KR20120019078A - Method for manufacturing carbon-ceramic composite - Google Patents

Abstract

PURPOSE: A manufacturing method of carbon ceramic composite is provided to manufacture the carbon ceramic composite with uniformly distributed silicon carbide by covering a formed body which is carbonized by a sintering inducing material. CONSTITUTION: A manufacturing method of carbon ceramic composite comprises the following steps: making a molding product(21); carbonizing the molding product; manufacturing a sintering derivative(31) which infiltrates silicon into the carbonized molding product; melting the silicon included in the sintering derivative; and infiltrating the silicon into to the carbonized molding product. The step of manufacturing a sintering derivative comprises the following steps: making a compound powder using silicon carbide powder, oxide ceramics powder, and silicon powder; dissolving an organic binder in distilled water and mixing the compound powder with the distilled water; covering the carbonized molding product with the mixture(the compound powder + an organic binder + the distilled water); and heating and drying the covered and carbonized molding product.

Description

How to make a carbon ceramic composite {METHOD FOR MANUFACTURING CARBON-CERAMIC COMPOSITE}

The present invention relates to a method of making a carbon ceramic composite.

Carbon ceramic composites have high strength and are excellent in corrosion resistance and abrasion resistance.

The carbon ceramic composite is made through a step of forming a molded body, carbonizing the molded body, and infiltrating silicon (Si) into the carbonized molded body.

As a method of infiltrating silicon into the carbonized molded body, silicon liquid phase reaction sintering is used.

The silicon liquid phase reaction sintering method is a method of making silicon carbide in a carbonized body (Silicon Carbide, SiC) by dissolving silicon in a carbonized body in a vacuum or inert atmosphere (Ar, N2).

The silicon liquid phase reaction sintering method has no shrinkage and expansion of the carbonized molded body during the sintering process, resulting in low final processing cost. In addition, silicon carbide can be produced in a carbonized molded body at a temperature (1500 ° C to 1600 ° C) relatively lower than the solid state sintering method (about 2000 ° C). For this reason, the silicon liquid phase reaction sintering method is widely used as a method of making silicon carbide in a carbonized molded body.

Hereinafter, the method of making silicon carbide in the conventional carbonized molded body and the method of making silicon carbide in the carbonized molded body which concerns on this invention are common in the point which uses the silicon liquid-phase reaction sintering method.

FIG. 1 is a view showing a state where a graphite crucible is placed in a vacuum resistance heating furnace, in which silicon and a carbonized compact molded object are placed. The compact molded product is a molded product whose height H is less than 50 cm.

The compact body shown in FIG. 1 has a square shape. Of course, the compact body may have various shapes such as rectangular and trapezoidal.

As shown in FIG. 1, a boron nitride film 2 is formed on the inner wall of the graphite crucible. The thickness of the boron nitride film 2 is 1 mm or less. Due to the boron nitride film 2, the graphite crucible 1 is prevented from contacting and reacting with the silicon 5.

Hereinafter, referring to FIG. 1, a conventional method of infiltrating silicon into a carbonized compact is described in detail.

The silicon 5 is put in the graphite crucible 1.

In the graphite crucible 1, the lower part of the carbonized compact 10 is buried in the silicon 5.

Silicon (5) is stacked on the upper surface of the carbonized compact (10).

A graphite crucible (1) is placed in a vacuum resistance heating furnace (3).

The vacuum resistance heating furnace 3 heats the graphite crucible 1 to 1-20 degreeC per minute in a vacuum or inert atmosphere, and heats it at 1500 degreeC-1600 degreeC.

The silicon 5 melts and penetrates into the porosity of the carbonized compact 10.

In order for the silicon 5 to penetrate smoothly into the pores of the carbonized compacts 10, the diameter of the silicon 5 is 1 mm or more, and the weight of the silicon 5 is 200% wt or less of the weight of the compacts 10. to be. Infiltrated silicon 5 and carbon contained in the carbonized compacts 10 react to form silicon carbide.

On the other hand, in the related art, since the silicon is accumulated on the upper surface of the carbonized compact molded body 10 and then the silicon is melted and infiltrated, it is not possible to place another carbonized compact molded body on the upper surface of the carbonized compact molded body 10. The reason for this is that when the carbonized compacts are placed on the upper surface of the carbonized compacts 10 and the silicon is infiltrated, the carbonized compacts 10 and the other carbonized compacts stick to each other. Therefore, the internal space S of the vacuum resistance heating furnace 3 cannot be utilized 100%, and a large amount of carbon ceramic composites cannot be produced.

Fig. 2 is a view showing a state where a graphite crucible is placed in a vacuum resistance heating furnace, in which silicon and a carbonized large molded body are placed. A large molded object is a molded object whose height H is 50 cm or more. The large molding shown in FIG. 2 has a trapezoidal shape. Of course, the large molded body may have various shapes such as square and rectangular.

In the case of the large molded body 11, there is a difference in reaction between carbon and silicon in the lower part and the upper part of the large molded body 11.

In more detail, the carbon contained in the lower part of the large molded body 11 reacts with the silicon 5 infiltrated with sufficient time. On the other hand, the carbon contained in the upper portion of the large molded body 11 can not react with the silicon 5 infiltrated with sufficient time.

This is because the silicon 5 placed on the upper surface of the large-scale molded body 11 descends by gravity before it sufficiently reacts with the carbon contained in the upper portion of the large-scale molded body 11. For reference, in the compact body 10 having a height of less than 50 cm, such a problem does not occur because the capillary force and gravity are balanced.

In order to solve this problem, conventionally, the large-scale molded body 11 into which silicon has been infiltrated first is turned upside down, and the silicon 5 is infiltrated into the upper part of the large-scale molded body 11 which has been lowered. However, since the lower portion of the large molded body 11 is upward, the first penetrated silicon in the lower portion of the large molded object 11 that has been raised upward has melted down.

On the other hand, with the conventional method mentioned above, it is difficult to evenly infiltrate silicon into the carbonized molded body which has a complicated shape.

An object of the present invention is to make a carbon ceramic composite in which silicon carbide is uniformly infiltrated by infiltrating silicon uniformly into a carbonized molded body, regardless of the size and shape of the carbonized molded body.

Another object of the present invention is to make a large amount of carbon ceramic composite by making full use of the space in a vacuum resistance heating furnace.

Method for making a carbon ceramic composite to achieve the above object, the step of making a molded body; Carbonizing the molded body; Making a sintered derivative, in which silicon is infiltrated into the carbonized molded body; And melting silicon contained in the sintered derivative and infiltrating the carbonized molded body.

The present invention wraps the molded body carbonized with the sintered derivative or inserts the sintered derivative into the carbonized molded body. Then, the sintered derivative is heated to dissolve silicon contained in the sintered derivative and infiltrate into the carbonized molded body. For this reason, regardless of the size and shape of the carbonized molded body, silicon is uniformly penetrated into the carbonized molded body and then reacts with the carbon contained in the carbonized molded body to form silicon carbide. Therefore, using the present invention, a carbon ceramic composite in which silicon carbide is uniformly distributed can be produced.

In addition, by using the present invention, the silicon can be dissolved and infiltrated into the carbonized molded bodies at once while the sintered derivative surrounding the carbonized molded body is placed on the sintered derivative surrounding the carbonized molded body. Therefore, it is possible to make full use of the space in the vacuum resistance heating furnace, thereby making it possible to make a carbon ceramic composite in large quantities.

FIG. 1 is a view showing a state where a graphite crucible is placed in a vacuum resistance heating furnace, in which silicon and a carbonized compact molded object are placed.
Fig. 2 is a view showing a state where a graphite crucible is placed in a vacuum resistance heating furnace, in which silicon and a carbonized large molded body are placed.
3 is a flowchart illustrating a method of making a carbon ceramic composite according to one embodiment of the present invention.
4 is a view showing a state in which a graphite crucible is placed in a vacuum resistance heating furnace, in which a carbonized large molded body wrapped with a sintered derivative is placed.
FIG. 5 is an enlarged view of a portion A of FIG. 4.
FIG. 6 is a view illustrating a state in which silicon included in the sintered conductor of FIG. 4 uniformly penetrates into a carbonized large molded body.
Fig. 7 is a view showing a state in which graphite crucibles are placed in a vacuum resistance heating furnace. In the graphite crucible, two small carbonized compacts wrapped with a sintering conductor are stacked on each other.

Hereinafter, a method of making a carbon ceramic composite according to an embodiment of the present invention will be described.

3 is a flowchart illustrating a method of making a carbon ceramic composite according to one embodiment of the present invention. As shown in FIG. 3, the method of making a carbon ceramic composite includes a step of making a molded body (S11), a step of carbonizing the molded body (S12), and a step of making a sintered derivative (S13) that infiltrates silicon into the carbonized molded body. , Melting the silicon contained in the sintered derivative and infiltrating the carbonized molded body (S14). The method for producing a carbon ceramic composite according to the embodiment of the present invention described above is equally applicable whether the molded body is large or small.

Hereinafter, the step (S11) of making a molded body will be described.

Activated carbon powder, pyrolytic carbon, pitch, silicon carbide powder are mixed to form a mixture. The weight of the activated carbon powder, pyrolytic carbon, and pitch in the final carbon ceramic composite is preferably 10 to 50% wt.

An organic binder may be added to the mixture to improve the durability of the carbon ceramic composite. As the organic binder, a vinyl binder or a cellulose binder may be used.

The mixture is pressed with a press to form a shaped body. If necessary, a heater may be installed in the press to heat the mixture simultaneously with pressurization.

Hereinafter, the step (S12) of carbonizing the molded body will be described.

The molded product is carbonized in a vacuum or inert atmosphere. Organic compounds (active carbon powder, pyrolytic carbon, pitch, silicon carbide powder) contained in the molded product are thermally decomposed to carbon. The organic compound is thermally decomposed and pores are formed in the remaining position.

Hereinafter, the step (S13) of making the sintered conductor surrounding the carbonized molded body will be described.

First, silicon carbide powder (5 ~ 10% wt), oxide ceramic powder (10 ~ 30% wt), silicon powder (50 ~ 90% wt) is mixed to make a mixed powder. The oxide ceramic powder is composed of silica, alumina, zirconia and titania. The average size of the mixed powder is 1 µm to 3000 µm.

Silicon carbide powder and oxide ceramic powders help the sintered derivatives to maintain their initial forming at high temperatures. In addition, silicon is prevented from agglomerating, so that the carbon contained in the carbonized molded body and the silicon are reacted uniformly.

On the other hand, when the carbon contained in the carbonized compact and silicon react to calculate the amount of silicon required to make silicon carbide and the amount of silicon filling the pores of the carbonized compact, the weight of the silicon powder in the mixed powder is 50-90% wt Is preferably. Based on the calculation, carbon and silicon were 1: 1 covalently bonded, the weight ratio of carbon to silicon was 1: 4, and the weight of carbon contained in the carbonized molded body was set to 20 to 70% wt.

On the other hand, when the weight of the carbonized molded body is 100% wt, the weight of the sintered derivative surrounding the carbonized molded body is preferably 100 ~ 300% wt.

On the other hand, it is preferable that the thickness of the sintering derivative surrounding the carbonized molded body is 20% of the thickness of the carbonized molded body.

On the other hand, when the inside is a hollow (for example, tube) carbonized molded body, the sintered derivative is inserted into the inside to permeate silicon. In this case, it is preferable that the thickness of the sintered conductor is -20% of the thickness of the carbonized molded body.

On the other hand, when the thickness of the carbonized molded body becomes thicker, the amount of silicon to react with carbon also increases, so that the thickness of the sintered derivative becomes thicker. When the thickness of the sintered conductor becomes thick, the internal binding force of the sintered conductor becomes strong, but it is difficult to separate the sintered derivative after silicon has penetrated into the carbonized molded body. In order to prevent this, the size of the remaining powder except the silicon powder in the mixed powder is increased to 1000㎛ or more.

On the other hand, when the thickness of the carbonized molded body becomes thin, the amount of silicon to react with carbon also decreases, so that the thickness of the sintered derivative becomes thin. When the thickness of the sintered derivative becomes thin, it is easy to separate the sintered derivative after silicon has penetrated the carbonized molded body, but the internal binding force of the sintered derivative is weakened. In order to prevent this, the size of the remaining powder except the silicon powder in the mixed powder is reduced to less than 1000㎛.

On the other hand, when the inside of the carbonized molded body is empty, silicon may melt from the upper part to the lower part of the inside, so that the size of the silicon powder is made very small (less than 100 µm).

Secondly, the organic binder is dissolved in distilled water, and distilled water (1-5% wt) in which the organic binder is dissolved is mixed in the mixed powder. 1 to 5% wt is the weight ratio to the mixed powder.

The organic binder maintains a complex shape or the shape of a large molded body at room temperature.

Third, the carbonized molded body is placed in a sealed plastic bag. The mixture (mixed powder + organic binder + distilled water) is placed in a plastic bag. Vacuum the inside of the plastic bag. The vinyl bag shrinks and presses the mixture, causing the mixture to encapsulate the carbonized moldings. Seal the plastic bag. On the outside of the plastic bag, it is pressurized to 0.1-1 kgf / cm² with vibration. The carbonized moldings in which the mixture is wrapped are taken out of the plastic bag. The carbonized molded body wrapped in the mixture is dried by heating to a temperature of 50 ℃ to 150 ℃. As the mixture hardens, micropores 31a (see FIG. 5) are formed between the powders. When the mixture is hardened, a sintered derivative is formed that wraps the carbonized molded body.

On the other hand, when the inside is an empty carbonized molded body, a sintered derivative is made inside the carbonized molded body. The method of making a sintered derivative in the carbonized molded body,

Preparing a powder by mixing silicon carbide powder, oxide ceramic powder, and silicon powder; Dissolving an organic binder in distilled water and mixing distilled water in which the organic binder is dissolved in the mixed powder; Inserting a mixture (the mixed powder + the organic binder + the distilled water) into the carbonized molded body; And heating and drying the carbonized molded body into which the mixture is inserted.

The method of making the sintered derivative in the carbonized molded body is the same as the method of making the sintered derivative wrapped around the carbonized molded body, except for inserting the mixture into the carbonized molded body, and thus, detailed description thereof will be omitted.

Hereinafter, the step (S14) of melting the silicon contained in the sintered derivative and penetrating the carbonized molded body will be described by dividing the case where the size of the carbonized molded body is large and small.

First, the case where the size of the carbonized molded body is large is demonstrated.

4 is a view showing a state in which a graphite crucible is placed in a vacuum resistance heating furnace, in which a carbonized large molded body wrapped with a sintered derivative is placed. Carbonized large parts are given reference numeral 21. Also, reference numeral 31 is given to the sintered derivative wrapped with the carbonized large molded product.

FIG. 5 is an enlarged view of a portion A of FIG. 4. FIG. 6 is a view illustrating a state in which silicon included in the sintered conductor of FIG. 4 uniformly penetrates into a carbonized large molded body. Solid arrows indicate the flow of silicon.

As shown in FIG. 4, the carbonized large molded body 21 wrapped with the sintered derivative 31 is placed in the graphite crucible 1.

The graphite crucible (1) is placed in a vacuum resistance heating furnace (3).

The vacuum resistance heating furnace 3 heats the graphite crucible 1 to 1-20 degreeC per minute in a vacuum or inert atmosphere, and heats it at 1500 degreeC-1600 degreeC.

The silicon contained in the sintered derivative 31 surrounding the carbonized large molded body 21 melts and penetrates into pores of the carbonized large molded body 21. Infiltrated silicon (6, see Fig. 5) and the carbon contained in the carbonized large molded body 21 reacts to form silicon carbide.

On the other hand, silicon does not melt 100% even when it reaches a melting point (1413 ° C). In order to melt the silicon 100%, it must be heated for at least 10 minutes at a temperature higher than the melting point of silicon (1500 ° C.). At this time, silicon melts from the surface to the inside. Since the large-size molded object 21 has gravity greater than capillary force, when the silicon melts, it flows down by gravity.

However, as shown in FIG. 5, the sintered derivative 31 fills the molten silicon 6 in the micropores 31a to prevent the silicon 6 from flowing down by gravity. Then, the molten silicon 6 is continuously contacted with the carbonized large molded body 21.

As a result, as shown in FIG. 6, the silicon filled in the micropores 31a may be uniformly infiltrated into the carbonized large molded body 21 with sufficient time.

On the other hand, the reaction to form silicon carbide between the carbon contained in the carbonized large molded body 21 and silicon 6 does not occur until the amount of molten silicon 6 is set. The sintered derivative 31 fills the molten silicon 6 as much as reaction occurs in the micropores 31a. For this reason, the reaction which makes silicon carbide between the carbon 6 and the silicon 6 contained in the carbonized large molded object 21 takes place actively.

The molten silicon 6 penetrates into the carbonized large molded body 21 to form silicon carbide, whereby a carbon ceramic composite is finally made.

Subsequently, the sintered conductor surrounding the carbon ceramic composite is removed by sandblasting. Then, the silicon lump remaining on the surface of the carbon ceramic composite is removed by sandblasting.

Next, the case where the size of the carbonized molded body is small will be described.

Fig. 7 is a view showing a state in which graphite crucibles are placed in a vacuum resistance heating furnace. In the graphite crucible, two small carbonized compacts wrapped with a sintering conductor are stacked on each other.

Reference numeral 22 is given to the carbonized compact, and reference 32 is given to the sintered conductor wrapped with the carbonized compact. Another carbonized compact is denoted by reference numeral 23, and the carbonized compact is denoted by 33.

If the carbonized compact is small, the capillary force and gravity are balanced so that not only the molten silicon can be in continuous contact with the carbonized compact, but the sintered derivatives 32 and 33 allow the molten silicon to be carbonized. It can be in constant contact with the compacts 22 and 23.

In addition, as illustrated in FIG. 7, the carbonized compacted body 23 wrapped with another sintered derivative 33 may be placed on the carbonized compacted body 22 wrapped with the sintered conductor 32 and the silicon may be infiltrated at once. have.

The reason is that the sintered inductor 32 wrapped with the carbonized compacts 22 and the sintered inductor 33 wrapped with another carbonized compacts 23 are carbonized with the compacted compact 22 and another carbonized product. This is because the compact molded body 23 prevents the silicon compact from sticking together.

For this reason, the internal space S of the vacuum resistance heating furnace 3 can fully be utilized.

Claims (10)

Making a shaped body;
Carbonizing the molded body;
Making a sintered derivative, in which silicon is infiltrated into the carbonized molded body; And
Dissolving silicon contained in the sintered derivative and infiltrating the carbonized molded body. The method of claim 1, wherein the step of making silicon sintered in the carbonized molded body,
Preparing a powder by mixing silicon carbide powder, oxide ceramic powder, and silicon powder;
Dissolving an organic binder in distilled water and mixing distilled water in which the organic binder is dissolved in the mixed powder;
Wrapping the carbonized molded body with a mixture (the mixed powder + the organic binder + the distilled water); And
Heating and drying the carbonized molded article wrapped with the mixture. The method of claim 2, wherein the step of wrapping the carbonized molded body comprises
Placing the carbonized molded body in a plastic bag;
Placing the mixture in the plastic bag;
Vacuuming the interior of the plastic bag;
Pressurizing the mixture as the vinyl bag shrinks, so that the mixture surrounds the carbonized molded body;
Sealing the vinyl bag;
Externally pressing the vibrating bag; And
And removing the carbonized molded article wrapped with the mixture from the vinyl bag. The method of claim 1, wherein the sintered derivative is provided with fine pores,
Dissolving silicon contained in the sintered derivative and penetrating the carbonized molded body, wherein the silicon filled in the micropores penetrates into the carbonized molded body. 5. The method according to claim 4, wherein the carbonized molded body wrapped with the sintered derivative is large in size. The method of claim 4, wherein the carbonized compacts wrapped with the sintered derivative are small in size, and the carbonized compacts wrapped with the sintered derivative are laminated to each other, and silicon is melted and impregnated at once. The method of claim 1, wherein when the weight of the carbonized molded body is 100% wt, the weight of the sintered derivative surrounding the carbonized molded body is 100 ~ 300% wt,
And a thickness of the sintered derivative surrounding the carbonized molded body is 20% of the carbonized molded body thickness. 8. The method according to any one of claims 2 to 7,
When the thickness of the carbonized molded body becomes thick, the thickness of the sintered derivative also becomes thick,
When the thickness of the carbonized molded body is thin, the thickness of the sintered derivative is also made a carbon ceramic composite. 8. The method according to any one of claims 2 to 7,
When the thickness of the carbonized molded body becomes thick, the size of the remaining powders except the silicon powder in the mixed powder is increased,
When the thickness of the carbonized molded body is thin, the size of the remaining powder except the silicon powder in the mixed powder to make a carbon ceramic composite. The method of claim 1, wherein the step of making a sintered derivative, in which silicon is infiltrated into the carbonized molded body when the inside of the carbonized molded body is empty,
Preparing a powder by mixing silicon carbide powder, oxide ceramic powder, and silicon powder;
Dissolving an organic binder in distilled water and mixing distilled water in which the organic binder is dissolved in the mixed powder;
Inserting a mixture (the mixed powder + the organic binder + the distilled water) into the carbonized molded body; And
Heating the carbonized molded body into which the mixture is inserted and drying the method; forming a carbon ceramic composite.

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