JP2016188439A - Crystalline silicon carbide ceramic fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable crystalline silicon carbide-based ceramic fiber having reduced residue C on a fiber cross surface and excellent heat resistance and physical property and a manufacturing method therefor, further a ceramic-based composite material excellent in oxidation resistance at high temperature, reinforced by the crystalline silicon carbide-based ceramic fiber.SOLUTION: There is provided a crystalline silicon carbide-based ceramic fiber having density of 2.7 to 3.2 g/cmand consisting of Si:50 to 70 wt.%, C:28 to 45 wt.%, Al:0 .05 to 3.8 wt.%, O:0.05 to 1.5 wt.% and B:0 .05 to 0.5 wt.% and having a sintered structure of SiC with excess C occupancy shown by area percentage of excess C on a fiber cross surface of 0.05% to 10%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a crystalline silicon carbide ceramic fiber that is stable even in a high temperature / oxidizing atmosphere and a method for producing the same. The present invention also relates to a ceramic matrix composite material that is reinforced with the crystalline silicon carbide-based ceramic fiber and has excellent oxidation resistance at high temperatures.

  Ceramic matrix composites reinforced with ceramic fibers are being developed as next-generation heat-resistant materials because of their excellent heat resistance not found in metals and damage tolerance not found in conventional single-phase ceramics. Among these, a composite material (hereinafter referred to as SiC / SiC composite material) in which silicon carbide is reinforced with silicon carbide-based ceramic fibers is attracting particular attention.

  In this SiC / SiC composite material, the bonding of the interface between the reinforcing fiber and the matrix is controlled by the interface layer, cracks are deflected at this interface when the material breaks, and the breakage progresses while the fiber pulls out, resulting in a large breaking energy. It is a big feature to show. As the interface layer, carbon C is mainly used. However, in recent years, in place of the carbon interface, research for adapting boron nitride BN or oxide having higher heat resistance to the interface has been actively conducted.

  On the other hand, crystalline silicon carbide ceramic fibers having improved heat resistance and the like from conventional amorphous structure fibers have been developed as silicon carbide ceramic fibers of reinforcing fibers (see, for example, Patent Document 1).

  This crystalline silicon carbide ceramic fiber is synthesized by heat-treating an amorphous structure fiber under high temperature conditions under strictly controlled atmosphere. Conventional silicon carbide-based ceramic fibers have been pointed out that surplus C remains with respect to the stoichiometric ratio of silicon carbide when the cross section of the fiber is observed with a scanning microscope (Non-Patent Documents 1 and 2). 3). According to this, the surplus C more than stoichiometric composition remains in the grain boundary of silicon carbide microcrystals in the silicon carbide ceramic fiber.

Japanese Patent Laid-Open No. 11-036142 T.A. Ishikawa / Adv Poly Sci (2005) 178: 109-144 L. Silvestroni et al. / Materials and Design 65 (2015) 1253-1263 Cedric Sauder and Jacques Lamon / J. Am. Ceram. Soc. , 90 [4] 1146-1156 (2007)

  However, conventional silicon carbide ceramic fibers have insufficient heat resistance and mechanical properties depending on applications, and further improvement is desired. The present invention provides a stable crystalline silicon carbide ceramic fiber having excellent heat resistance and mechanical properties in which excess C remaining in the fiber is reduced, and a method for producing the same. Another object of the present invention is to provide a ceramic matrix composite material reinforced with the silicon carbide ceramic fiber and having excellent oxidation resistance at high temperatures.

The present invention has a density of 2.7 to 3.2 g / cm ³ , Si: 50 to 70 wt%, C: 28 to 45 wt%, Al: 0.05 to 3.8 wt%, O: 0 A crystalline silicon carbide fiber having a sintered structure of SiC consisting of 0.05 to 1.5% by weight and B: 0.05 to 0.5% by weight, with an area ratio of surplus C in the fiber cross section The present invention relates to a crystalline silicon carbide ceramic fiber having a surplus C occupation ratio of 0.05% to 10%.

  Further, the present invention provides an amorphous silicon carbide fiber containing Al: 0.05 to 3.8% by weight and B: 0.05 to 0.5% by weight in advance in the atmosphere at 1000 ° C to 1400 ° C. An oxide layer is formed on the fiber surface by heat treatment in a range, and then heat treatment is performed at a temperature in the range of 1600 to 2100 ° C. in an inert atmosphere. It is about.

  Furthermore, the present invention relates to a ceramic matrix composite material using the crystalline silicon carbide ceramic fiber as a reinforcing fiber and a ceramic as a matrix.

  The present invention provides a stable silicon carbide ceramic fiber having a reduced excess C existing in the fiber and having excellent heat resistance and mechanical properties, and a method for producing the same. By reinforcing the ceramics with this fiber, a ceramic matrix composite having excellent heat resistance and mechanical properties at high temperatures can be provided.

2 is a SEM photograph of a fiber cross section obtained in Example 1. 3 is a SEM photograph of a fiber cross section obtained in Example 2. 4 is a SEM photograph of a fiber cross section obtained in Example 3. 4 is a SEM photograph of a fiber cross section obtained in Comparative Example 1.

Hereinafter, the present invention will be described in detail.
The crystalline silicon carbide-based ceramic fiber of the present invention has a density of 2.7 to 3.2 g / cm ³ , and by weight ratio, Si: 50 to 70 wt%, C: 28 to 45 wt%, O: 0 0.05 to 1.5 wt%, Al: 0.05 to 3.8 wt%, preferably 0.13 to 1.25 wt%, and B: 0.05 to 0.5 wt%, preferably It consists of 0.06 to 0.19% by weight, and the total of these is 100% by weight, and is a crystalline silicon carbide ceramic fiber having a sintered structure of SiC, defined by the area ratio of surplus C in the fiber cross section The surplus C occupancy is 0.05% to 10%. The crystalline silicon carbide-based ceramic fiber of the present invention has a dense SiC polycrystalline structure composed of fine SiC crystal grains, and the composed SiC crystal grains are firmly bonded to each other and exhibit a intragranular fracture behavior. I am making.

  Usually, the crystalline silicon carbide-based ceramic fiber described in Patent Document 1 is a polymer fiber obtained from an organosilicon polymer containing excess C and oxygen at a temperature in the range of 1600 to 2100 ° C. in an inert atmosphere. In the process of heat treatment, the desorption of CO gas proceeds quantitatively, Si and C in the fiber approach the stoichiometric composition of the SiC crystal, and then sintering of the SiC fine particles proceeds inside the fiber. However, since the desorption of CO gas was not strictly controlled, surplus C remained inside the fiber. In addition, surplus C means the carbon which exists exceeding the stoichiometric composition amount which can exist as SiC with respect to Si contained in a fiber. Although excess C exceeding the stoichiometric composition remains at the grain boundaries of the silicon carbide microcrystals, the crystalline silicon carbide ceramic fiber of the present invention exists in the fibers, that is, at the grain boundaries of the silicon carbide microcrystals. Surplus C is effectively reduced, and a dense microstructure is obtained. Further, when the cross section of the crystalline silicon carbide-based ceramic fiber is observed with a scanning electron microscope, the surplus C is observed in black in a form reflecting the composition on the crystal grain boundary of silicon carbide. Since non-excess C exists in the fiber in the form of SiC crystals, the reflected electron image is observed in a brighter color than the excess C. The area ratio of surplus C calculated here is a value representing the area ratio of surplus C in the cross-sectional area when the cross section of the crystalline silicon carbide based ceramic fiber is observed with a scanning electron microscope. C occupancy is defined. The area of surplus C is calculated by digitizing the portion observed in black in the reflected electron image by image analysis software.

  The crystalline silicon carbide based ceramic fiber of the present invention is characterized in that the excess C is small, and the excess C occupancy in the fiber cross section is 0.05% to 10%. The bonding between SiC crystal grains is strengthened, a dense SiC polycrystal structure can be obtained, and high mechanical strength can be obtained. If the surplus C occupancy is more than 10%, there is a lot of surplus C on the grain boundaries of the SiC crystal grains, so that the bonding between the SiC crystal grains is inhibited and a dense SiC polycrystal structure is obtained. Cannot be obtained, and high mechanical strength cannot be obtained. If the surplus C occupancy is 0.05% or less, there is little surplus C on the grain boundaries of the SiC crystal grains, so that the grain growth between the SiC crystal grains proceeds remarkably, and the coarse SiC crystallites A polycrystalline structure is formed. If the SiC crystallites are coarse, tensile stress concentrates on the coarse particles, so that breakage is likely to occur.

Moreover, since the crystalline silicon carbide based ceramic fiber of the present invention has a sintered structure of SiC, the density is in the range of 2.7 to 3.2 g / cm ³ .

  The crystalline silicon carbide based ceramic fiber of the present invention is mainly composed of silicon and carbon, and is composed of aluminum and boron as sintering aid components. The preferred proportions of these components are: Si: 50-70 wt%, C: 28-45 wt%, Al: 0.05-3.8 wt%, O: 0.05-1.5 wt%, and B: 0.05 to 0.5% by weight.

  In the present invention, surplus C means carbon that exceeds the stoichiometric composition that can exist as SiC with respect to Si contained in the fiber. The fiber diameter of the crystalline silicon carbide ceramic fiber is not particularly limited, but is usually 50 μm or less. Moreover, it is preferable that the form of the fiber is generally a continuous shape.

  When the proportion of aluminum is less than 0.05% by weight, the alkali resistance of the crystalline silicon carbide-based ceramic fiber is lowered, and when the proportion is higher than 3.8% by weight, the mechanical properties at high temperature are lowered. . If the proportion of boron is less than 0.05% by weight, it will not be a fully sintered crystalline fiber, and the density of the fiber will decrease, conversely, the proportion will be higher than 0.5% by weight. Then, the alkali resistance of the fiber is lowered.

  Next, the manufacturing method of the crystalline silicon carbide ceramic fiber of this invention is demonstrated. First, amorphous silicon carbide fibers containing 0.05 to 3.8% by weight of Al and 0.05 to 0.5% by weight of B were heat-treated in the range of 1000 ° C. to 1400 ° C. in the atmosphere. An oxide layer is formed on the fiber surface. Hereinafter, this heat treatment is referred to as atmospheric heat treatment. Next, after forming an oxide layer on the fiber surface, it is heated to a temperature in the range of 1600 to 2100 ° C. in an inert gas atmosphere. Hereinafter, this treatment is referred to as heat treatment in an inert gas. As described above, after forming an oxide layer on the fiber surface by heat treatment in the atmosphere, excess C in the fiber is removed by performing heat treatment in an inert gas at a temperature in the range of 1600 to 2100 ° C. to form a dense microstructure. The crystalline silicon carbide ceramic fiber of the present invention is obtained. Examples of the inert gas include argon and helium.

  The amorphous silicon carbide fiber preferably contains 8 to 16% by weight of oxygen. When the amorphous silicon carbide fiber is heated, this oxygen desorbs the aforementioned excess carbon as CO gas. The amount of oxygen is adjusted by subjecting a spun polymer, which is a raw material for amorphous silicon carbide fibers, to thermal oxidation treatment in air.

  The amorphous silicon carbide fiber may contain SiC fine crystals of 50 nm or less that are produced in the adjustment process from the raw material aluminum-containing organosilicon polymer.

  The amorphous silicon carbide fiber can be prepared, for example, by the following method. First, for example, according to the method described in “Chemistry of Organosilicon Compounds” Chemistry Dojin (1972), one or more dichlorosilanes are dechlorinated with sodium to prepare a linear or cyclic polysilane. The number average molecular weight of polysilane is usually 300-1000. In this specification, the polysilane is obtained by heating the chain or cyclic polysilane to a temperature in the range of 400 to 700 ° C., or adding a phenyl group-containing polyborosiloxane to the chain or cyclic polysilane. Also included is a polysilane partially having a carbosilane bond obtained by heating to a temperature in the range of 250 to 500 ° C. The polysilane can have a hydrogen atom, a lower alkyl group, an aryl group, a phenyl group or a silyl group as a side chain of silicon.

  A phenyl group-containing polyborosiloxane is prepared by dehydrochlorination condensation reaction between boric acid and one or more kinds of diorganochlorosilanes according to the methods described in Japanese Patent Nos. 3417459, 53-42330, and 53-50299. The number average molecular weight is usually 500 to 10,000.

  Next, a predetermined amount of an aluminum alkoxide, acetylacetoxide compound, carbonyl compound, or cyclopentadienyl compound is added to the polysilane, and 1 to 10 at a temperature usually in the range of 250 to 350 ° C. in an inert gas. By reacting for a period of time, an aluminum-containing organosilicon polymer that is a raw material for spinning can be prepared. The amount of the aluminum compound used is usually 0.14 to 0.86 mmol per 1 g of polysilane.

  An aluminum-containing organosilicon polymer is spun by a method known per se such as melt spinning and dry spinning to prepare a spun fiber. Next, the spinning fiber is infusibilized to prepare an infusible fiber. As the infusibilization method, generally used heating in air or a combination of heating in air and heating in an inert gas can be preferably employed.

  An infusible fiber is heated in an inert gas such as nitrogen or argon at a temperature in the range of 800 ° C. to 1500 ° C., and is an amorphous fiber that is a precursor fiber of the crystalline silicon carbide ceramic fiber of the present invention. Silicon carbide fibers are prepared. This amorphous silicon carbide fiber usually contains 1% by weight or more of excess carbon relative to Si. This amorphous silicon carbide fiber is heat-treated in the air in the range of 1000 ° C. to 1400 ° C. in advance to form an oxide layer on the fiber surface, and finally, heat treatment in an inert gas at a temperature in the range of 1600 to 2100 ° C. By doing so, the crystalline silicon carbide based ceramic fiber of the present invention is prepared. Preparation of the amorphous silicon carbide fiber from the infusible fiber and preparation of the crystalline silicon carbide-based ceramic fiber from the fiber can be performed independently or continuously and consistently.

  In the process of heat-treating the infusible fiber, aluminum and boron contained in the fiber play an important role as sintering aids for SiC crystals constituting the fiber material and must be strictly controlled. When the proportion of aluminum in the amorphous silicon carbide fiber exceeds 3.8% by weight, a lot of aluminum is ubiquitous in the grain boundary of the sintered SiC crystal in the fiber after sintering. It occurs predominately, high strength cannot be obtained, and the deterioration of mechanical properties at high temperatures becomes significant. When the proportion of aluminum in the fiber is less than 0.05% by weight, a sufficiently sintered crystalline fiber cannot be obtained. When the proportion of boron in the amorphous silicon carbide fiber exceeds 0.5% by weight, the alkali resistance of the resulting crystalline silicon carbide fiber is extremely reduced, and conversely, when the proportion is less than 0.05% by weight. A sufficiently sintered crystalline fiber cannot be obtained.

The crystalline silicon carbide-based ceramic fiber of the present invention is obtained by heat-treating amorphous or microcrystalline silicon carbide fiber in the air in the range of 1000 ° C. to 1400 ° C. in advance to form an oxide layer on the fiber surface. It is produced by heat treatment in an inert gas at a temperature in the range of ˜2100 ° C. Here, the oxide layer is a layer composed of an oxide formed by oxidizing the surface portion of amorphous or microcrystalline silicon carbide fiber by heat treatment in the atmosphere. As the oxide of the oxide layer, Examples thereof include those obtained by partially oxidizing Si, C, Al, B, etc. present on the surface portion of the silicon carbide fiber before the heat treatment. The main component is SiO ₂ , and examples thereof include Al ₂ O ₃ and B ₂ O ₃ . In the present invention, the form of the oxide is not particularly limited. The heat treatment conditions in the atmosphere depend on the method for treating amorphous or microcrystalline silicon carbide fibers. When batch processing a fiber bundle or a woven fabric woven into a desired shape, heat treatment is preferably performed at 1000 to 1400 ° C. in the atmosphere for 2 to 1 minute. When the fiber bundle is continuously heat-treated, it is preferably heat-treated at a temperature of 1000 to 1400 ° C. for 5 minutes to 1 second. Crystalline silicon carbide with less excess C, effectively promoting CO desorption when heat treatment in the atmosphere generates an oxide layer on the fiber surface, and then heat treatment in the inert gas of the amorphous silicon carbide fiber. Ceramic fiber can be obtained.

  If the heat treatment temperature in air is less than 1000 ° C., it takes time to produce an oxide layer having a desired thickness, which is not industrially preferable. Further, if the heat treatment in the air is performed at a temperature exceeding 1400 ° C., the generation of the oxide layer is not uniform, and it is difficult to form a desired oxide layer thickness, which is not preferable. If the subsequent heat treatment temperature in the inert gas is lower than 1600 ° C., it takes a long time to produce the desired crystalline silicon carbide ceramic fiber, which is not practical, and the crystalline silicon carbide ceramic in the produced fiber. There is also a possibility that the generation ratio of the system fiber may be lowered. If the heat treatment temperature in the inert gas exceeds 2100 ° C., the crystalline silicon carbide ceramic fiber is decomposed, and an undesirable situation may occur in which C is generated on the fiber surface.

  If the heat treatment in the air is excessively performed, silicon carbide derived from the oxide layer remains on the surface of the crystalline silicon carbide ceramic fiber, which causes a decrease in fiber strength. Therefore, the thickness of the oxide layer on the fiber surface is 400 nm or less. Furthermore, it is preferable to set the heat treatment conditions in the atmosphere so that the thickness is 200 nm or less. The thickness of the oxide layer is preferably larger than 10 nm. If the oxide layer is 10 nm or less, the effect due to the formation of the oxide layer cannot be sufficiently obtained, and a large amount of surplus C remains.

  In addition, according to the present invention, a ceramic matrix composite material in which the crystalline silicon carbide-based ceramic fiber in which the excess C is reduced is used as a reinforcing fiber and ceramic is used as a matrix can be obtained. There is no particular limitation on the form of the crystalline silicon carbide-based ceramic fiber in which the excess C, which becomes the reinforcing fiber, is reduced. It may be. Moreover, the nonwoven fabric using the chopped short fiber which cut | disconnected the continuous fiber may be sufficient. Although there is no special restriction | limiting about the volume ratio of the surface carbon rich layer removal silicon carbide ceramic fiber in a composite material, 20 to 50% is common. The interface layer is preferably boron nitride.

  The ceramic matrix of the ceramic matrix composite material of the present invention includes crystalline or amorphous oxide ceramics, crystalline or amorphous non-oxide ceramics, glass, solid solutions thereof, and particles of inorganic substances in these ceramics. And the like are preferred.

  Specific examples of oxide ceramics include aluminum, magnesium, silicon, yttrium, indium, uranium, calcium, scandium, tantalum, niobium, neodymium, lanthanum, ruthenium, rhodium, beryllium, titanium, tin, strontium, barium, zinc, zirconium. And oxides of elements such as iron and complex oxides of these metals.

  Specific examples of non-oxide ceramics include carbides, nitrides and borides. Specific examples of the carbide include carbides of elements such as silicon, titanium, zirconium, aluminum, uranium, tungsten, tantalum, hafnium, boron, iron, and manganese, and composite carbides of these elements. Examples of this composite carbide include inorganic substances obtained by heating and baking polytitanocarbosilane or polyzirconocarbosilane.

Specific examples of nitrides include nitrides of elements such as silicon, boron, aluminum, magnesium, and molybdenum, composite oxides of these elements, and sialon. Specific examples of borides include borides of elements such as titanium, yttrium, and lanthanum, and platinum boride lanthanoids such as CeCoB ₂ , CeCo ₄ B ₄ , and ErRh ₄ B ₄ .

Examples of the glass include amorphous glass and crystalline glass. Specific examples of the amorphous glass include silicate glass, phosphate glass, and borate glass. Specific examples of the crystallized glass include LiO ₂ —Al ₂ O ₃ —MgO—SiO ₂ glass and LiO ₂ —Al ₂ O ₃ —MgO—SiO ₂ —Nb ₂ O ₅ whose main crystal phase is β-spudene. system glass, the main crystal phase _MgO-Al 2 O 3 -SiO ₂ based glass is cordierite, the main crystal phase is barium male solid light _BaO-MgO-Al 2 O 3 -SiO ₂ based glass, the main crystalline phase Examples thereof include BaO—Al ₂ O ₃ —SiO ₂ based glass that is mullite or hexacelsian, and CaO—Al ₂ O ₃ —SiO ₂ based glass whose main crystal phase is anorthite. The crystal phase of these crystallized glasses may contain cristobalite. Examples of the ceramic in the present invention include solid solutions of the above-mentioned various ceramics.

  Specific examples of inorganic substance particles dispersed in ceramics include inorganic nitride spheres selected from silicon nitride, silicon carbide, zirconium oxide, magnesium oxide, potassium titanate, magnesium borate, zinc oxide, titanium boride and mullite. Examples thereof include particles, polyhedral particles, plate-like particles, rod-like particles, and whiskers. The dispersion amount of the inorganic substance particles and the like is preferably 0.1 to 60% by volume. The particle size of spherical particles and polyhedral particles is 0.1 μm to 1 mm, and the aspect ratio of plate-like particles, rod-like particles and whiskers is generally 1.5 to 1000.

  As a composite method, for example, the surface of crystalline silicon carbide ceramic fibers as reinforcing fibers is coated with boron nitride to form a molded body of boron nitride-coated crystalline silicon carbide ceramic fibers. Further, a polymer impregnation / firing method in which a ceramic precursor polymer, for example, polycarbosilane, polymetallocarbosilane, polysilazane, or the like is impregnated and then heated and fired can be employed. Other manufacturing methods include impregnating a slurry of matrix raw material powder and hot-pressing and sintering at high temperature, sol-gel method using matrix element alkoxide as raw material, or chemical vapor deposition method using reactive gas Alternatively, there is a reactive sintering method in which a molten metal is impregnated and ceramicized by reaction.

  Examples and comparative examples are shown below. In the following, unless otherwise specified, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively.

(Reference Example 1)
To anhydrous xylene containing 400 parts of sodium, 1034 parts by weight of dimethyldichlorosilane was added dropwise while heating and refluxing xylene under a nitrogen gas stream, followed by heating to reflux for 10 hours to form a precipitate. The precipitate was filtered, washed with methanol and then with water to obtain 420 parts of white polydimethylsilane.

(Reference Example 2)
By heating 750 parts of diphenyldichlorosilane and 124 parts of boric acid in a nitrogen gas atmosphere in n-butyl ether at 100 to 120 ° C., and further heating the resulting white resinous material at 400 ° C. in vacuum for 1 hour. , 530 parts of phenyl group-containing polyborosiloxane was obtained.

(Reference Example 3)
4 parts of the phenyl group-containing polyborosiloxane obtained in Reference Example 2 was added to 100 parts of the polydimethylsilane obtained in Reference Example 1, and heat condensed at 350 ° C. for 5 hours in a nitrogen gas atmosphere. An organosilicon polymer was obtained. Polyaluminocarbosilane was obtained by adding 7 parts of aluminum-tri (sec-butoxide) to a xylene solution in which 100 parts of this organosilicon polymer was dissolved, and carrying out a crosslinking reaction at 310 ° C. under a nitrogen gas stream.

  This polyaluminocarbosilane was melt-spun at 245 ° C., heat-treated in air at 140 ° C. for 5 hours, and further heated in nitrogen at 300 ° C. for 10 hours to obtain infusible fibers. The infusible fiber was continuously fired in nitrogen at 1500 ° C. to obtain amorphous silicon carbide fiber. This amorphous silicon carbide fiber has a chemical composition of Si: 52.5%, C: 34.1%, O: 12.5%, Al: 0.7%, B: 0.1%. It was.

Example 1
This amorphous silicon carbide fiber was charged into a firing furnace in the air atmosphere, heated to 1200 ° C. in the air atmosphere, and kept in air for 5 minutes. When the fiber heat-treated in the atmosphere was taken out and the cross section of the fiber was observed with a scanning electron microscope, the thickness of the oxide layer was 210 nm. This amorphous monosilicon fiber is placed in an electric furnace capable of controlling the atmosphere, introduced with argon gas, heated to 1800 ° C., maintained for 1 hour, and heat-treated in an inert gas to produce crystalline silicon carbide ceramics Fiber was obtained. The chemical composition of the obtained crystalline silicon carbide-based ceramic fiber was Si: 68.0%, C: 31.0%, O: 0.3%, Al: 0.14%, B: 0.15%. Yes, the atomic ratio was Si: C: O: Al: B = 1: 1.06: 0.01: 0.002: 0.006. The density of this fiber was 3.0 g / cm ³ and consisted of a dense sintered structure of SiC.

  FIG. 1 shows an SEM image obtained by polishing a cross section of the obtained crystalline silicon carbide ceramic fiber and photographing it with a scanning electron microscope. When the amount of residual carbon was calculated by image analysis, the area ratio (surplus C occupation ratio) of surplus C in the fiber cross section was 3.6%. Image analysis software Image-Pro Plus manufactured by Media Cybernetics was used for image analysis.

  Further, when the cross-section of the crystalline silicon carbide-based ceramic fiber was observed with a scanning electron microscope, the surplus C was observed in black in a form reflecting the composition on the crystal grain boundary of silicon carbide. Since non-surplus C exists in the fiber in the form of SiC crystals, the reflected electron image was observed in a lighter color than surplus C. The area ratio of surplus C calculated here was a value representing the area ratio of surplus C in the cross-sectional area when the cross section of the crystalline silicon carbide-based ceramic fiber was observed with a scanning electron microscope. The area of surplus C was calculated by digitizing the portion observed in black in the reflected electron image with image analysis software. It was also confirmed that the fiber surface was kept very clean. The mechanical properties of the fiber were a tensile strength of 3.21 (GPa) and an elastic modulus of 393 (GPa). The results are shown in Table 1.

(Example 2)
The same amorphous silicon carbide fiber as in Example 1 was heated to 1200 ° C. in a firing furnace in the air atmosphere and held for 15 minutes. When the fiber heat-processed in air | atmosphere was taken out and the cross section of the fiber was observed with the scanning electron microscope, the thickness of the oxide layer was 340 nm. This amorphous silicon carbide fiber is placed in an electric furnace capable of controlling the atmosphere, introduced with argon gas, heated to 1800 ° C., and subjected to heat treatment in an inert gas maintained for 1 hour, to produce crystalline silicon carbide ceramic fiber Got.

  FIG. 2 shows an SEM image obtained by polishing a cross section of the obtained crystalline silicon carbide-based ceramic fiber and photographing with a scanning electron microscope. When the residual carbon amount by image analysis was calculated, the area ratio (surplus C occupation ratio) of surplus C in the fiber cross section was 1.0%. It can be seen that almost the same results as in Example 1 are obtained. The mechanical properties of this fiber were a tensile strength of 3.72 (GPa) and an elastic modulus of 404 (GPa). The results are shown in Table 1.

Example 3
The same amorphous silicon carbide fiber as in Example 1 was heated to 1100 ° C. in a firing furnace in the air atmosphere and held for 15 minutes. When the fiber heat-processed in air | atmosphere was taken out and the cross section of the fiber was observed with the scanning electron microscope, the thickness of the oxide layer was 150 nm. This amorphous silicon carbide fiber is placed in an electric furnace capable of controlling the atmosphere, introduced with argon gas, heated to 1800 ° C., and subjected to heat treatment in an inert gas maintained for 1 hour, to produce crystalline silicon carbide ceramic fiber Got.

  FIG. 3 shows an SEM image obtained by polishing a cross section of the obtained crystalline silicon carbide ceramic fiber and photographing it with a scanning electron microscope. When the amount of residual carbon was calculated by image analysis, the area ratio (surplus C occupancy) of surplus C in the fiber cross section was 7.1%. The mechanical properties of this fiber were a tensile strength of 2.74 (GPa) and an elastic modulus of 388 (GPa). The results are shown in Table 1.

(Comparative Example 1)
The same amorphous silicon carbide fiber as in Example 1 was put in an electric furnace capable of controlling the atmosphere without being heat-treated in the atmosphere in a firing furnace in the atmosphere, introduced with argon gas, heated to 1800 ° C., heated for 1 hour Holding and heat-treating in an inert gas, a crystalline silicon carbide ceramic fiber was obtained. The chemical composition of the obtained crystalline silicon carbide-based ceramic fibers is Si: 66.6%, C: 31.6%, O: 0.8%, Al: 0.20%, B: 0.10%. Yes, the atomic ratio was Si: C: O: Al: B = 1: 1.11: 0.02: 0.003: 0.004. The density of this fiber was 2.9 g / cm ³ and consisted of a dense sintered structure of SiC.

  FIG. 4 shows an SEM image obtained by polishing a cross section of the obtained crystalline silicon carbide-based ceramic fiber and photographing with a scanning electron microscope. When the amount of residual carbon was calculated by image analysis, the area ratio (surplus C occupation ratio) of surplus C in the fiber cross section was 18.4%. The results are shown in Table 1.

  The tensile strength and elastic modulus of this fiber were 1.94 GPa and 284 GPa, respectively, and both values were low as compared with the fibers of Examples 1 to 3 with little excess C. If a large amount of surplus C remains at the interface of the silicon carbide microcrystals, sintering of the silicon carbide microcrystals is suppressed, and the silicon carbide ceramic fibers are not densified, resulting in a decrease in the tensile strength of the fibers. Moreover, when the excess C in a fiber segregates, it will become a defect which affects intensity | strength and this will also cause the fall of tensile strength. It is considered that the mechanical properties were lowered due to these causes.

(Comparative Example 2)
The same amorphous silicon carbide fiber as in Example 1 was heated to 1500 ° C. in a firing furnace in the atmospheric air and held for 5 minutes. When the fiber heat-treated in the atmosphere was taken out, the growth of the oxide layer was remarkable, and the accompanying fiber fusion occurred, and the fiber form could not be obtained.

  The present invention provides a stable crystalline silicon carbide-based ceramic fiber in which residual carbon present in the fiber is reduced and has excellent heat resistance and mechanical properties, and a method for producing the same. By reinforcing the ceramics with this fiber, a ceramic matrix composite having excellent heat resistance and mechanical properties at high temperatures can be provided.

Claims (5)

Density is 2.7-3. 2 g / cm ³ , Si: 50 to 70 wt%, C: 28 to 45 wt%, Al: 0. 05-3.8 wt%, O: 0.05-1.5 wt%, and B: 0. A crystalline silicon carbide-based fiber having a sintered structure of SiC consisting of 05 to 0.5% by weight, and the surplus C occupancy indicated by the surplus C area ratio in the fiber cross section is 0.05% to 10%. A certain crystalline silicon carbide ceramic fiber.   By heat-treating amorphous silicon carbide fibers containing Al: 0.05 to 3.8% by weight and B: 0.05 to 0.5% by weight in the range of 1000 ° C. to 1400 ° C. in the air in advance. The method for producing a crystalline silicon carbide ceramic fiber according to claim 1, wherein after forming the oxide layer on the fiber surface, heat treatment is performed at a temperature in the range of 1600 to 2100 ° C in an inert atmosphere.   The method for producing a crystalline silicon carbide-based ceramic fiber according to claim 2, wherein the oxide layer has a thickness of 10 nm to 400 nm.   A ceramic matrix composite material comprising the crystalline silicon carbide-based ceramic fiber according to claim 1 as a reinforcing fiber and a ceramic as a matrix.   The ceramic matrix composite material according to claim 4, wherein the reinforcing fiber is a two-dimensional or three-dimensional woven fabric, a unidirectional sheet-like material or a laminate thereof, or a non-woven fabric.

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