JPH0462362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a mirror having a high reflectance and particularly suitable for high energy beams. Generally, mirrors are made by forming an aluminum or silver film on the back surface of an ordinary plate glass, and backing this with paint or the like. Such mirrors cannot be used in special atmospheres because the glass has poor corrosion resistance and heat resistance. On the other hand, many ceramic materials such as silicon carbide have high corrosion resistance and heat resistance, but generally have low reflectance, and many of them cannot be used as they are as high-precision mirrors. In order to increase the reflectance, it is preferable to polish the surface to make it smooth, but conventional silicon carbide has pores, crystallinity,
There was no suitable mirror in terms of size, etc. The present inventors have made this invention as a result of studying silicon carbide, which is suitable as a material, and the conditions preferable for mirrors.
It is manufactured by a CVD method, etc., and especially when it is produced by a hot press method or a self-sintering method, it is not suitable as a mirror because of the presence of many impurities and pores. or
Even when using the CVD method, reflectances of 60% or higher are not observed. This is based on the discovery that silicon carbide crystals are fine and have poor crystallinity, which is the reason why the reflectance cannot be improved. In the present invention, it has been revealed that silicon carbide crystals obtained by chemical vapor deposition (CVD) have a close relationship with reflectance when the manufacturing conditions are varied. That is, this reflectance is approximately proportional to the crystallinity and size of the obtained silicon carbide crystal. Crystallinity and size can be measured by X-ray diffraction and are related by the following formula. β·cosθ/λ=Ι/ε+η·sinθ/λ where β is the half-width, θ is the Bragg angle, λ is the wavelength of the characteristic X-ray, ε is the crystallite size, and η is the effective strain of the lattice. It was also found that the smaller the value of the half width β, the better the reflectance and the better the mirror characteristics. In addition, the deposited surface was polished and etched to clarify the crystal shape on the polished surface, and the maximum width of each particle was measured to be 20 μm.
The area occupied by the above particles was measured. Comparing the results with the reflectance, it was found that the area of large crystal particles (20μ or more) was 20% of the polished surface.
% or more, it became clear that the reflectance was high. Examples of the present invention will be described below. Example 1 CVD on the surface of a high-purity treated carbon plate
Four types of silicon carbide films were formed by changing the conditions according to the method. This surface was polished to a mirror finish under the same polishing conditions. The average width of the diffraction line of the (200) plane using Cu-Kα rays was determined using an X-ray diffractometer for these mirror surfaces, and as a result, a mirror exhibiting crystallinity as shown in FIG. 1 was obtained. Table 1 shows the results of determining the reflectance of each visible light beam.

[Table] As a result, it became clear that the reflectance of a material with a half-width exceeding 0.40° decreases rapidly. Example 2 CVD on the surface of a high-purity treated carbon plate
Six types of silicon carbide films were formed by changing the conditions according to the method. This surface was polished to a mirror finish under the same polishing conditions. When we measured the maximum width of the crystal grains on those mirror surfaces and determined the area of the grains that were 20μ or more, the areas were 5%, 9%, 15%, 20%, 25%,
It was 30%. Table 2 shows the results of determining the reflectance by visible light for each of these.

[Table] As a result, it became clear that when the area ratio of particles of 20μ or more was less than 20%, the reflectance decreased significantly. In the above examples, the reflectance of visible light was measured, but the reflectance of each wavelength such as infrared rays and X-rays showed the same tendency as that of visible light. Furthermore, the conditions of the CVD method and the size of the crystal do not necessarily match. It is thought that a crystal with a relatively small half-width at least has a good arrangement of atoms in the crystal, and that its crystallinity also has a good effect on workability during polishing. In the above example, silicon carbide was formed on the surface of high-purity carbon, but the base material is not necessarily limited to carbon.
For example, other materials such as silicon carbide and alumina may be used.

[Brief explanation of the drawing]

FIG. 1 shows an X-ray diffraction pattern of a silicon carbide mirror.

Claims (1)

[Claims] 1. The half-width of the (200) plane of the silicon carbide crystal on the polished surface, which is composed of a β-type silicon carbide surface formed by chemical vapor deposition, is 0.40 degrees or less according to X-ray diffraction. Characteristic silicon carbide mirror. 2. The silicon carbide mirror according to claim 1, wherein the area ratio of crystals having a maximum width of crystal boundaries of 20 μ or more on the polished surface is 20% or more.