KR970008715B1 - Process for the preparation of coating - Google Patents

Abstract

In the coating process, carbon material or carbon composite material was implanted in a first coating powder mixture comprising 30- 50 wt.% of halogenated chromium powder and 50- 70 wt.% of inactive antisintering powder, and heat-treated in a non-oxidative atmosphere to give a first antioxidizing coating. The coated carbon material was implanted in the second coating powder containing metal nickel powder, halogenated nickel or its composite powder and inactive antisintering powder, and heat-treated at 850- 1,200 deg.C for 1- 5 hours in a nonoxidative atmosphere to give the second antioxidizing coating.

Description

Double coating method to prevent oxidation of carbon material

1 is a schematic view showing a coating apparatus for a carbon material which can be used in the implementation of the method according to the present invention.

2 is a graph showing the amount of loss of oxides of carbon material according to oxidation time

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

5 is a graph showing the weight change by oxidation of the carbon material subjected to the secondary coating treatment of nickel-based and aluminum-based of the present invention.

* Explanation of symbols for main parts of the drawings

1: heating element 2: reaction tube

3: plate material specimen 4: crucible

5: support base 6: inert gas source

7: mixed powder for coating

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for preventing oxidation of a carbon material or a carbon composite material (hereinafter referred to as a "carbon material") used in brake materials such as high-speed aircraft, racing cars, and complicated electrodes and heating elements. The present invention relates to a coating method for preventing oxidation of a carbon material by double coating which prevents oxidation by first forming a chromium-based film on the surface of the carbon material and forming a nickel-based film secondly on the chromium-based film.

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

In order to compensate for this defect, various coating methods for the antioxidant coating have been studied. Coating methods to prevent oxidation of carbon materials include coating by chemical vapor deposition (CVD) such as silicon carbide (SiC), silicon nitride (Si ₂ N ₄ ), magnesia (MgO), alumina (Al ₂ O ₃ ), and chromium oxide Plasma spraying, such as (Cr ₂ O ₃ ), is performed. (Jaurna of Material Science, Vol 24 (1989), P.3511-3520)

However, the coating method by Chemical Vapor Deposition (CVD) has a disadvantage 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 is not thick, it is difficult to form a stable anti-anode film, and there is a problem of being limited in 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 of preventing the oxidation of the carbon material by heat-treating the carbon material in a mixed powder of chromium halide powder and inert sintering inhibitor powder or mixed powder of chromium oxide powder and chromium halide compound powder in order to improve the above problems. Patent application has been filed (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 (Cr ₂ O ₃ ) when it is used for a long time at a high temperature (1000 ° C. or more) for a very small amount but evaporates, and thus there is a problem in that stability for oxidation prevention is long. In addition, a patent application has been proposed for the carbon material oxidation prevention method by double coating which prevents oxidation by coating chromium based on the surface of the carbon material as the primary application method and covering aluminum based on the chromium second. Patent Application No. 92-14096.

The applied method is superior to the case of coating only the primary chromium-based, but the antioxidant effect is excellent, but when the secondary coating layer is oxidized for a long time at high temperature (1000 ℃ or more), the initial melting point of aluminum is low, the surface thickness is heterogeneous It is formed in such a way that the oxide layer is uneven and micropores are formed on the surface so that the chromium layer in the aluminum layer is in contact with the high temperature atmosphere, so that the chromium layer is traced in the gaseous phase of chromium trioxide (O ₃ ), but the stability is lowered.

Accordingly, an object of the present invention is to provide a double coating method for the oxidation of the carbon material that can effectively prevent the high temperature oxidation of the improved carbon material to solve the above problems.

According to one aspect of the present invention, in the coating method for preventing oxidation of a carbon material or a carbon composite material, the first composition is composed of chromium halide powder: 30-50% by weight and 50-70% inert sintering inhibitor powder by weight%. A carbonaceous material or carbon composite material was embedded in the coating mixture powder, and heat-treated in a non-oxidizing atmosphere in a conventional manner to form a primary oxidation resistant film, and then composed of metal nickel powder, nickel halide powder alone or a composite powder, and an inert sintering powder. A carbon material characterized by burying the first coated carbon material as described above in the secondary coating mixture powder and heat-treating at a temperature of 850-1200 ° C. for 1-5 hours in a non-oxidizing atmosphere to form a secondary oxidation resistant film. The coating method for the oxidation prevention of the present invention is provided.

According to another aspect of the present invention, in the coating method for preventing oxidation of a carbon material or a carbon composite material, the first composition is composed of weight percent, chromium oxide powder: 85-95%, and halogen compound powder: 5-15%. After coating carbon powder in coating mixture powder and heat-treating in a non-oxidizing atmosphere in the usual way to form primary oxidation resistant film, secondary coating composed of nickel powder and nickel halide powder alone or composite powder and inert sintering inhibitor powder To prevent oxidation of the carbon material characterized in that the buried carbon material in the mixed powder as described above and heat-treated for 1-5 hours at a temperature of 850-1200 ℃ in a non-oxidizing atmosphere to form a secondary oxidation resistant film A coating method is provided. EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention forms a chromium film layer having a strong bond with carbon on the surface of the carbon material and a nickel film layer thereon, thereby forming a double oxidation resistant film having excellent oxidation resistance and stability even at high temperatures, thereby effectively preventing high temperature oxidation of the carbon material. I would like to.

In one aspect of the present invention, the primary coating is a carbon material to be coated on the primary coating mixture composed of a mixed powder of chromium halide and inert antisintering agent powder and heat treated in a conventional manner, wherein the heat treatment is argon gas Heat treatment at 850-1050 ℃ under a non-oxidizing gas atmosphere such as chromium chloride or chromium fluoride is liquefied or vaporized by the heat treatment in this way is deposited on the surface of the carbon material is coated.

As the chromium halide powder, chromium chloride powders such as CrCl ₂ and CrCl ₃ or chromium fluoride powders such as CrF ₂ and CrF ₃ may be used alone or in combination. The powder for preventing inert sintering may be Al ₂ O ₃ , SiO ₂ and MgO powders may be used alone or in combination.

In addition, in the mixing ratio of the chromium halide and the inert sintering inhibitor, when the mixing amount of the chromium halide powder is 50% by weight or more, the chromium halide is liquefied or vaporized at a predetermined temperature, thereby increasing the amount of activated chromium and increasing the diffusion rate. On the other hand, metal chromium precipitates on the surface of the carbon material so much that it forms a non-uniform surface layer, and when the mixing amount is 30% by weight or less, the amount of activated chromium in the chromium halide decreases and the diffusion rate is slowed and the carbon material is coated. Since there is a problem that takes a long time at the time of mixing the amount of the chromium halide powder and the inert sintering inhibitor is preferably limited to 30-50% by weight and 50-70% by weight, respectively. Further, in another aspect of the present invention, chromium is deposited on the surface of a carbon material by burying a carbonic acid material to be coated in a primary coating mixture adjusted with chromium oxide powder and a halogenated compound powder and heat-treating the same method as described above. And coated.

As described above, the primary coating forms a uniform and dense chromium carbide layer as an intermediate layer and a metal chromium layer as a coating layer.

Cr ₂ O ₃ powder is used as the chromium oxide powder, NaCl, NH ₄ Cl and NH ₄ F powder may be used alone or in combination as the halogen compound powder.

On the other hand, in the mixing ratio of the chromium oxide powder and the halogen compound powder, when the amount of the halogen compound is 15% by weight or more, the reaction rate of the chromium oxide and the halogen compound is increased so that the amount of activated chromium increases, so that the surface of the carbon material is Chromium precipitates to form a non-uniform surface layer, and if it is less than 5% by weight, the reaction rate of chromium oxide and halogen compound decreases, so the amount of activated chromium decreases, so that the diffusion rate is slowed and it takes a long time to coat the carbon material surface. Since there is a problem, the amount of the chromium oxide powder and the halogen compound powder is preferably limited to 85-95% by weight and 5-15% by weight, respectively.

The secondary coating is buried in a secondary coating mixture composed of a metal nickel powder and a nickel halide alone or a mixed powder and an inert sintering agent powder, and the primary coating of carbon material as described above and scattered such as nitrogen or argon gas. Heat treatment is performed at a temperature of 850-1200 ° C. under a chemical atmosphere.

When the heat treatment temperature during the secondary coating is 850 ℃ or less, the reaction rate is slowed down and the added nickel adheres to the chromium layer as it is, so that the film is not uniformly formed. When the temperature is above 1200 ℃, the film of the metal chromium layer formed during the primary coating is It is preferable to heat-treat at 850-1200 ° C. for the secondary coating, which is a nickel coating, because the surface defects are caused by the reaction with the halogen element in the coating reactor.

Nickel halides used in the secondary coating may be NiCl ₂ and Al ₂ O ₃ , SiO ₂ and MgO powders may be used as powders for sintering prevention. In addition, a secondary coating mixture may be prepared by further adding a halogen compound powder to the secondary coating mixture, wherein the halogen compound may be NaCl, NH ₄ Cl, and NH ₄ F powder.

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 the physical properties as shown in Table 1 and the coating as shown in Table 2 in the reaction tube 2 heated as the heating element 1 is shown in FIG. The crucible 4 containing the mixed powder 7 is fixed to the support 5, and argon gas is supplied to the inert gas source 6 from the lower end of the reaction tube 2 at 20 ml / min. The internal pressure of the reaction tube 2 was kept constant by making the inside sufficiently non-oxidative atmosphere and releasing gas from the upper part 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. In acetone bath, it is dried after ultrasonic cleaning. The crucible 4 is a graphite crucible having an inner diameter of 15 mm and an outer diameter of 25 mm.

After 30 minutes from the start of argon supply, the temperature increased at 10 ° C./min. After the heat treatment under the heat treatment conditions of <Table 2>, the coating amount was measured and the measurement results are shown in the following <Table 3>. The oxidation resistance test was carried out and the results are shown in FIG. 2 together with the results of the uncoated carbon material specimen. The oxidation resistance test was carried out by placing the specimen in a thermosquan previously heated to 900 ° C. and supplying dry air at 600 cc / min. And it is shown by measuring the weight loss according to the oxidation time (minutes).

Chromium chloride in Table 2 below is a powder having a purity of 99% and a particle size of 325 mesh or less, and alumina is a powder having a purity of 99.9% and a 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 Comparative Example (1) and the secondary coating mixture powder prepared as shown in <Table 4> are applied to the graphite crucible of the coating apparatus shown in FIG. Put it in.

Nickel chloride (NiCl ₂ ) used as the coating mixture powder of Table 4 below is a powder having a purity of 99% and 325 mesh or less, respectively, and the alumina powder has a purity of 99.9% and 325 mesh passages calcined at 1000 ° C. Metal nickel powder was 99.9% pure and 325 mesh was passed. As ammonium chloride and sodium chloride powder, 100 mesh passed was used, having 98% purity.

As in the primary coating, the crucible was placed inside the reaction tube and placed in an argon atmosphere, followed by secondary coating treatment under the conditions of <Table 4>, followed by naturally cooling to room temperature, and then taking out the specimen to perform an oxidation experiment. Is shown in FIG.

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 an electric furnace, and in this state, the temperature is raised to a temperature of 1300 ° C. to extinguish the weight change. It is measured.

TABLE 4

As shown in FIG. 3, in the case of the double-coated invention material (1-3) according to the present invention, there is only an increase of 0.07% or less due to oxidation in the coating even after oxidizing at 1300 ° C for 9 hours. On the other hand, in the case of the comparative example (1) which performed only the primary coating process on the contrary, there is no weight loss by oxidation.

Example 2

Using the coating treatment device shown in FIG. 1, a carbon material having physical properties as shown in Table 5 was buried in the primary coating mixture powder mixed with the following Table 6, and the coating treatment conditions shown in Table 6 below. After coating, the coating amount was measured, and the measurement results are shown in Table 7 below.

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

In addition, an oxidation test was conducted 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 previously heated to 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

The primary coated specimen according to Comparative Example (4) among the primary coated specimens as described above and the secondary coating mixture powder prepared as shown in Table 8 are placed in the graphite crucible of the coating apparatus shown in FIG. .

The NiCl ₂ powder used as the coating mixture powder of Table 8 is 99% pure and 325 mesh or less, respectively, and the Al ₂ O ₃ powder is 99% pure and 325 mesh passed at 100 ° C., and the metal nickel powder is As a purity of 99.9%, 325 meshes were passed, and NH ₄ Cl and NaCl powders were 98% pure and 100 meshes passed.

After putting the crucible inside the reaction tube as in the primary coating and argon atmosphere, after secondary coating treatment under the conditions of the following <Table 4>, naturally cooling to room temperature, taking out the specimen and performing an oxidation experiment. 4 is shown.

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 (4-6) which is double-coated according to the present invention, even if it is oxidized at 1300 ° C. for 9 hours, there is only an increase of 0.08% or less due to the acidity of the coating layer. On the other hand, in the case of Comparative 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 according to the present invention is placed in a high temperature oxidation atmosphere, nickel on the surface of the carbon material is oxidized to form nickel oxide, which is an oxide film. The film has an effect of preventing oxygen permeation, and extremely thin chromium carbide is formed between the carbon material, and even if chromium is deposited thereon, the adhesion between the carbon material and chromium is very good, and the chromium surface layer is formed by oxidation. Will change.

Example 3

In this embodiment, when double coating the primary coating treated specimen prepared as in Example 1, the case of using the nickel-based and aluminum-based (Korean Patent Application No. 92-14096) as the coating material As a test for comparison, the double coating method was performed in the same manner as in Example 2, and the conditions for the respective chemical compositions of the present examples are shown in Table 9 below, and the coating treatment conditions were 1 hour at 1000 ° C. for 5 hours. The experimental apparatus of FIG. Was used, and double-coated specimens were prepared based on aluminum and nickel, respectively.

In addition, the prepared coated specimen was naturally cooled to room temperature, the specimen was taken out, an oxidation experiment was performed in the same manner as in Example 1, and the weight change was measured. The results are shown in FIG.

As can be seen from the comparative graph of FIG. 5 and the comparative example of the present invention, it can be seen that the weight change of oxidation is stable in the present invention. It can also be seen that the loss of oxide is almost absent. On the other hand, in the case of the comparative example, the oxidation test shows that the loss of oxide occurs after 12 hours, which is completed by the oxidation of the aluminum layer and the oxidation of the internal chromium layer and the evaporation of a very small amount by the vaporization of chromium oxide (Cr ₂ O ₃ ). It can be seen that the loss occurs. That is, in the case of the comparative example, when the carbon layer is directly oxidized at a high temperature, rapid oxidation loss is shown, whereas in the case of the present invention, it is found to be very stable.

TABLE 9

According to the present invention, even though the coating is carried out with a double coating layer, the coating film is actually formed into four layers of the nickel oxide-nickel-metal chromium-chromium carbide layer and the chromium oxide layer is oxidized by oxidizing the metal chromium layer even when a defect of the nickel layer occurs at a high temperature. It has a dual effect of forming to prevent oxidation. In other words, by coating the carbon material with the double coating treatment by the method of the present invention, a coating having excellent oxidation resistance at high temperature can be formed.

Claims (4)

In the coating method for preventing oxidation of a carbon material or a carbon composite material, the carbon material or the first coating mixture powder, which is composed of a weight%, chromium halide powder: 30-50%, and inert sintering agent powder: 50-70%. After buried a carbon composite material and heat-treated in a non-oxidizing atmosphere in a conventional manner, a primary oxidation resistant film was formed, and then in a secondary coating mixture powder composed of a metal nickel powder, nickel halide alone or a composite powder, and an inert sintering inhibitor powder. Double coating for preventing oxidation of the carbon material, which is buried as above and the primary coated carbon material is heat-treated at a temperature of 850-1200 ° C. for 1-5 hours in a non-oxidizing atmosphere to form a secondary oxidation resistant film. Way. The double coating method for preventing oxidation of a carbon material according to claim 1, wherein a halogen compound powder is further added to said secondary coating mixture powder. In the coating method for preventing oxidation of a carbon material or a carbon composite material, the carbon material or carbon in the primary coating mixture powder, which is composed of weight%, chromium oxide powder: 85-95%, and halogen compound powder: 5-15%. After burying the composite material and heat-treating in a non-acid-free atmosphere in a conventional manner to form a primary oxidation resistant film, the secondary coating mixture powder composed of nickel powder and nickel halide powder alone or composite powder and inert sintering inhibitor powder A double coating method for preventing oxidation of a carbon material, wherein the first coated carbon material is buried and heat treated at a temperature of 850-1200 ° C. for 1-5 hours in a non-oxidizing atmosphere to form a secondary oxidation resistant film. . The double coating method for preventing oxidation of a carbon material according to claim 2, wherein a halogenated compound powder is further added to the secondary coating mixture powder.