JPH0476360B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for forming a thin graphite coating on the surface of SiC whiskers. [Prior Art] SiC whiskers are used as composite reinforcing materials for metals, plastics, etc., but research into composites is also being actively conducted to improve fracture toughness, which is the biggest drawback of ceramic materials. The improvement in fracture toughness due to the composite of SiC whiskers is due to the fact that the highly elastic, microfibrous SiC whiskers dispersed in the ceramic material stop or suppress cracks that occur, or bend the propagation direction to alleviate stress concentration. At the same time, it is said that this effect is achieved by absorbing energy at the tip of the crack through its pulling effect. Therefore, if the bonding force at the interface between the ceramic material serving as the matrix and the composite SiC whiskers is too high, the above-mentioned effects will be diminished and the improvement of fracture toughness will not proceed smoothly. However, when SiC whiskers are directly composited, the interfacial bonding force with the ceramic matrix tends to become extremely strong. For this reason, attempts have been made to reduce the interfacial bonding force with the ceramic matrix by forming a carbon film on the surface of SiC whiskers.
The present applicant has already proposed a developed technology (Japanese Patent Application No. 157520/1982). [Problems to be Solved by the Invention] The method for forming a carbon film according to the above-mentioned Japanese Patent Application No. 157520/1980 is to deposit a thin layer of thermosetting resin on the surface of SiC whiskers, and then apply the film in a non-oxidizing atmosphere. 800
The main feature of this product is firing and carbonizing at ~1200°C, and effective surface modification can be performed to improve the drawing effect. However, if this carbon coating can be converted into graphite, the interface will become more slippery, making it possible to further improve the drawing effect. Normally, high heat treatment exceeding 2500°C is required to convert carbon into graphite, and in particular, the glassy carbonaceous carbon film formed by the above-mentioned prior invention is difficult to graphitize. It is known that it does not easily transition to the crystal structure of graphite. Therefore, 2000 without alteration of SiC whiskers.
It was considered technically impossible to form a graphite film at temperatures below ℃. However, in the course of research to develop peripheral technology for the earlier invention, the inventors discovered that the carbon film formed by the invention of patent application No. 157520/1982 was only able to withstand temperatures of 1500 to 1800°C.
The researchers discovered the surprising fact that it converts into a graphite film even in the temperature range of . The present invention was developed based on the above knowledge, and its purpose is to develop a method for forming a graphite film on SiC whiskers, which can form a graphite film by low-temperature heat treatment, which was considered impossible with conventional technology. It's there to provide. [Means for Solving the Problems] That is, the method of forming a graphite film on SiC whiskers according to the present invention involves dispersing SiC whiskers in a solution that has been sufficiently homogenized by dissolving a thermosetting resin in an organic solvent. The structural feature is that the organic solvent is removed by over-drying, the adhered thermosetting resin is then heated and cured, and then treated at a temperature of 1500 to 1800°C in a non-oxidizing atmosphere. . SiC whiskers have a diameter of 0.1 to 2 μm and a length of
Acicular single crystals with aspect properties of 30-100 μm are used. The solution for dispersing SiC whiskers is created by dissolving the thermosetting resin in an organic solvent and leaving it to stand for a long period of time to create a homogenized state in which the polymers that make up the resin form a microscopically uniform phase in the organic solvent. shall be. As the thermosetting resin, highly carbonizable resins such as phenol resin, furan resin, and divinylbenzene resin are preferably used, and as the organic solvent, ethanol, acetone, benzene, toluene, etc. are used. In addition, the solution concentration is
It is desirable to set the concentration to a dilute concentration of 1.0% or less; if it exceeds 1.0%, it becomes difficult to deposit a homogeneous resin thin film. The SiC whiskers are placed in the homogenized resin solution prepared above and stirred and mixed to be uniformly dispersed.
At this time, the amount of SiC whiskers added is desirably set in the range of 50 to 200 g/in view of the degree of dispersion. Next, the SiC whiskers are filtered and dried to volatilize and remove the remaining organic solvent. At this stage,
Since SiC whiskers exhibit entangled aggregates, they are loosened and heated to a temperature of 150 to 180°C to harden the deposited resin layer. The SiC whiskers with the resin film formed thereon are transferred to a heating furnace and treated at a temperature of 1,500 to 1,800°C while maintaining the inside of the furnace in a non-oxidizing atmosphere such as argon or nitrogen. If the treatment temperature is less than 1500°C, the transition of graphitization will not proceed sufficiently, while if it exceeds 1800°C, it will lead to deterioration of the SiC whiskers. Note that it is best to raise the temperature of the furnace as slowly as possible, and it is desirable to adjust the temperature increase rate to about 10°C/min. The film formed in this way is a homogeneous thin layer with a thickness of about 10 to 70 Å and has the properties of perfect graphite. [Function] In the above steps, the process from carbonization to graphitization of the thermosetting resin adhered to the surface of the SiC whiskers can be explained as follows. (1) The resin film gradually begins to carbonize around 400°C, and at a temperature of 800 to 1000°C, a carbon film with random crystal planes is formed as shown in Figure 1. (2) When the temperature rises further, the SiC whiskers on the base material and the surrounding carbon film undergo thermal expansion. However, the thermal expansion of SiC whiskers is much larger, and this difference gives the carbon film tensile stress in the long axis direction of the SiC whiskers, and through this action, the crystal planes change as shown in Figure 2. The structure approaches a graphitized structure. (3) When the temperature reaches 1500 to 1800°C, it transforms into a complete graphite structure with crystal planes arranged in layers as shown in Figure 3. Due to this mechanism, the shape of the graphite film can be achieved even during low-temperature treatment at temperatures of 1,500 to 1,800 degrees Celsius. Therefore, SiC with a graphite coating formed in the present invention
Composite ceramic materials (FRC) using whiskers as reinforcement have enhanced pull-out effects and significantly improved fracture toughness. [Example] Phenol resin [Manufactured by Gunei Chemical Co., Ltd., “Resitop”
After dissolving 45 g of PGA-4508'' in 5000 ml of ethanol (resin concentration 0.9 wt%), it was left to stand for 7 days to prepare a solution in which the polymer chains of the phenolic resin were homogenized with the ethanol. SiC whiskers (0.1-2 μm in diameter,
(Length: 30 to 100 μm) was added and thoroughly stirred and mixed to disperse. Next, the dispersion was filtered, and the resulting SiC whiskers were air-dried to volatilize and remove residual ethanol, loosen entanglements, and heat-cure the adhered resin at 170° C. for 2 hours. The SiC whiskers on which the resin film was formed in this way were transferred to a high-frequency heating furnace, and the furnace was kept in an argon gas atmosphere and heated to 1000°C at a heating rate of 10°C/min.
The temperature was raised to 1600°C and maintained at this temperature for 2 hours. In order to investigate the degree of graphitization of the carbonaceous film (approximately 50 Å thick) formed by the above treatment, surface modification was performed.
The true specific gravity and compressive electrical resistivity of SiC whiskers were measured. The results are shown in Table 1.

[Table] Measured.
From the results in Table 1, it is recognized that graphitization progresses in the example treated at 1600°C compared to the example treated at 1000°C. . In addition, we observed the surface crystal structures of the 1600°C and 1000°C treated examples using a transmission electron microscope (TEM).
The photographs (magnification: 1.5 million times) are shown in Figures 4 and 5, respectively. In FIG. 4 (1600° C. treatment example), compared to FIG. 5, it is clearly confirmed that the graphite crystal planes on the surface are arranged in a layered manner. Next, the obtained surface-modified SiC whiskers were composited with silicon nitride using a powder sintering method. the
The fracture toughness and bending strength of FRC were measured and Table 2
It was shown to.

【table】

〔Effect of the invention〕

As described above, according to the present invention, it is possible to form a graphite film on the surface of SiC whiskers by treating a thin film of thermosetting resin at a low temperature of 1500 to 1800°C. Therefore, by combining it with various ceramic materials such as silicon carbide, titanium carbide, silicon nitride, and alumina, composite performance such as fracture toughness and bending strength can be improved.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic diagrams of the crystal plane state during the heat treatment process on the surface of SiC whiskers.
1000°C treatment stage, Figure 2 shows the 1000-1500°C treatment stage, and Figure 3 shows the 1500-1800°C treatment stage. Figure 4 is a transmission electron micrograph (magnification: 1.5 million times) showing the surface crystal structure of the product treated at 1600°C according to the example, and Figure 5 is a transmission electron micrograph showing the surface crystal structure of the product treated at 1000°C according to the comparative example. Electron micrograph (magnification
1.5 million times). 1...SiC whisker, 2...carbonaceous film, 3...crystal plane.

Claims (1)

[Claims] 1 Disperse SiC whiskers in a solution that has been sufficiently homogenized by dissolving the thermosetting resin in an organic solvent,
A graphite coating on SiC whiskers characterized by over-drying to remove the organic solvent, then heating and curing the adhered thermosetting resin, and then treating it at a temperature of 1500 to 1800°C in a non-oxidizing atmosphere. Formation method.