KR940005405B1 - Method of preventing an oxidation of carbon materials by double coating - Google Patents

Abstract

The oxidation method of carbon material comprises (a) putting carbon material or carbon composite to the mixed coating powder composed of 20-50 wt.% chromium halide powder and 50-70 wt.% inert sintering resisting powder, (b) heating them at oxidation atmosphere in the conventional condition for forming the first antioxidation film, (c) putting the first coated carbon material to the second mixed coating powder composed of aluminum or aluminum halide or mixed powder of them and inert sintering resisting powder, (d) reheating them at 600-1,000 deg.C for 1-5 hrs. in oxidation atmosphere for the second antioxidation film.

Description

Method of preventing oxidation of carbon material by double coating

1 is a schematic diagram of a film forming apparatus for forming a double film for the oxidation prevention of a carbon material according to the present invention.

2 is a graph showing the change in the amount of lost oxide with oxidation time.

3 and 4 are graphs showing weight change by oxidation of carbon material after double coating.

* Explanation of symbols for main parts of the drawings

1: heating element 2: reaction tube

3: carbon material specimen 4: crucible

5: support base 6: inert gas source

7: mixed powder for coating

The present invention relates to a method for preventing oxidation of carbon materials or carbon composite materials used in brake materials such as high-speed aircraft, racing cars, and complicated electrodes and heating elements. More specifically, the present invention relates primarily to the surface of carbon materials or carbon composite materials. A method of preventing oxidation of a carbon material by double coating which forms a chromium-based film and prevents oxidation by forming an aluminum-based film on the chromium-based film secondly.

Carbon materials are lightweight, have high specific strength, are extremely resistant to thermal shock and corrosion, and are good conductors of heat and electricity. Therefore, it is used as a complex electrode and a heating element, and also used as a brake material such as a high-speed aircraft, a racing car, and a high-temperature material for aerospace, but there is a fatal defect in which oxidation proceeds rapidly at 500 ° C or higher in the air.

In order to compensate for this drawback, various coating methods for the antioxidant coating have been studied.

Coating methods to prevent oxidation of carbon materials or carbon composite materials include coating by chemical vapor deposition (CVD) such as silicon carbide (SiC) and silicon nitride (Si ₃ N ₄ ), and magnesia (MgO) and alumina (Al ₂ O _3). ) And chromium oxide (Cr ₂ O ₃ ) are sprayed (Journal of Material Science, Vol 24 (1989), p 3511-3520).

However, the coating method by Chemical Vapor Deposition (CVD) has a disadvantage in that a treatment temperature requires a high temperature of 1300 ° C. or more and repeated coating several times in order to deposit the entire surface of the coated object.

Therefore, if the coating layer of silicon carbide or alumina or the like is not thick, it is difficult to form a stable antioxidant film, and there is a problem such as being limited in the size and shape of the material.

On the other hand, in the anti-oxidation coating method by plasma spraying, since the adhesion to the material is poor and peeling easily occurs, there is a problem that the coating layer must be thickened.

The present invention proposes a method for preventing oxidation of carbon material by heat treatment in a mixed powder or a chromium oxide powder and a mixed powder of chromium halide compound powder in order to improve the above problems. (Korean Patent Application No. 91-25123).

In the case of coating only the metal chromium layer according to the previously applied method, when the oxide is oxidized in air, the surface of the coating layer is formed with chromium oxide, and the chromium oxide layer functions as an anti-oxidation coating without passing air. However, chromium oxide becomes a gas of chromium trioxide (CrO ₃ ) when it is used for a long time at a high temperature (1000 ° C. or more), so it is extremely small but increases, and thus there is a problem in that stability for oxidation prevention is long.

In order to solve the above problems, the present invention provides a chromium carbide layer having a strong bond with carbon on the surface of a carbon material, and forms a metal aluminum layer on the metal chromium layer. The purpose of the present invention is to effectively prevent high temperature oxidation of a carbon material by forming an oxidation resistant film.

The present invention is a method for double coating to prevent oxidation of a carbon material or a carbon composite material, the weight ratio of the first coating mixture is composed of chromium halide powder: 30-50% and inert sintering agent powder: 50-70% A secondary coating mixture powder composed of aluminum powder and / or aluminum halide and inert sintering inhibitor powder after buried a carbon material or carbon material in the powder and heat-treated in a non-oxidizing atmosphere in a conventional manner to form a primary oxidation resistant film. Buried carbonaceous material coated as above in the secondary coating mixture to which the halogen compound powder was added, and heat-treated for 1-5 hours at a temperature of 600-1000 ° C. in a non-oxidizing atmosphere to form a secondary oxidation resistant film. The present invention relates to a method for preventing oxidation of a carbon material by double coating. In addition, in the present invention, in preventing the oxidation of a carbon material or a carbon composite material, the carbon material in the primary coating mixture powder, which is composed of weight%, chromium oxide powder: 85-95%, and halogen compound powder: 5-15% Or buried in a carbon composite material and heat-treated in a non-oxidizing atmosphere in a conventional manner to form a primary oxidation resistant film, followed by a secondary coating mixture powder composed of aluminum powder and / or aluminum halide powder and inert sintering inhibitor powder. Oxidation of carbonaceous material by double coating which is buried in secondary coating mixture added with halogenated powder and heat treated at 600-1000 ℃ and heat treatment condition of 1-5 hours under non-oxidizing atmosphere. It is about a prevention method.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

As the chromium halide powder forming the primary coating film, one or two or more powders selected from the group consisting of chromium chloride powder such as CrCl ₂ or CrCl ₃ or chromium fluoride powder such as CrF ₂ or CrF ₃ are preferable. As the inert sintering prevention powder, Al ₂ O ₃ , SiO ₂ or MgO may be mentioned.

The primary coating is a chromium chloride which is coated with a carbon material or a carbon composite material to be coated in the mixed powder of the chromium halide powder and the inert sintering prevention powder and heat treated at a temperature of 800-1100 ° C. under a non-oxidizing gas atmosphere such as argon gas. Alternatively, chromium fluoride is liquefied or vaporized to precipitate on the surface of the carbon material and coated.

In addition, in another primary coating of the present invention, the chromium oxide powder forming the primary coating film may include Cr ₂ O ₃ powder, and the like, and the halogen compound powder may be NaCl, NH ₄ Cl, MH ₄ F. Powder, and the like.

In the mixed powder of the chromium oxide powder and the halogen compound powder, chromium is deposited on the surface of the material by coating the carbon material or the carbon composite material and heat-treating the same method as described above.

The primary coated material as described above is formed of a chromium carbide layer which is a uniform and dense intermediate layer and a metal chromium which is a coating layer.

The aluminum halide used in the secondary coating may include AlCl ₃ , AlF ₃ , and the like. Al ₂ O ₃ , SiO _2, or MgO may be used as the anti-sintering powder. NaCl, NH ₄ Cl may be used as the halogenated compound. And MH ₄ F powders. The secondary coating is applied at a temperature of 600-1000 ° C. under a non-oxidizing gas atmosphere such as argon gas even when the powder is mixed with metal aluminum powder and aluminum halide alone or mixed powder with inert sintering inhibitor powder or mixed powder with halogen compound added thereto. Heat treatment.

In case of the second coating, if the heat treatment temperature is 600 ℃ or less, the reaction rate is slow and the injected aluminum adheres to the chromium layer as it is, so that the film is not formed uniformly. Since the film re-reacts with the halogen element in the coating reactor, it may cause surface defects. Therefore, the heat treatment temperature for the second coating, which is an aluminum coating, is preferably selected to be 600-1000 ° C.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

As shown in FIG. 1, the carbon composite material specimen 3 having physical properties as shown in Table 1 in the inside of the reaction tube 2 heated as the heating element 1 and the mixed powder for coating as shown in Table 2 ) And the crucible (4), which is placed therein, is fixed to the support (5), and argon gas is supplied at 20 ml / min from the lower end of the reaction tube (2) to the inert gas source (6), and the inside of the reaction tube (2) is sufficiently deoxidized. The internal pressure of the reaction tube 2 was kept constant by setting the atmosphere and releasing gas from the upper portion of the reaction tube 2.

The carbon composite material specimen 3 is a composite material composed of PAN (polyacrylonitrile) -based carbon fibers and pitch-based carbon matrices, the size of which is 5 × 5 × 10 mm, and the surface is polished on abrasive paper No. 800. Dry after ultrasonic cleaning in acetone bath.

The crucible 4 is a graphite crucible having an inner diameter of 15 mm, an outer diameter of 25 mm, and a height of 25 mm.

After 30 minutes from the start of argon supply, the temperature was raised at a rate of 10 ° C./min, and heat-treated under the heat treatment conditions shown in Table 2 below. Then, the coating amount was measured, and the measurement results are shown in Table 3 below. The oxidative test was carried out and the result is shown in FIG. 2 together with the result of the uncoated carbon material specimen. This oxidative resistance test was carried out by placing the specimen in a thermosquan previously heated to 900 ° C, supplying dry air at 600cc / min, and oxidizing it. It is shown by measuring the weight loss over time (minutes).

The chromium chloride of Table 2 below is a powder having 99% purity and a particle size of 325 mesh or less, and alumina is a powder having 99.9% purity and particle size of 325 mesh or less calcined at 1000 ° C.

TABLE 1

TABLE 2

TABLE 3

Among the first coated specimens as described above, the coated specimen coated according to the Invention Example (1) and the coated mixture powder as shown in Table 4 are placed in the graphite crucible of the coating apparatus shown in FIG.

Aluminum chloride (AlCl ₃ ) and aluminum sulfide (AlF ₃ ) used as the coating mixture powder of Table 4 are powders of 99% purity and 325 mesh or less, respectively. The alumina powder is 99.9% pure and calcined at 1000 ° C., 325 mesh. Passing minutes. In addition, the powder of metallic aluminum was also 325 mesh through powder with 99% purity, and the ammonium chloride and sodium chloride powder were 98% pure and 100 mesh passed powder.

As in the primary coating, the crucible was placed inside the reaction tube, placed in an argon atmosphere, coated with the conditions shown in Table 4 below, then cooled to room temperature, and the specimen was taken out and subjected to oxidation experiments. Shown in The oxidation experiment is first made of a mesh that can suspend the specimen with platinum wire, put the secondary coated specimen in the mesh and then suspended in the electric furnace, and in this state by raising the temperature to a predetermined temperature 1300 ℃ to measure the weight change It is.

TABLE 4

As shown in FIG. 3, in the case of the double-coated invention material (1-4) according to the present invention, there is only an increase of 0.08% or less due to oxidation of the coating layer even after oxidizing at 1300 ° C for 9 hours. On the other hand, in the case of Inventive Example (1) in which only the primary coating treatment was performed, there was no loss, and it was found that the weight was reduced by oxidation.

Example 2

Using the coating treatment device shown in FIG. 1, the carbonaceous material having the properties shown in Table 5 was buried in the primary coating mixture powder mixed at the mixing ratio as shown in Table 6, and then coated under the coating treatment conditions shown in Table 6 below. , The coating amount was measured, and the measurement results are shown in Table 7 below.

The carbon material is an isotropic graphite material, the size of which is acetone washing after cutting and grinding to 5 × 5 × 10 mm, chromium oxide (Cr ₂ O ₃ ) powder and sodium chloride powder in the coating mixture powder of Table 6 below Silver has a purity of 99% and a particle size of 325 mesh or less.

In addition, an oxidation resistance test was performed on the primary coated specimens using ten thousand square meters, and the results are shown in FIG. 2. In this experiment, the specimens were placed in a ten thousand square sheets heated to a mesh of 900 ° C. Supplying dry air at 600cc / min and measuring the weight loss according to the oxidation time (minutes).

TABLE 5

TABLE 6

TABLE 7

As described above, the primary coated coating specimen according to the invention example (4) and the coating mixture powder prepared as shown in Table 8 are placed in the graphite crucible of the coating apparatus shown in FIG.

AlCl ₃ ), and AlF ₃ powder used as the coating mixture powder of Table 8 are 99% purity and 325 mesh or less, respectively.Al ₂ O ₃ powder is 99.9% pure and calcined at 325 mesh at 100 ° C. to be.

In addition, the metal Al powder was 99.9% pure, 325 mesh through powder, and NH ₄ Cl and NaCl powders were 98% pure and 100 mesh passed powder.

As in the primary coating, the crucible was placed inside the reaction tube, placed in an argon atmosphere, coated with the conditions shown in Table 4 below, and then cooled naturally to room temperature, and then the specimen was taken out and subjected to oxidation experiments. Shown in Oxidation experiment was carried out in the same manner as in Example 1 to measure the weight change.

TABLE 8

As shown in FIG. 4, in the case of the present invention (5-8) double-coated according to the present invention, even if it was oxidized at 1300 ° C for 9 hours, there was only an increase of 0.08% or less due to oxidation of the coating layer. On the other hand, in the case of Inventive Example (4) in which only the primary coating treatment was performed, there was no weight loss due to oxidation.

As shown in FIGS. 3 and 4, when the double coated carbon material is placed in a high temperature oxidation atmosphere according to the present invention, aluminum on the surface of the carbon material is oxidized to form an alumina (Al ₂ O ₃ ) as an oxide film. Therefore, this alumina film has an effect of preventing oxygen permeation, and extremely thin chromium carbide is formed between the carbon material, and even if chromium precipitates thereon, the adhesion between the carbon material and chromium is very good and oxidation is prevented. The chromium surface layer is changed.

In the case of coating with a double coating layer according to the present invention, it is actually formed of four layers of an alumina-aluminum-metal chromium-chromium carbide layer and the metal chromium layer is oxidized to form a chromium oxide layer even when a defect of the alumina layer occurs at a high temperature. It has a dual effect of preventing oxidation.

As described above, the present invention is capable of low temperature operation when coating carbon materials or carbon composite materials, compared to CVD or plasma spraying, and is capable of treating coatings at low cost and energy savings without limiting the size and shape of materials. It is effective in forming a high temperature oxidation resistant film by double coating.

Claims (4)

In preventing the oxidation of the carbon material or the carbon composite material, the carbon material or the carbon composite material in the primary coating mixture powder, which is composed of weight%, chromium halide powder: 30-50%, and inert sintering inhibitor powder: 50-70%. And then heat-treated in a non-oxidizing atmosphere in a conventional manner to form a primary oxidation resistant film, and then a single or mixed powder of aluminum powder and aluminum halide powder is buried in a secondary coating mixture powder composed of inert sintering inhibitor powder and is in a non-oxidizing atmosphere. Heat treatment for 1-5 hours at a temperature of 600-1000 ℃ at to form a secondary oxidation resistant coating, characterized in that the oxidation of the carbon material by a double coating. The method for preventing oxidation of carbon material by double coating according to claim 1, wherein a halogenated compound powder is further added to said secondary coating mixture powder. In preventing the oxidation of the carbon material or the carbon composite material, the carbon material or the carbon composite material in the primary coating mixture powder, which is composed of weight%, chromium oxide powder: 85-95%, and halogen compound powder: 5-15%. Heat-treated in a conventional manner in a non-oxidizing atmosphere to form a primary oxidation resistant film, and then buried in a secondary coating mixture powder composed of an aluminum powder and an aluminum halide powder alone or a composite powder and an inert sintering inhibitor powder. Method of preventing oxidation of carbon material by double coating by heat treatment at 600-1000 ° C. for 1-5 hours to form secondary oxidation resistant film. 4. The method for preventing oxidation of carbon material by double coating according to claim 3, wherein a halogen compound powder is further added to said secondary coating mixture powder.