JPH02217367A - Composite ceramic formed product and its production - Google Patents

Abstract

PURPOSE:To enable industrial production of formed products which can stand sufficiently elevated temperature and whose temperature can be raised in a relatively rapid rate by firing a preform obtained from an inorganic short-cut fibers suspending organosilicon polymer solution in an organic solvent. CONSTITUTION:An organosilicon polymer is dissolved in an organic solvent and inorganic short-cut fibers are suspended in the solution. The suspension is cast on a support or poured into a mold. The preform from which at least a part of the solvent is removed is fired in an inert atmosphere to give a ceramic formed product for electric resistance heating elements which is mainly composed 20 to 90divided by t.% of silicon carbide in which inorganic short-cut fibers are uniformly dispersed. The inorganic short-cut fibers are, for example, silicon carbide whiskers, potassium titanate whiskers, silicon nitride whiskers or the like. The organosilicon polymer is particularly preferably a polycarbosilane styrene copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a composite ceramic molded article for an electric resistance heating element that generates heat to a high temperature when energized, and a method for manufacturing the same. More specifically, a composite ceramic molded product (preferably a ceramic sheet) that provides an electrical resistance heating element that can sufficiently withstand high temperatures and can be heated relatively rapidly, and a method for industrially manufacturing the molded product. It is related to.

[Prior Art] It is a well-known fact that ceramics are used as a heating element for electric heaters, especially electric heaters for high temperatures. However, Hiramix has the disadvantage that it has low thermal shock resistance and is easily destroyed by rapid temperature changes. This drawback is particularly noticeable in large products that are prone to temperature distribution, and it is assumed that the temperature will be raised gradually during use, and it usually takes several minutes to raise the temperature to a specified level even for ultra-small products. be. Particularly in the case of heaters used at high temperatures, this problem is serious even though ceramics have high heat resistance, and even in thin sheet-like materials, the problem of thermal shock resistance is serious. Therefore, in a ceramic heater, the initial usage conditions and the usage conditions during the regular usage period are usually significantly different. For example, silicon carbide is a well-known heater material, but heaters made of silicon carbide are extremely susceptible to breakage when heated rapidly. For this reason, the use of this type of heater is almost limited to industrial use where it is relatively easy to adjust the temperature rise, and a heater having a thin sheet-like heating element has not yet been provided.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks of conventional ceramic heating elements, and provides a ceramic molded article that becomes a heating element that can raise the temperature relatively rapidly, and the molded ceramic material. The aim is to provide a method for manufacturing products industrially.

[Means for Solving the Problems] As a result of intensive research on the above-mentioned problems, the present inventors have found that in ceramics mainly composed of silicon carbide, a specific amount of short fibers is approximately The present invention was completed based on the discovery that by uniformly dispersing and containing it, thermal shock resistance can be significantly improved without impairing heat generation properties.

That is, the present invention provides a ceramic molded article for an electric resistance heating element mainly composed of silicon carbide, in which inorganic short fibers are almost uniformly dispersed in the molded article at a ratio of 20 to 90% by weight. be.

In recent years, it has been found that ceramics as composite materials can be provided with various new functions by selecting their composition. Among ceramics that change their composition, those that are reinforced by adding fibers are called fiber-reinforced ceramics.
mics = FRC).

This material is stronger than the original ceramic.

Improvements in toughness and thermal shock resistance can be expected rather than improvements in modulus.

From this point of view, the use of ceramic fibers such as silicon carbide fibers and/or fabrics thereof as reinforcing materials has already been considered. The present inventors have also studied such reinforcing materials, and found that if the coefficients of thermal expansion of the matrix ceramic and the reinforcing W4 material are not the same over a wide range, they are likely to break during use. In solving this problem, the present inventors have discovered that it is preferable to use short fibers, particularly milled fibers or whiskers, as the reinforcing material, and have arrived at the present invention.

The short fibers used in the present invention need to be able to withstand the temperatures required for sintering silicon carbide. The usual sintering temperature of silicon carbide powder is preferably i, ao
The temperature should be 0°C or higher and 2,200°C or lower.

Therefore, heat-resistant inorganic short fibers such as carbon whiskers and silicon carbide whiskers are used, and by adjusting the sintering conditions, silicon nitride whiskers and potassium titanate whiskers can be used. For example, if organosilicon polymers are used as raw materials or sintering aids, the sintering temperature can be lowered to about 1,200°C, so carbon whiskers, silicon carbide whiskers, and silicon nitride whiskers can naturally be used, and titanate Potassium whiskers can also be used.

The size of these whiskers is not particularly limited, but
Rather than those that are too fine, the diameter is about 1 to 2 μm and the length is 1
A thickness of about 0 to 100 μm is preferable.

A composite ceramic molded product having such a structure and having a matrix of ceramics mainly composed of silicon carbide can withstand a relatively rapid temperature increase due to energization, that is, a rapid start of the heating element. Such a composite ceramic molded article has a weight percentage of at least 20% or more9.
It is necessary to contain less than 0% short fibers. If the amount of short fibers is less than this, the compositing effect will be poor and the intended purpose will not be fully achieved. On the other hand, if the amount is more than this, it may not be possible to obtain a uniform resistance heating element, and in some cases, the molding itself may be difficult. The short fiber content is particularly preferably 3
It is 0-60%.

In addition, in practice, heating elements made of such composite ceramic moldings may break at the interface unless the linear expansion coefficients of the matrix ceramic and short fibers are similar over a wide temperature range. be. Carbon whiskers, silicon nitride whiskers,
Examples include a combination of silicon carbide whiskers and silicon carbide as a matrix conductive heating element. Such a combination is particularly effective among those included in the present invention.

A specific method for manufacturing such a composite ceramic molded product for a heating element includes adding a sintering aid to silicon carbide powder and dispersing it in water, and then separately dispersing it in water to form short particles such as whiskers.
Mix with l fiber, if necessary? There is a method of filtering it, molding it into a green sheet, and heating and firing it in an inert atmosphere to make ceramics. The firing temperature in this case depends on the type of whiskers used, but is at least 1,300 m
℃, preferably 1,800°C or more and 2,200°C or less. It is preferable to use an organosilicon polymer as the sintering aid, and when an organosilicon polymer is used as the sintering aid, benzene is used as the sintering aid.

It is also possible to dissolve it in an organic solvent such as alkylbenzene, add silicon carbide powder to this solution, mix it, dry it, crush it, add whiskers, etc., mix it thoroughly, heat press it, and heat and bake it as a green sheet. .

When at least a portion of the silicon carbide raw material is an organosilicon polymer, it is dissolved in an organic solvent, and short particles such as whiskers and, if necessary, silicon carbide powder are added to this solution to form a suspension. This suspension can also be cast onto a support or poured into a mold or the like, dried, removed and heated and fired.

This method is particularly advantageous when producing sheets with special shapes, for example notches. In the case of a sheet-shaped heating element, it is necessary to generate heat uniformly in the sheet in order to uniformly heat the object to be heated. It is preferable that the shape has the following. In order to efficiently obtain such a heating element sheet, it is preferable to form a raw material intermediate into the shape, and the latter method, the casting/casting method, has the advantage of being easy to carry out.

The silicon carbide powder used here is preferably a fine powder with high purity. The particle size of the powder is 10 μm or less, preferably 2 μm or less, particularly preferably about 0.2 μm. Organosilicon polymers are polysilane, polycarbosilane, and polysilastyrene.

Polymers that become silicon carbide-based ceramics when fired, such as polycarbosilastyrene copolymers, are preferred, and polycarbosilastyrene copolymers are particularly preferred.

According to this method, thin sheets with a thickness of 1 mm or less, which were conventionally thought to be difficult to manufacture, can be easily manufactured.

In the molded product of the present invention, if necessary, the surface layer of the molded product can be covered with a layer having a relatively higher volumetric electrical efficiency than the inner layer of the molded product.

[Effects of the Invention] According to the present invention, there is provided an electrical resistance heating element that is made mainly of silicon carbide and that does not break even when the temperature is changed relatively rapidly. This composite ceramic heating element is easier to use than conventional heaters of the same type, and can be used in a wide variety of applications from household to industrial use.

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

100 parts of the above polycarbosilastyrene copolymer to 13
Dissolved in 0 parts of toluene and mixed with 100 parts of Tokamax ■ silicon carbide whiskers manufactured by Tokai Carbon ■ from which lumps had been removed.The resulting suspension was cast onto a support and dried. (solvent removal) to form a sheet. The obtained sheet was fired at 1.500° C. in argon to obtain a composite ceramic sheet. This ceramic sheet was repeatedly passed through electricity until it became red hot for 2 minutes, but it did not break even after 10 times.

Example 2 Polycarbosilastyrene copolymer 10 used in Example 1
Dissolve 0 part in 130 parts of toluene and add silicon carbide whiskers [Tokamax J 100] manufactured by Tokai Carbon ■.
Department and IBIDEN (IIar Ultra Fine J 200
1q of the suspension was cast and dried to form a sheet. The obtained sheet was placed in a nitrogen stream for 1,30
Fired at 0℃ to make a composite ceramic sheet (q.

This ceramic sheet has an electrical resistance of 1 Ωcm, and it was repeatedly passed through electricity for about 2 minutes until it became red hot.
It did not break even if it was performed 0 times.

Example 3 Polycarbosilastyrene copolymer 10 used in Example 1
Dissolve 0 parts in 130 parts of xylene and add commercially available silicon carbide whiskers [manufactured by Tokai Carbon ■ [Tokamax ■ J] 5
0 parts were added, mixed, dried and ground. This powder was hot-pressed at 4t/cm2 and 240℃ to a thickness of 0.7Il.
It was made into a sheet of llIl.

This sheet is heated to 210°C in the atmosphere to make it infusible,
The temperature was raised at 50° C./hr in a nitrogen stream, and the material was fired at 1,300° C.

The electrical resistance of the obtained composite ceramic sheet is 10 cm
I repeatedly passed electricity through it for about 2 minutes until it became red hot, but it did not break even after 10 attempts.

Example 4 Polycarbosilastyrene copolymer 10 used in Example 1
Dissolve 0 parts in 130 parts of toluene and add potassium titanate whiskers [manufactured by Daikyu Kagaku ■] to this.
O parts were dispersed, 1q of the suspension was cast on glass, and dried and peeled off. The molded product was heated for 5 minutes in a nitrogen stream.
The temperature was raised to 1,250″C at a rate of 0°C/hr for firing.

The 1q sample (ceramic sheet) had some damage, but the unbroken parts were conductive and could glow red hot after being repeatedly energized.

Example 5 Polysilane was obtained by polymerizing dichlorodimethylsilane in toluene with the addition of metallic sodium. This polysilane was treated at 450° C. for 30 hours in a nitrogen atmosphere to yield 1 q of polycarbosilane polymer. The softening point of this polymer is 2
The temperature is 20°C.

This polycarbosilane was heated to 600° C. in a nitrogen stream and calcined. 30 parts of the remaining sample and 70 parts of polycarbosilane were dissolved in xylene. Add commercially available silicon carbide powder [manufactured by IBIDEN ■ [Ultra Fine ■] to this solution.
J] and 100 parts of commercially available silicon nitride whiskers [5N-WI3 manufactured by Ube Industries Ltd.] were added and mixed, and the mixed solution was charged into a mold and dried to form a flat sheet.

The obtained sheet was heated in a high temperature bath to make it infusible. 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 jqed sheet was taken out and fired in a firing furnace in a nitrogen atmosphere. That is, the sheet was placed in a firing furnace purged with nitrogen, and the temperature was gradually raised while nitrogen was flowing, and finally the temperature was raised to 1,300° C. and fired. The total heating time was 36 hours, and when the temperature reached 1,300°C, the temperature started to decrease, and the temperature was returned to room temperature in 12 hours.

The resulting sample was electrically conductive and could be uniformly heated to red by repeatedly passing electricity through it.

Example 6 Polycarbosilastyrene copolymer 100 same as Example 1
1 part was dissolved in 130 parts of toluene, mixed with 100 parts of commercially available silicon nitride whiskers (5N-WB manufactured by Ube Industries, Ltd.), and 1 q of the solution was cast onto a support to form a sheet. The obtained sheet was successively heated to 210°C in the atmosphere to make it infusible, and then heated in an inert gas at a rate of 50°C/h for 1,3
The temperature was raised to 00°C, and after 6 hours, the temperature was returned to room temperature and fired. 1q
The thickness of the product obtained was 150 μm.

Electrical resistance was 30 cm.

This sample was repeatedly heated to 1,100°C by passing electricity through it for 5 minutes and then cooled down, but no noticeable cracks appeared even after 7 times.

Comparative Example 1 The same polymer as in Example 1 was melted and 230
A sheet-like molded product having a thickness of about 180 μm was extruded at 191° C., and the temperature was successively raised to 210° C. in the atmosphere to make it infusible. This infusible material was heated to 1,300° C. at a rate of 50° C./hr in an inert atmosphere, and returned to room temperature in 6 hours for firing. The thickness of the obtained product was 150 μm, and the electrical resistance was 0.80 CIII. When this sample was repeatedly heated to i,ioo°C by passing electricity through it for 5 minutes and then cooled down, a crack appeared five times.

Example 7 Same polycarbosilastyrene copolymer 100 as Example 1
300 parts of the silicon carbide powder and 1 part of the silicon nitride whiskers of Example 1 were dissolved in 130 parts of toluene.
00 parts were dispersed. The sheet obtained by casting and drying this was infusible by raising the temperature to 210° C. in the air, and was fired at 1,300° C. in an inert atmosphere. The thickness of the fired product is 0
．． 7 mm, and the electrical resistance was 40 cm. This sample was subjected to electrical continuity and temperature rise tests in the same manner as in Example 1.

No "cracks" were observed even after the 6th test.

Comparative Example 2 80 parts of silicon carbide powder (Mitsui Toatsu N5C-20) and 20 parts of the polycarbosilastyrene copolymer used in Example 1
and 10 parts of carboxymethyl cellulose (CMC) were added and pressed to form a sheet, and the sheet was diluted with 1.
It was fired at 300°C. The 1q ceramic sheet had a thickness of 1 mm and a volume resistivity of 3 Ωcm. This sample was subjected to electrical continuity and temperature rising tests in the same manner as in Example 6, but the occurrence of "cracks" was observed in the sixth test.

Comparative Example 3 Polycarbosilastyrene copolymer 10 used in Example 1
0 part was dissolved in 200 parts of toluene, 900 parts of the silicon nitride whiskers used in Example 6 were added to form a sheet, and the ceramic sheet was fired under the same conditions as Example 1 to form a ceramic sheet. However, this product did not become a practical ceramic heater.

Example 8 Commercially available silicon carbide powder [manufactured by Showa Denko: r
DENsIc ULTRAFINEJ A-23] 1
A small amount of water was added to 00 parts of carboxymethylcellulose (CMC), 25 parts of carboxymethyl cellulose (CMC), and 1 part of carbon powder to form a slurry.

50 parts of silicon nitride whiskers used in Example 6.

A small amount of water was added to 0 parts of CMCl to form a slurry.

Both were mixed, a) filtered, and a sheet for the door body was made. It was placed in a thoroughly dried mold and molded using a hot press. The pressure is 2,000 KMccm2, m degrees is 1,
The temperature is 800°C. The electrical resistance of the obtained sample was 4X102
It was Ωcm. Although this product was repeatedly energized, no "cracks" were observed.

Claims (6)

[Claims] (1) A ceramic molded article for an electric resistance heating element mainly composed of silicon carbide, characterized in that inorganic short fibers are almost uniformly dispersed in the molded article at a ratio of 20 to 90% by weight. Composite ceramic molded product. (2) The composite ceramic molded article according to claim 1, wherein the inorganic short fibers are silicon carbide whiskers, potassium titanate whiskers, or silicon nitride whiskers. (3) The composite ceramic molded article according to claim (1), wherein the molded article is a sheet-like piece having a thickness of 1 mm or less. (4) After dissolving the organosilicon polymer in an organic solvent and suspending the inorganic short fibers in this solution, the solution is cast onto a support or poured into a mold, and at least a portion of the organic solvent is removed. 1. A method for producing a composite ceramic molded article for an electric resistance heating element, the method comprising taking out a preform obtained by the process and firing it in an inert atmosphere. (5) The manufacturing method according to claim (4), wherein silicon carbide powder is suspended together with inorganic short fibers in a solution in which an organosilicon polymer is dissolved in an organic solvent. (6) Claim (4) in which polysilane, polysilastyrene, polycarbosilastyrene copolymer, polycarbosilane, or a mixture thereof is used as the organosilicon polymer.
Or the manufacturing method described in (5).