WO2012046897A1

WO2012046897A1 - Method for manufacturing porous silicon carbide ceramics

Info

Publication number: WO2012046897A1
Application number: PCT/KR2010/006885
Authority: WO
Inventors: 김득중
Original assignee: 성균관대학교 산학협력단
Priority date: 2010-10-08
Filing date: 2010-10-08
Publication date: 2012-04-12

Abstract

The present invention relates to a method for manufacturing porous silicon carbide ceramics, and more particularly, to a method for manufacturing porous silicon carbide ceramics which have improved strength by virtue of the mesh network structure of same in which plate-shaped particles are mutually entangled, and which are formed through phase transformation in which beta-type silicon carbide powder is oxidation treated and sintering is prevented during heat treatment in order to transform the powder to an alpha phase as well as to rapidly grow the particles.

Description

Manufacturing Method of Porous Silicon Carbide Ceramics

The present invention relates to a method for producing porous silicon carbide ceramics, and more particularly, to prevent sintering during heat treatment by oxidizing beta-type silicon carbide powder, and to achieve a planar shape through rapid grain growth that occurs simultaneously with a phase change to an alpha phase. The present invention relates to a method for producing porous silicon carbide ceramics in which the particles are entangled with each other to improve the strength of the porous silicon carbide ceramics.

Silicon carbide has been developed for high temperature structural materials because of its excellent physical properties and chemical stability at high temperatures. In particular, porous silicon carbide ceramics are attracting attention as materials for diesel engine dust filters, heat exchanger power plant dust filters, and casting filters because of their excellent heat resistance, corrosion resistance, and thermal shock resistance.

Conventional methods for producing porous silicon carbide ceramics include partial sintering and recrystallization, reaction sintering, template, and polyurethane foam. In the case of these methods, the inter-particle bonding is partially formed, or in the case of using a polyurethane foam, which is the most preferred method, the place where the urethane is removed is removed at high temperature, and the void remains in the void space, and the strength is lowered. Has been.

An object of the present invention was devised to solve the problems of the prior art, the beta-type silicon carbide powder pre-treated using the point that the beta-type silicon carbide rapidly changes to alpha-type silicon carbide at a high temperature as a starting material It is to provide a high-strength porous silicon carbide ceramics of a network structure in which enormous plate particles are entangled, and a method of manufacturing the same.

Another object of the present invention is to provide a method for controlling the density, porosity, or pore size of the porous silicon carbide ceramics by adding various additives to the pretreated beta-type silicon carbide powder.

Still another object of the present invention is to provide a use of porous silicon carbide ceramics having the above excellent physical properties.

In order to achieve the above object, the present invention provides a porous silicon carbide ceramics of the network structure in which the plate-shaped particles are entangled with each other.

The invention also

Oxidizing the beta-type silicon carbide powder; And

It provides a method for producing porous silicon carbide ceramics comprising a heat treatment step of the oxidation-treated beta-type silicon carbide powder.

The present invention also provides a method for controlling the density and porosity of porous silicon carbide ceramics comprising the step of heat treatment by mixing the oxidized beta-type silicon carbide powder, the phase change promoting material and the sintering aid.

The present invention also provides a method for controlling pore size of porous silicon carbide ceramics, which comprises a step of mixing and heat-treating an oxidized beta-type silicon carbide powder, a phase change promoting material, and an alpha-type silicon carbide powder.

The present invention also provides diesel engine dust filters, porous heat exchanger dust filters, foundry filters, incineration dust filters, hot corrosive gas filters, CVD or burner gas distributors, or high temperature applications comprising porous silicon carbide ceramics of such excellent properties. To a membrane support for hydrogen separation and lightweight structural components.

The present invention, unlike the conventional partial sintering, recrystallization method, reaction sintering, template method, polyurethane foam method and the like has a disadvantage in that the strength is lowered due to weak particle bonding, the growth of particles and the cross-linked network structure Porous silicon carbide is formed by forming, and the porous silicon carbide of such a microstructure has an effect of maintaining a high strength due to strong bonding between particles.

Figure 1 shows the microstructure of the porous silicon carbide ceramics prepared using the oxidation-treated beta-type silicon carbide (Predmaterial) powder of the present invention.

Figure 2 shows the microstructure of the porous silicon carbide ceramics prepared using the oxidation-free beta-type silicon carbide (Predmaterial, Inc.) powder.

Figure 3 shows the microstructure of the sintered body prepared using the oxidation-treated beta-type silicon carbide (Ibiden) powder of the present invention.

Figure 4 shows the microstructure of the sintered body prepared using beta-type silicon carbide (Ibiden) powder not treated.

Figure 5 shows the porosity change of the specimen prepared by adding the sintering aid to the oxidation-treated beta-type silicon carbide powder of the present invention.

Figure 6 shows the microstructure of the specimen prepared by adding 5 parts by weight of the sintering aid to the oxidation-treated beta-type silicon carbide powder of the present invention.

Figure 7 shows the microstructure of the porous silicon carbide sintered body by adding the alpha-type silicon carbide seed (seed) to the oxidized beta-type silicon carbide powder of the present invention.

Figure 8 shows the change in pore size of the porous silicon carbide sintered body by the addition of alpha-type silicon carbide seed to the oxidation-treated beta-type silicon carbide powder of the present invention.

Figure 9 shows the change in strength of the silicon carbide sintered body according to the addition of alpha-type silicon carbide seed to the oxidized beta-type silicon carbide powder of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, the structure of this invention is demonstrated concretely.

The present invention relates to porous silicon carbide ceramics having a network structure in which plate-shaped particles are entangled with each other.

Porous silicon carbide ceramics of the present invention using a beta-type silicon carbide powder to prevent shrinkage due to sintering at high temperature and to control the particle growth of the alpha-type silicon carbide particles in the process of phase change to the alpha phase well shaped plate-shaped particles It is characterized by having a high strength by allowing the to form a network structure intertwined with each other.

The porous silicon carbide ceramics have a network structure and thus may exhibit high strength of 35 to 45 MPa according to the four-point strength measurement method.

In addition, the porous silicon carbide ceramics of the present invention exhibit a network structure of alpha-type silicon carbide particles through a phase change of the beta-type silicon carbide powder, and polymorphism transition analysis results through the pretreatment process of oxidizing the beta-type silicon carbide powder. Type 3C is characterized by the polymorphism transition to 6H to 30 to 100%.

Porous silicon carbide ceramics of the present invention represent a network structure of alpha-type silicon carbide particles, characterized in that the pore size of the network structure is 1 to 30 ㎛.

The invention also

Oxidizing the beta-type silicon carbide powder; And

It relates to a method for producing porous silicon carbide ceramics comprising the heat treatment step of the oxidation-treated beta-type silicon carbide powder.

In general, there are two types of silicon carbide beta phase and alpha phase, and the alpha phase is stable at high temperature, so when the beta phase silicon carbide raw material is used, the phase change occurs at an temperature of 2000 ° C. or higher. In this process, abrupt grain growth is observed. In the present invention, porous silicon carbide ceramics having a network structure are manufactured by using the steep grain growth simultaneously with the phase change to the alpha phase that occurs during the high temperature heat treatment process using the beta-phase silicon carbide powder as a raw material. Can be.

The beta-type silicon carbide powder may have a particle size of 10 nm to 2 μm, but is not particularly limited thereto.

In addition, most silicon carbide raw material powder has an oxide as an impurity on the surface, which acts as an obstacle to prevent sintering. Therefore, in order to manufacture the sintered body, it is a general method to remove the surface oxide through a carbon heat reduction reaction by further adding carbon to heat treatment at high temperature.

The present invention is to produce a porous ceramics of low density, the oxide present on the surface is effective for the production of silicon carbide porous in order to suppress the sintering in the heat treatment process and to generate grain growth by the evaporation-condensation process.

In order to manufacture the desired porous silicon carbide ceramics, oxides present on the surface of the silicon carbide raw material powder are used as they are or artificially heat-treated at 300 to 1400 ° C in air to remove excess carbon or oxides on the surface. It is good to form on the surface and use it as raw material powder.

On the other hand, when the non-oxidized beta-type silicon carbide powder is used, the porous silicon carbide ceramics having a relatively high density of the silicon carbide microstructure and the network structure in which the particles are grown are not produced, and the non-oxidized beta is not produced. Unreacted carbon is present in the type silicon carbide powder, which may adversely affect the preparation of the porous body.

The mixed raw materials may be molded into a desired shape and heat-treated at 1900 to 2200 ° C. to produce porous silicon carbide ceramics of high strength.

More specifically, the molded article may be placed in a graphite crucible and heated to 1000 to 1500 ° C. in a vacuum atmosphere, and the atmosphere may be changed to an argon atmosphere and raised to 1900 to 2200 ° C., followed by cooling for 0 to 180 minutes.

A phase change promoting material may be additionally used to promote phase change in the heat treatment of the oxidized raw material powder.

The phase change promoting material may be one or more metals or salts thereof selected from the group consisting of B, Al, or iron-based metals such as Fe, Ni, Cr, or the like, but is not particularly limited thereto.

The phase change promoting material may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the beta-type silicon carbide powder. This is because when the content is less than 0.1 part by weight, uniform mixing is difficult and when it exceeds 10 parts by weight, other compounds may be produced.

The present invention also relates to a method for controlling the density and porosity of porous silicon carbide ceramics comprising the step of mixing and heat-treating an oxidized beta-type silicon carbide powder, a phase change promoting material, and a sintering aid.

Density and porosity control method of the porous silicon carbide ceramics of the present invention is characterized by controlling the density and porosity of the ceramics by adjusting the amount of the sintering aid when the porous silicon carbide ceramics of the present invention. As the amount of the sintering aid increases, the density increases and the porosity decreases.

The oxidation treatment of the beta-type silicon carbide powder is as described above.

The oxidized beta-type silicon carbide powder may be included in an amount of 80 to 99.9 parts by weight based on 100 parts by weight of the mixed powder. If the content is less than 80 parts by weight, the properties are limited by the decrease in the number of manufactured products, and if it exceeds 99.9 parts by weight because the phase change is slow.

The type of phase change promoting material is as described above.

The phase change promoting material may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the mixed powder. This is because when the content is less than 0.1 part by weight, uniform mixing is difficult and when it exceeds 10 parts by weight, other compounds may be produced.

The sintering aid may be used alone or two or more kinds of organic polymers such as carbon or carbon remaining after heat treatment such as a phenol resin, but are not particularly limited thereto.

The sintering aid may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the mixed powder. As the amount of the sintering aid is increased, the microstructure of the silicon carbide ceramics exhibits a grain growth pattern of a general shape rather than a network shape, and the density of the sintered body. Increasing the porosity may decrease.

In addition, to control the density and porosity of the porous silicon carbide ceramics of the present invention may further include a removable organic material, that is, a plastic material that is decomposed at a high temperature during the heat treatment. The site where the plastic material was located may remain as pores after the heat treatment to decrease the density and increase the porosity.

The plastic material may be paper, sawdust, or organic polymer, but is not particularly limited thereto.

The density of the ceramics prepared according to the porosity control method of the porous silicon carbide ceramics of the present invention may be 10 to 80%, the porosity may be 20 to 90%.

The present invention also relates to a method for controlling pore size of porous silicon carbide ceramics comprising the step of mixing and heat-treating an oxidized beta-type silicon carbide powder, a phase change promoting substance, and an alpha-type silicon carbide powder.

The method for controlling the pore size of the porous silicon carbide ceramics of the present invention is characterized in that the pore size is controlled by adding an alpha type silicon carbide powder as a seed when the porous silicon carbide ceramics of the present invention are seeded.

The oxidized beta-type silicon carbide powder may be included in an amount of 90 to 99.9 parts by weight based on 100 parts by weight of the mixed powder. If the content is less than 90 parts by weight, the amount of seeds is increased, the structure is similar to the case of using the alpha-type raw material, and if it exceeds 99.9 parts by weight, the seed amount is small and the effect of addition is less.

The type of phase change promoting material is as described above.

The phase change promoting material may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the mixed powder. If the content is less than 0.1 parts by weight of the seed effect is small, if it exceeds 10 parts by weight because the seed amount is large because the structure is similar to the case of using the alpha-type raw material.

The alpha-type silicon carbide powder may be used having a particle size of 10 nm to 5 ㎛, but is not particularly limited thereto.

The alpha-type silicon carbide powder may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the mixed powder. As the content of the alpha-type silicon carbide powder increases, the porosity is similar, but the pore size becomes smaller.

In addition, to control the pore size of the porous silicon carbide ceramics of the present invention, it may further include a removable organic material that is decomposed at high temperatures during heat treatment, that is, a plastic material.

The kind of the plastic material is as described above.

The pore size of the ceramics according to the pore size control method of the porous silicon carbide ceramics of the present invention may be 1 to 30 ㎛.

The invention also provides diesel engine dust filters, heat exchanger power plant dust filters, foundry filters, incineration dust filters, hot corrosive gas filters, gas distributors for CVD or burners, or high temperature applications comprising the porous silicon carbide ceramics of the present invention. And a membrane support for hydrogen separation and lightweight structural components.

Porous silicon carbide ceramics of the present invention exhibit a network structure in which alpha-type silicon carbide particles are entangled with each other to maintain high strength, so that diesel engine dust filters, heat exchanger power plant dust filters, casting filters, incineration dust filters, and high temperature corrosive gases It can be used in filters, gas distributors for CVD or burners, or membrane supports for hydrogen separation and lightweight structural components for high temperature applications.

Hereinafter, the present invention will be described in more detail through examples according to the present invention, but the scope of the present invention is not limited to the following examples.

Example 1 Preparation of Porous Silicon Carbide Ceramics Using Oxidized Beta-Type Silicon Carbide Powder

After mixing β-silicon carbide (SiC) (Pred material) having an average particle size of 50-100 nm for 1 hour in air at 650 ° C, 1 part by weight of boron carbide was added to promote phase change, followed by mixing and drying. The starting powder was obtained by grinding. The powder thus obtained was uniaxially press-molded at a pressure of 150 MPa with a mold mold to prepare a molded body. The molded body was placed in a graphite crucible and the atmosphere was changed to 1450 ° C. in a vacuum atmosphere, and the atmosphere was changed to an argon atmosphere, raised to 2100 ° C., and then cooled for 10 minutes.

The heat treated specimens had a relative density of 53%, strength of 45 MPa, and average pore size of 7.26 ㎛.

The microstructure showed the network structure of FIG. 1 as the rapid grain growth progressed.

Comparative Example 1 Preparation of Porous Silicon Carbide Ceramics Using Beta-Type Silicon Carbide Powder without Oxidation

The specimen was prepared in the same manner as in Example 1 by adding 1 part by weight of boron carbide to the non-oxidized beta-type silicon carbide powder.

As shown in FIG. 2, the microstructure of the specimen exhibited a high density of 74%, and it was difficult to prepare porous silicon carbide ceramics having high porosity of the network structure in which the particles were grown as shown in FIG. 1. It was thought that about 3% of unreacted carbon was present in the powder of β-silicon carbide (SiC) (Pred material), which is a raw material used, and this was considered to adversely affect the preparation of the porous body.

Example 2 Fabrication of Ceramics Using Beta-Type Silicon Carbide with Less Oxide

After oxidizing high purity β-silicon carbide (Japan Ibiden Co. Ltd) powder having an average particle size of 0.3 μm as in Example 1, 1 part by weight of boron carbide was added to promote phase change, followed by mixing, drying, and grinding. Through this, two kinds of starting powders were obtained. The powder thus obtained was placed in a mold mold and press-molded at 150 MPa pressure to produce a disk-shaped molded body.

The molded product was placed in a graphite crucible and heated to 1450 ° C. in a vacuum atmosphere, raised from 1450 ° C. to 2100 ° C. in an argon atmosphere, and then cooled for 30 minutes.

As shown in FIG. 3, when the oxidized powder is used, sintering is inhibited by silicon oxide on the surface of the powder, so that phase change occurs and rapid grain growth proceeds, and the porous silicon carbide has a density of 52% and a porosity of 48%. The sintered compact of was manufactured.

Comparative Example 2 Preparation of Ceramics Using Silicon Carbide Powders

A specimen was prepared in the same manner as in Example 2 except that the silicon carbide powder of Example 2 was not oxidized.

As shown in FIG. 4, in the case of the sintered body using the non-oxidized powder, the sintering was partially performed, and the relative density was 82%, and the microstructure showed a general grain growth pattern.

Example 3 Density and Porosity Control of Silicon Carbide Ceramics by Addition of Sintering Aid

In order to see the change of silicon carbide sintered body according to the addition of carbon, 1 to 5 parts by weight of carbon was added to the powder oxidized by the method of Example 1 by using 1 part by weight of boron carbide and a liquid carbon resin as a sintering aid. It was.

As shown in FIGS. 5 and 6, as the amount of carbon added as the sintering aid increases, the silicon carbide microstructure shows the grain growth of the general form rather than the network type of FIG. 1, and the density of the sintered body is also increased to decrease the porosity. .

Example 4 Pore Size Control of Silicon Carbide Ceramics According to Seed Addition

In order to compare the microstructure of the silicon carbide sintered body according to the addition of α-silicon carbide, the experiment was conducted in the same manner as in Example 1, but α-silicon carbide (Norton) was added in an amount of 2 to 10 parts by weight, followed by sintering. It was.

As shown in Figures 7 and 8, the sintered compact showed a more dense network structure as the amount of α-silicon carbide added. That is, the pore size tended to decrease as the amount of α-silicon carbide added. The porosity of the addition of α-silicon carbide was similar from 53.5% to 55.5%, and the average pore size was 3.29㎛ at 2 parts by weight, 2.15㎛ at 5 parts by weight, and 2.11㎛ at 10 parts by weight.

In addition, as shown in Fig. 9, as the amount of α-silicon carbide addition increased, it showed a denser network structure, but the strength was similar to 33 to 36 MPa.

The porous silicon carbide ceramics of the present invention have a high strength due to the network structure, so that diesel engine dust filters, heat exchanger power plant dust filters, casting filters, incineration dust filters, hot corrosion gas filters, CVD or burner gas distributors, or It can be used for hydrogen separation for high temperature applications and membrane support for lightweight structural components.

Claims

Porous silicon carbide ceramics with a network of plate-shaped particles intertwined.
The method of claim 1,

Porous silicon carbide ceramics containing 30 to 100% of an alpha type polytype.
The method of claim 1,

Porous silicon carbide ceramics having an average pore size of 1 to 30 μm.
Oxidizing the beta-type silicon carbide powder; And

Method for producing a porous silicon carbide ceramics comprising the heat treatment step of the oxidation-treated beta-type silicon carbide powder.
The method of claim 4, wherein

Beta type silicon carbide powder is a method for producing porous silicon carbide ceramics having a particle size of 10 nm to 2 ㎛.
The method of claim 4, wherein

Oxidation is a method for producing porous silicon carbide ceramics which is heat-treated at 300 to 1400 ℃ in air.
The method of claim 4, wherein

Heat treatment is a method for producing porous silicon carbide ceramics carried out at 1900 to 2200 ℃.
The method of claim 4, wherein

Method for producing porous silicon carbide ceramics further comprising a phase change promoting material during heat treatment.
The method of claim 8,

Phase change promoting material is a method for producing porous silicon carbide ceramics comprising at least one metal selected from the group consisting of B, Al and iron-based metals or salts thereof.
The method of claim 9,

Phase change promoting material is a method for producing porous silicon carbide ceramics is contained in 0.1 to 10 parts by weight with respect to 100 parts by weight of the beta-type silicon carbide powder.
A method of controlling the density and porosity of porous silicon carbide ceramics comprising the step of mixing and heat-treating an oxidized beta-type silicon carbide powder, a phase change promoting substance, and a sintering aid.
The method of claim 11,

The sintering aid is a method of controlling the density and porosity of porous silicon carbide ceramics comprising at least one selected from the group consisting of carbon or an organic polymer in which carbon remains after heat treatment.
The method of claim 11,

Sintering aid is a density and porosity control method of the porous silicon carbide ceramics is contained in 1 to 10 parts by weight with respect to 100 parts by weight of the mixed powder.
The method of claim 11,

A density and porosity control method of porous silicon carbide ceramics having a theoretical density of 10 to 80%.
The method of claim 11,

A method of controlling the density and porosity of porous silicon carbide ceramics having a porosity of 20 to 90%.
A method of controlling pore size of porous silicon carbide ceramics, comprising the step of mixing and heat-treating an oxidized beta-type silicon carbide powder, a phase change promoting substance, and an alpha-type silicon carbide powder.
The method of claim 16,

Alpha-type silicon carbide powder is 0.1 to 10 parts by weight based on 100 parts by weight of the beta-type silicon carbide powder pore size control method of the ceramic ceramics.
The method of claim 16,

A pore size control method for porous silicon carbide ceramics having a pore size of 1 to 30 μm.
Diesel engine dust filter comprising the porous silicon carbide ceramics of claim 1, heat exchanger power plant dust filter, casting filter, incineration dust filter, hot corrosive gas filter, gas distributor for CVD or burner, or hydrogen separation for high temperature application and An article selected from any one of the membrane supports for lightweight structural components.