JPH0421583A - Oxidation-resistant treatment of carbon fiber-reinforced carbon material - Google Patents

Abstract

PURPOSE:To obtain a reinforced carbon substrate having excellent oxidation resistance even in a high-temperature oxidizing atmosphere, by forming a SiC coating film layer on the surface of a carbon fiber-reinforced carbon substrate, cleaning the surface, sensitizing, activating and coating the surface with Fe, Co, or Ni. CONSTITUTION:Carbon fibers are blended with a matrix resin, molded, cured, burnt, carbonized to give a carbon fiber-reinforced carbon substrate and a SiO gas is brought into contact with the surface of the carbon fiber-reinforced carbon substrate to form a SiC coating film layer by conversion method. Then the surface of the coated layer is cleaned, sensitized, activated and coated with Fe, Co or Ni or an alloy consisting essentially of theses metals by electroless plating to subject the carbon fiber-reinforced carbon substrate to oxidation resistant treatment. In the cleaning, ultrasonic cleaning is effectively used. The sensitizing and the activating are carried out in order to provide the SiC coating film layer with electrical conductivity.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to a carbon fiber reinforced carbon material (rC
/C material.” ) regarding an oxidation-resistant treatment method.

[Prior Art] C/C materials have excellent specific strength and specific modulus, as well as excellent heat resistance and corrosion resistance, so they are in the spotlight as structural materials in many fields including aerospace applications.

The C/C material is usually reinforced with carbon fiber woven cloth, felt, tow, etc., impregnated or coated with a matrix resin liquid with a high carbonization residual rate, laminated and molded, and then hardened and sintered to carbonize. However, this material inherits the material disadvantage of carbon material, which is its inherent oxidizability, and this is the biggest bottleneck that hinders its versatility. For this reason, attempts have been made to modify the surface of C/C materials by coating them with oxidation-resistant coatings, such as Z roz , A/! z 03 , S i
A method of coating with a ceramic material such as C has been proposed. However, with coating layers other than SiC, interlayer peeling and cracking occur at the coating interface due to thermal cycles during use, and the function of sufficiently inhibiting the progress of oxidation is not exhibited.

Even in the SiC coating layer, peeling between the eyebrows may occur frequently depending on the method of film formation. That is, methods for coating the surface of a C/C base material with SiC include a conversion method in which carbon in the base material is used as a reaction source to convert it into SiC, and a CVD method in which SiC precipitated by a gas phase reaction is directly deposited. (chemical vapor deposition) method. The former method involves forming 31 layers on the substrate surface by hydrogen reduction of a silicon halide compound such as S i CjL, or forcibly impregnating the substrate with an organosilicon compound such as polycarbonane in a solution state. or S10□ and S on the base material surface.
Contact with SiO gas generated by reacting L, C, etc.,
By heating and reacting these silicon components with the carbon structure of the base material, S
This is due to the mechanism of conversion to iC, and since the SiC layer is formed as a continuous structure on the surface of the base material, there is no coating interface, and exhibits coating characteristics that prevent peeling between the eyebrows. On the other hand, the latter CVD method uses silicon compounds such as 5icfn and hydrocarbons (e.g. C
3H8) or by reductive thermal decomposition of hydrocarbon-containing halogenated organic compounds such as trichloromethylsilane (CHzSiCIi), SiC is deposited on the surface of the substrate. Because the coating interface is clearly separated, when a thermal shock is applied, delamination tends to occur frequently due to the difference in thermal expansion between the layers.

Therefore, as a method for forming an oxidation-resistant film by SiC coating on a C/C material, it is desirable to apply a conversion method, particularly a method of contacting with SiO gas that converts into a dense SiC layer.

[Problems to be Solved by the Invention] In the conversion method using a contact mechanism of SiO gas, a reaction as shown in the following formula occurs between the SiO gas and the carbon component of the C/C base material texture surface.

S io+c-+s i C+CO Therefore, in the reaction stage of the coating process, the carbon component constituting the C/C base material texture surface becomes CO and does not degas, so it becomes Si
Conversion to C progresses, and this gas desorption causes a situation in which minute voids (pinholes) are formed between SiC particles. Furthermore, even with a SiC film produced by the conversion method, depending on the layer thickness and other conditions, microscopic racks may be produced during the reaction, which, together with the aforementioned microporosity, reduces the oxidation resistance. .

As a result of repeated research on methods to solve the above problems, the inventors of the present invention discovered that a metal belonging to the iron group was further applied by electroless plating to the SiC coating surface formed on the C/C substrate surface by a conversion method using SiO contact. It was also confirmed that when coated with an alloy containing these metals, a dense, highly adhesive, and substantially gas-impermeable film was formed.

The present invention was developed based on the above findings, and its purpose is to provide an oxidation-resistant treatment method for C/C material that can impart excellent oxidation resistance even in a high-temperature oxidizing atmosphere.

[Means for Solving the Problems] In order to achieve the above object, the method for oxidation-resistant treatment of C/C material according to the present invention is a method for oxidation-resistant treatment of C/C material, which is obtained by composite molding carbon fibers with matrix resin, hardening and firing carbonization treatment. A SiC coating layer is formed by a conversion method by contacting the surface of a carbon fiber-reinforced carbon substrate with SiO gas, and the surface of the coating layer is cleaned, sensitized, and activated, and then Fe, Co is coated by an electroless plating method. Alternatively, the structure is characterized by being coated with N1 or an alloy containing these metals as main components.

Carbon fibers that serve as reinforcement materials include polyacrylonitrile,
Woven fabrics such as plain weave and twill weave, felt or tow made from various raw materials such as rayon and pitch are used.
As the matrix resin, phenol-based, furan-based, or other liquid thermosetting resins with good carbonizability are used. The carbon fibers are sufficiently wetted with a matrix resin by dipping, impregnation, coating, etc., and then semi-cured to form a prepreg, which is then laminated and pressure-molded. The molded body is heated to completely harden the resin component, and then subjected to firing carbonization treatment or further graphitization according to a conventional method to obtain a C/C base material.

The obtained C/C base material may be repeatedly impregnated with a matrinox resin, hardened, and carbonized to make the structure denser, if necessary.

A SiC coating layer is formed on the C,/C substrate thus obtained by a conversion method. The process is
This is carried out by mixing SiO□ powder with Si or C powder, storing the mixture in a closed heating system, setting a C/C base material in the system, and causing a heating reaction. The conditions at this time are 5i
It is preferable that the molar ratio of Oz:Si or C is 2=1 and the heating temperature is set in the range of 1850 to 2000°C.

In the above-mentioned coating process, SiO
Convert to iC.

Next, the surface of the C/C substrate on which the SiC coating layer is formed is subjected to cleaning, sensitization, and activation treatments as pretreatment for electroless plating. The cleaning process is performed, for example, to remove unfixed SiC particles from the surface, and ultrasonic cleaning is effectively used. Sensitizing treatment and activation treatment are steps carried out to impart electrical conductivity to the surface of the SiC coating layer. For example, in the former treatment, the C/C substrate is treated with stannous chloride (SnC1z). The palladium ions are immersed in a hydrochloric acid mixture and then in the latter treatment, for example, in a hydrochloric acid solution of palladium chloride (PdCIz).
A method of depositing metallic palladium on the SiC-coated surface by unifying with valent tin ions is commonly used.

The SiC-coated C/C substrate that has been subjected to the cleaning, sensitization, and activation treatments in this manner is subsequently subjected to an electroless plating treatment.

The metal to be plated is selected from simple substances such as Fe, Co, and N1, which have a relatively high melting point and are easy to obtain electroless/8 liquid, or alloys containing these metals as main components. This type of alloy includes Ni-Co, Co-N1-PXCo
-Fe-P, Co-N1B, etc. can be mentioned.

(g) There are no particular restrictions on the electrolytic plating conditions (generally known processes can be applied.

[Function] According to the present invention, first, the surface layer of the C/C base material is converted into a dense SIC layer by a conversion method using a SiO contact mechanism. In this process, formation phenomena such as minute voids (pinholes) and cranks between SiC particles occur due to the separation of CO gas from the structural surface of the C/C base material during heating, but these defective sites are It is completely filled with fine metal or alloy particles deposited by electroless plating, and at the same time the entire surface is covered with a dense plating layer. At this time, the formed metal or alloy plating layer adheres to the unevenness of the voids and cracks interposed on the SiC coating surface, so that
Forms an extremely strong plating layer due to its anchoring action.

When this state is shown macroscopically, it becomes a schematic diagram as shown in the figure, and C
The electroless plated film 3 completely fills and covers the pinholes and other irregularities in the SiC film 2 forming the surface layer of the /C base material 1.

Through the action of such a two-stage coating process, a gas-impermeable, highly oxidation-resistant coating is formed on the entire surface of the C/C substrate.

(Example] Hereinafter, the present invention will be explained based on examples.

Example I (1) Preparation of C/C base material A polyacrylonitrile-based high-elasticity plain-woven carbon fiber cloth was impregnated by immersing it in a matrix resin liquid consisting of a phenolic resin initial condensate. Laminate 14 sheets of this and put it in a mold, heating temperature 110°C, applied pressure 20kg/
Composite molding was performed under the condition of cm2.

After heating the molded product to a temperature of 250°C to completely cure it, it was transferred to a firing furnace maintained in a nitrogen atmosphere and heated at 5°C/h.
The temperature was raised to 1000°C at a rate of 100°C and held for 5 hours for firing and carbonization.

The obtained C/C material was impregnated with a phenolic resin liquid under vacuum pressure and fired at 1000°C in the same manner as above three times to produce a C/C base material with a dense structure.

(2) SiC coating 5iOzN powder and Si powder were mixed at a molar ratio of 2:1, and the mixed powder was placed in a graphite crucible and a C/C base material was placed on top. It was covered with a graphite lid.

Next, while maintaining the inside and outside of the crucible in an Ar gas atmosphere, a reaction was carried out at a temperature of 1850'C for 2 hours to convert the surface layer of the C/C material into SiC by the conversion method, with an average density of 1
A 50μ-thick SiC coating layer was formed.

(3) The C/C substrate on which the Ni electroless plating S i C1l film layer was formed was ultrasonically cleaned, then washed with water, and then treated with 10 g/l of stannous chloride at room temperature.
A sensitization treatment was performed by immersing it in an acidic solution of hydrochloric acid, and then an activation treatment was performed by immersing it in an acidic solution of 0.3 g of palladium chloride/42 hydrochloric acid.

Nickel sulfate 30g/l, sodium acetate 10g/!
In an aqueous solution of lI! After adding 0.5 g of activated carbon per bottle, stirring, standing still, and filtering, sodium hypophosphite was added to 108 g of activated carbon.
/N to prepare a plating solution. A plating tank was filled with the plating solution, and the C/C base material that had undergone the activation treatment was immersed in the tank to perform Ni electroless plating for 1 hour.

The conditions of the plating bath are pH: 4.0-4.2, temperature:
It was set at 90'C. Average plating thickness after treatment is 8μm
Met.

(4) Evaluation of oxidation resistance The C/C material on which the SiC coating layer and N1 plating film were formed by the above two-step coating process was placed in an electric furnace, and
The weight loss rate due to oxidation was measured when the sample was cooled at a temperature of 1500°C and 1500°C for 30 minutes. As a result, the weight reduction rate of C/C material was 0.5 when treated at 1000'C.
%, and 2.1% when treated at 1500°C.

This value indicates that the weight loss rate of the C/C material with only the SiC coating layer tested in the same manner for comparison was 4 when treated at 1000'C.
．． This is a significant decrease compared to 11.8% when treated at 0% and 1500°C, and it is clear that the oxidation resistance performance is significantly improved.

Although the Ni plating film was oxidized by this treatment,
It remained on the surface layer and no diffusion into the interior was observed.

Example 2 C/C coated with SiC under the same conditions as Example 1
After the material was similarly cleaned, made susceptible to irradiation, and activated, Co electroless plating was performed in the following manner.

The composition of the plating solution is Kohar sulfate H2g/j2, sodium malonate log#, trimethylamine borane Ig, #
It was sealed and impurities were removed using activated carbon (0.5 g/l) in the same manner as in Example 1, and then used.

The conditions of the plating bath are pH: 5.1 to 6.0, temperature: 90
It was set as ゛C. The average plating thickness after treatment was 17 μm.

The weight loss rate due to oxidation of the C/C material subjected to the two-stage coating treatment was measured under the same conditions as in Example 1. It showed good oxidation resistance of 2.0%.

〔Effect of the invention〕

As described above, according to the present invention, SiO is formed on the surface of the C/C material.
A high degree of oxidation resistance can be imparted by forming a SiC film layer by a conversion method using a contact mechanism, and then performing a two-step coating process of electrolytically plating a high melting point metal or alloy on the top surface.

Therefore, it can be used for structural members exposed to severe conditions under high-temperature oxidizing atmospheres, resulting in effects such as ensuring stable performance and extending service life.

[Brief explanation of the drawing]

The figure is a schematic diagram showing a cross-sectional state of the oxidation-resistant coating according to the present invention. 1... C/C base material 2... SiC coating 3...
Electroless plating film applicant Tokai Carbon Co., Ltd. agent Patent attorney Masaya Takahata

Claims (1)

[Claims] 1. A SiC coating layer is formed by a conversion method by bringing SiO gas into contact with the surface of a carbon fiber-reinforced carbon base material obtained by composite molding carbon fibers with a matrix resin, curing and firing carbonization treatment, and cleaning the surface of the coating layer. 1. A method for oxidation-resistant treatment of a carbon fiber-reinforced carbon material, which comprises sensitizing and activating the material and then coating it with Fe, Co, Ni, or an alloy containing these metals as main components by electroless plating.