JP2874045B2 - Method for producing porous silicon nitride-based fiber ceramic body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a porous silicon nitride-based fiber-structured ceramic body. The silicon nitride-based fiber-structured ceramic porous body manufactured by the present invention has a uniform fibrous structure and a specific porosity. For example, a filler (reinforced) of a heat-resistant material used for a power generation gas turbine, a space shuttle, and the like is used. Material) is expected. When used as a reinforcing material, it is possible to easily impart a specific member shape to the porous body. Therefore, after the base material component is impregnated in the porous body, the porous body can be easily manufactured by baking. Can be. The fibrous tissue porous material can also be expected to be used as a filter for purifying high-temperature gas discharged from various plants.

[0002]

Hitherto, whiskers have been produced as a silicon nitride-based ceramic fibrous structure. The whisker production method is as follows: 1) Nitriding method of metal silicon (AL Cunningham and LG Da)
vis, SAMPE, 15, 120 (1986). ),
2) Reduction nitridation method of silica (RC Johnson)
tal. , "Synthesis of Fibrou
s Silicon Nitrid ", US Pa
t. 3,244,480 (1966); Tanaka et al., "Method of Manufacturing Silicon Nitride Whiskers", Patent No. 1,324,47.
No. 9), 3) Sublimation method (Shintoku et al., “Method for producing silicon nitride whiskers”, JP-A-61-275199), 4) Gas phase reaction method (K. kijima et al., J. Cryst.
Growth, 52, 285 (1981); Mot
ojima et al. , J. et al. Cryst. Grow
th, 96, 383 (1989)) and 5) Flux method (K. kijima et al., J. Crys).
t. Growth, 21, 317 (1974)).

[0003] However, in the conventional production method, a large amount of starting material remains, an impurity metal such as iron (Fe) is added for forming a fibrous structure (whisker formation), and further, the whisker shape is reduced. In addition, since the composition and the crystal phase become non-uniform, a step of separating and purifying whiskers, which is an object, is required, and there is a problem that the production efficiency is very poor. Whiskers that have been separated and refined have been commercialized as fine fibrous powders, and their application as reinforcing materials for various structural materials has been studied.However, in recent years, from the viewpoint of safety and health, their handling has been restricted. There's a problem.

[0004]

Under these circumstances, the present inventors have developed a new silicon nitride-based fiber structure capable of solving the various problems of the above-mentioned prior art in view of the above-mentioned prior art. As a result of intensive research aimed at developing a method of manufacturing porous ceramics, it was found that it was composed of a uniform and strict chemical composition obtained by thermally decomposing organometallic compounds whose composition was controlled at the atomic and molecular levels. It has been found that the intended purpose can be achieved by heating the amorphous powder in nitrogen after molding the amorphous powder, and the present invention has been completed. That is, the present invention provides a new silicon nitride-based fiber-structured ceramic porous body capable of producing a silicon nitride-based fiber-structured ceramic porous body having a very uniform fibrous structure and a specific porosity without leaving any starting material. It is an object of the present invention to provide a production method of Another object of the present invention is to provide a method for producing a silicon nitride-based fibrous ceramic porous body having good production efficiency, which does not require a whisker separation / purification step as in the conventional method.

[0005]

In order to solve the above-mentioned problems, the present invention provides an amorphous powder, which is molded and then heated in nitrogen to have a uniform fibrous structure and to have an air content of 10 to 50%.
A method of manufacturing a silicon nitride based fibrous tissue ceramic porous body having a porosity, the general formula [Si-A (-B) -
C—O—N] (1) (wherein, Si is silicon, A is yttrium or a rare earth element, and in the case of AB, A and B are different elements selected from yttrium, rare earth element and aluminum, C represents carbon, O represents oxygen and N represents nitrogen), the content of silicon is 50% or more, the content of nitrogen is 25% or more, and the total content of the A element and the B element is 6% or more. A silicon powder having an oxygen content of 5% or more and a carbon content of 5% or more and having a uniform and strict chemical composition (amorphous powder). This is a method for producing a porous body. Further, the present invention, the amorphous powder is one obtained by pulverizing a material obtained by thermally decomposing atoms, an organometallic compound composition control at the molecular level at 600 to 1200 ° C., after molding it, nitrogen 1-4 Heating in atmospheric pressure
To a process for the manufacture of the above silicon nitride based fibrous tissue ceramic porous body, wherein Rukoto to form a porous body, a silicon nitride based fibrous tissue porous body has a uniform fibrous tissue, and porosity 10 In a preferred embodiment, the above-described method for producing a porous silicon nitride-based fibrous ceramic body characterized by being 50%.

[0006]

Next, the present invention will be described in more detail. The present invention solves the above-mentioned problem by heating an amorphous powder composed of a uniform and strict chemical composition obtained by thermally decomposing an organometallic compound whose composition is controlled at the atomic and molecular levels, and then heating the powder in nitrogen. The problem is solved by providing a method for producing a silicon nitride-based fibrous ceramic porous body having a uniform fibrous structure and a porosity of 10 to 50%. According to the present invention, a general formula [Si-A (-B) -CO-O-] obtained by thermally decomposing an organometallic compound whose composition is controlled at the atomic and molecular levels.
N] (1) (wherein, Si is silicon, A is yttrium or a rare earth element, where A and B are different elements selected from yttrium, a rare earth element and aluminum, C is carbon, O represents oxygen and N represents nitrogen), wherein silicon is 50% or more and nitrogen is 25%
The above content, and the total content of the element A and the element B is 6% or more, the oxygen content is 5% or more, and the carbon content is 5% or more.
% Of amorphous powder composed of a uniform and strict chemical composition and then heated in nitrogen to form a silicon nitride base having a uniform fibrous structure and a porosity of 10 to 50%. A porous fibrous ceramic body is provided.

[0007] Polycarbosilane, polysilazane, and the like can be used for the production of the organometallic compound whose composition is controlled at the atomic and molecular levels used in the present invention.
145943, JP-A-60-226890, JP-A-6-1986
1-89230). By chemically modifying these organometallic compounds with various reactants such as alcohols, alkoxides, and metal amides, it is possible to produce an intended organometallic compound having a controlled composition. These chemical modification reactions include, for example, a method of chemically modifying polysilazane with a metal alkoxide (JP-A-2-77427 or the like), or
A method of chemically modifying polycarbosilane with a metal alkoxide (for example, JP-A-56-74126, JP-A-56-92923, etc.) (hereinafter, referred to as a chemical modification method) can be used. In addition, those obtained by physically mixing an organosilicon-based polymer and various organometallic reactants physically can be used (hereinafter, referred to as a physical mixing method). However, in order to obtain a uniform fiber structure, strictly and uniformly controlled amorphous powder is indispensable.In the production of such an amorphous powder, a chemical modification method is used as compared to a physical mixing method. It is preferable to use an organometallic compound whose composition is controlled at the atomic and molecular levels.

As the above polycarbosilane, those synthesized by a transfer reaction of dimethylpolysilane, perhydropolysilazane as polysilazane, normal decyl alcohol as alcohol, trimethoxyyttrium as alkoxide, and triethylaluminum as metal amide are preferable. Is exemplified. Also,
Examples of the rare earth element include La (lanthanum), Nd (neodymium), Dy (dysprosium), and Yb (ytterbium). Further, as a method for producing the organometallic compound, for example, after dissolving polysilazane in a solvent, adding an alcohol and refluxing to obtain an alcohol adduct, trimethoxyyttrium, triethylaluminum and the like are added, and the mixture is refluxed. After completion of the reaction, a method of producing an organometallic compound whose composition is controlled at the atomic and molecular levels by distilling off the solvent after removing the solvent is exemplified as a suitable method. As described above, an appropriate method can be used, and the present invention is not limited thereto.

An amorphous phase can be synthesized by thermally decomposing the organometallic compound produced by these methods in an atmosphere gas (argon, nitrogen, ammonia, etc.). In this pyrolysis step, it is necessary to select an atmosphere gas that matches the type and composition of the organometallic compound to be used in order to synthesize a desired strictly and uniformly controlled amorphous phase. In addition, the thermal decomposition temperature is from 600 ° C to 12 ° C.
00 ° C is preferred. When the temperature is higher than this temperature range, crystallization of silicon nitride occurs partially, so that a uniform fiber structure cannot be finally obtained. Also, a porous body can be formed.
Will not be able to. When the temperature is lower than this temperature range, the organometallic compound remains in the amorphous phase. Since the remaining organometallic compound is thermally decomposed when the molded body is heated in nitrogen, cracks and the like occur in the molded body, making it difficult to impart a shape to the final product.

The obtained amorphous phase is pulverized using a pulverizer or the like to be pulverized and molded, and then heated in nitrogen to produce a silicon nitride-based fibrous ceramic porous body. The heating temperature is desirably 1600 ° C to 1800 ° C. The heating rate is preferably 10 ° C./min to 20 ° C./min, and the maximum holding temperature is 1 hour to 5 hours. The atmospheric nitrogen pressure is desirably 1 to 4 atm. Meet these conditions
Otherwise, the desired uniform fibrous tissue porous body is not obtained.
No longer. Furthermore, when the amorphous powder compact is heated in a heating furnace in the present invention, it is desirable to use a furnace material made of silicon nitride.

By adopting the above structure, the silicon nitride-based fiber structure ceramic porous material having no residual starting material, having a very uniform fibrous structure, and having a porosity of 10 to 50%. The body can be manufactured. According to the method of the present invention, there is no need for a step of separating and purifying the target whisker, and there is an advantage that the production efficiency is very good as compared with the conventional method. Further, since the composition having excellent heat resistance can be selected for the binder phase of the fiber structure and the shape of the porous body can be easily provided, the silicon nitride-based fiber structure ceramic porous body of the present invention is, for example, heat-resistant. It is useful as a material reinforcement, a high temperature gas purification filter, and the like.

[0012]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. Example 1 (Production of organometallic compound) perhydropolysilazane (1
After dissolving 4.6 g) in anhydrous xylene (100 ml), normal decyl alcohol (0.53 g) was added at room temperature and refluxed for 1 hour. After completion of the reaction, the solvent xylene was distilled off under reduced pressure to produce the product (15 g, hereinafter referred to as an alcohol adduct).
I got Next, an alcohol adduct of anhydrous pyridine (40
0 ml) solution to which trimethoxyyttrium (0.18 g) was added at room temperature. After hydrogen gas generation ceased, reflux was continued for 2 hours. After completion of the reaction, pyridine as a solvent was distilled off under reduced pressure to obtain a reaction product (14 g, white solid).

(Production of Amorphous Powder) The obtained reaction product is heated at a rate of 3 ° C. per minute in a stream of nitrogen for 100 minutes.
It was thermally decomposed by holding at 0 ° C. for 3 hours to obtain an amorphous phase (12 g). FIG. 1 shows the results of X-ray diffraction analysis of the obtained amorphous phase. No crystal phase is observed,
It was confirmed that it was an amorphous phase. As a result of elemental analysis, the obtained amorphous phase was composed of a chemical composition of 53.7% of silicon, 26.5% of nitrogen, 6.9% of yttrium, 6.9% of oxygen, and 6.4% of carbon. The obtained amorphous phase was lightly pulverized in a mortar and sized with a sieve of 60 mesh to obtain an amorphous powder.

(Manufacture of Porous Silicon Nitride-Based Ceramic Fiber Body) This amorphous powder (1.5 g) was molded at a molding pressure of 150 MPa into a mold having a diameter of 15 mm and a thickness of 4 m.
m in the form of a pellet. This compact was heated at 1800 ° C. for 1 hour in 4 atmospheres of nitrogen to obtain a pellet-like fired product. FIG. 2 shows an electron micrograph of the fired product. It was confirmed that the fired product was a uniform fibrous tissue porous body. FIG. 3 shows the microstructure of the porous fibrous structure. The fibrous structure was found to be composed of fibrous crystal particles having a length of about 15 μm and a width of about 0.5 μm. Further, as a result of density measurement by the Archimedes method, it was confirmed that the fired product was a porous material having a porosity of 35%. FIG. 4 shows the results of X-ray diffraction analysis of the fired product. It was confirmed that the fired product contained silicon nitride as a main component and further contained a small amount of silicon carbide having higher heat resistance than silicon nitride. From these evaluation results, it was confirmed that the fired product was a silicon nitride-based fiber structure ceramic porous body having a uniform fibrous structure and a porosity of 35%.

Example 2 (Production of organometallic compound) Perhydropolysilazane (1
After dissolving 4.6 g) in anhydrous xylene (100 ml), normal decyl alcohol (0.53 g) was added at room temperature and refluxed for 1 hour. After cooling to room temperature, triethylaluminum (0.08 g) was added under a nitrogen stream, and the mixture was refluxed for 5 hours. The solvent xylene was distilled off under reduced pressure to obtain a product (15.1 g). Next, a solution of the obtained product in anhydrous pyridine (400 ml) was prepared, and trimethoxyyttrium (0.14 g) was added thereto at room temperature. After hydrogen gas generation ceased, reflux was continued for 2 hours. After completion of the reaction, pyridine as a solvent was distilled off under reduced pressure, and the reaction product (13.
6 g, a white solid).

(Production of Amorphous Powder) The obtained reaction product was heated at a rate of 3 ° C./min in a nitrogen stream to 100
It was thermally decomposed by holding at 0 ° C. for 3 hours to obtain an amorphous phase (11.5 g). FIG. 5 shows the results of X-ray diffraction analysis of the obtained amorphous phase. No crystalline phase was observed, confirming that it was an amorphous phase. As a result of elemental analysis, the obtained amorphous phase was 54.5% silicon,
It consisted of a chemical composition of 26.9% nitrogen, 1.1% aluminum, 5.5% yttrium, 5.5% oxygen and 6.5% carbon. The obtained amorphous phase was lightly pulverized in a mortar and sized with a sieve of 60 mesh to obtain an amorphous powder.

(Production of Silicon Nitride-based Fiber-structured Ceramic Porous Material) This amorphous powder (1.5 g) was molded at a molding pressure of 150 MPa into a mold having a diameter of 15 mm and a thickness of 4 m.
m in the form of a pellet. This compact was heated at 1800 ° C. for 1 hour in 4 atmospheres of nitrogen to obtain a pellet-like fired product. As a result of observation with an electron microscope, it was confirmed that the fired product was a uniform fibrous tissue porous body. FIG. 6 shows the microstructure of the porous fibrous structure. The fiber tissue is about 10μ in length
m and about 0.8 μm in width. Further, as a result of density measurement by the Archimedes method, it was confirmed that the fired product was a porous material having a porosity of 32%. As a result of X-ray diffraction analysis of the fired product, it was confirmed that the fired product contained silicon nitride as a main component and further contained a small amount of silicon carbide having higher heat resistance than silicon nitride. From these evaluation results, it was confirmed that the fired product was a silicon nitride-based fiber structure ceramic porous body having a uniform fibrous structure and a porosity of 32%.

[0018]

According to the method of the present invention, no starting material remains. In addition, a silicon nitride-based fibrous ceramic porous body having a very uniform fibrous structure and a specific porosity can be obtained. Furthermore, the step of separating and purifying the whisker, which is the target substance, is not required at all, and the composition having excellent heat resistance can be selected for the binder phase of the fibrous structure, and the shape of the porous body can be easily provided. The porous body can be safely and stably handled as a reinforcing material or as a filter without decomposing and purifying the porous body.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction pattern of an amorphous phase produced in Example 1 of the present invention.

FIG. 2 shows an electron micrograph of a porous silicon nitride-based fiber ceramic body of Example 1 of the present invention.

FIG. 3 is a microstructure photograph of the silicon nitride based fiber structure ceramic porous body of Example 1 of the present invention.

FIG. 4 shows an X-ray diffraction diagram of the silicon nitride-based fiber-structured ceramic porous body of Example 1 of the present invention.

FIG. 5 shows an X-ray diffraction analysis result of an amorphous phase obtained in Example 2 of the present invention.

FIG. 6 shows a microstructure micrograph of a porous silicon nitride-based fiber microstructure of Example 2 of the present invention.

Continuation of the front page Examiner Yoichi Gotani (56) References JP-A-2-204313 (JP, A) JP-A-2-289408 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) C04B 35/584 C04B 35/626 C04B 38/00 304

Claims (3)

(57) [Claims] After the amorphous powder is molded, it is heated in nitrogen to have a uniform fibrous structure and 10 to 50%.
A method for producing a porous silicon nitride-based fibrous ceramic having a porosity , comprising the general formula [Si-A (-B)
-CON] (1) (wherein, Si is silicon, A is yttrium or a rare earth element, and in the case of AB, A and B are different elements selected from yttrium, a rare earth element and aluminum. ,
C represents carbon, O represents oxygen and N represents nitrogen), the content of silicon is 50% or more, the content of nitrogen is 25% or more, and the total content of the A element and the B element is 6% or more. A silicon powder having an oxygen content of 5% or more and a carbon content of 5% or more and having a uniform and strict chemical composition (amorphous powder). A method for producing a porous body. 2. The amorphous powder contains an organometallic compound whose composition is controlled at an atomic or molecular level by 600 to 1200.
The product obtained by pulverizing the material decomposed by thermal decomposition at a temperature of 1 ° C., after molding, heating in 1 to 4 atm of nitrogen to form a porous body . A method for producing a porous ceramic body having a silicon nitride-based fiber structure. 3. The ceramic porous body of silicon nitride-based fiber structure according to claim 1, wherein the porous silicon nitride-based fiber structure has a uniform fibrous structure and a porosity of 10 to 50%. Manufacturing method.