KR100838825B1 - Sic fiber reinforced reaction bonded sic porous body and its fabrication process - Google Patents

Abstract

An SiC fiber reinforced reaction bonded SiC porous body of which pore size and porosity are adjustable, and which has improved mechanical properties is provided, and a fabrication process of the SiC fiber reinforced reaction bonded SiC porous body is provided. As an SiC porous body comprising an SiC powder(1), an SiC fiber(2), a carbon powder(4), and Si, an SiC fiber reinforced reaction bonded SiC porous body is characterized in that: the SiC fiber has a length being five times as long as a mean particle diameter of the SiC powder to 10 mm, and is contained in a fabricated SiC porous body(3) in the amount of 1 to 15 wt.%; and the silicon is formed by melt infiltration in inner and outer portions of the porous body. The fabricated SiC porous body has a porosity of 10 to 60 vol.%. A fabrication process of an SiC fiber reinforced SiC porous body comprises performing melt infiltration of molten silicon from an outer portion into an inner portion of a green compact at a temperature of 1450 to 1650 deg.C under a vacuum of 1 to 10 torr or an inert gas atmosphere, the green compact comprising an SiC powder, an SiC fiber which has a length of five times a mean particle diameter of the SiC powder to 10 mm, and is contained in a fabricated SiC porous body in the amount of 1 to 15 wt.%, and a carbon powder.

Description

Silicon carbide fiber reinforced reaction sintered silicon carbide porous body and its manufacturing method {SiC fiber reinforced reaction bonded SiC porous body and its fabrication process}

1 is a microstructure of the silicon carbide porous body prepared in Example 1 according to the present invention, 1: silicon carbide powder used as starting materials, 2: silicon carbide fibers, 3: silicon carbide formed during reaction sintering, 4: residual Carbon or graphite, 5: residual silicon, and 6: pores.

Figure 2 is a SEM photograph of the silicon carbide fiber-reinforced silicon carbide porous body prepared in Example 1 according to the present invention, (a) is the residual silicon (14.2% by weight), (b) is the residual silicon (22% by weight) It is shown.

Figure 3 shows the three-point bending strength of the silicon carbide fiber reinforced silicon carbide porous body prepared in Example 1 according to the present invention.

Figure 4 shows the change in porosity and pore size according to the amount of residual silicon of the silicon carbide fiber-reinforced silicon carbide porous body prepared in Example 1 according to the present invention.

Figure 5 shows the XRD pattern of the silicon carbide fiber reinforced silicon carbide porous body prepared from Example 1.

Figure 6 shows the fracture strength according to the displacement of the silicon carbide fiber-reinforced silicon carbide porous body prepared in Example 1.

The present invention relates to a silicon carbide fiber reinforced reaction sintered silicon carbide porous body and a method for manufacturing the same, and more particularly, to contain silicon carbide fibers, silicon carbide powder, carbon powder, and silicon The silicon is a reaction-sintered silicon carbide porous body formed by melting and infiltrating by injecting from the outside or contained in a molded body, and controlling pore size and porosity by controlling the amount of silicon infiltrated and the size of silicon carbide powder. And reinforcing the newly formed neck phase between the silicon carbide powders formed with the cut silicon carbide fibers and continuously connecting the silicon carbide particles used as the raw powder in the silicon carbide porous body to break the strength of the silicon carbide porous body. Not only does it improve, but it also induces delayed fracture when destroying, which leads to improved reliability. Large body temperature as relates to the particulate filter, the particulate filter for diesel engines, in particular of silicon carbide can take advantage of the hot-gas filter material for coal gasification power generation reaction sintered silicon carbide fiber-reinforced porous body and a method.

Reaction sintered silicon carbide is mainly applied to high temperature heat exchanger materials, high temperature structural materials and general corrosion resistant industrial materials because of its excellent heat resistance, corrosion resistance and mechanical properties as well as high economic efficiency of the manufacturing process. In addition, since the reaction sintered silicon carbide can maintain the original size and shape of the molded body after sintering, it is evaluated to have high commercial value because it can produce a silicon carbide product in a desired form with minimal processing.

Such reaction-sintered silicon carbide is composed of silicon carbide and residual silicon, it is possible to manufacture a product having a variety of mechanical and electrical properties by controlling the microstructure and density of the molded body. In particular, high-purity reaction-sintered silicon carbide is developed and used as reaction tubes, susceptors and heaters used in semiconductor processes, and recently, porous reaction-sintered silicon carbide products are used as dust filters for diesel engines. .

In order to develop a porous reaction sintered silicon carbide material having high cost competitiveness and excellent thermal and mechanical properties for the development of a filter for high temperature, the reaction sintered silicon carbide produced by infiltration of molten silicon into a molded body made of silicon carbide and carbon is not less than 1800 ° C. Known techniques for producing porous reaction sintered silicon carbide by evaporating some of the residual silicon at high temperature, and techniques for producing porous reaction sintered silicon carbide by oxidizing and removing graphite after reaction sintering using excess graphite particles [US Pat. Nos. 4,525,429, 4,532,091, 4,564,496]. However, the known porous reaction sintered silicon carbide manufacturing process has difficulty in controlling the microstructure and porosity of pores in the porous reaction sintered silicon carbide.

In addition, clay-bonded porous silicon carbide materials in which necks are formed between silicon carbide particles using inorganic materials have been developed and used as diesel engine dust filter materials. However, the porous silicon carbide material developed to date has many problems in application as a high temperature gas filter material for power generation, which requires high reliability because brittle fracture occurs at breakage.

Therefore, various kinds of composite materials have been developed to overcome brittle fracture characteristics of porous silicon carbide materials. For example, fiber reinforced porous silicon carbide composite materials have been developed to improve the thermal and mechanical properties of porous silicon carbide materials. .

Fiber-reinforced porous silicon carbide composites manufacturing technology uses a silicon carbide fiber mat made of finely cut silicon carbide fibers to produce a molded body, and then carbonizes the surface of the silicon carbide fibers in the mat by carbon coating. A method of producing a porous silicon carbide by forming a neck between silicon fibers and a method of manufacturing a porous body by forming a bonding layer between the fibrous phases by chemical vapor deposition after producing a molded body using a woven fabric and felt made of ceramic fibers. And the like (US Patent Publication Nos. 5,552,049 and 5,075,160).

However, since the ceramic fiber-reinforced ceramic porous body produced by this method requires a high volume ratio of ceramic fiber to form the porous structure, the manufacturing cost is significantly higher than that of the general silicon carbide porous body and the pore structure control is not easy. There are many limitations in the practical application of the developed ceramic fiber reinforced silicon carbide porous body.

In conclusion, the ceramic fiber reinforced porous filter material known to date is manufactured using a ceramic fiber mat or woven fabric, and then a ceramic bond phase is formed between the ceramic fiber phases in various ways to produce a ceramic fiber reinforced porous silicon carbide material. Therefore, the expensive ceramic fiber phase must maintain a high fraction.

In addition, silicon carbide fiber-reinforced silicon carbide porous bodies manufactured by bonding the silicon carbide fibrous phases in various ways by using a molded body made of a high fraction of silicon carbide fibers are difficult to achieve high strength because they do not have strong bonding on the fibers. There is.

Accordingly, the present inventors endeavor to develop a silicon carbide fiber reinforced reaction sintered silicon carbide porous body that can significantly lower the manufacturing cost by minimizing the fraction of the ceramic fiber contained while maintaining physical properties equivalent to those of the conventional ceramic fiber reinforced silicon carbide porous body. It was. As a result, a component such as silicon carbide powder, carbon powder, and silicon is used as a starting material, but a small amount of silicon carbide fiber finely cut to a specific size is added to a fiber-reinforced phase to form a molded body. A reaction-sintered silicon carbide porous body formed by injecting or contained in a molded body to perform melting and infiltration reaction, and the pore size and porosity in the reaction-sintered silicon carbide porous body can be controlled by controlling the amount of silicon infiltrated and the size of silicon carbide powder. And reinforcing the neck phase between the silicon carbide powders formed with the cut silicon carbide fibers and continuously connecting the silicon carbide particles used as the raw material powder in the silicon carbide porous body together with the neck phase and the silicon carbide. It not only improves the breaking strength of the porous body, but also induces the delayed fracture phenomenon when destroying, thus improving the reliability. It was found that the present invention was completed.

Accordingly, an object of the present invention is to provide a pore size and porosity control, and to provide a silicon carbide fiber reinforced reaction sintered silicon carbide porous body having improved mechanical properties and a method of manufacturing the same.

The present invention is a silicon carbide porous body containing silicon carbide powder, silicon carbide fibers, carbon powder and silicon, the length of the silicon carbide fiber is 5 times to 10 mm of the average particle diameter of silicon carbide powder, the silicon is a porous body The silicon carbide fiber reinforced reaction sintered silicon carbide porous body formed by melting and infiltrating externally has its characteristics.

Hereinafter, the present invention will be described in detail.

The present invention relates to a silicon carbide fiber reinforced reaction sintered silicon carbide porous body capable of controlling the pore size and porosity, and improved mechanical properties such as delayed fracture phenomena, which contribute to the improvement of breaking strength and reliability compared to the prior art.

The silicon carbide porous body is generally manufactured by sintering silicon carbide powder, carbon powder, silicon carbide fiber, silicon, and the like. The present invention is a ceramic fiber which is in the form of the silicon carbide fiber while maintaining physical properties equivalent to those of the conventional silicon carbide porous body. By minimizing the fraction used, the manufacturing cost is significantly lowered.

In this manner, the present invention forms a bond with silicon carbide and residual silicon in a newly formed neck phase by the high temperature reaction of silicon and carbon formed by cutting the length of the silicon carbide fiber phase into a specific range. Breaking strength and retardation of porous silicon carbide composites by cutting the silicon carbide fibers on the neck and at the same time improving the bonding strength between silicon carbide particles used as raw material powder in porous composites and the connectivity between silicon carbide particles in a wide range It will improve the breakdown phenomenon.

In addition, the present invention can control the pore size and porosity in the silicon carbide porous body by controlling the amount of silicon infiltrated and the size of the silicon carbide powder.

The silicon carbide fiber reinforced reaction sintered silicon carbide porous body of the present invention is a silicon carbide fiber having a great influence on the economics of a product manufactured from components such as silicon carbide powder, silicon carbide fiber, carbon powder, and silicon, which are generally used. Use a small amount of finely cut to length. That is, the mechanical properties are also improved with the increase in the amount of silicon carbide fibers, but the price is increased at the same time to improve the problem of limiting the length of silicon carbide fibers to ensure the same or more physical properties than the conventional.

The present invention is characterized by the technical configuration of using a limited silicon carbide fiber length in a specific range, the length of the silicon carbide fiber ranges from 5 times to 10 mm of the average particle diameter of the silicon carbide powder used as a starting material It is desirable to maintain. If the length is less than 5 times the average particle diameter of the silicon carbide powder used as the starting material, the mechanical property improvement effect by the mesh effect connecting the silicon carbide particles with the particles is reduced, and if it exceeds 10 mm, the manufacturing process It is preferable to maintain the above range because the problem of reducing the limiting effect on the difficulty and the improvement of the mechanical properties.

At this time, the average particle diameter of the silicon carbide powder is not particularly limited in the present invention because it is determined by the pore size required in the field in which the silicon carbide fiber porous composite material is used.

Such silicon carbide fibers are used in the range of 1 to 15% by weight with respect to the manufactured silicon carbide porous body, and when the amount is less than 1% by weight, the amount is insignificant, and thus it is difficult to achieve the effect desired by the present invention, and exceeds 15% by weight. In this case, the dispersion of the silicon carbide fibers in the silicon carbide porous body is difficult to produce, which makes it difficult to manufacture the porous silicon carbide porous material having a uniform microstructure.

The other components, specifically silicon carbide powder, carbon powder and silicon, etc. are not particularly limited because various combinations are possible in the remaining amount except for the silicon carbide fiber. That is, the silicon carbide porous body is formed by any combination of the above components, and the present invention can achieve the object of the present invention by the limitation of the silicon carbide fibers. Of these, silicon is used for controlling the pore size and porosity, and it is preferable to use it in the range of more than the number of moles of the carbon powder used. When the amount of silicon used is less than the amount of carbon powder, the amount of residual carbon is increased to lower the mechanical properties of the porous silicon carbide composite material.

On the other hand, when the silicon carbide fiber reinforced reaction sintered silicon carbide porous body manufacturing method of the present invention will be described in detail.

The present invention is produced by infiltration of molten silicon into a molded body containing silicon carbide powder / silicon carbide fiber / carbon powder, or by forming a molded body on silicon carbide powder / silicon carbide fiber / silicon / carbon powder and then heating the It can be carried out by the method of dissolving and infiltrating the silicon powder in the molded body.

The silicon carbide fibers are chopped silicon carbide fibers to a predetermined size after washing with water and dried with dilute nitric acid solution (<10%) so that the silicon carbide fibers in the sized silicon carbide fiber bundles can be divided individually. Use

The powder mixture of the molded component is uniformly mixed so as not to change the size of the silicon carbide particles using an aqueous solution or a non-aqueous solution to which a binder commonly used in the art is added, and then the solution is dried to form silicon carbide and silicon carbide fibers. Or a mixed powder in which the silicon particle surface is coated with the carbon powder.

The binder may be a phenolic resin, polyvinyl alcohol, and the like, and the carbonization process is performed by them. It is preferable to use 2 to 10% by weight of such a component with respect to the molded powder mixture, in order to activate the infiltration of the molten silicon when the molded powder mixture reacts with silicon at a high temperature. Thereafter, a binder having a high carbon content, specifically, phenolic resin or methylcellulose is added and mixed in a range of 5 to 40% by weight to perform a molding process. The molding may be performed by extrusion and uniaxial pressure molding. Can be.

When the molten silicon is infiltrated into the molded body from the outside to produce a sintered body, the infiltration reaction is performed under vacuum or in an inert atmosphere in which the silicon is meltable, specifically, in the range of 1450 to 1650 ° C. and 1 to 10 torr.

In addition, in the case of manufacturing a molded body by containing a silicon component in the molded body, a sintering process is performed after the molded body is manufactured. The sintering is performed in a vacuum or inert atmosphere of 1 to 10 torr using a graphite reactor at 1450 to 1650 ° C. Perform under

The silicon carbide porous body manufactured as described above is infiltrated into the carbonaceous molded body by melting silicon supplied from the silicon in the carbonized molded body or the outside of the carbonized molded body, and the infiltration of molten silicon from the outside of the carbonized molded body into the carbonized molded body is carbonized. It occurs along a capillary in a carbon woven fabric placed between the surface of the molded body and the molten silicon. The molten silicon infiltrated into the carbonaceous molded body reacts with the carbon on the silicon carbide surface to form new silicon carbide and carbonizes the neck phase between the silicon carbide particles used as starting materials with the remaining unreacted or excess silicon. It is formed like silicon fibers.

Figure 1 shows the microstructure of the silicon carbide fiber-reinforced reaction sintered silicon carbide prepared according to the present invention, the finely cut silicon carbide fiber is beta-phase carbonization formed when newly reaction sintered between the silicon carbide powder used as the starting material It is located on the free surface of the neck matrix or silicon carbide powder consisting of silicon, unreacted carbon and residual silicon. In addition, the silicon carbide fibers in the porous body continuously connect the silicon carbide particles used as starting materials by the length of the silicon carbide fibers used.

The average pore size and porosity of the silicon carbide fiber-reinforced porous silicon carbide sintered body thus prepared are determined by the size of silicon carbide particles and the amount of silicon used as starting materials, and the pore size is from several nanometers (nm) to several hundred micrometers (㎛). ) Can be controlled in size and porosity can be controlled in the range of 10 to 60% by volume, preferably 30 to 60% by volume. In the porous silicon carbide composite material reinforced with silicon carbide fiber, the fracture strength is improved by up to 200% or more than the existing porous silicon carbide material, and the delayed fracture phenomenon occurs. Therefore, the silicon carbide fiber reinforced reaction sintered silicon carbide porous body of the present invention Specifically, the filter material can be used as a material for high temperature filter, a diesel dust filter, and a water filtration filter, such as an integrated gasification combined cycle.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1

Silicon Carbide Fiber Reinforced Reaction Sintered Silicon Carbide Powders 54 to 62 wt%, 28 wt% silicon ingot, 4 wt% phenol resin, and 4 wt% carbon black to produce silicon carbide porous matrix And 2 to 10% by weight of Hi-Nicalon silicon carbide fibers (Nippon carbon). In this case, the silicon carbide fibers are finely cut into 5 to 7 mm long silicon carbide fibers so as to disperse the force acting on the porous silicon carbide at the time of breakdown, and then the silicon carbide fibers of the silicon carbide bundles are diluted with dilute nitric acid. It was used separately.

The finely divided fibers in which the silicon carbide fibers were separately separated were dispersed in 70 wt% of an aqueous slurry composed of silicon carbide particles / carbon black / phenol resins of 180 μm and 250 μm in size to prepare a slurry for forming a molded article. The amount of silicon carbide fibers used was carried out while varying in the range of 2 to 10% by weight based on the molded slurry. The prepared silicon carbide fiber / silicon carbide particles / carbon black / phenol resin slurry was defoamed, injected into a mold, and dried at 80 ° C. for 24 hours to prepare a composite powder. 96% by weight of the composite powder prepared above Phenol resin, which is an organic and inorganic binder, was uniformly mixed by 4% by weight to prepare a molded body by a uniaxial pressure molding method.

The dried molded body is infiltrated with molten silicon from the outside into the molded body to prepare a porous silicon carbide fiber reinforced reaction sintered silicon carbide composite material. It was carried out using a graphite reactor for 30 minutes in a vacuum atmosphere of less than about 10 ^-1 torr ℃.

Next, FIG. 2 shows a SEM image of (a) residual silicon (14.2% by weight) and (b) residual silicon (22% by weight) using 4% by volume of silicon carbide fibers in 180 µm-sized silicon carbide particles. As shown in the SEM photograph, the silicon carbide fibers are located on the neck base and the surface of the silicon carbide powder formed between the silicon carbide powders used as starting materials and connect the silicon carbide powders.

In addition, as shown in Figure 3, the silicon carbide fiber reinforced reaction sintered silicon carbide porous body produced during the three-point bending strength test using specimens of 3 mm, 4 mm and 30 mm in size, width and height are The escape phenomenon of the silicon carbide fiber caused the delayed fracture phenomenon and the displacement amount was 4 mm or more and the displacement amount increased as the volume fraction of the silicon carbide fiber increased.

Figure 4 shows the change in porosity and pore size according to the amount of residual silicon of the silicon carbide porous body prepared in Example 1 according to the present invention.

The calculated amount of residual silicon in the prepared porous silicon carbide fiber reinforced reaction sintered silicon carbide composite was 12 to 22% by weight. The average pore size of the prepared silicon carbide fiber reinforced reaction sintered silicon carbide porous body was about 70 μm, the porosity was about 30 to 40% by volume, and the breaking strength was 50 to 70 MPa. An X-ray diffraction analysis pattern of the prepared silicon carbide porous body is shown in FIG. 5. As a result, it was confirmed that residual silicon, residual carbon, and graphite were present in the prepared fiber-reinforced sintered silicon carbide porous body.

As the volume fraction of silicon carbide fibers and the amount of residual silicon increased, the increase in fracture strength was low when the silicon carbide fiber volume fraction was more than 7%, and the fracture strength decreased as the porosity in the porous body increased. Could confirm. In addition, when the bending strength test of the prepared silicon carbide fiber-reinforced silicon carbide porous body showed a delayed fracture characteristic that appears in the dense ceramic fiber reinforced ceramic composite material. This is because finely chopped silicon carbide fibers contained in the prepared silicon carbide porous bodies are delayed by pull-out of ceramic fibers appearing in a dense ceramic fiber reinforced ceramic composite material. Stress-displacement curves appearing in the 3-point breakdown strength measurement of Example 1 are shown in FIG. 6.

Example 2

Silicon carbide fiber reinforced reaction sintered To produce silicon carbide porous matrix, 66% by weight of 10 µm silicon carbide particles, 4% by weight of phenol resin, 4% by weight of carbon black, and Hi-Nicalon silicon carbide fibers (Nippon carbon) as a reinforcing material 4 wt% and 22 wt% silicon powder were used.

At this time, the silicon carbide fiber is finely cut silicon carbide fibers to 0.1 ~ 0.2 mm long so that the force acting on the porous silicon carbide at the time of breakage, and then the silicon carbide fibers of the silicon carbide bundle using dilute nitric acid It was used separately.

The finely divided fibers in which the silicon carbide fibers were separately separated were dispersed in 70 wt% of an aqueous slurry composed of silicon carbide particles / carbon black / phenol resin / silicon powder having a size of 10 μm to prepare a slurry for producing a molded product.

The prepared silicon carbide fiber / silicon carbide particles / carbon black / phenol resin slurry was defoamed, injected into a mold, and dried at 80 ° C. for 24 hours to prepare a composite powder. 96% by weight of the composite powder prepared above Phenol resin, which is an organic and inorganic binder, was uniformly mixed by 4% by weight to prepare a molded body by a uniaxial pressure molding method.

Thereafter, the reaction sintering process was performed, and a graphite reactor was used for about 30 minutes in an argon (Ar) atmosphere at about 1500 ° C.

The calculated amount of residual silicon in the porous silicon carbide fiber reinforced reaction sintered silicon carbide composite material prepared above was 15% by weight.

The average pore size of the silicon carbide fiber reinforced reaction sintered silicon carbide porous body prepared above was about 2 μm, the porosity was 35% by volume, the breaking strength was 50 MPa on average, and the average pore size in the porous body was decreased and the porosity was not significantly different. And the fracture strength of the silicon carbide fiber reinforced reaction sintered silicon carbide porous body produced by infiltration of molten silicon into the molded body outside the molded body.

In addition, the silicon carbide fiber reinforced reaction sintered silicon carbide porous body prepared during the bending strength test in the same manner as in Example 1 exhibited a delayed fracture phenomenon and the displacement amount was about 2 to 3 mm, and the silicon carbide / silicon Silicon carbide fibre-reinforced reaction sintered silicon carbide fabricated using a molded body made of carbon black / silicon carbide fibers was also observed to escape the silicon carbide fibers upon fracture, but the length of the fibers was reduced.

As described above, the present invention is a silicon carbide porous body formed by melting and infiltration of finely chopped silicon carbide fibers and silicon may not only have high reliability due to high strength and delayed fracture phenomenon, but also control of a starting material to form a matrix phase. It is easy to control pore size and porosity, and it is possible to reduce the manufacturing cost by using a small amount of silicon carbide fiber compared to the conventional ones. In addition, since it can be used as a hot gas filter material for coal gasification power generation, which is being actively developed recently, it is possible to advance the industrialization of future industries and the practical use of new power generation technology.

Claims (7)

A silicon carbide porous body containing silicon carbide powder, silicon carbide fibers, carbon powder and silicon, The silicon carbide fiber has a length of 5 to 10 mm of the average particle diameter of silicon carbide powder, and contains 1 to 15% by weight based on the manufactured silicon carbide porous body, The silicon carbide fiber reinforced reaction sintered silicon carbide porous body, characterized in that formed by melting and infiltrating the inside and outside of the porous body. The silicon carbide fiber reinforced reaction sintered silicon carbide porous body according to claim 1, wherein the prepared silicon carbide porous body has a porosity of 10 to 60% by volume. delete The filter material manufactured using the silicon carbide fiber reinforced reaction sintered silicon carbide porous body of any one of Claims 1 or 2 as a material. The filter material according to claim 4, wherein the filter material is a material for a hot gas filter, a diesel dust filter, and a water filtration filter. In a molded body containing silicon carbide powder, silicon carbide fibers having a content of 1 to 15% by weight based on the silicon carbide porous body having a length of 5 to 10 mm of the average particle diameter of the silicon carbide powder, and carbon powder, A method for producing a silicon carbide fiber-reinforced silicon carbide porous body, characterized in that the molten silicon is produced by infiltration reaction from the outside of the molded body to the inside under a vacuum of 1450-1650 ° C., 1-10 torr or in an inert atmosphere. A molded article containing silicon carbide fibers, silicon powder, and carbon powder containing 1 to 15% by weight of the silicon carbide powder, the length of which is 5 to 10 mm of the average particle diameter of the silicon carbide powder, and produced from the porous silicon carbide porous body was prepared. , Method for producing a silicon carbide fiber-reinforced silicon carbide porous body, characterized in that the sintering process is carried out in a vacuum range of 1450 ~ 1650 ℃, 1 to 10 torr or inert atmosphere to dissolve and infiltrate the silicon powder in the molded body .

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