JP2007139668A - Control rod for reactor and manufacturing method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control rod made of an integral molding having a sufficient strength, having a sufficient neutron absorption capacity and having a structure facilitating emission of helium produced by controlling the porosity of the molding, and a manufacturing method for the same. <P>SOLUTION: The control rod includes a carbon nanostructure containing boron at least as part of a member. The carbon nanostructure, a boron compound and a thermosetting resin composition are mixed, molded, and heated and burned to make the control rod. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control rod for controlling the output of a nuclear reactor and a method for manufacturing the same. In particular, the present invention relates to a control rod suitably used for a boiling water reactor and a method for manufacturing the same.

  As is generally known, the control rods in the reactor serve to control the reaction. This is generally accomplished by providing a plurality of control rods containing neutron absorbing material and operating the control rods in a nuclear reactor. In general, control rods used in boiling water reactors (BWRs) are cruciform and extend into complementary cruciform gaps between fuel channels.

  Various types of control rods are conventionally known.

Patent Document 1 includes four blades containing boron carbide as a neutron absorber, and has a cross-shaped cross section, and a control rod for controlling the output of a nuclear reactor includes carbonization contained in the blades. A control rod characterized in that ¹⁰ B is distributed so that the concentration of ¹⁰ B in boron decreases from the outside toward the inside of the control rod is disclosed. In this control rod, the concentration of ¹⁰ B, which is a neutron absorber, is changed in the height and radius method of the control rod, and the efficiency is increased by using ¹⁰ B which is small in proportion to the amount of neutrons to be absorbed.

  Patent Document 2 discloses a control rod in which a neutron absorbing material such as boron carbide pellets is housed inside a neutron absorbing material housing container formed of a 2D-carbon fiber reinforced carbon composite material. In this control rod, the container body is made of a 2D-carbon fiber reinforced carbon composite material to make the container body high in strength and easy to manufacture.

  In Patent Document 3, a control rod molded body made of carbon fiber is manufactured, the molded body is impregnated with coal tar pitch, carbonized and sintered, and boron carbide powder is sealed in the outer cylinder of the molded body. As a result, an integrated control rod is disclosed.

  In Patent Document 4, a control rod container made of a boron mixed carbon fiber reinforced carbon composite material obtained by combining a carbon fiber reinforced carbon composite material (CC composite) and boron and a neutron absorber stored therein are integrated. A nuclear reactor control rod is disclosed. By integrating the structure and the neutron absorber, there is no interaction between the structure and the neutron absorber, and manufacturing is easy.

However, the control rods shown in Patent Documents 1 and 2 are composed of boron carbide or ¹⁰ B, which is a neutron absorbing material, and a container body that houses this, and the structure is complicated. For this reason, there existed a problem that homogenization of neutron absorption performance was difficult and manufacturing cost became high.

  In addition, the control rod shown in Patent Document 3 requires 1 to 10 days for the production of the outer cylinder, and 1 to 5 days for the sintering of the packing made of boron carbide. There was a problem that the control rod could be damaged by swelling with helium.

Further, in the control rod shown in Patent Document 4, since a CC composite is impregnated with a boron dispersion to form an absorbent material, the boron concentration cannot be increased by the impregnation amount, and a sufficient neutron absorption amount can be obtained. In addition, the control rod may be damaged by swelling with helium after neutron absorption.
Japanese Patent Laid-Open No. 10-293188 JP 2004-119386 A Japanese Patent No. 2784304 JP 2004-132758 A

  Accordingly, an object of the present invention is to provide a control rod for a nuclear reactor and a method for manufacturing the same, which solve the problems of the control rod in the conventional technology as described above. The present invention further provides a control rod having sufficient strength against swelling of the control rod by helium after neutron absorption, has sufficient neutron absorption capability, and further controls the porosity of the molded body. It is an object of the present invention to provide a control rod having a structure that easily releases generated helium and a method for manufacturing the same.

  The present invention for solving the above problems is a control rod for a nuclear reactor characterized in that a carbon nanostructure containing boron is used as at least a part of the member.

  The present invention also provides a control rod characterized in that the boron content in the carbon nanostructure containing boron is preferably 10 to 70% by mass in terms of atomic units. .

  In the present invention, the carbon nanostructure is preferably a three-dimensional network-like carbon fiber structure composed of carbon fibers having an outer diameter of 15 to 100 nm, and the carbon fiber structure includes the carbon fibers. The carbon fiber structure is a carbon fiber structure that has a granular portion that binds the carbon fibers to each other, and the granular portion is formed in the growth process of the carbon fiber. The present invention provides a control rod characterized by the above.

  The present invention preferably provides a control rod formed by integrally molding carbon nanostructures containing boron as members.

  The present invention that solves the above-mentioned problems also provides a method for producing a control rod, which comprises mixing a carbon nanostructure, a boron compound, and a thermosetting resin composition, followed by heating and firing. .

  The present invention also provides a method for producing a control rod, in which a mixture of a carbon nanostructure, a boron compound, and a thermosetting resin composition is cast and polymerized.

  The present invention further provides a method for producing a control rod having a heating and firing temperature of preferably 1500 to 2800 ° C.

  The control rod of the present invention is simple in structure and low in manufacturing cost, and has sufficient strength by taking advantage of the high strength of carbon nanostructures, while retaining boron efficiently and sufficiently absorbing neutrons. It has a structure that is easy to release helium generated after neutron absorption because it can easily control the porosity of the molded body, and can exhibit stable characteristics with little risk of damage during use. It becomes.

  Hereinafter, the present invention will be described in detail based on preferred embodiments.

  The control rod of the present invention is characterized in that a carbon nanostructure containing boron is at least a part of the member.

The control rod of the present invention can be obtained, for example, by a manufacturing method as described later. However, since the carbon constituting the carbon nanostructure has a sp ² bond having a curvature, it is completely flat like graphite. Compared with the sp ² bond that gives the structure, it is rich in reactivity. For this reason, even if a compound such as boric acid is used as the boron source, the carbon nanostructure and the boron compound are mixed and then heated. By applying the treatment, boron carbide can be generated, and boron having neutron absorption ability can be immobilized efficiently, and a high-strength molded body can be obtained.

  In the control rod of the present invention, the “carbon nanostructure containing boron” is not necessarily a state in which boron atoms are chemically bonded to the carbon atoms constituting the carbon nanostructure by a covalent bond. This means that boron is physically attached to or adsorbed to the carbon nanostructure, but preferably, at least a part thereof is chemically bonded as described above. It is desirable that it is fixed in the state.

In such a control rod of the present invention, the content of boron in the carbon nanostructure containing boron is not particularly limited, but for example, preferably 10 to 70% by mass in terms of atomic unit, More preferably, the content is 10 to 40% by mass. The boron content is preferably 10 to 70% by mass in order to achieve a sufficient neutron absorption capacity and to form a stable structure as a control rod member. As the boron to be contained in the control rod of the present invention, from the economic point of view, the content of which is sufficient in natural boron content of ¹⁰ B having a neutron absorbing capability is about 20%, of course ¹⁰ B It is also possible to use concentrated boron whose proportion is increased to a high concentration, for example, 60% by mass or more. In this case, it is sufficient even if the boron content in the control rod is lower than the above range. It is possible to exhibit neutron absorption ability.

  Moreover, it is desirable that the carbon fiber structure used in the present invention has a combustion start temperature in air of 700 ° C. or higher, more preferably 750 to 900 ° C. As described above, since the graphene sheet of the carbon fiber structure contains boron and the carbon fiber has an intended outer diameter, it has such a high thermal stability.

  Since the control rod of the present invention is preferably molded integrally, the shape or the like can be any shape such as a cross, a cylinder, or a ring.

  Further, the control rod of the present invention is not particularly limited, but the porosity is preferably, for example, preferably about 0.05 to 10%, and more preferably about 0.1 to 2%. When the porosity is in the range of 0.05 to 10%, helium generated by neutron absorption can be easily released, and the mechanical strength of the control rod is sufficiently excellent. is there.

  Such a control rod according to the present invention can be manufactured, for example, as follows.

That is, the control rod according to the present invention is a mixture of a carbon nanostructure, a boron compound, and a thermosetting resin composition for molding at a predetermined ratio, for example, from room temperature (25 ° C. ± 5 ° C.) to 140 ° C. After heating and forming into a rod shape, heating to 600-1500 ° C. to carbonize the thermosetting resin and immobilize boron to the carbon nanostructure, preferably by reacting the carbon nanostructure with the boron compound It can be manufactured by producing boron carbide. As described above, since the carbon constituting the carbon nanostructure has a sp ² bond having a curvature, the carbon nanostructure is rich in reactivity compared to the sp ² bond that gives a complete planar structure like graphite. For this reason, for example, even when a compound such as boric acid is used as a boron source, boron carbide is efficiently produced by mixing the carbon nanostructure and the boron compound and then heat-treating, and has a good neutron absorption capability. Can be fixed, and a high-strength molded body can be obtained. Moreover, the porosity of this structure is controllable by adjusting the addition amount of the said thermosetting resin composition.

  In such a production method, the method of molding the mixture of the carbon nanostructure, the boron compound and the thermosetting resin composition into a predetermined rod shape is not particularly limited. It is preferable to perform molding by casting polymerization, which is a general molding method.

  Next, the carbon nanostructure used in the present invention is mainly a structure having a carbon six-membered ring arrangement structure, and at least one of the three-dimensional dimensions of the structure is nanometer. In the region, for example, about 10 to 150 nm, preferably 20 to 90 nm.

  A typical example of the carbon six-membered ring arrangement structure is a sheet-like graphite graphene sheet. Further, for example, a five-membered ring or seven-membered ring is combined with a six-membered ring of carbon. The structure etc. can also be included.

  More specifically, as the carbon nanostructure, for example, a single-walled carbon nanotube having a diameter of about several nanometers, which is a single graphene sheet rounded into a cylindrical shape, or a cylindrical graphene sheet laminated in a direction perpendicular to the axis Examples include multi-walled carbon nanotubes (multi-walled carbon nanotubes), carbon nanohorns in which the ends of single-walled carbon nanotubes are closed in a conical shape, and carbon nanohorn aggregates in which the carbon nanohorn is a spherical aggregate having a diameter of about 100 nm. Can do. Further, carbon onions having a carbon six-membered ring arrangement structure, fullerenes and nanocapsules in which a five-membered ring is introduced into the carbon six-membered ring arrangement structure, and the like are included. In the present invention, these carbon nanostructures can be a single type of the above-mentioned type or a mixture of two or more types.

  Among these carbon nanostructures, in particular, the use of carbon nanotubes having a cylindrical graphene sheet having a polygonal shape in which the axis orthogonal to the cross section is a polygon is a heat used as a kind of excipient in the production method of the present invention described later. This is preferable from the viewpoint of enhancing the dispersibility of the carbon nanostructure in the curable resin composition. The fact that the carbon nanotube has a polygonal cross section perpendicular to the axis is due to heat treatment at a temperature of 2500 ° C. or higher. This heat treatment causes the carbon nanotubes to be dense in both the fiber direction and the lamination direction. The bending rigidity can be remarkably improved with few defects. As a result, it is difficult to bend and elasticity, that is, a property of returning to the original shape even after deformation can be imparted, so that it is difficult to form an entangled structure and it can be easily dispersed in a thermosetting resin. The carbon nanotubes may be single-walled, but a multi-layered structure in which graphene sheets are laminated in the direction perpendicular to the axis is preferable in terms of improving bending rigidity.

  Further, as the carbon nanostructure, it is preferable to use a three-dimensional network-like carbon fiber structure having a predetermined structure as described in detail below.

  The carbon fiber structure preferably used in the present invention is preferably a three-dimensional structure composed of carbon fibers having an outer diameter of 15 to 100 nm, as can be seen from the TEM photographs shown in FIGS. 4 (a) and 4 (b). It is a network-like carbon fiber structure, and the carbon fiber structure has a granular portion that binds the carbon fibers to each other in a form in which a plurality of the carbon fibers extend.

  The outer diameter of the carbon fiber constituting the carbon fiber structure is preferably in the range of 15 to 100 nm. In this range, the carbon fiber has a polygonal cross section, as will be described later, and a thermosetting resin. This is because it is preferable from the viewpoint of increasing the dispersibility of the carbon nanostructure therein and from the viewpoint of manufacturing a high-strength control rod.

  In addition, especially as an outer diameter of the carbon fiber in a carbon fiber structure, it is more desirable to exist in the range of 20-70 nm. In this outer diameter range, a cylindrical graphene sheet laminated in a direction perpendicular to the axis, that is, a multilayer, is not easily bent, and is elastic, that is, has the property of returning to its original shape even after deformation. Therefore, even after the carbon fiber structure is once compressed, it is easy to adopt a sparse structure after being disposed in the thermosetting resin composition.

Incidentally, when annealing at 2400 ° C. or higher, with a true density narrowed spacing of graphene sheets stacked is increased from 1.89 g / cm ³ to 2.1 g / cm ^3, perpendicular to the axis the cross-section of the carbon fiber becomes a polygonal shape The carbon fiber having this structure is dense and has few defects both in the laminating direction and in the plane direction of the cylindrical graphene sheet constituting the carbon fiber, so that the bending rigidity (EI) is improved.

  In addition, it is desirable that the outer diameter of the carbon nanostructure used in the present invention or the fine carbon fiber in the carbon fiber structure changes along the axial direction. Thus, if the outer diameter of the carbon fiber is not constant along the axial direction and changes, it is considered that a kind of anchor effect occurs in the carbon fiber in the thermosetting resin composition, In this case, the dispersion stability is increased.

  In the carbon fiber structure preferably used in the present invention, fine carbon fibers having such a predetermined outer diameter exist in a three-dimensional network, and these carbon fibers are formed during the growth process of the carbon fibers. The granular parts are bonded to each other and have a shape in which a plurality of the carbon fibers extend from the granular part. In this way, the fine carbon fibers are not simply entangled with each other, but are tightly bonded to each other in the granular part, so when disposed in the matrix of the thermosetting resin composition The structure can be dispersed and blended in the matrix as a bulky structure without being dispersed as a single carbon fiber.

Since the granular part is formed in the growth process of the carbon fiber as described above, the carbon-carbon bond in the granular part is sufficiently developed, and although it is not exactly clear, sp ² bond and It seems to include a mixed state of sp ³ bonds. And after the generation (first intermediate and second intermediate described later), the granular part and the fiber part are continuous with a structure in which patch-like sheet pieces made of carbon atoms are bonded together, After the subsequent high-temperature heat treatment, as shown in FIGS. 4 (a) and 4 (b), at least a part of the graphene layer constituting the granular part is graphene constituting the fine carbon fiber extending from the granular part It will be continuous in layers. In the carbon fiber structure according to the present invention, between the granular portion and the fine carbon fiber, it is symbolized that the graphene layer constituting the granular portion as described above is continuous with the graphene layer constituting the fine carbon fiber. As described above, they are connected by carbon crystal structural bonds (at least a part thereof), whereby a strong bond between the granular portion and the fine carbon fiber is formed.

  In the present specification, the term “extending” the carbon fiber from the granular part simply means that the granular part and the carbon fiber are apparently connected by other binder (including carbonaceous material). It does not indicate such a state, but mainly means a state in which they are connected by carbon crystal structural bonds as described above.

  Further, as described above, the granular part is formed in the carbon fiber growth process. As a trace, at least one catalyst particle or the catalyst particle is volatilized and removed in the subsequent heat treatment process. And the resulting voids. These pores (or catalyst particles) are essentially independent from the hollow portions formed inside the fine carbon fibers extending from the granular portions (note that only a small part is accidental) In addition, it is also observed that it is continuous with the hollow part.)

  The number of catalyst particles or holes is not particularly limited, but is about 1 to 1000, more preferably about 3 to 500, per granular part. By forming the granular portion in the presence of such a number of catalyst particles, it is possible to obtain a granular portion having a desired size as described later.

  The size of each catalyst particle or hole present in the granular part is, for example, 1 to 100 nm, more preferably 2 to 40 nm, and further preferably 3 to 15 nm.

  Further, although not particularly limited, it is desirable that the particle size of the granular portion is larger than the outer diameter of the fine carbon fiber as shown in FIG. Specifically, for example, the outer diameter of the fine carbon fiber is preferably 1.3 to 250 times, more preferably 1.5 to 100 times, and still more preferably 2.0 to 25 times. In addition, the said value is an average value. Thus, when the particle diameter of the granular part which is a bonding point between carbon fibers is sufficiently large as 1.3 times or more of the outer diameter of the fine carbon fiber, it is higher than the carbon fiber extending from the granular part. When the carbon fiber structure is disposed in a matrix such as a thermosetting resin composition resin, a bonding force is provided, and a three-dimensional network structure is maintained even when a certain amount of elasticity is applied. It can be dispersed in the matrix as it is. On the other hand, if the size of the granular part is extremely large exceeding 250 times the outer diameter of the fine carbon fiber, the fibrous characteristics of the carbon fiber structure may be impaired, and the control rod finally obtained This is not desirable because there is a possibility that the characteristics of the above will not be expected. The “particle size of the granular part” in the present specification is a value measured by regarding the granular part, which is a bonding point between carbon fibers, as one particle.

  The specific particle size of the granular part depends on the size of the carbon fiber structure and the outer diameter of the fine carbon fibers in the carbon fiber structure, but for example, an average value of preferably 20 to 5000 nm is more preferable. Preferably it is 25-2000 nm, More preferably, it is about 30-500 nm.

  Furthermore, since this granular part is formed in the growth process of the carbon fiber as described above, it has a relatively nearly spherical shape, and the circularity is preferably 0.2 to 1, more preferably 0.5 to 0.99, and still more preferably about 0.7 to 0.98.

  In addition, the granular portion is formed in the carbon fiber growth process as described above, and, for example, the joining point between the fine carbon fibers is adhered by the carbonaceous material or the carbide after the carbon fiber synthesis. Compared with the structure, etc., the bonds between the carbon fibers in the granular part are very strong, and even under conditions where the carbon fiber breaks in the carbon fiber structure, the granular part (Coupling part) is held stably. Specifically, for example, as shown in the examples described later, the carbon fiber structure is dispersed in a liquid medium, and ultrasonic waves with a predetermined output and a predetermined frequency are applied to the carbon fiber structure so that the average length of the carbon fibers is almost halved. Even when the load condition is such that the change rate of the average particle diameter of the granular part is less than 10%, more preferably less than 5%, the granular part, that is, the bonded part between the fibers is stably held. It is what.

  In addition, the carbon fiber structure preferably used in the present invention has an area-based circle-equivalent mean diameter of 50 to 100 μm, more preferably about 60 to 90 μm. Here, the area-based circle-equivalent mean diameter is obtained by photographing the outer shape of the carbon fiber structure using an electron microscope or the like, and in this photographed image, the contour of each carbon fiber structure is represented by an appropriate image analysis software such as WinRoof. (Trade name, manufactured by Mitani Shoji Co., Ltd.) is used to determine the area within the contour, calculate the equivalent circle diameter of each fiber structure, and average it.

  This circle-equivalent mean diameter is a factor that determines the longest length of the carbon fiber structure when blended in a matrix such as a resin. In general, the mechanical strength of the obtained control rod is desired. The average equivalent circle diameter is from 50 to 100 μm from the point that it can be obtained at a standard level, and that there is no significant increase in viscosity when mixing into a matrix by kneading or the like, and that the mixing and dispersibility or moldability is good. preferable.

  Further, as described above, the carbon fiber structure used in the present invention has a shape in which carbon fibers existing in a three-dimensional network are bonded to each other in the granular portion, and a plurality of the carbon fibers extend from the granular portion. However, in a single carbon fiber structure, when a plurality of granular parts connecting carbon fibers are present to form a three-dimensional network, the average distance between adjacent granular parts is preferably 0, for example. 0.5 to 300 μm, more preferably 0.5 to 100 μm, and still more preferably about 1 to 50 μm. In addition, the distance between this adjacent granule part measures the distance from the center part of one granular material to the center part of the granule part adjacent to this. When the average distance between the granular materials is 0.5 to 300, the carbon fiber is sufficiently developed into a three-dimensional network, so that the obtained control rod can form a good porosity. And, when dispersed and blended in the matrix, it is preferable because the viscosity is not increased and the dispersibility of the carbon fiber structure in the matrix is not lowered.

Furthermore, in the carbon fiber structure used in the manufacture of the control rod of the present invention, as described above, the carbon fibers existing in a three-dimensional network are bonded to each other in the granular portion, and a plurality of the carbon fibers extend from the granular portion. For this reason, the structure has a bulky structure in which carbon fibers are sparsely present. Specifically, for example, the bulk density is 0.0001 to 0.05 g / cm ³ , More preferably, it is 0.001 to 0.02 g / cm ³ . If the bulk density exceeds 0.05 g / cm ³ , the controllability of the porosity of the resulting control rod may be reduced.

In addition, the control rod of the present invention is composed of carbon nanostructures containing boron. From the standpoint of exhibiting high strength and stable neutron absorption capability, the control rods of the graphene sheet constituting the carbon nanostructures The boron atom is desirably bonded, and the I _D / I _G ratio measured by Raman spectroscopy (measured using a wavelength of 514 nm of an argon laser) of the carbon nanostructure raw material giving the boron atom is 0. It is desirable that it is 2 or less, more preferably 0.1 or less. Here, in the Raman spectroscopic analysis, only a peak (G band) near 1580 cm ⁻¹ appears in large single crystal graphite. A peak (D band) appears in the vicinity of 1360 cm ⁻¹ due to the crystal having a finite minute size or lattice defects. Therefore, a low I _D / I _G suggests a carbon nanostructure having a graphite structure with few defects.

Boron tends to generate sp2 hybrid orbitals, and is easily replaced with graphite carbon composed of the same bonds. Therefore I _{D /} I _G is The use of low carbon fibrous structures may be boron content to obtain a control rod elevated.

  The carbon fiber structure suitably used in the present invention preferably has a combustion start temperature in air of 750 ° C. or higher, more preferably 800 to 900 ° C. As described above, since the carbon fiber structure has few defects and the carbon fiber has an intended outer diameter, the carbon fiber structure has such a high thermal stability.

  Although the said carbon fiber structure used suitably in this invention is not specifically limited, For example, it can prepare as follows.

  Basically, an organic compound such as hydrocarbon is chemically pyrolyzed by CVD using transition metal ultrafine particles as a catalyst to obtain a fiber structure (hereinafter referred to as an intermediate), which is further heat-treated.

  As the raw material organic compound, hydrocarbons such as benzene, toluene and xylene, alcohols such as carbon monoxide (CO) and ethanol can be used. Although not particularly limited, in obtaining the fiber structure according to the present invention, it is preferable to use at least two or more carbon compounds having different decomposition temperatures as the carbon source. The “at least two or more carbon compounds” described in this specification does not necessarily mean that two or more kinds of raw material organic compounds are used, but a case where one kind of raw material organic compound is used. However, in the process of synthesizing the fiber structure, for example, a reaction such as hydrodealkylation of toluene or xylene occurs, and in the subsequent thermal decomposition reaction system, two decomposition temperatures are different. The aspect which becomes the above carbon compound is also included.

  In addition, when two or more types of carbon compounds are present as carbon sources in the thermal decomposition reaction system, the decomposition temperature of each carbon compound is not limited to the type of the carbon compound, but the carbon compound in the raw material gas. Since it varies depending on the gas partial pressure or molar ratio, a relatively large number of combinations can be used as carbon compounds by adjusting the composition ratio of two or more carbon compounds in the raw material gas.

  For example, alkanes or cycloalkanes such as methane, ethane, propanes, butanes, pentanes, hexanes, heptanes, cyclopropane, cyclohexane, etc., particularly alkanes having about 1 to 7 carbon atoms; ethylene, propylene, butylenes, Alkenes or cycloolefins such as pentenes, heptenes and cyclopentenes, especially alkenes having about 1 to 7 carbon atoms; alkynes such as acetylene and propyne, especially alkynes having about 1 to 7 carbon atoms; benzene, toluene, styrene, xylene, naphthalene , Aromatic or heteroaromatic hydrocarbons such as methylnaphthalene, indene and phenanthrene, especially aromatic or heteroaromatic hydrocarbons having about 6 to 18 carbon atoms, alcohols such as methanol and ethanol, especially about 1 to 7 carbon atoms Of alcohol; its Combine two or more carbon compounds selected from carbon monoxide, ketones, ethers, etc., by adjusting the gas partial pressure so that different decomposition temperatures can be exhibited in the desired thermal decomposition reaction temperature range. The carbon fiber structure according to the present invention can be efficiently produced by using the material and / or adjusting the residence time in a predetermined temperature range and optimizing the mixing ratio.

  Among such combinations of two or more carbon compounds, for example, in the combination of methane and benzene, the molar ratio of methane / benzene is 1 to 600, more preferably 1.1 to 200, and even more preferably 3 It is desirable to set it to -100. This value is the gas composition ratio at the entrance of the reactor. For example, when toluene is used as one of the carbon sources, toluene is decomposed 100% in the reactor, and methane and benzene are 1 In consideration of the occurrence of: 1, a shortage of methane may be supplied separately. For example, when the methane / benzene molar ratio is 3, 2 moles of methane may be added to 1 mole of toluene. In addition, as methane added to such toluene, not only a method of preparing fresh methane separately, but also the unreacted methane contained in the exhaust gas discharged from the reactor is circulated and used. It is also possible to use it.

  By setting the composition ratio within such a range, it becomes possible to obtain a carbon fiber structure having a structure in which both the carbon fiber part and the granular part are sufficiently developed.

  Note that an inert gas such as argon, helium, or xenon, or hydrogen can be used as the atmospheric gas.

  As the catalyst, a transition metal such as iron, cobalt or molybdenum, or a mixture of a transition metal compound such as ferrocene or metal acetate and sulfur or a sulfur compound such as thiophene or iron sulfide is used.

  The synthesis of the first intermediate, which will be described later, is carried out using the usual CVD method for hydrocarbons, etc., evaporating the mixed liquid of hydrocarbons and catalysts as raw materials and introducing hydrogen gas etc. into the reactor as a carrier gas And pyrolyzed at a temperature of 800 to 1300 ° C. Thereby, from several centimeters in which a plurality of carbon fiber structures (intermediates) having a sparse three-dimensional structure in which fibers having an outer diameter of 15 to 100 nm are bonded together by granular materials grown using the catalyst particles as nuclei are collected. Synthesize an aggregate of several tens of centimeters.

  The thermal cracking reaction of the hydrocarbon as a raw material mainly occurs on the surface of the granular particles grown using the catalyst particles or the core, and the recrystallization of carbon generated by the decomposition proceeds in a certain direction from the catalytic particles or granular materials. Grows in a fibrous form. However, in obtaining the carbon fiber structure according to the present invention, the balance between the thermal decomposition rate and the growth rate is intentionally changed. For example, as described above, at least two carbon sources having different decomposition temperatures are used. By using the above carbon compound, the carbon material is grown three-dimensionally around the granular material without growing the carbon material only in a one-dimensional direction. Of course, the growth of such three-dimensional carbon fibers does not depend only on the balance between the thermal decomposition rate and the growth rate, but the crystal surface selectivity of the catalyst particles, the residence time in the reactor, and the furnace temperature. The balance between the pyrolysis reaction and the growth rate is influenced not only by the type of carbon source as described above but also by the reaction temperature and gas temperature, etc. When the growth rate is faster than the thermal decomposition rate, the carbon material grows in a fibrous form. On the other hand, when the thermal decomposition rate is faster than the growth rate, the carbon material grows in the circumferential direction of the catalyst particles. To do. Therefore, by intentionally changing the balance between the pyrolysis rate and the growth rate, the carbon material growth direction as described above is made to be a multi-direction under control without changing the growth direction to a constant direction, as in the present invention. A three-dimensional structure can be formed. In order to easily form the three-dimensional structure in which the fibers are bonded to each other by the granular material in the produced intermediate, the composition of the catalyst, the residence time in the reaction furnace, the reaction temperature, and the gas temperature Etc. are desirable.

  In addition, as a method for efficiently producing the carbon fiber structure according to the present invention, the carbon fiber structure is supplied to the reactor in addition to the approach using two or more carbon compounds having different decomposition temperatures at an optimal mixing ratio as described above. An approach for generating turbulent flow in the vicinity of the supply port of the raw material gas can be mentioned. The turbulent flow here is a flow that is turbulent and turbulent and flows in a spiral.

  In the reaction furnace, immediately after the raw material gas is introduced into the reaction furnace from the supply port, metal catalyst fine particles are formed by the decomposition of the transition metal compound as the catalyst in the raw material mixed gas. It is brought about through such a stage. That is, first, the transition metal compound is decomposed to become metal atoms, and then cluster generation occurs by collision of a plurality of, for example, about 100 atoms. At the stage of this generated cluster, it does not act as a catalyst for fine carbon fibers, and the generated clusters are further aggregated by collision and grow into crystalline particles of about 3-10 nm metal to produce fine carbon fibers. It will be used as metal catalyst fine particles.

  In this catalyst formation process, if there is a vortex due to intense turbulence as described above, more intense collision is possible compared to collisions between metal atoms or clusters with only Brownian motion, and by increasing the number of collisions per unit time Metal catalyst fine particles can be obtained in a high yield in a short time, and metal catalyst fine particles having a uniform particle size can be obtained by equalizing the concentration, temperature, etc. by vortex. Furthermore, in the process of forming the metal catalyst fine particles, an aggregate of metal catalyst fine particles in which a large number of metal crystalline particles are gathered is formed by vigorous collision due to the vortex. In this way, the metal catalyst fine particles are rapidly generated, so that the decomposition of the carbon compound is promoted and sufficient carbon material is supplied, and the metal catalyst fine particles of the aggregate are radially formed as nuclei. On the other hand, when the fine carbon fibers grow, and as described above, when the thermal decomposition rate of some of the carbon compounds is faster than the growth rate of the carbon material, the carbon material also grows in the circumferential direction of the catalyst particles, A granular part is formed around the body, and a carbon fiber structure having an intended three-dimensional structure is efficiently formed. The metal catalyst fine particle aggregate may include a part of catalyst fine particles that are less active than other catalyst fine particles or have been deactivated during the reaction. A non-fibrous or very short fibrous carbon material layer that has grown on the surface of such a catalyst fine particle before agglomeration or has grown into an aggregate after such a fine particle has become an aggregate. It seems that the granular part of the carbon fiber structure according to the present invention is formed by being present at the peripheral position of the body.

  The specific means for generating a turbulent flow in the raw material gas flow in the vicinity of the raw material gas supply port of the reaction furnace is not particularly limited. For example, the raw material gas introduced into the reaction furnace from the raw material gas supply port It is possible to adopt means such as providing some type of collision part at a position where it can interfere with the current flow. The shape of the collision part is not limited in any way, as long as a sufficient turbulent flow is formed in the reactor by the vortex generated from the collision part. It is possible to adopt a form in which one or a plurality of plates, paddles, taper tubes, umbrellas, etc. are arranged alone or in combination.

  In this way, the first intermediate obtained by heating and generating the catalyst and hydrocarbon mixed gas at a constant temperature in the range of 800 to 1300 ° C. seems to have a patch-like sheet piece made of carbon atoms bonded together. When it is analyzed by Raman spectroscopy, the D band is very large and there are many defects. The produced intermediate contains unreacted raw material, non-fibrous carbide, tar content and catalytic metal.

  Therefore, in order to remove these residues from such an intermediate and obtain an intended carbon fiber structure with few defects, high-temperature heat treatment at 2400 to 3000 ° C. is performed by an appropriate method.

  That is, for example, the first intermediate is heated at 800 to 1200 ° C. to remove volatile components such as unreacted raw materials and tars, and then annealed at a high temperature of 2400 to 3000 ° C. At the same time, the catalyst metal contained in the fibers is removed by evaporation. At this time, a reducing gas or a small amount of carbon monoxide gas may be added to the inert gas atmosphere in order to protect the material structure.

  When the intermediate is annealed at a temperature in the range of 2400 to 3000 ° C., the patch-like sheet pieces made of carbon atoms are bonded to each other to form a plurality of graphene sheet-like layers.

  Moreover, before or after such high-temperature heat treatment, a step of crushing the equivalent circle average diameter of the carbon fiber structure to several centimeters, and a circle equivalent average diameter of the crushed carbon fiber structure of 50 to A carbon fiber structure having a desired circle-equivalent mean diameter is obtained through a step of pulverizing to 100 μm. In addition, you may perform a grinding | pulverization process, without passing through a crushing process. Moreover, you may perform the process which granulates the aggregate | assembly which has two or more carbon fiber structures which concern on this invention in the shape, size, and bulk density which are easy to use. More preferably, in order to effectively utilize the structure formed at the time of the reaction, if annealing is performed in a state where the bulk density is low (a state where the fiber is fully stretched and the porosity is large), further conductivity to the resin is achieved. It is effective for imparting sex.

Next, in the production method of the present invention, the boron compound to be used is not particularly limited, and the elemental boron can also be used as “boron” contained in the finally obtained control rod according to the present invention. It is a concept that includes not only boron compounds. Specifically, for example, elemental boron, H ₃ BO ₄ (boric acid) or a salt thereof, B ₂ O ₃ , NaBH ₄ , BF _3. (C ₂ H ₅ ) ₂ O can be exemplified. However, among these, a compound that can be mixed with the carbon nanostructure with an aqueous solution of H ₃ BO ₄ or a methanol solution of NaBH ₄ is preferable. Here, in order to efficiently contain boron in the carbon nanostructure, it is necessary to mix the carbon nanostructure and boron well so that they are in uniform contact. For this purpose, it is preferable to use boron compound (or boron) particles having a particle size as small as possible. If the particles are large, a high concentration region is partially generated, which may cause solidification. When boric acid or the like is used as the boron source, a method of adding a solution and evaporating the solvent in advance or a method of evaporating the solvent during the heating process can also be used. If the solution is mixed uniformly, the boron compound can be uniformly attached to the fiber surface after evaporation of the solvent. On the other hand, when boron is used, specifically, the average particle size of boron is 100 μm or less, preferably 50 μm or less, more preferably 20 μm or less.

  In the production method of the present invention, the thermosetting resin composition used for shaping is not particularly limited. For example, epoxy resin, vinyl ester resin, phenol resin, unsaturated polyester resin, Use compositions of various thermosetting resins such as furan resins, imide resins, urethane resins, melamine resins, silicone resins and urea resins (compositions containing precured or uncrosslinked prepolymers, oligomers, monomers, etc.). Can do.

  In addition, since the thermosetting resin composition used is carbonized at the time of heating and firing after molding to cause a volume reduction, a gap is formed in the finally obtained control rod. The porosity of the control rod obtained by controlling the amount added can be controlled. The addition amount is, for example, 0.08 to 17% by mass, more preferably 0.17 to 3%, based on the total amount of the mixture of the carbon nanostructure, the boron compound, and the thermosetting resin composition (in terms of vehicle solid content). About 3% by mass is suitable for obtaining the desired porosity as described above.

  In manufacturing the control rod according to the present invention, the method of doping (doping) boron into the carbon nanostructure is not particularly limited to the above-described method. For example, a low temperature (for example, 1500) A carbon nanostructure that has been heat-treated at a temperature below (° C.) and has not yet developed crystals, and a carbon nanostructure precursor that has not been heat-treated (as-grown) and boron (including a boron compound). When mixing and then heating in the high temperature range as described above, carbon nanostructure or precursor thereof is graphitized (annealing treatment) so that boron is contained in the carbon fiber structure. You can also. Boron also acts as a catalyst to promote crystallization of carbon nanostructures, and is effective in removing the catalytic metal during annealing. Thus, boron is contained before the annealing treatment. By doing so, it can be expected that a carbon nanostructure having higher crystallinity is formed.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to the following Example at all.

  In addition, below, each physical-property value of the carbon fiber structure used for this invention was measured as follows.

<Area-based circle equivalent average diameter>
First, a photograph of the pulverized product is taken with an SEM. In the obtained SEM photograph, only the carbon fiber structure with a clear outline was targeted, and the carbon fiber structure with a broken outline was not targeted because the outline was unclear. All carbon fiber structures (about 60 to 80) that can be targeted in one field of view were used, and about 200 carbon fiber structures were targeted in three fields of view. Trace the contour of each carbon fiber structure targeted using image analysis software WinRoof (trade name, manufactured by Mitani Corp.), obtain the area within the contour, and calculate the equivalent circle diameter of each fiber structure This was averaged.

<Measurement of bulk density>
A transparent cylinder with an inner diameter of 70 mm is filled with 1 g of powder, and air with a pressure of 0.1 Mpa and a capacity of 1.3 liters is sent from the lower part of the dispersion plate to blow out the powder and let it settle naturally. At the time of blowing out 5 times, the height of the powder layer after settling is measured. At this time, the number of measurement points was six, and after calculating the average of the six points, the bulk density was calculated.

<Raman spectroscopy>
Using a LabRam800 manufactured by Horiba Jobin Yvon, measurement was performed using a wavelength of 514 nm of an argon laser.

<TG combustion temperature>
Using TG-DTA manufactured by Mac Science, the temperature was increased at a rate of 10 ° C./min while circulating air at a flow rate of 0.1 L / min, and the combustion behavior was measured. During combustion, TG indicates a decrease in weight and DTA indicates an exothermic peak. Therefore, the top position of the exothermic peak was defined as the combustion start temperature.

<Powder resistance and resilience>
1 g of CNT powder is weighed, filled and compressed in a resin die (inner dimensions 40 L, 10 W, 80 Hmm), and the displacement and load are read. When a constant current was passed by the 4-terminal method, the voltage at that time was measured, and when the density was measured to a density of 0.9 g / cm ³ , the pressure was released and the density after restoration was measured. As for powder resistance, resistance when compressed to 0.5, 0.8 and 0.9 g / cm ³ is measured.
<Average particle size of granular part, circularity, ratio with fine carbon fiber>
Similar to the measurement of the area-based circle-equivalent mean diameter, first, a photograph of the carbon fiber structure is taken with an SEM. In the obtained SEM photograph, only the carbon fiber structure with a clear outline was targeted, and the carbon fiber structure with a broken outline was not targeted because the outline was unclear. All carbon fiber structures (about 60 to 80) that can be targeted in one field of view were used, and about 200 carbon fiber structures were targeted in three fields of view.

  In each of the targeted carbon fiber structures, a granular portion that is a bonding point between carbon fibers is regarded as one particle, and its outline is defined by using image analysis software WinRoof (trade name, manufactured by Mitani Corporation). By tracing, the area in the contour was obtained, the equivalent circle diameter of each granular part was calculated, and this was averaged to obtain the average particle diameter of the granular part. Further, the circularity (R) is calculated based on the following equation from the area (A) in the contour measured using the image analysis software and the measured contour length (L) of each granular portion. Was averaged.

R = A × 4π / L ²
Furthermore, the outer diameter of fine carbon fibers in each targeted carbon fiber structure is obtained, and the size of the granular portion in each carbon fiber structure is determined from this and the equivalent circle diameter of the granular portion in each carbon fiber structure. It calculated | required as a ratio with a fine carbon fiber, and averaged this.

<Average distance between granular parts>
Similar to the measurement of the area-based circle-equivalent mean diameter, first, a photograph of the carbon fiber structure is taken with an SEM. In the obtained SEM photograph, only the carbon fiber structure with a clear outline was targeted, and the carbon fiber structure with a broken outline was not targeted because the outline was unclear. All carbon fiber structures (about 60 to 80) that can be targeted in one field of view were used, and about 200 carbon fiber structures were targeted in three fields of view.

  In each target carbon fiber structure, find all the places where the granular parts are connected by the fine carbon fibers, and the distance between adjacent granular parts connected by the fine carbon fibers in this way (the center of the granular material at one end) The length of the fine carbon fiber including the part to the central part of the granular material at the other end) was measured and averaged.

<Destructive test of carbon fiber structure>
A carbon fiber structure was added to 100 ml of toluene in a vial with a lid at a rate of 30 μg / ml to prepare a dispersion sample of the carbon fiber structure.

  The dispersion sample of the carbon fiber structure thus obtained was subjected to ultrasonic waves using an ultrasonic cleaner having a transmission frequency of 38 kHz and an output of 150 w (trade name: USK-3, manufactured by SND Co., Ltd.). Irradiation was performed, and changes in the carbon fiber structure in the dispersion liquid sample were observed over time.

First, ultrasonic waves are irradiated, and after 30 minutes, a predetermined amount of 2 ml of the dispersion liquid sample is extracted from the bottle, and a photograph of the carbon fiber structure in the dispersion liquid is taken with an SEM. 200 fine carbon fibers (fine carbon fibers having at least one end bonded to the granular part) in the carbon fiber structure of the obtained SEM photograph were randomly selected, and the length of each selected fine carbon fiber It was measured to obtain the D ₅₀ average, which was used as the initial average fiber length.

On the other hand, 200 granular parts which are the bonding points between carbon fibers in the carbon fiber structure of the obtained SEM photograph are selected at random, and each selected granular part is regarded as one particle, and its outline is defined. Then, the image analysis software WinRoof (trade name, manufactured by Mitani Corporation) was traced to determine the area within the contour, calculate the equivalent circle diameter of each granular portion, and determine the D ₅₀ average value. And the resulting D ₅₀ average value as the initial average diameter of the granular part.

Thereafter, a fixed amount of 2 ml of the dispersion liquid sample was taken out from the bottle at regular intervals in the same manner as described above, a photograph of the carbon fiber structure in the dispersion liquid was taken with an SEM, and the carbon fiber of the obtained SEM photograph the D ₅₀ average diameter of D ₅₀ average length and granular part of the carbon fibers in the structure in was determined in the same manner as above.

And the D ₅₀ average length of the calculated fine carbon fiber is about half of the initial average fiber length (in this example, after irradiating ultrasonic waves and 500 minutes have elapsed), the D of the granular portion _{The 50} average diameter was compared with the initial average diameter, and the variation ratio (%) was examined.

<Porosity>
Measurement was performed in a pressure range of 15 kPa to 70 MPa using a mercury intrusion type porosimeter PASCAL (manufactured by Thermofinigan).

<Bending elastic modulus>
It measured according to JIS K7203.

Synthesis example 1
A carbon fiber structure was synthesized using toluene as a raw material by a CVD method.

  A mixture of ferrocene and thiophene was used as a catalyst, and the reaction was performed in a hydrogen gas reducing atmosphere. Toluene and the catalyst were heated to 380 ° C. together with hydrogen gas, supplied to the production furnace, and pyrolyzed at 1250 ° C. to obtain a carbon fiber structure (first intermediate).

  In addition, the schematic structure of the production | generation furnace used when manufacturing this carbon fiber structure (1st intermediate body) is shown in FIG. As shown in FIG. 8, the production furnace 1 has an introduction nozzle 2 for introducing a raw material mixed gas composed of toluene, a catalyst, and hydrogen gas as described above into the production furnace 1 at its upper end. Further, a cylindrical collision portion 3 is provided outside the introduction nozzle 2. The collision unit 3 is capable of interfering with the flow of the raw material gas introduced into the reaction furnace from the raw material gas supply port 4 located at the lower end of the introduction nozzle 2. In the production furnace 1 used in this embodiment, the inner diameter a of the introduction nozzle 2, the inner diameter b of the production furnace 1, the inner diameter c of the cylindrical collision portion 3, and the raw material mixed gas inlet 4 from the upper end of the production furnace 1 are used. Distance d, the distance e from the raw material mixed gas inlet 4 to the lower end of the collision part 3, and the distance from the raw material mixed gas inlet 4 to the lower end of the production furnace 1 are f, : B: c: d: e: f = 1.0: 3.6: 1.8: 3.2: 2.0: 21.0. The raw material gas introduction rate into the reactor was 1850 NL / min, and the pressure was 1.03 atm.

  1 and 2 show SEM and TEM photographs observed after the first intermediate was dispersed in toluene and the sample for the electron microscope was prepared.

  The first intermediate synthesized as described above was calcined at 900 ° C. in nitrogen to separate hydrocarbons such as tar to obtain a second intermediate. The R value of this second intermediate measured by Raman spectroscopy was 0.98.

  Further, this second intermediate was heat treated at 2600 ° C. in argon at high temperature, and the resulting aggregate of carbon fiber structures was pulverized with an airflow pulverizer to obtain a carbon fiber structure used in the present invention.

  FIGS. 3 and 4 show SEM and TEM photographs of the obtained carbon fiber structure dispersed in toluene with ultrasonic waves and observed after preparing a sample for an electron microscope.

  Further, FIG. 5 shows an SEM photograph of the obtained carbon fiber structure as it is placed on an electron microscope sample holder, and Table 1 shows the particle size distribution.

  Furthermore, before and after the high temperature heat treatment, the carbon fiber structure was subjected to X-ray diffraction and Raman spectroscopic analysis, and the change was examined. The results are shown in FIGS.

In addition, the obtained carbon fiber structure had an equivalent circle average diameter of 72.8 μm, a bulk density of 0.0032 g / cm ³ , a Raman ID / IG ratio value of 0.090, a TG combustion temperature of 786 ° C., and a face spacing. Was 3.383 Å, the powder resistance value was 0.0083 Ω · cm, and the density after restoration was 0.25 g / cm ³ .

  Further, the average particle size of the granular portion in the carbon fiber structure was 443 nm (SD 207 nm), which was 7.38 times the outer diameter of the fine carbon fiber in the carbon fiber structure. Further, the circularity of the granular portion was 0.67 (SD 0.14) on average.

Moreover, when the destruction test of the carbon fiber structure was performed according to the above-described procedure, the initial average fiber length (D ₅₀ ) after 30 minutes of application of the ultrasonic wave was 12.8 μm. The average fiber length (D ₅₀ ) was almost half of 6.7 μm, indicating that many cuts were generated in the fine carbon fibers in the carbon fiber structure. However, when the average diameter (D ₅₀ ) of the granular part 500 minutes after application of ultrasonic waves is compared with the initial initial average diameter (D ₅₀ ) 30 minutes after application of ultrasonic waves, the variation (decrease) rate is only 4 .8%, and taking into account measurement errors, etc., even under load conditions where many cuts occurred in fine carbon fibers, the cut granular parts themselves are hardly destroyed and function as bonding points between the fibers. It became clear.

  Various physical property values measured in Synthesis Example 1 are summarized in Tables 1 and 2.

Synthesis example 2
Part of the exhaust gas from the production furnace was used as a circulating gas, and carbon compounds such as methane contained in this circulating gas were used as a carbon source together with fresh toluene, and fine carbon fibers were synthesized by the CVD method. .
The synthesis was performed in a hydrogen gas reducing atmosphere using a mixture of ferrocene and thiophene as a catalyst. As fresh raw material gases, toluene and a catalyst were heated to 380 ° C. in a preheating furnace together with hydrogen gas. On the other hand, a part of the exhaust gas taken out from the lower end of the production furnace is used as a circulating gas, and its temperature is adjusted to 380 ° C., then mixed in the middle of the supply path for the fresh raw material gas and supplied to the production furnace. did.

In addition, the composition ratio in the used circulating gas is a molar ratio of volume ratio CH ₄ 7.5%, C ₆ H ₆ 0.3%, C ₂ H ₂ 0.7%, C ₂ H ₆ 0.1%. , CO 0.3%, N ₂ 3.5%, H ₂ 87.6%, and by mixing with fresh raw material gas, mixing molar ratio of methane and benzene in raw material gas supplied to the production furnace CH ₄ / C ₆ H ₆ (note that toluene in fresh raw material gas was considered to have been 100% decomposed into CH ₄ : C ₆ H ₆ = 1: 1 by heating in a preheating furnace). The mixing flow rate was adjusted to be .44.

In addition, in the final raw material gas, C ₂ H ₂ , C ₂ H ₆ and CO contained in the mixed circulation gas are naturally included as carbon compounds, but these components are All of these were extremely small amounts and could be substantially ignored as a carbon source.

  And like the synthesis example 1, it thermally decomposed at 1250 degreeC in the production | generation furnace, and obtained the carbon fiber structure (1st intermediate body).

  In addition, the structure of the production | generation furnace used when manufacturing this carbon fiber structure (1st intermediate body) is the same as that of the structure shown in FIG. 8 except there is no cylindrical collision part 3, The raw material gas introduction rate into the reactor was 1850 NL / min and the pressure was 1.03 atm, as in Synthesis Example 1.

  When the first intermediate was dispersed in toluene and observed after preparation of a sample for an electron microscope, the SEM and TEM photographs thereof were almost the same as those of Synthesis Example 1 shown in FIGS.

  The first intermediate synthesized as described above was calcined at 900 ° C. in argon to separate hydrocarbons such as tar to obtain a second intermediate. The R value of this second intermediate measured by Raman spectroscopy was 0.83.

  Further, the second intermediate was heat treated at 2600 ° C. in argon at high temperature, and the resulting aggregate of carbon fiber structures was pulverized with an airflow pulverizer to obtain a carbon fiber structure according to the present invention.

  The SEM and TEM photographs observed after the obtained carbon fiber structure was dispersed in toluene with ultrasonic waves and the sample for the electron microscope was prepared were almost the same as those in Synthesis Example 1 shown in FIGS. .

  The obtained carbon fiber structure was placed on an electron microscope sample holder as it was and observed to examine the particle size distribution. The obtained results are shown in Table 3.

  Further, before and after the high-temperature heat treatment, the carbon fiber structure was subjected to X-ray diffraction and Raman spectroscopic analysis, and the changes were examined. The results were almost the same as the results of Synthesis Example 1 shown in FIGS.

Furthermore, the circle-equivalent mean diameter of the obtained carbon fibrous structures, 75.8Myuemu, bulk density of 0.004 g / cm ^3, Raman _I D / _{I G} ratio is 0.086, TG combustion temperature of 807 ° C., The face spacing was 3.386 Å, the powder resistance value was 0.0077 Ω · cm, and the density after restoration was 0.26 g / cm ³ .

  Further, the average particle size of the granular portion in the carbon fiber structure was 349.5 nm (SD180.1 nm), which was 5.8 times the outer diameter of the fine carbon fiber in the carbon fiber structure. Further, the circularity of the granular part was 0.69 (SD 0.15) on average.

Moreover, when the carbon fiber structure was subjected to a destructive test according to the procedure described above, the initial average fiber length (D ₅₀ ) after 30 minutes of application of ultrasonic waves was 12.4 μm. The average fiber length (D ₅₀ ) was about 6.3 μm, which was almost half of the length, indicating that many cuts occurred in the fine carbon fibers in the carbon fiber structure. However, when the average diameter (D ₅₀ ) of the granular part 500 minutes after application of ultrasonic waves is compared with the initial initial average diameter (D ₅₀ ) 30 minutes after application of ultrasonic waves, the variation (decrease) rate is only 4 .2%, taking into account measurement errors, etc., even under load conditions where many cuts occurred in the fine carbon fiber, the cut granular part itself hardly functions and functions as a bonding point between the fibers. It became clear.

  Various physical property values measured in Synthesis Example 2 are summarized in Tables 3 and 4.

Example 1 Manufacture of control rod Three roll mill of a mixture of 1 Kg of carbon microstructure obtained in Synthesis Example 1, 170 g of epoxy resin (Adeka Resin EP-4930), 68 g of curing agent (Adeka Hardener EH-4334) and 2580 g of boric acid For 20 minutes. The obtained mixture was heated at room temperature for 10 minutes, at 80 ° C. for 5 minutes, at 600 ° C. for 30 minutes, in a 30 mmφ × 1 m steel tube under a 10 MPa load in an argon atmosphere, and the contents were taken out alone. And further heated at 2600 ° C. for 6 minutes in an Ar atmosphere to obtain a control rod of 28 mmφ × 0.95 m. The flexural modulus was 6 GPa, the porosity was 9%, and the boron content was 30% by mass.
When this control rod was exposed to the neutron beam of a high temperature engineering test reactor in a helium atmosphere at a maximum temperature of 2400 ° C. for 100 hours, no cracks due to helium swelling occurred.

It is a SEM photograph of the 1st intermediate body of the carbon fiber structure used for the composite material of this invention. It is a TEM photograph of the 1st intermediate body of the carbon fiber structure used for the composite material of this invention. It is a SEM photograph of the carbon fiber structure used for the composite material of the present invention. (A) (b) is a TEM photograph of the carbon fiber structure used for the composite material of the present invention, respectively. It is a SEM photograph of the carbon fiber structure used for the composite material of the present invention. 2 is an X-ray diffraction chart of a carbon fiber structure used in the composite material of the present invention and an intermediate of the carbon fiber structure. It is a Raman spectroscopic analysis chart of the carbon fiber structure used for the composite material of this invention, and the intermediate body of this carbon fiber structure. It is drawing which shows schematic structure of the production | generation furnace used for manufacture of the carbon fiber structure in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Generation furnace 2 Introduction nozzle 3 Collision part 4 Raw material gas supply port a Inner nozzle inner diameter b Generation furnace inner diameter c Collision inner diameter d Distance from upper end of production furnace to raw material mixed gas inlet e From raw material mixed gas inlet Distance from the lower end of the collision part f Distance from the raw material mixed gas inlet to the lower end of the generating furnace

Claims (7)

  A control rod for a nuclear reactor comprising a carbon nanostructure containing boron as at least a part of a member.   The control rod according to claim 1, wherein the boron content in the carbon nanostructure containing boron is 10 to 70 mass% in terms of atomic units.   The carbon nanostructure is a three-dimensional network-like carbon fiber structure composed of carbon fibers having an outer diameter of 15 to 100 nm, and the carbon fiber structure is a mode in which a plurality of the carbon fibers extend, The carbon fiber structure is a carbon fiber structure having a granular part for bonding the carbon fibers to each other, and the granular part is formed in the growth process of the carbon fiber. Item 3. The control rod according to Item 1 or 2.   The control rod according to any one of claims 1 to 3, which is formed by integrally forming a carbon nanostructure containing boron as a member.   A method for producing a control rod for a nuclear reactor, comprising: mixing a carbon nanostructure, a boron compound, and a thermosetting resin composition;   The method for producing a control rod for a nuclear reactor according to claim 5, wherein the molding is performed by cast polymerization of a mixture of a carbon nanostructure, a boron compound and a thermosetting resin composition.   The method for producing a control rod according to claim 5 or 6, wherein the heating and baking temperature is 1500 to 2800 ° C.