JP3417459B2 - Crystalline silicon carbide fiber having good alkali resistance and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has high mechanical characteristics,
Has good alkali resistance and also excellent heat resistance,
It relates to crystalline silicon carbide fibers.

[0002]

2. Description of the Related Art Silicon carbide fibers are used as reinforcing fibers for plastics or ceramics by taking advantage of their excellent heat resistance and mechanical properties. As the silicon carbide fiber, an amorphous or microcrystalline fiber obtained by a heat treatment at a relatively low temperature, for example, a temperature of 1300 ° C. or lower (hereinafter, this fiber is referred to as “amorphous silicon carbide fiber”). Is widely known and is put to practical use as a reinforcing fiber for various matrices.

Many proposals have already been made for this amorphous silicon carbide fiber and its manufacturing method. For example, in Japanese Examined Patent Publication No. 58-38535, an organosilicon polymer containing silicon and carbon as main skeletal components is spun, and the spun fiber is heated at a low temperature in an oxidizing atmosphere to be infusible. A method for producing silicon carbide fibers by high temperature firing is disclosed. Further, JP-B-62-52051 discloses a silicon carbide fiber composed of silicon-carbon-titanium-oxygen, and JP-B-58-5286 discloses a part of silicon atoms of polycarbosilane. Spinning polytitanocarbosilane bonded through a titanium atom and an oxygen atom,
A method for producing a silicon carbide fiber composed of the above silicon-carbon-titanium-oxygen by infusible spun fiber and firing the infusible fiber is disclosed.

The above-mentioned amorphous silicon carbide fiber is further heat-treated under the action of a sintering aid at a higher temperature, for example, a temperature of 1500 ° C. or higher to sinter the silicon carbide particles to obtain crystalline carbonization. Silicon fiber is being developed. Some proposals have been made for this crystalline silicon carbide fiber. For example, U.S. Pat. No. 5,268,336 discloses crystalline silicon carbide fibers containing 0.2% by weight or more of boron and having a density of 2.9 g / cm ³ or more. Further, US Pat. No. 5,366,943 discloses crystalline silicon carbide fibers composed of silicon, carbon, titanium and / or zirconium, and sintering aids such as boron.

[0005]

While the amorphous silicon carbide fiber has excellent heat resistance and mechanical properties,
It is pointed out that the alkali resistance is not sufficient and that the oxygen in the fiber is desorbed as CO gas and / or SiO at a high temperature of more than 1300 ° C, and the mechanical properties are deteriorated due to the rapid growth of β-SiC crystals. Has been done.

A method of testing the alkali resistance of silicon carbide fibers is described in Journal of American Ceramics.
Society, 78 [7] 1992-96 (1995)
It is described in. This test method is a method in which silicon carbide fibers are immersed in a saturated aqueous solution of sodium chloride at room temperature, dried, and then heat-treated in air at 1000 ° C. for 2 hours, and then the mechanical properties thereof are measured (hereinafter, this method). Is referred to as "alkali resistance test").

This alkali resistance test method is an accelerated test method carried out to examine the durability of silicon carbide fibers to NaCl. According to this document, when a silicon carbide fiber is subjected to an alkali resistance test method, the fiber is significantly decomposed due to oxidation, and a crystal phase of tridymite (scale silica salt) is formed on the fiber surface, and β- The growth of SiC grains is also observed and is described as having a significant adverse effect on the mechanical properties of the fiber.

Further, the crystalline silicon carbide fiber composed of the above-mentioned sintered silicon carbide particles exhibits excellent mechanical properties even at a temperature of higher than 1300 ° C., while it has poor alkali resistance. It has the same problems to be solved as fibers.

[0009]

DISCLOSURE OF THE INVENTION The present inventors have found that a silicon carbide fiber obtained from an organosilicon polymer obtained by introducing aluminum and boron, or further yttrium and / or magnesium in a specific ratio into the organosilicon polymer is 1
The SiC crystal in the fiber effectively sinters at a high temperature of 500 ° C. or higher. Compared to the case where aluminum and boron are used alone, by using both in combination, extremely high strength and low strength can be obtained. It has been found to give crystalline silicon carbide fibers having an elastic modulus. Further, it was also revealed that the crystalline silicon carbide fiber thus obtained exhibits excellent alkali resistance due to the presence of aluminum.

According to the present invention, the density is 2.7-3.2 g.
/ Cm ³ , and in a weight ratio (total 100% by weight), Si: 55-70%, C: 30-45%, A
A crystalline silicon carbide fiber having an alkali resistance of 1 to 0.06 to 3.8% and B to 0.06 to 0.5% and having a sintered structure of SiC is provided. Further, the density is in the range of 2.7 to 3.2 g / cm ³ , and the weight ratio (total 100% by weight) is Si: 55 to 70%, C: 30.
~ 45%, Al: 0.06 to 3.8%, B: 0 to 0.2
%, And Y: 0.06 to 3.8% and / or Mg: 0.
Provided is a crystalline silicon carbide fiber having a good alkali resistance, which is characterized by comprising a sintered structure of SiC, which is composed of 06 to 3.8%.

Further, according to the present invention, Al is 0.05%.
To 3 wt%, B to 0.05 to 0.4 wt%, and silicon carbide fibers containing 1 wt% or more of excess carbon with respect to Si at a temperature in the range of 1600 to 2100 ° C. There is provided a method for producing crystalline silicon carbide fibers having good alkali resistance, which comprises heat treatment in the atmosphere. Further, Al is 0.05 to 3% by weight, B is 0 to 0.1% by weight, Y is 0.05 to 3% by weight and / or Mg is 0.05.
~ 3 wt% and silicon carbide fibers containing 1 wt% or more of excess carbon with respect to Si are heat-treated in an inert gas at a temperature in the range of 1600 to 2100 ° C. Provided is a method for producing a crystalline silicon carbide fiber having good alkalinity.

The crystalline silicon carbide fiber of the present invention will be described first. This crystalline silicon carbide fiber has a sintered structure of SiC, has a density in the range of 2.7 to 3.2 g / cm ³ , and has strength and elastic modulus of 2 GPa or more and 250 GPa or more, respectively. It has good mechanical properties. What is more remarkable is that this crystalline silicon carbide fiber has a strength retention of 50% after an alkali resistance test.
That is all. As far as the inventors know,
The crystalline silicon carbide fiber having such excellent strength retention after the alkali resistance test was first introduced by the present invention.

The crystalline silicon carbide fiber of the present invention contains silicon and carbon as main components, and aluminum and boron as sintering aid components, or yttrium and / or magnesium. A preferable ratio of these components is Si: 55 to 70%, C: 30 to 45%, A:
1: 0.06 to 3.8%, particularly 0.13 to 1.25%,
B: 0.06 to 0.5%, especially 0.06 to 0.19%. Moreover, when yttrium and / or magnesium coexist, Si: 55-70%, C: 30-45
%, Al: 0.06 to 3.8%, particularly 0.13 to 1.2
5%, B: 0 to 0.2%, Y: 0.06 to 3.8%,
Particularly 0.13 to 1.25% and / or Mg: 0.06 to
It is 3.8%, especially 0.13 to 1.25%.

When the proportion of aluminum is excessively low, the alkali resistance of the crystalline silicon carbide fiber is lowered, and when the proportion thereof is excessively high, the mechanical properties at high temperature are deteriorated. If the proportion of boron is too small, it will not be a fully sintered crystalline fiber and the density of the fiber will decrease. Conversely, if the proportion is too high, the alkali resistance of the fiber will decrease. become. On the other hand, when yttrium and / or magnesium coexist, sufficient sinterability and excellent alkali resistance can be exhibited even if the content of boron is reduced.

The crystalline silicon carbide fiber may contain a small amount of oxygen and an excess of carbon, but each contains 2% by weight.
The following is preferable. In the present specification, the surplus carbon means carbon existing in excess of the stoichiometric composition amount that can exist as SiC with respect to Si contained in the fiber. The fiber diameter of the crystalline silicon carbide fiber is not particularly limited, but is usually 50 μm or less. In addition, it is generally preferable that the fibers have a continuous shape.

The method for producing the crystalline silicon carbide fiber of the present invention will be described below. This crystalline silicon carbide fiber is made of Al
0.05 to 3% by weight, preferably 0.1 to 1% by weight,
And B in an amount of 0.05 to 0.4% by weight, preferably 0.05
1 to 2100 of amorphous silicon carbide fiber containing 0.1 to 0.15% by weight of carbon and 1% by weight or more of surplus carbon with respect to Si, preferably 1.5 to 2.5% by weight.
Prepared by heating to a temperature in the range of ° C. Further, Al is 0.05 to 3% by weight, preferably 0.1 to 1
% By weight, 0 to 0.1% by weight of B, 0.05 to 3% by weight of Y, preferably 0.1 to 1% by weight and / or 0.1% by weight of Mg.
05-3% by weight, preferably 0.1-1% by weight, and S
It is prepared by heating an amorphous silicon carbide fiber containing 1% by weight or more of excess carbon to i to a temperature in the range of 1600 to 2100 ° C. This heat treatment is performed in an inert gas atmosphere such as argon or helium.

When the proportion of aluminum in the amorphous silicon carbide fiber exceeds 3% by weight, a large amount of aluminum is ubiquitous in the grain boundaries of the sintered SiC crystal in the fiber of the sintered fiber, so that the grain size of the grain is increased. Since the field destruction predominantly occurs, high strength cannot be obtained, and the deterioration of mechanical properties at high temperature becomes remarkable. If the proportion of aluminum in this 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 0.4% by weight, the alkali resistance of the obtained crystalline silicon carbide fiber is extremely lowered, and conversely, when the proportion is less than 0.05% by weight. However, a sufficiently sintered crystalline fiber cannot be obtained. On the other hand, when yttrium and / or magnesium coexist, sufficient sinterability and excellent alkali resistance can be exhibited even if the content of boron is reduced.

Further, the amorphous silicon carbide fiber contains 8% oxygen.
It is preferable that the content is ˜16% by weight. When heating the amorphous silicon carbide fiber, this oxygen causes CO
Desorb as gas.

The above-mentioned amorphous silicon carbide fiber is, for example,
It can be prepared by the following method. First, for example, "Chemistry of Organosilicon Compounds", Chemistry Doujin (1972
), One or more dichlorosilanes are subjected to a dechlorination reaction with sodium to prepare a chain or cyclic polysilane. The number average molecular weight of polysilane is usually 300 to 1000. In the present specification, the polysilane is the above chain-like or cyclic polysilane from 400 to
It is obtained by heating to a temperature in the range of 700 ° C., or by adding a phenyl group-containing polyborosiloxane to the above chain or cyclic polysilane and heating to a temperature in the range of 250 to 500 ° C. It also includes polysilane partially having a carbosilane bond. Polysilane is
The side chain of silicon may have a hydrogen atom, a lower alkyl group, an aryl group, a phenyl group or a silyl group.

The phenyl group-containing polyborosiloxane is prepared by a dehydrochlorination condensation reaction of boric acid and one or more kinds of diorganochlorosilanes according to the method described in JP-B Nos. 53-42330 and 53-50299. The number average molecular weight is usually 500 to 1,000.
It is 0.

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

The aluminum-containing organosilicon polymer is spun by a method known per se such as melt spinning or dry spinning to prepare spun fibers. Next, the spun fiber is infusibilized to prepare an infusibilized fiber. As the infusibilizing method, generally used heating in air or a method combining heating in air and heating in an inert gas can be preferably adopted.

The infusible fiber is heat-treated in an inert gas such as nitrogen or argon at a temperature in the range of 800 ° C. to 1500 ° C. to obtain a precursor fiber of the crystalline silicon carbide fiber of the present invention, that is, an amorphous fiber. Quality silicon carbide fibers are prepared. Finally,
As described above, the amorphous silicon carbide fiber is
The crystalline silicon carbide fibers of the present invention are prepared by heating to a temperature in the range of 100 ° C. The preparation of the amorphous silicon carbide fiber from the infusibilized fiber and the preparation of the crystalline silicon carbide fiber from this fiber can be performed independently or continuously and continuously.

[0024]

EXAMPLES Examples and comparative examples will be shown below. In the following, "parts" and "%" represent "parts by weight" and "% by weight", respectively, unless otherwise specified.

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 stream of nitrogen gas, followed by heating and refluxing for 10 hours to form a precipitate. . The precipitate is filtered,
It was washed with methanol and then with water to obtain 420 parts of white polydimethylsilane.

Reference Example 2 750 parts of diphenyldichlorosilane and 124 parts of boric acid were added in an amount of 100 to 100 parts in n-butyl ether under a nitrogen gas atmosphere.
The resulting white resinous material was further heated at 400 ° C. in vacuum for 1 hour to obtain 530 parts of a phenyl group-containing polyborosiloxane.

Example 1 To 100 parts of the polydimethylsilane obtained in Reference Example 1 was added 4 parts of the phenyl group-containing polyborosiloxane obtained in Reference Example 2, and thermal condensation was carried out at 350 ° C. for 5 hours in a nitrogen gas atmosphere. Thus, a high molecular weight 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 performing a crosslinking reaction at 310 ° C. under a nitrogen gas stream.

This polyaluminocarbosilane was treated at 245 ° C.
After melt-spinning in (1), the mixture was 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 an amorphous silicon carbide fiber. The chemical composition of this amorphous silicon carbide fiber is: Si: 56%, C: 30%,
O was 13%, Al was 0.6%, and B was 0.05%.

Next, 19 parts of this amorphous silicon carbide fiber was prepared.
Continuous heat treatment was carried out in argon at 00 ° C to obtain crystalline silicon carbide fibers. The chemical composition of the obtained crystalline silicon carbide fiber is as follows: Si: 67%, C: 31%, O: 0.3%, A
l: 0.8%, B: 0.06%, and in atomic ratio, S
i: C: O: Al: B = 1: 1.08: 0.008:
It was 0.012. The density of this fiber is 2.9 g / cm
³ and had a dense sintered structure of SiC.

The mechanical properties of this fiber before and after the alkali resistance test were as follows. Before the test After the test Tensile strength (GPa) 2.6 2.1 (Strength retention rate: 80.7%) Elastic modulus (GPa) 314 301 It was observed that the fiber surface after the alkali resistance test was kept in a very clean state. Was done. Further, this crystalline silicon carbide fiber retained the strength of 94% of the strength before the treatment even after the heat treatment in argon at 1600 ° C. for 1 hour.

Comparative Example 1 The phenyl group-containing polyborosiloxane 20 obtained in Reference Example 2 was added to 100 parts of the polydimethylsilane obtained in Reference Example 1.
After adding 10 parts by weight and thermally condensing at 350 ° C. for 10 hours in a nitrogen gas atmosphere, heat treatment was performed at 160 ° C. for 9 hours in air to obtain an infusible fiber. This infusible fiber was continuously fired in nitrogen at 1500 ° C. to obtain an amorphous silicon carbide fiber. This fiber 1
Continuous heat treatment was performed in argon at 900 ° C. to obtain crystalline silicon carbide fibers.

The chemical composition of the obtained fiber is Si: 62.
%, C: 37%, O: 0.5%, B: 0.3%,
The atomic ratio was Si: C: O = 1: 1.4: 0.014. The tensile strength and elastic modulus of this fiber are
The values are 1.3 GPa and 205 GPa, which are lower than those of the fiber of Example 1 in which aluminum coexists. When this crystalline silicon carbide fiber was subjected to an alkali resistance test, adhesion between the fibers occurred and the strength could not be measured.

Comparative Example 2 100 parts of the polydimethylsilane obtained in Reference Example 1 was thermally condensed in nitrogen gas at 470 ° C. for 4 hours to obtain a high molecular weight polycarbosilane. A xylene solution containing 100 parts of this polycarbosilane was added to aluminum-tri (sec.
-Butoxide) 10 parts and added under nitrogen gas stream to 320
Polyaluminocarbosilane was obtained by carrying out a cross-linking reaction at ℃. This aluminocarbosilane was melt-spun at 255 ° C., heat-treated in air at 150 ° C. for 6 hours, and further heated in nitrogen at 300 ° C. for 10 hours to obtain infusible fibers.

This infusible fiber was continuously fired in nitrogen at 1400 ° C. to obtain an amorphous silicon carbide fiber. 18 of this fiber
A crystalline silicon carbide fiber was prepared by continuous heat treatment in argon at 00 ° C. The chemical composition of the obtained fiber is Si:
66%, C: 32%, O: 0.3%, Al: 1.1%, and in atomic ratio, Si: C: O: Al = 1: 1.1.
It was 3: 0.013: 0.017. The tensile strength and elastic modulus of this fiber are 1.8 GPa and 294, respectively.
Although it was GPa and showed a low value as compared with the fiber of Example 1 in which boron coexists, it was composed of a SiC crystal structure. The tensile strength and the elastic modulus of the crystalline silicon carbide fiber after being subjected to the alkali resistance test are respectively 1.3.
GPa and 245 GPa, the tensile strength retention rate is 7
It was 2%.

Example 2 100 parts of the polydimethylsilane obtained in Reference Example 1 was mixed with 100 parts of the polyphenylsilane containing the phenyl group obtained in Reference Example 2.
5 parts was added and the mixture was thermally condensed at 410 ° C. for 5 hours in a nitrogen gas atmosphere to obtain a high molecular weight organosilicon polymer. Aluminum-tri- (sec-butoxide) (4 parts) and magnesium acetylacetonate (3 parts) were added to a xylene solution in which 100 parts of this organosilicon polymer was dissolved, and a crosslinking reaction was performed at 310 ° C. under a nitrogen gas stream to obtain aluminum. In addition, modified polycarbosilane having magnesium introduced therein was obtained.

The modified polycarbosilane was melt-spun at 255 ° C., heat treated in air at 150 ° C. for 3 hours, and further heated in nitrogen at 300 ° C. for 9 hours to obtain infusible fibers. Continuously firing the infusible fiber at 1450 ° C. in argon,
Amorphous silicon carbide fiber was synthesized. The chemical composition of this amorphous silicon carbide fiber is Si: 53 wt%, C: 33.4 wt.
%, O: 13 wt%, Al: 0.34 wt%, B: 0.01
wt% and Mg: 0.30 wt%.

Next, 18 parts of this amorphous silicon carbide fiber was added.
A crystalline silicon carbide fiber was synthesized by continuous heat treatment in argon at 50 ° C. The chemical composition of the obtained silicon carbide-based continuous inorganic fiber is Si: 66.5 wt%, C: 32.5 wt%
%, O: 0.2 wt%, Al: 0.43 wt%, B: 0.0
1 wt%, Mg: 0.38 wt%, atomic ratio Si: C:
O: Al: Mg = 1: 1.14: 0.005: 0.00
It was 67: 0.0066. The density of this fiber is 2.8.
It was 7 g / cm ³ , and was composed of a dense sintered structure of SiC.

The mechanical properties of this fiber before and after the alkali resistance test were as follows. Before the test After the test Tensile strength (GPa) 2.4 2.1 (Strength retention rate: 87.5%) Elastic modulus (GPa) 305 298 The fiber surface after the alkali resistance test may be kept extremely clean. Was observed. Further, this crystalline silicon carbide fiber retained the strength of 91% of the strength before the treatment even after the heat treatment in argon at 1600 ° C. for 1 hour.

Example 3 100 parts of the polydimethylsilane obtained in Reference Example 1 was added to the phenyl group-containing polyborosiloxane 0.1% obtained in Reference Example 2.
Two parts were added and the mixture was thermally condensed at 420 ° C. for 5 hours in a nitrogen gas atmosphere to obtain a high molecular weight organosilicon polymer. Aluminum-tri- (sec-butoxide) (4 parts) and yttrium acetylacetonate (4 parts) were added to a xylene solution in which 100 parts of the organosilicon polymer was dissolved, and a crosslinking reaction was performed at 300 ° C under a nitrogen gas stream to obtain aluminum. A modified polycarbosilane containing yttrium was also obtained.

The modified polycarbosilane was melt-spun at 265 ° C., heat-treated in air at 155 ° C. for 3 hours, and further heated in nitrogen at 300 ° C. for 10 hours to obtain infusible fibers. The infusible fiber was continuously fired in argon at 1450 ° C. to synthesize an amorphous silicon carbide fiber. The chemical composition of this amorphous silicon carbide fiber is Si: 52.5 wt%, C: 3
4.5 wt%, O: 12 wt%, Al: 0.35 wt%, B:
It was 0.005 wt% and Y: 0.56 wt%.

Next, 19 parts of this amorphous silicon carbide fiber was prepared.
Crystalline silicon carbide fibers were synthesized by continuous heat treatment in argon at 00 ° C. The chemical composition of the obtained silicon carbide-based continuous inorganic fiber was Si: 67 wt%, C: 31.5 wt%,
O: 0.1 wt%, Al: 0.41 wt%, B: 0.01 wt%
%, Y: 0.73 wt%, atomic ratio of Si: C: O: A
l: Y = 1: 1.1: 0.0026: 0.0064:
It was 0.0034. The density of this fiber is 3.01 g /
cm ³ and was composed of a dense SiC sintered structure.

The mechanical properties of this fiber before and after the alkali resistance test were as follows. Before test After test Tensile strength (GPa) 2.5 2.2 (Strength retention rate: 88%) Elastic modulus (GPa) 325 315 It was observed that the fiber surface after the alkali resistance test was kept in a very clean state. It was Further, this crystalline silicon carbide fiber retained the strength before the treatment even after the heat treatment in argon at 1600 ° C. for 1 hour.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-52-59725 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) D01F 9/10

Claims (4)

(57) [Claims] 1. A density range of 2.7 to 3.2 g / cm ³ and a weight ratio (total 100% by weight) of Si: 55.
~ 70%, C: 30-45%, Al: 0.06-3.8.
% And B: 0.06 to 0.5%, and a crystalline silicon carbide fiber having good alkali resistance, characterized by having a sintered structure of SiC. 2. The density is in the range of 2.7 to 3.2 g / cm ³ , and the weight ratio (total 100% by weight) is Si: 55.
~ 70%, C: 30-45%, Al: 0.06-3.8.
%, B: 0 to 0.2%, and Y: 0.06 to 3.8% and / or Mg: 0.06 to 3.8%, and is characterized by having a sintered structure of SiC. Crystalline silicon carbide fiber with good alkali resistance. 3. Al: 0.05 to 3% by weight, B: 0.05
~ 0.4 wt% and 1600 to 2100 ° C silicon carbide fibers containing 1 wt% or more of excess carbon with respect to Si
A method for producing a crystalline silicon carbide fiber having good alkali resistance, which comprises heat-treating in an inert gas at a temperature within the range. 4. Al in an amount of 0.05 to 3% by weight and B in an amount of 0 to 0.
1% by weight, 0.05 to 3% by weight of Y and / or 0.05 to 3% by weight of Mg, and 1 of surplus carbon with respect to Si.
1600 to 210 containing silicon carbide fibers containing at least wt%
A method for producing a crystalline silicon carbide fiber having good alkali resistance, which comprises performing a heat treatment in an inert gas at a temperature within a range of 0 ° C.