JPH02267167A - Composite ceramic sheet-like molded product and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject molded product having excellent resistance to oxidation and resistance to thermal shock by molding a composite ceramic sheet-like molded product composed of a dense layer of silicon carbide as the surface layer part and a composite material layer of silicon carbide containing inorganic short fiber as inner part. CONSTITUTION:The aimed short fiber-reinforced ceramic sheet-like molded product is obtained by comprising a dense layer mainly containing silicon carbide as the surface layer part and a composite material layer mainly containing inorganic short fiber in matrix of silicon carbide as inner part. Besides, the reinforcing short fiber is milled fiber or whisker having about 0.2-5mu diameter and about 3-50 aspect ratio and is contained about >=10wt.%, preferably 20-60wt.%. Furthermore, denseness of the surface layer part is made as about >=5 times of the inner part and the thickness is made as about >=1mu. By said method, a molded product useful for heater having excellent resistance to thermal shock, etc., is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a short fiber-reinforced composite ceramic sheet-like molded product having a matrix of silicon carbide ceramics and a method for manufacturing the same.

More specifically, the present invention relates to a sheet-like composite ceramic molded product having a dense surface and excellent oxidation resistance and thermal shock resistance, and a method for producing the same.

[Prior Art] Silicon carbide ceramics have been developed as heat-resistant ceramics and are widely used. However, silicon carbide ceramics have low fracture toughness and thermal shock resistance, and therefore various improvements have been investigated. This improvement is mainly achieved by obtaining a mixed sintered product with silicon nitride and by reinforcing it with fibers, that is, fiber-reinforced ceramics.
-The name of the shrimp is FRC). Silicon nitride has lower heat resistance than silicon carbide, but it has superior fracture toughness and thermal shock resistance. Therefore, a product obtained by mixing and sintering silicon nitride and silicon carbide can have excellent fracture toughness and thermal shock resistance. An example of a method proposed based on this idea is the method disclosed in Japanese Patent Publication No. 6026075. This method involves mixing and molding a precursor that will become silicon carbide fiber or the like with silicon nitride powder and firing it, and the silicon nitride is reinforced with silicon carbide fiber or the like and is similar to FRC. Examples of the latter type of fiber reinforcement include reinforcement using silicon carbide fibers, which was shown in Japanese Patent Application Laid-open No. 52144001, etc., and Japanese Patent Publication No. 62-19391 and JP-A No. 63.
Reinforcement has been achieved using silicon carbide whiskers (crystal short fibers) as shown in No. 277563 and the like.

The present inventors have also studied such composite material ceramics, for example, researched silicon nitride whisker-reinforced silicon carbide ceramics and their manufacturing method. however,
Although the fracture toughness of such fiber-reinforced ceramics is improved, it has been found that there are other problems. That is, in general, fiber-reinforced ceramics are particularly prone to surface roughness and to open microscopic pores leading to the interior. Such pores often have a significant effect on the erosion of ceramics by gases at high temperatures. In other words, the presence of pores in the ceramic increases the contact area with the atmospheric gas and increases the amount of corrosion. For this reason, the presence of pores on the surface of the molded product is undesirable, but the conventional molded product inevitably has a porous surface, making it impossible to obtain a product without such pores.

[Problems to be Solved by the Invention] The present invention aims to reduce the pores on the surface of conventional fiber-reinforced silicon carbide-based composite ceramic moldings and provide a sheet-like molded product with improved corrosion resistance. . If such a sheet-like composite ceramic molded product can be provided, it is expected that the usefulness of fiber-reinforced ceramics will increase in various applications, especially in applications as sheet-like heaters.

[Means for Solving the Problems] According to the present invention, the surface layer is a dense layer mainly made of silicon carbide, and the inside is a composite material layer containing reinforcing short fibers in a matrix mainly made of silicon carbide. A novel composite ceramic sheet-like molded product is provided.

It has been found that ceramics as composite materials can be provided with various new functions by selecting their composition. The present invention utilizes this idea. Particularly, in the present invention, the inside of the molded product is made of a composite material reinforced with short fibers, etc., and the outermost part is made of a dense ceramic layer, preferably a dense layer made of glass or similar ceramic. The internal short fiber-reinforced ceramic layer has a ceramic matrix mainly composed of silicon carbide, and the reinforcing short fibers contained therein are milled fibers or whiskers.

Milled fibers are crushed ceramic fibers in cloth, and whiskers are not particularly limited and may be commercially available whiskers. These generally have a diameter of about 0.2 to 5 μm and an aspect ratio of 3.
The diameter is preferably 1 to 50, particularly preferably 1 to 3.
μm, and the aspect ratio is about 5 to 15.

The content of short fibers is preferably 10% by weight or more, and 20 to 6% by weight.
Particularly preferred is 0% by weight. A portion containing such short fibers inevitably has a rough structure with communicating holes.

On the other hand, the dense layer on the surface is a ceramic without continuous pores mainly composed of silicon carbide, and is preferably a fired product of an organosilicon polymer. Ceramics made by firing organosilicon polymers include those that cannot be chemically called silicon carbide, but the present invention includes such ceramics.

In some cases, it is preferable that the ceramic be made by rendering the organosilicon polymer invulnerable and then firing it. - X-ray analysis shows that the crystallinity is 25%, which is considered glassy for boat fishing.
The content below is particularly preferably 15% or less. Such materials are licks that can easily be made difficult for gas to pass through. It is well known that this standard does not indicate pure crystallinity. It is preferable that the density of the surface is 5 times or more compared to that of the center.

The thickness of this dense layer is 1 μm as the thickness of one surface layer.
It is preferable that the thickness is more than this, and if it is thinner than this, the effect of forming a dense layer tends to be poor.

In principle, the molded product is in the form of a sheet, but its shape and thickness can be arbitrarily selected. The thickness may be partially changed, for example, the thickness may be different between the peripheral edge and the center of the sheet.

Further, the change in density from the surface to the inside of the molded article is preferably continuous, but may be changed stepwise or discontinuously.

Next, a method for manufacturing the above-mentioned novel composite molded article will be explained.

In the present invention, reinforcing short fibers (and silicon carbide powder) are dispersed in an organosilicon polymer solution to create a suspension.
After this suspension is injected into a mold or cast onto a suitable support (substrate) to form a sheet, the sheet is removed from the mold or support and the two sheets are separated as described below. A method in which the materials are bonded together to form a firing raw material (green sheet) is preferably adopted. At this time, it is important to attach the sheets so that the lower side when forming the sheet is inward and these surfaces are in contact with each other. This firing raw material is fired under predetermined conditions. If necessary, you can make it invincible before firing. For infusibility, known methods such as oxidation and crosslinking polymerization are employed.

In addition, the ceramic molded article according to the present invention can be formed by mixing silicon carbide powder and whiskers, and after drying, coating the surface with a slurry of silicon carbide powder or a solution of organosilicon polymer, and drying it with an inert gas. It can also be produced by firing inside.

Generally, fibers used to reinforce silicon carbide ceramics need to be able to withstand the temperatures required for sintering silicon carbide. The usual sintering temperature of silicon carbide powder is preferably 1,900°C or higher and 2,100°C or lower. Therefore, carbon fibers and silicon carbide fibers are used as reinforcing fibers, and long fibers are usually used. Based on recent research, when organosilicon polymers are used as sintering aids or raw materials, the sintering temperature of silicon carbide can be lowered to around 1,300°C, and therefore, in addition to carbon fibers and silicon carbide fibers, silicon nitride It can be assumed that fibers can also be used. However, when actually firing, the organosilicon polymer has a considerably significant firing shrinkage of more than about 15%, making it difficult to fire it together with long fibers.

Also, even if it appears that the firing is successful, -i
It becomes fragile.

The present inventor has conducted research to solve these problems, and has developed ceramic composite materials using short fibers, particularly milled fibers or whisker ceramic fibers as reinforcement materials, using organosilicon polymer as a raw material or a part of the raw material or sintered material. In the case of the silicon carbide ceramic composite material used as an auxiliary agent, the firing shrinkage was as small as about 9 to 3%, and it was confirmed that there was no such problem. Therefore, in the present invention, the reinforcing short fibers include milled fibers such as carbon fibers, silicon carbide fibers, silicon nitride fibers, and alumina fibers, silicon carbide fibers,
Inorganic short fibers having a decomposition point of 1.200° C. or higher, which is the firing temperature of an organosilicon polymer such as a whisker such as silicon nitride, carbon, alumina, titanium]-potassium octate, etc., are used.

In addition, organosilicon polymers can be mixed as a powder with ceramic short fibers (and silicon carbide powder), molded and fired, or molten organosilicon polymer and ceramic short fibers (and silicon carbide powder) can be molded and fired. However, in the present invention, the organosilicon polymer is dissolved in a suitable organic solvent, ceramic short fibers (and silicon carbide powder) are dispersed in the solution, injection molding or casting is performed to form a sheet, and this sheet is fired. The most preferred method is This is because this system is extremely easy to mix.

The amount of short fiber used is 1 based on the weight of the precursor sheet.
0% or more is preferable, and 20 to 60% is particularly preferable. In addition to short fibers, silicon carbide powder can also be used.

Silicon carbide powder is 60% based on the weight of the precursor sheet.
%, and the total amount of short fibers and silicon carbide powder is preferably 90% or less.

B The method of using an organosilicon polymer solution as described above tends to create uneven distribution of short fibers (and silicon carbide powder) in the sheet 1 to 1 when producing the precursor sheet, and therefore,
Short fibers and silicon carbide powder are substantially present on the surface (upper layer) of the sheet, and in the center and bottom (lower layer),
Shorty! A large amount of fiber (and silicon carbide powder) will be present. Therefore, by stacking two of these sheets so that their bottom surfaces are in contact with each other, the surface is made essentially only of organosilicon polymer, and the inside is rich in short fibers (and silicon carbide powder) and contains an appropriate amount of organosilicon polymer. Contains green sheets (raw materials for firing).

Furthermore, it may be preferable to further cover the outside with a dense silicon carbide ceramic layer, for example, a layer formed by CVD method, and even in such cases, the above-mentioned method gives favorable results. However, it has been found that bonding of cast sheets as described above is an extremely effective method for suppressing or preventing bending of cast green sheets.

The organosilicon polymer used in the present invention is a polymer that becomes a silicon carbide ceramic when fired, such as poly]2 silane, polycarbosilane, polysilastyrene, and polycarbosilastyrene. Polymers are particularly preferred. Part or all of these organosilicon polymers may be calcined before use. Calcination refers to heating these polymers to a temperature of approximately 400 to 500°C, at which a large amount of decomposed gas is generated. This operation can reduce the amount of gas generated during firing.However, this operation reduces the adhesiveness of the organosilicon polymer, and in some cases, the adhesiveness of the organosilicon polymer is It may be necessary to add.

When adding silicon carbide powder, it is preferably a highly purified and fine powder. The particle size of the powder is 10 μm or less, preferably 2 μm or less, particularly preferably about 0.2 μm. Adding silicon carbide powder is useful in bringing the internal carbon/silicon ratio of the resulting ceramic composite closer to 1:0.

If necessary, it is preferable to subject inorganic short fibers such as whisker milled fibers to a surface treatment in advance, and this treatment may be similar to the surface treatment of carbonized carbon fibers or the treatment of silicon nitride from 71 to Lix ceramics. For example, JP-A-63-277563 and JP-A-277566 disclose that compounds such as boron, beryllium, silicon, and aluminum are effective, and the same applies to the present invention.

A glue may be added when forming into a green sheet. This makes it possible to easily handle the green sheet, that is, the precursor, which is a molded product of the raw material. The use of glue may be preferred to enhance adhesion, depending on the choice of organic adhesive polymer.

Similarly, other sintering aids such as organic carboxylic acids, boron, etc. may be added separately. Even when an organosilicon polymer is used, depending on the selection of the organosilicon polymer, it may be preferable to enhance sinterability.

When using organosilicon polymers, it may be preferable to render the molded article invulnerable prior to firing. Vitrification of the silicon carbide component from the organosilicon polymer is a measure that can increase the effect and at the same time increase the amount of residue after firing, and may be essential depending on the organosilicon polymer. For this infusibility method, methods mainly used for producing fibers, such as surface oxidation, crosslinking polymerization, and iodine infusibility, can be applied mutatis mutandis.

The laminated molded product precursor (green sheet) and infusible molded product precursor are subjected to pressure and heat treatment if necessary, and then fired in an inert gas atmosphere such as nitrogen or argon. The firing temperature is selected depending on the raw material composition. Generally, when containing an organosilicon polymer, 1200 to 1.800 °C
is suitable, particularly preferably 1,300 to 1.500
It is ℃.

[Effects of the Invention] According to the present invention, a molded composite ceramic mainly composed of silicon carbide and having good atmospheric resistance such as oxidation resistance and excellent thermal shock resistance can be obtained, and this composite ceramic can be used in a wide variety of applications. It can be used as an improved ceramic for various purposes.

For example, it is useful as a heat-resistant LY8 silvicultural material, a heater that is resistant to thermal shock, and the like.

[Example] Next, Examples and Comparative Examples of the present invention will be given, but the present invention is not limited thereto. In addition, unless otherwise specified, "parts" in each example are parts by weight.

Example 1 and Comparative Example] Polysilastyrene was obtained by polymerizing equimolar amounts of dichlorodimethylshicine and dichloromethylphenylsilane in toluene with the addition of metallic sodium. This polysilastyrene was treated at 400'C in a nitrogen atmosphere for 60 minutes to obtain a polycarbosilastyrene copolymer with a softening point of 190 to 200C.

100 parts of this polymer was dissolved in 150 parts of 1- to luene, and a commercially available silicon nitride whisker (manufactured by Ube Industries: 5N-W) was dissolved.
Mix with 100 parts of BI and cast the resulting suspension onto a flat substrate to form a sheet. The obtained sheet was heated to 1.300°C at a rate of 50°C/hr in a nitrogen stream, and
After a while, it was brought back to room temperature and fired. The resulting product has a thickness of approximately 0
．． Although the composite molded product had a good thickness of 6 mm, the surface was somewhat rough.

In the same manner, a cast sheet was obtained, and as it was, it was heated at 240°C, 4t/
Press with cJ. The obtained sheet has a dense surface and is heated to 1.300°C at a rate of 50°C/hr in a nitrogen stream.
Raise the temperature to 6 hours, then return to room temperature and continue baking. The obtained product was a good composite molded product, and the surface was apparently dense.

Two similarly obtained casting sheets were placed one on top of the other so that the surfaces in contact with the casting substrate were in contact with each other, and heated at 240°C54.
It was pressed at a pressure of t/cr&. The obtained sheet has a dense surface and is heated at a rate of 50°C/hr in a nitrogen stream.
．． The temperature was raised to 300°C, and the temperature was returned to room temperature for 6 hours for firing. The obtained product was a good composite molded product and had a dense surface.

These three samples were placed in an electric furnace at 1.200°C and held for 100 hours. When the first sample was taken out and the weight change was measured, it was found that the weight of the first sample had decreased by 14%.
The second sample had a weight loss of 2.1%, but the third sample had a weight loss of about experimental error (substantially no change).

Example 2 and Comparative Example 2 100 parts of the polysilastyrene was dissolved in 160 parts of toluene to form a solution, and 200 parts of silicon carbide (Ultra Fine J manufactured by IBIDEN) and 100 parts of the same silicon nitride whiskers as in the example were added to the solution. Dispersion.

This was cast in the same manner, and the two sheets obtained by drying were pasted together with the substrate surface at the time of casting facing inside. Press as in Example 1 above. However, the temperature is 270℃ and the pressure is 4t/
−.

The obtained sheet and the sheet immediately after casting and drying were fired at 1,300° C. in a nitrogen stream. 1 at a rate of 50℃/hr
．． The temperature was raised to 300°C, and after 6 hours, the temperature was returned to room temperature for firing.

All of the fired products were good composite ceramics.

However, while the former had a dense surface, the latter had a slightly rough surface.

After holding these in an electric furnace at 1,200°C for 100 hours, the weight change was less than 1% for the former and 7% for the latter.

Example 3 and Comparative Example 3 100 parts of the commercially available silicon carbide powder (manufactured by Ibiden [Ultra Fine J]), 100 parts of the same silicon nitride whisker as in Example 1, 10 parts of carbomethoxycellulose, and 10 parts of carbon powder were mixed. This was hot-pressed at 180°C, and the resulting sheet was dried at a rate of 50°C/hr in an argon stream and fired at 1,500°C. The fired product had a thickness of 1.0 mm and was a good composite ceramic material. However, the surface was rough.

A polycarbosilastyrene copolymer with a pour point of 240°C obtained in the same manner as used in Example 1 was dissolved in toluene and applied uniformly to this sample, and dried to form a copolymer layer. Ta. This was fired at 1.300°C in a nitrogen stream. The temperature was increased at a rate of 50°C/hr, and the mixture was cooled over 6 hours after the temperature was raised. The surface became blackish and dense glassy.

This sample and the original baked sample are 1200
Hold at 'C for 10 hours and check the conductivity. The original sample had lost its conductivity and the treated sample had 4 Ωam. Note that the weight of the original sample has increased by 6%,
The treated samples showed virtually no change.

Example 4 Pour points of 120°C and 240°C were prepared in substantially the same manner as in Example 1.
°C polycarbosilastyrene copolymerization was obtained.

Grind 100 parts of the former and 300 parts of the latter on a mixing table, and dissolve the pulverized product in 500 parts of toluene. To this solution, 400 parts of silicon carbide powder (“Ultra Fine” manufactured by IBIDEN),
and silicon nitride whiskers (manufactured by Ube Industries: 5N-WB)
) 400 parts were dispersed and cast onto a "Teflon" film to obtain a sheet after drying. Two of the obtained sheets,
After hot-pressing and heat-bonding the surfaces that will be in contact with Teflon, it was heated at 50°C/hr in a nitrogen stream for 1.30°C.
Raise the temperature to 0℃ and do not bake. A good composite material molded product was obtained.

Example 5 100 parts of the polycarbosilastyrene copolymer of Example 4 was dissolved in 160 parts of xylene. Add to this a commercially available silicon carbide whisker (“Tokamax J” made by Tokai Carbon).
100 parts and 200 parts of the silicon carbide powder used in Example 3 were added and mixed, and the mixture was cast into a mold and dried to form a flat thin sheet.

The two obtained sheets were laminated so that the lower surfaces at the time of casting were in contact with each other, heated and pressurized, and heated and infusible in a high-temperature bath. In an air atmosphere, the temperature was gradually increased and finally held at 230°C for 3 hours. The total heating time is 15 hours.

After cooling, the obtained sheet was taken out and fired in a firing furnace in a nitrogen atmosphere. Place it in a nitrogen-substituted firing furnace, gradually raise the temperature while flowing nitrogen, and finally raise the temperature to 1300°C and do not fire. Total heating time is 36 hours, 1,30
When the temperature reached 0° C., the temperature was started to decrease and the temperature was returned to room temperature in 12 hours, and a good sample with a dense surface was obtained.

Example 6 The polycarbosilastyrene copolymer of Example 4 was calcined by heating to 600'C in a nitrogen stream. 100 parts of the original polycarbosilane were dissolved in 150 parts of toluene. 200 parts of the above-mentioned calcined polycarbosilane and 100 parts of the silicon nitride whiskers used in Example 1 were added and mixed, and the mixture was poured into a mold and dried to form a flat thin sheet.

These two sheets were bonded together under heat and pressure in the same manner as in Example 4. The obtained sheet was heated and infusible in a high temperature bath in the same manner as in Example 5. In an atmospheric atmosphere, the temperature is gradually increased until finally 2.
Hold at 30°C for 3 hours. Total heating time is 15 hours. After cooling, the obtained sheet was taken out and fired in a firing furnace in a nitrogen atmosphere.

Place it in a nitrogen-substituted firing furnace and gradually raise the temperature while flowing nitrogen until it reaches 1,300°C and do not fire it. The total heating time was 36 hours. When the temperature reached 1jOO'C, start lowering the temperature and return it to room temperature in 12 hours.

In this way, a good composite molded product with a dense surface was obtained.

Example 7 Polysilane was obtained by polymerizing dichlorodimethylsilane in toluene with the addition of metallic sodium. This polysilane was treated at 450° C. in a nitrogen atmosphere for 30 hours to obtain a polycarbosilane polymer. The softening point of this copolymer is 2
The temperature is 20°C.

100 parts of this polycarbosilane was dissolved in xylene.

100 parts of the silicon nitride whiskers of Example 3 and 100 parts of silicon carbide powder were added and mixed, and the mixture was poured into a mold and dried to form a flat thin sheet.

Two of the obtained sheets are heated and pressed together with their bottom surfaces facing each other during casting, and heated in a high temperature bath to make them invulnerable. The temperature was gradually raised one after another in an air atmosphere and finally held at 230°C for 3 hours.

Total heating time is 15 hours.

After cooling, the obtained sheet is taken out and fired in a firing furnace in a nitrogen atmosphere. The product was placed in a nitrogen-substituted firing furnace, and the temperature was gradually raised while nitrogen was flowing, and finally the temperature was raised to 1.300°C, and fired. Total heating time is 36 hours, 1.30
Start lowering the temperature when it reaches 0°C and return it to room temperature within 12 hours. The obtained sample had a dense surface, was a good composite molded product, and did not break even when repeatedly heated to 1,000°C and cooled.

Example 8 Polycarbosilastyrene copolymer 75 with a pour point of 240°C
25 parts of a polycarbosilastyrene copolymer having a pour point of 120°C was dissolved in 100 parts of toluene, and 50 parts of the silicon nitride whiskers used in Example 1 were dispersed therein.

This was cast, peeled and recovered, and a toluene solution of polycarbosilastyrene copolymer was applied to the cast surface, and the two sheets were pressed together by butting the coated surfaces together.

The sheet was dried, held in the atmosphere for 6 hours at 120°C, 6 hours at 180°C, and 6 hours at 210°C, cooled, taken out, and fired in a nitrogen atmosphere. The firing temperature is 1.3
Raise the temperature to 00℃ in 28 hours. After cooling, take it out to obtain a short fiber reinforced ceramic fired product with a dense surface.

Claims (6)

[Claims] (1) A composite ceramic sheet-like molded article characterized in that the surface layer is a dense layer mainly made of silicon carbide, and the inside is a composite material layer containing inorganic short fibers in a matrix mainly made of silicon carbide. (2) A claim in which the dense layer mainly composed of silicon carbide constituting the surface layer and the matrix mainly composed of silicon carbide constituting the internal composite material layer are both formed by firing the same type of organosilicon polymer ( 1) The composite ceramic sheet-like molded article described above. (3) The dense layer that makes up the surface layer is formed by firing an organosilicon polymer, and the matrix that makes up the internal composite material layer, which is mainly silicon carbide, is made by sintering silicon carbide powder and organosilicon polymer. The composite ceramic sheet-like molded article according to claim 1, which is a composite ceramic sheet-like molded article that is fired using a composite ceramic material. (4) Dissolve the organosilicon polymer in a solvent, suspend inorganic short fibers in the resulting solution, inject it into a mold or cast it on a substrate to form a sheet, and then use this sheet as a mold or A method for producing a composite ceramic sheet-like molded article, which comprises removing the sheet from the substrate, laminating the two sheets so that their downward surfaces touch each other during molding, and firing the obtained laminate. (5) Dissolve the organosilicon polymer in a solvent, inject inorganic short fibers and silicon carbide powder into a suspended mold in the resulting solution, or cast it onto a substrate and form it into a sheet. A composite ceramic sheet-like molded product, characterized in that the sheet is removed from the mold or the substrate, the two sheets are laminated so that their downward surfaces touch each other during molding, and the resulting laminate is fired. Production method. (6) Production of a composite ceramic sheet-like molded product according to claim (4) or (5), wherein the organosilicon polymer is any one of polysilane, polycarbosilane, polysilastyrene, and polycarbosilastyrene copolymer. Method.