JPH04238874A - Ceramic form and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title form imparted with sufficient mechanical strength and crack resistance, also improved in the high-temperature strength of the baked form therefrom, by incorporating a ceramic stock with ceramic powder or ceramic fibers of specific composition followed by molding. CONSTITUTION:The objective form incorporated with amorphous or crystalline ceramic fibers or powder comprising (A) 50-70wt.% of Si, (B) 10-30wt.% of N, (C) <=20wt.% of C, and (D) as impurities, <=5wt.% of O. The fibers or powder can be obtained by melt spinning of polysilazane followed by baking or pyrolysis.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a ceramic molded body having good mechanical strength and a method for manufacturing the same, and in particular:
The present invention relates to a ceramic molded body whose green strength can be improved by blending ceramic fiber or ceramic powder, and which can improve the high-temperature strength of ceramics obtained by firing the same, and a method for producing the same.

0002

[Prior Art] Ceramic sintered bodies are generally produced by forming ceramic powder into a certain shape to make a compact (green).
Obtained by sintering. Ceramics are difficult to process once sintered, so they are formed into a desired shape before sintering. Methods for manufacturing such ceramic molded bodies include pressing using a mold, injection molding, slip casting by casting ceramic slurry into a plaster mold, cold isostatic pressing using a rubber press, etc. However, in order to obtain thin-walled objects or molded objects with complex shapes, there is a slip casting method in which ceramic slurry (or kneaded material such as resin) is injected into a mold of a predetermined shape.
Injection molding method, molding method using a doctor blade, etc. are preferred.

In the slip casting method, a ceramic raw material is powdered and dispersed in water, and the resulting slurry is placed in a plaster mold to absorb and permeate water. As a result, a molded body (green) in which the ceramic powder is solidified is obtained.

By the way, silicon nitride ceramics have excellent heat resistance, high strength, high hardness, and are relatively lightweight, so they have been attracting attention as materials to replace metal materials. This silicon nitride ceramic is generally difficult to sinter, so Y2 O3 and Al are added to the silicon nitride powder.
A molded body was first produced by the slip casting method described above by adding powder of a sintering aid such as 2 O3 and other additives, and this was then sintered.

[0005]

[Problem to be Solved by the Invention] However, when a ceramic molded body is made by the above-mentioned slip casting method, even if a binder or the like is mixed with the ceramic powder, the bonding force between the ceramic powder particles is not necessarily large. , mechanical strength is not high and there is a high risk of breakage. Further, the ceramic molded body shrinks due to dehydration and drying in the plaster mold, and is likely to cause cracks. For this reason, it has been difficult to manufacture thin-walled molded bodies or molded bodies with complex shapes without fear of damage or cracks.

Therefore, in the production of silicon nitride ceramics, for example, a sintering aid such as Al2 O3 is made into fibers and added to the raw materials, thereby creating a (green)
Proposals have been made to increase the strength of the molded body. However, it is difficult to uniformly disperse the fibrous sintering aid within the molded body, and if the sintering aid is sintered in a non-uniformly dispersed form, the strength of the resulting ceramic will be reduced. In addition, when using the sintering aid in the form of fibers,
In order to improve sintering, it may be necessary to add a slightly larger amount of sintering aid, but in general, the higher the amount of sintering aid, the lower the high temperature strength of the resulting ceramic.

Therefore, an object of the present invention is to solve the problems of the prior art, provide a ceramic molded body with sufficient mechanical strength and crack resistance to prevent breakage and cracking, and furthermore, It is an object of the present invention to provide a ceramic molded body that can also improve the high-temperature strength of the resulting ceramic, and a method that can produce such a molded body with good yield.

[0008]

[Means for Solving the Problems] As a result of intensive research to achieve the above object, the present inventors have discovered that, when forming a ceramic molded body, it is possible to add ceramic fiber or ceramic powder of a specific composition to the ceramic raw material. They discovered that the strength of the resulting molded body is improved, and that the strength of the ceramics obtained by sintering at high temperatures is improved because the amount of sintering aid can be reduced, and the present invention was conceived.

That is, the first ceramic molded body of the present invention contains 50 to 70% by weight of Si, 10 to 30% by weight of N, 20% by weight or less of C, and 5% by weight of impurities.
It is characterized by containing an amorphous or crystalline ceramic fiber having the following composition of O.

The second ceramic molded body of the present invention also contains 50 to 70% by weight of Si, 10 to 30% by weight of N, 20% by weight or less of C, and 5% by weight or less of O as impurities. It is characterized by containing an amorphous or crystalline ceramic powder having a composition consisting of:

[0011] In a particularly preferred embodiment, a fiber obtained by melt-spinning and firing polysilazane and a powder obtained by thermally decomposing polysilazane are used as the ceramic fiber and ceramic powder, respectively.

[0012] Furthermore, the method for producing a ceramic molded body of the present invention includes 50 to 70% by weight of Si and 10 to 30% by weight of N.
A slurry is prepared by uniformly dispersing amorphous or crystalline ceramic fibers or ceramic powder having a composition consisting of 20% by weight or less of C, and 5% by weight or less of O as an impurity, and the slurry is shaped into a predetermined shape. It is characterized by being molded by casting into a mold and then dehydrated and dried.

The present invention will be explained in detail below. Although the present invention is applicable to any ceramic molded body, a silicon nitride ceramic molded body will be specifically explained here.

When producing ceramics mainly composed of silicon nitride, both α-type and β-type silicon nitride powders can be used, and the production methods include direct nitriding of Si and reduction of silica.・Nitriding method, silicon diimide thermal decomposition method, SiH4 +NH3 +N2 gas phase reaction method, etc. The silicon nitride powder has an average particle size of 3 to 0.
01 μm is preferable, more preferably 1.5 to 0.01 μm.
It is 0.1 μm.

[0015] Ceramic additives that can be added to silicon nitride include alumina, yttria, magnesia, calcia, aluminum nitride, etc., but in general, ceramics such as alumina, yttria, and magnesia are silicon nitride ceramics. In this case, it acts as a sintering aid.

[0016] Ceramics are Si3 N4 + Y2 O
3 +Al2O3 system, instead of adding sintering aid components such as Al2O3 or Y2O3 in the form of fibers to increase green strength, in the present invention, ceramic fibers or ceramic powders as detailed below are added. to improve green strength.

First, the ceramic fiber contains 5% by weight or less of O as an impurity, and Si; 50 to 70%.
Amorphous or crystalline ceramic fibers having a composition of weight %, N: 10 to 30 weight %, and C: 20 weight % or less are used. As such a ceramic fiber, one obtained by melt-spinning polysilazane and then firing it can be suitably used.

[0018] First, the method for manufacturing this ceramic fiber will be explained. The ceramic fiber used in the present invention is manufactured from polysilazane as described above, and this polysilazane is a combination of cyclosilazane such as (R2SiNR)3 (where R represents H or an alkyl group) and chlorosilane (RnSiCl4-n, but n=0,
1,2,3, R is H or an alkyl group).

First, hexamethylcyclosilazane (Me2SiNH)3 is used as cyclosilazane, and trichloromethylsilane is mixed therein as chlorosilane. The mixing ratio of hexamethylcyclosilazane to trichloromethylsilane is 1:1 to 1:5 in terms of molar ratio, preferably about 1:3. If the mixing ratio falls outside of this range, S
When i: 50 to 70% by weight, N: 10 to 30% by weight, and C: 20% by weight or less, it is impossible to obtain a ceramic fiber containing 5% by weight or less of O as an impurity. With such a composition, the mechanical strength and high-temperature strength of the ceramic after sintering can be maintained at high levels. On the other hand, if a ceramic fiber having a composition outside this range is used, no improvement in the mechanical strength and high-temperature strength of the ceramic can be expected.

[0020] The above-mentioned mixture of hexamethylcyclosilazane and trichloromethylsilane was heated at 190 to 195°C.
Heat to reflux. As a result, hexamethylcyclosilazane is ring-opened, and a chlorosilazane oligomer is produced.

[0021] The process of producing chlorosilazane oligomer from hexamethylcyclosilazane and trichloromethylsilane is completed in about 12 hours.

Furthermore, ammonia gas is blown into this solution to perform ammonolysis. The amount of ammonia gas to be blown is about 70 liters/hour, and the blowing is preferably carried out for 3 to 4 hours. Through this ammonolysis, the chlorosilazane oligomer becomes an aminosilazane oligomer.

[0023] Next, this aminosilazane oligomer is heated in an inert gas such as nitrogen gas to a temperature of about 250 to 400°C to undergo a deammonization process to prepare a thermoplastic polysilazane. The softening point of polysilazane can be adjusted by heating conditions, but is preferably about 50 to 200°C.

The obtained polysilazane is melted while being kept at a temperature above its softening point and then spun. The winding speed at this time is preferably about 100 to 400 m/min, thereby obtaining fibers with a diameter of 5 to 30 μm.

The obtained fiber is fired in an inert gas such as argon gas at 800 to 1400° C. for about 1 to 4 hours to form a fiber having the above composition (containing Si, N, and C in the above amounts, Further, a ceramic fiber containing O in the above amount as an impurity is obtained. Note that the diameter of the finally obtained ceramic fiber is about 1 to 20 μm.

[0026] The average diameter of the ceramic fibers used in the ceramic molded body is 20 μm or less, especially 3 to 10 μm.
μm, fiber length is 10 to 500 μm, especially 100 to 500 μm
The thickness is preferably 300 μm. If the average diameter and fiber length become too large, the dispersibility will decrease, there is a large possibility that defects will occur in the molded product after sintering, and the sintered density will decrease.

On the other hand, if the average diameter or fiber length is too small, a sufficient reinforcing effect cannot be obtained by adding ceramic fibers.

Next, to produce the ceramic powder for reinforcing the molded body used in the present invention, first, polysilazane is produced in the same manner as the above-mentioned method for producing ceramic fibers, and this polysilazane is heated while being sprayed at 800 to 1400°C. This can be done by disassembling it.

The average particle size of the obtained ceramic powder is 0.
The thickness is preferably 1 to 1 μm.

Ceramic fibers and ceramic powder obtained by such a method can be made amorphous or crystalline depending on the heat treatment conditions, but it is preferable to make them amorphous in view of sinterability. When amorphous ceramic fiber or ceramic powder is added to the ceramic raw material, the sinterability is improved and the amount of sintering aid can be further reduced.

A ceramic molded body is manufactured by adding the above-mentioned ceramic fiber or ceramic powder to silicon nitride, which is the main component, together with a sintering aid component. The proportion of ceramic fibers or ceramic powder produced from the above-mentioned polysilazane is preferably 1 to 10% by weight. Also, Al2 O3, Y2
The amount of the sintering aid such as O3 is preferably 3 to 8% by weight. If the amount of ceramic fiber or ceramic powder blended is less than the lower limit above, the reinforcing effect will not be sufficient,
Ceramic molded bodies are more likely to break or crack.

In addition to the above-mentioned components, the ceramic molded article of the present invention may optionally contain a small amount of an organic binder such as wax or resin, an organic substance, or metal fiber.

Next, a method for manufacturing the ceramic molded body of the present invention will be explained. First, silicon nitride powder, which is the main component, sintering aids such as Al2 O3 and Y2 O3, and ceramic fibers or ceramic powder made from polysilazane are uniformly dispersed in a dispersion medium consisting of water or an organic solvent to form a slurry. . At this time, all the ceramic raw materials may be mixed at the same time, but first Si3N, which has good dispersibility,
4 After blending the powder and Y2 O3 powder, Al2
Preferably, ceramic fibers or ceramic powders made from O3 powder and polysilazane are incorporated.

[0034] When water is used as a dispersion medium, it is preferable to add aqueous ammonia. Since NH4OH has good dispersibility, it is possible to prepare a ceramic slurry with high concentration and low viscosity, and after drying, a molded body with high density can be obtained. In addition, impurities such as sodium and calcium do not remain in the molded product after sintering, making it possible to obtain a high-purity sintered body.Furthermore, the glass phase at the grain boundaries can be reduced, increasing the high-temperature strength of the sintered body. (If the glass phase at the grain boundaries increases, the strength of the sintered body at high temperatures will decrease.) It is also suitable to use a highly polar organic solvent such as formamide as a dispersion medium in order to prevent oxidation of silicon nitride and maintain high high temperature strength of the sintered body.

[0035] In addition to the above components, a small amount of a binder or the like may be added.

Although there are no particular limitations in the present invention, the concentration of the slurry is preferably 40 to 60% by volume from the viewpoint of moldability.

[0037] In the present invention, in order to mold the molded article,
Injection molding, slip cast molding, molding using a doctor blade, etc. are applicable, and particularly good results are obtained in the case of slip cast molding.

In the case of slip casting, this slurry is cast into a mold made of a water-absorbing and water-permeable material such as plaster. The dispersion medium is separated through the mold so that the slurry is dewatered. After that, it is removed from the mold and dried thoroughly. During this dehydration and drying process, there is a risk of breakage or cracks in the compact, but because it is uniformly dispersed and reinforced with ceramic fibers, or because the ceramic powder works well as a binder, breakage and cracks are sufficiently prevented. can do.

Finally, the obtained silicon nitride ceramic molded body is sintered. In this sintering step, the ceramic fibers in the compact are melted and fluidized and lose their fiber shape, thereby forming a uniform ceramic. The ceramic powder will also be melted and incorporated uniformly within the ceramic matrix. As a result, a sintered body with good mechanical properties and heat resistance can be obtained.

[0040]

[Function] According to the present invention, the molded body made of solidified ceramic powder, which is very easily damaged, is reinforced by using ceramic fibers or ceramic powder as a reinforcing material, so that the mechanical strength and elongation of the ceramic molded body are improved. , strain resistance etc. can be significantly improved. Moreover, shrinkage of the ceramic molded body during drying can be reduced. As a result, damage and cracks in the molded body are significantly reduced.

The above effect can be obtained because when ceramic fibers are used, the ceramic fibers uniformly dispersed in the main component ceramic powder are moderately intertwined, resulting in improved mechanical strength such as tensile strength and breaking strength. This is thought to be due to not only an improvement in the resistance but also an increase in the elongation (bending) until breakage.

It is also believed that when ceramic powder is used as a reinforcing material, this reinforcing ceramic powder acts as a good binder and causes the main component ceramic particles to coagulate with each other.

Furthermore, regardless of whether ceramic fiber or ceramic powder is used, the sintering aid can be made into a fine powder, so the sintering aid can be distributed more uniformly than when using a fiberized sintering aid. can be dispersed, thereby reducing the amount of sintering aid added. This further improves the high temperature strength of the ceramics obtained by sintering. Furthermore, variations in high-temperature strength between products are also reduced.

According to the method of the present invention, the moldability of the ceramic molded body is improved as described above, so that a molded body with a complex shape can be easily produced.

[0045]

EXAMPLES The present invention will be explained in more detail with reference to the following examples.

Example 1 Hexamethylcyclosilazane and trichloromethylsilane were mixed in a molar ratio of 1:3. Add this mixture to 190
The mixture was heated under reflux for 12 hours while being maintained at ~195°C to obtain a chlorosilazane oligomer.

The obtained chlorosilazane oligomer was dissolved in cyclohexane, and ammonia gas was blown into this solution at a rate of 70 liters/hour for 3 hours to carry out ammonolysis to obtain an aminosilazane oligomer.

The obtained aminosilazane oligomer was heat-treated at 350° C. for 30 minutes in a nitrogen gas atmosphere to obtain a thermoplastic polysilazane.

This polysilazane is heated above its softening point to melt it, and the winding speed is 170, 300, and 400.
Each was spun at m/min. The average diameters of the resulting fibers were 15, 10, and 8 μm, respectively.

[0050] These fibers were heated to 120% in nitrogen gas.
It was fired at 0°C to obtain the desired reinforcing ceramic fiber.

[0051] All of the obtained ceramic fibers had a tensile strength level (30 kg/
mm2 or more).

Among the ceramic fibers obtained above, those with an average diameter of 8 μm (average fiber length 400 μm)
0.5 to 30 parts by weight, and silicon nitride powder (average particle size 0.5 to 30 parts by weight).
5 μm) 96 to 66.5 parts by weight, and yttria powder (
2.5 parts by weight of alumina powder (average particle size: 0.8 μm) and 1 part by weight of alumina powder (average particle size: 0.4 μm) were mixed uniformly in water using a ball mill.

[0053] Next, this mixture was poured into a plaster mold, a rotor-shaped molded body was formed by a slip cast molding method, and after being taken out from the plaster mold, the temperature was further slowly raised from room temperature and dried at 180°C for 15 hours. .

[0054] The fracture strength of the obtained molded body was determined according to JISR16.
It was measured in accordance with 01. The results are shown in Figure 1. Note that this molded product did not break or crack during handling, and the shrinkage after drying was small.

[0055] Next, this molded body was heated to 180°C in nitrogen gas.
Sintering was carried out at a temperature of 0° C. for 4 hours. The density of the obtained silicon nitride sintered body was 99% or more, and the shape accuracy was good. Next, the breaking strength of the fired body obtained by adding 5% by weight of fiber was measured by JI
Measured in accordance with SR1601 (1981). The results are shown in Figure 2.

Comparative Example 1 As a comparison, the ceramic fiber of Example 1 was not included, but instead alumina was made into a fiber to serve as a sintering aid (average diameter 3 to 5 μm, average fiber length 400 μm) 1
Part by weight, silicon nitride powder (average particle size 0.5 μm) 96
．． 5 parts by weight, yttria powder (average particle size 0.8 μm)
) 2.5 parts by weight was manufactured in the same manner as in Example 1, and the fracture strength was measured in the same manner as in Example 1. The results are also shown in Figure 2.

Example 2 Polysilazane was produced in the same manner as in Example 1. The obtained polysilazane was melted and spray pyrolyzed at 1000°C to obtain a ceramic powder.

5 parts by weight of the ceramic powder obtained above (average particle size 0.3 μm) and silicon nitride powder (average particle size 0.
．． 5 μm), 2.5 parts by weight of yttria powder (average particle size 0.8 μm), and alumina powder (
1 part by weight (average particle size: 0.4 μm) and uniformly mixed in water using a ball mill. Next, this mixture was poured into a plaster mold, a rotor-shaped molded body was formed by a slip cast molding method, and after being taken out from the plaster mold, the temperature was further slowly raised from room temperature and dried at 180° C. for 15 hours.

[0059] The fracture strength of the obtained molded body was determined according to JISR16.
01 (1981), Example 1
It was found that the ceramic molded body had good strength as well.

[0060]

Effects of the Invention As described above, the ceramic molded body of the present invention has ceramic fibers made by heat-treating fibers produced from polysilazane, or ceramic powder made by spraying polysilazane at high temperature as the main ceramic component. Since it contains as a reinforcing material, it has high mechanical strength and elongation until breakage (flexibility), and has a low shrinkage rate. Therefore, even if the ceramic molded body of the present invention is made thin or has a complicated shape, there is no risk of breakage or cracking.

Furthermore, according to the method of the present invention, since the amount of sintering aid added can be reduced, the resulting sintered body has high high-temperature strength.

The sintered body obtained from the ceramic molded body of the present invention has good mechanical strength and heat resistance, and is suitable for use in automobile parts such as rotor blades of turbochargers.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the amount of ceramic fiber added and the strength of the ceramic molded body obtained in Example 1.

FIG. 2 is a graph showing the breaking strength of the fired bodies obtained in Example 1 and Comparative Example 1 at temperatures from room temperature to 1300°C.

Claims (6)

[Claims] Claim 1: 50-70% by weight of Si and 10-3
A ceramic molded body characterized by containing amorphous or crystalline ceramic fibers having a composition of 0% by weight of N, 20% by weight or less of C, and 5% by weight or less of O as impurities. 2. The ceramic molded body according to claim 1, wherein the ceramic fiber is a fiber obtained by melt-spinning polysilazane and then firing it. 3. 50 to 70% by weight of Si and 10 to 3% by weight of Si;
A ceramic molded body comprising an amorphous or crystalline ceramic powder having a composition of 0% by weight of N, 20% by weight or less of C, and 5% by weight or less of O as impurities. 4. The ceramic molded body according to claim 3, wherein the ceramic powder is a powder obtained by thermally decomposing polysilazane. 5. The ceramic molded body according to claim 1, wherein the base material of the ceramic molded body is a silicon nitride ceramic. 6. 50 to 70% by weight of Si and 10 to 3% by weight of Si;
A slurry is prepared in which amorphous or crystalline ceramic fibers or ceramic powder having a composition consisting of 0% by weight of N, 20% by weight or less of C, and 5% by weight or less of O as impurities are uniformly dispersed. 1. A method for manufacturing a ceramic molded body, which comprises molding by casting into a mold of a predetermined shape, and dehydrating and drying the molded body.