, and DMSO was used as the solvent.
First, 5% by mass of PVA was added to DMSO and stirred at 120° C. to prepare a DMSO solution of PVA. Next, 0, 5% by mass, 10% by mass, or 15% by mass of 1M hydrochloric acid aqueous solution (1 mol/liter HCl aqueous solution) was added to the DMSO solution of PVA, and further boric acid was added. was added in an amount to give a molar ratio of boric acid:PVA=1:4 to prepare a boric acid-PVA/DMSO solution, ie, a solution containing boron and an organic compound. (Process I)

This boric acid-PVA/DMSO solution was then electrospun to obtain boric acid-PVA condensate fibers. Electrospinning conditions are an applied voltage of 20 kV to 22.5 kV. (Step II)
Next, the boric acid-PVA condensate fibers obtained by electrospinning were thermally decomposed in the atmosphere to obtain B ₂ O ₃ -carbon structure fibers. The thermal decomposition conditions were a heating temperature of 550° C. and a heating time of 2.5 hours in the air, or a heating temperature of 600° C. and a heating time of 2 hours. (Step III)

FIG. 2 shows an FE-SEM photograph of boric acid-PVA condensate fibers obtained by electrospinning the boric acid-PVA/DMSO solution prepared by the above method.
FIG. 2 is a graph showing FE-SEM photographs of boric acid-PVA condensate fibers obtained by electrospinning boric acid-PVA/DMSO solutions prepared with different amounts of hydrochloric acid added, and the fiber diameter distribution thereof. In FIG. 2, chlorine is indicated as HCl, and the amount of chlorine added is indicated as 0 wt %, 10 wt %, and 15 wt %, respectively. In the present disclosure, wt% is synonymous with mass%.
When the amount of hydrochloric acid added was 0% by mass, spinning was impossible because the boric acid-PVA solution had a high viscosity.
FIG. 2 shows FE-SEM photographs of boric acid-PVA condensate fibers obtained by electrospinning with 0, 5% by weight, 10% by weight, or 15% by weight of hydrochloric acid added. The distribution of the condensate fibers is shown in histograms when the amount of hydrochloric acid added is 10% by mass and 15% by mass.

As shown in FIG. 2, when the amount of hydrochloric acid added was 5% by mass, a film-like product was observed together with the fibers, and stable fiber formation was not achieved. On the other hand, when the amount of hydrochloric acid added was 10% by mass, a fibrous body with a uniform fiber diameter could be obtained. The fiber diameter is approximately 5 μm. In addition, when the amount of hydrochloric acid added was 15% by mass, it was possible to obtain a fibrous body, and although the fiber diameter was smaller than that of 10% by mass, the fiber shape became heterogeneous. .
This experimental result shows that adding hydrochloric acid to the boric acid-PVA/DMSO solution can adjust the viscosity of the solution, the viscosity of the boric acid-PVA/DMSO solution decreases, and the boric acid-PVA condensate fiber It is shown that non-woven boric acid-PVA condensate fibers can be produced by electrospinning after adding hydrochloric acid to the boric acid-PVA/DMSO solution.

The condensed state of the boric acid-PVA condensate fiber obtained by adding 10% by mass of hydrochloric acid, in which the most homogeneous fiber shape was observed, was measured by TG-DTA for the obtained boric acid-PVA condensate fiber. Alternatively, it was evaluated by performing FT-IR measurement. As a result, behavior derived from B—O—C bond formation reported in previous studies was observed. Therefore, it was confirmed that the obtained fibers were sufficiently condensed. Thus, a non-woven boric acid-PVA condensate fiber could be produced by electrospinning the boric acid-PVA/DMSO solution.

FIG. 3 shows an FE-SEM photograph and an appearance photograph of the pyrolyzate obtained by pyrolyzing the boric acid-PVA condensate fiber obtained by the above method in the atmosphere.
The pyrolyzate was obtained in the form of a nonwoven fabric reflecting the nonwoven form of the boric acid-PVA condensate fiber, and as can be seen from the FE-SEM photograph, its fine structure also maintained the fiber form.

In order to observe the structure of the pyrolyzate obtained by thermally decomposing the boric acid-PVA condensate fiber in the air, the obtained pyrolyzate was washed with warm water to remove B ₂ O ₃ . The morphology was observed by FE-SEM. FIG. 4 is an FE-SEM photograph of the morphology of the pyrolyzate after B ₂ O ₃ is removed by washing with warm water, and a graph showing the pore size distribution of the pyrolyzate.
The vacant portion corresponds to B ₂ O ₃ . A structure in which B ₂ O ₃ particles were dispersed in a carbon matrix was observed, similar to the boric acid-PVA condensate powder (not fibrous) previously reported by the present inventors. The D ₅₀ of the pore size (corresponding to B ₂ O ₃ particles) observed in the B ₂ O ₃ -carbon structure after washing with warm water was 25 nm (calculated from the graph shown in FIG. 4). A report by the inventor of the present application has revealed that the formation of such a finely dispersed B ₂ O ₃ -carbon structure is advantageous for the synthesis of boron carbide at low temperatures. Therefore, by thermally decomposing the boric acid-PVA condensate fiber in the air, it is possible to produce a fibrous and finely dispersed B ₂ O ₃ -carbon structure that is advantageous for the synthesis of boron carbide.

Next, the B ₂ O ₃ -carbon structure formed in the form of a nonwoven fabric containing fibrous aggregates produced by the above-described method is sintered under Ar gas flow, and a B ₄ C synthesis operation is performed to form a fibrous structure. Boron carbide was obtained. (Step IV)
FIG. 5(a) is an XRD pattern of a fired product obtained by firing a B ₂ O ₃ -carbon structure under Ar gas flow, and FIG. 5(b) is an SEM photograph of the fired product.
In the experiment, the firing temperature was 1150° C. to 1250° C., the heating rate was 10° C./min, and the firing time was 5 hours under Ar gas flow (flow rate: 200 mL/min).
In FIG. 5(a), a B ₄ C peak can be confirmed for the material sintered at 1200° C., indicating that boron carbide is formed. A small amount of B ₄ C is also generated in the material fired at 1150°C.

From the SEM photograph of the fired product shown in FIG. 5(b), it can be seen that by firing the fibrous B ₂ O ₃ -carbon structure, the granular boron carbide bodies are fine particles of boron carbide having a size of about 1 μm or less. It can be seen that it is formed in a fibrous form in which is gathered. Such a form of boron carbide body in which fine particles of boron carbide are aggregated and formed into a fibrous form composed of a plurality of granular particles is obtained from boron carbide obtained from unfiberized boric acid-PVA condensate powder. It is completely different from the powder (powder described in Non-Patent Document 1 and Non-Patent Document 2) which is shaped.

In the experimental example <Production Example 1> described above, the boric acid-PVA condensate fiber was produced by adjusting the viscosity of the boric acid-PVA solution using hydrochloric acid when producing the boric acid-PVA condensate fiber. The adjustment of the viscosity of the boric acid-PVA solution is important in making fibrous boric acid-PVA condensate fibers. Further, the properties of the condensate fiber are such that the condensate fiber is thermally decomposed in the air to produce a B ₂ O ₃ -carbon structure, and the B ₂ O ₃ -carbon structure is fired in an inert gas atmosphere. It is important for fabricating a fibrous boron carbide body.

<Preparation example 2 of fibrous boron carbide>
In this experiment <Production Example 2>, as a method of adjusting the viscosity of the boric acid-PVA solution, a method of adjusting the viscosity by adding a plasticizer of an organic compound (polyol) to the solution was tried. PVA was actually used as the polyol, and glycerin was used as the plasticizer for the PVA.

The electrospinning solution used PVA as an organic compound (polyol), glycerin as a plasticizer for the organic compound (polyol), and DMSO as a solvent. In the experiments, solutions containing 10% by mass, 15% by mass, or 20% by mass of glycerin relative to PVA were used, and the solutions were prepared under the following conditions. The solution is prepared by adding glycerin to a boric acid-PVA/DMSO solution (9% by mass), and adding boric acid at a molar ratio of 4:1 for PVA and boric acid, and 1:1 for glycerin and boric acid. A boric acid-PVA-glycerin/DMSO solution was prepared by mixing with the solution prepared as above. (Process I)

This boric acid-PVA-glycerin/DMSO solution was then electrospun to make boric acid-PVA-glycerin condensate fibers. The electrospinning condition is an applied voltage of 20 kV. (Step II)
Then, the boric acid-PVA-glycerin condensate fiber was pyrolyzed in air at 640° C. for 2 hours to produce a B ₂ O ₃ -carbon structure fiber. (Step III)
Finally, the B ₂ O ₃ -carbon structure fiber is sintered under Ar gas flow (flow rate: 200 mL/min) (sintering temperature 1200° C. to 1400° C., heating rate 10° C./min, sintering time 5 hours). , a fibrous carbon boron body was obtained. (Step IV)

FIG. 6 shows boric acid-PVA-glycerin condensation obtained by electrospinning using a boric acid-PVA-glycerin/DMSO solution in which the amount of glycerin added to PVA is 10%, 15%, or 20% by weight. 1 is a SEM photograph of a material fiber and a graph showing each fiber diameter distribution. In FIG. 6, the amounts of glycerin added are indicated as 10 wt %, 15 wt %, and 20 wt %, respectively. Here, wt % is synonymous with mass %.
From FIG. 6, it can be seen that when the amount of glycerin added is 10% by mass, the fibers have a uniform fiber shape and the average fiber diameter is 2.5 μm, and when the amount of glycerin added is 15% by mass, compared to 10% by mass, the fibers While the uniformity of the diameter is slightly inferior, the average fiber diameter is 2.3 μm and the fiber diameter is thin. Moreover, when the added amount was 20% by mass, the fibers did not have an appropriate fiber shape, resulting in poor spinnability. When the amount of addition was 20% by mass, glycerin remaining after baking might have caused fiber coagulation inhibition.

FIG. 7 shows the morphology of the B ₂ O ₃ -carbon structure obtained by pyrolyzing the boric acid-PVA-glycerin condensate fiber in air. FIG. 7(a) is an appearance photograph of a fibrous B ₂ O ₃ -carbon structure, FIG. 7(b) is an FE-SEM photograph, and FIG. 7(c) is a fibrous B ₂ O ₃ after hot water washing. - FE-SEM photographs of carbon structures. It can be seen from FIGS. 7(a) and 7(b) that the fibrous B ₂ O ₃ -carbon structures reflect the morphology of boric acid-PVA condensate fibers. Also, from FIG. 7(c), extremely fine dispersion of B ₂ O ₃ and carbon is observed in the fibrous B ₂ O ₃ -carbon structure, and the fibrous B ₂ O ₃ -carbon structure has a high Reactive.

FIG. 8 is a SEM photograph of a fired product obtained by firing a fibrous B ₂ O ₃ -carbon structure under Ar gas flow. Fig. 8(a) is a SEM photograph of a fired product fired at a firing temperature of 1300°C, and Fig. 8(b) is a SEM photograph of a fired product fired at a firing temperature of 1400°C.
FIG. 9 shows XRD analysis data of a sintered product obtained at a sintering temperature of 1400°C. From FIG. 9, it can be seen that B ₄ C with few impurities was produced by sintering the fibrous B ₂ O ₃ -carbon structure.

As shown in FIGS. 8(a) and 8(b), both the fired products with firing temperatures of 1300° C. and 1400° C. are fired products formed by connecting a plurality of particles made of boron carbide in a fibrous form. I know there is. That is, it was possible to obtain fibrous boron carbide. Comparing the fibrous material sintered at 1300° C. with the sintered material sintered at 1400° C., the fibrous material sintered at 1300° C. has finer particles.

Claims (9)

preparing a solution comprising boric acid and an organic compound;
A step of spinning a condensate fiber of boric acid and an organic compound using a solution containing boric acid and an organic compound;
pyrolyzing the condensate fibers in the atmosphere to produce B ₂ O ₃ -carbon structure fibers;
a step of sintering the B ₂ O ₃ -carbon structure fiber in vacuum or under an inert gas atmosphere to produce fibrous boron carbide in which granular boron carbide is linked;
A method for producing fibrous boron carbide. The fiber of claim 1, wherein in the step of preparing a solution containing boric acid and an organic compound, the viscosity of the solution is adjusted using an acid, and electrospinning is applied in the step of spinning the condensate fiber. A method for producing spheroidal boron carbide. In the step of preparing a solution containing boric acid and an organic compound, the viscosity of the solution is adjusted using the plasticizer of the organic compound, and electrospinning is applied in the step of spinning the condensate fiber. Item 1. A method for producing fibrous boron carbide according to item 1. 4. The method for producing fibrous boron carbide according to claim 3, wherein glycerin is used as a plasticizer for said organic compound. 5. The method for producing fibrous boron carbide according to claim 3, wherein the viscosity of the solution of said boric acid and organic compound is adjusted using hydrochloric acid and a plasticizer for said organic compound. The method for producing fibrous boron carbide according to any one of claims 1 to 5, wherein the organic compound contains a polyol. 7. The method for producing fibrous boron carbide according to claim 6, wherein said polyol contains polyvinyl alcohol, and said solution of boric acid and organic compound contains dimethylsulfoxide as a solvent. A fibrous boron carbide in which granular boron carbide is connected, wherein the fibrous boron carbide is formed in a fibrous form by connecting a plurality of granular boron carbide particles having a particle size of 1 μm to 5 μm. fibrous boron carbide; 9. The fibrous boron carbide according to claim 8, wherein each of said granular boron carbide contains secondary particles each composed of a plurality of aggregated fine particles of boron carbide having a particle size of 1 μm or less.

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