JPS6251890B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a boron thin plate,
The present invention provides a method for manufacturing a thin plate that is lightweight and has a high specific modulus. The thin plate materials conventionally used for diaphragms of speakers, microphones, etc. are mainly:
Paper-like diaphragms made of a mixture of paper, resin, and carbon fiber, polymer foams, polymer films, and metal thin plates made of aluminum, titanium, and the like have been used. The above-mentioned various diaphragm materials have a relatively low sound velocity (6000 m/sec or less), and it is difficult to extend the frequency characteristics of the speaker to high frequencies. The requirements for a diaphragm for speakers and microphones are that it be light and have a high specific modulus (modulus of elasticity/specific gravity). In other words, the speed of sound is high. On the other hand, boron is known to have the highest speed of sound among the elements. However, since boron is a very hard material with poor workability, it is difficult to make it into a diaphragm by rolling or the like. Therefore, in the past, a diaphragm was made by forming a boron layer on Tetan foil or aluminum foil by physical vapor deposition or chemical vapor deposition. However, with these methods, it is not possible to obtain a diaphragm made solely of boron, and the characteristics of boron are not fully utilized. The method of the present invention solves the problems of the conventional method and provides a thin plate for a diaphragm made solely of boron, which has mechanical strength and has a high sound velocity. The method of the present invention will be specifically explained below. A method for forming boron on a substrate by chemical vapor deposition (CVD) is, for example, heating a substrate placed in a reactor and depositing boron through a reductive decomposition reaction as shown in the following formula. 2BX ₃ +3H ₂ →2B+6HX (However, X is a halogen element such as Cl, Br, I, etc.) In addition, in this boron precipitation reaction, heating temperature, amount of raw material gas flowing into the reactor, reactor Various crystal forms can be obtained depending on the pressure and other factors. Among various crystal systems, the boron film is preferably β-rombohedral, tetragonal, or amorphous because it is dense and has excellent mechanical properties. Next, boron is deposited on the graphite substrate as described above, and then the graphite substrate is mechanically removed to obtain a boron plate. The temperature at which CVD is performed next is
A temperature of 800℃ or higher is required. Furthermore, if there is temperature unevenness, the boron layer attached to the substrate becomes uneven, and cracks occur due to differences in internal stress. Therefore, it is necessary to heat the reactor using a high frequency heating method, an infrared heating method, or a resistance heating method (a method of heating by attaching a heater such as a nichrome wire to the outside of the reactor). Especially when the graphite substrate is thin, high frequency heating is difficult, and infrared heating and resistance heating are better. Regarding the pressure inside the reaction vessel, it is better to keep it at a reduced pressure than at normal pressure (760 Torr) because the mean free path of the reaction gas will be longer, and the temperature of the substrate will not become uneven due to the gas. This is effective because it can lower the boron precipitation temperature. If the reduced pressure is less than 100 Torr, the boron precipitation rate will be slow, and if it exceeds 200 Torr, the temperature of the substrate will likely become non-uniform, which is undesirable. The optimal pressure is 10~
It is in the range of 200Torr. By forming a chromium or chromium boride layer on a graphite substrate and then forming a titanium or titanium boride layer thereon, boron can be directly deposited on a conventional metal substrate or on a graphite substrate. The yield of the vibrating thin plate was greatly increased compared to the case where the vibrating thin plate was deposited. The reason for this is presumed to be that the above layer relieves the stress generated during boron deposition. Also,
The thickness of chromium or chromium boride layer is 0.5~
The reason why the thickness is 10 μm is that if it is less than 0.5 μm, it will be too thin and will not be effective in improving the yield, and if it is more than 10 μm, it will be too thick and the boron film will be deformed. The titanium or titanium boride layer is made to have a thickness of 0.2 to 15 .mu.m. If it is less than 0.2 .mu.m, it is too thin and has no effect on improving the yield, and if it is 15 .mu.m or more, it is too thick and the boron film is deformed. Further, the Cr or Cr boride material, Ti, or Ti boride layer can be formed by a vacuum evaporation method or a sputtering method. Detailed embodiments of the present invention will be described below. On a graphite substrate with a width of 20 mm, a length of 200 mm, and a thickness of 100 μm, chromium was deposited to a thickness of 0.5 μm by vacuum deposition, and then titanium was deposited to a thickness of 0.2 μm. This substrate was then heated to 1000° C. in a reaction vessel using an infrared lamp. In this state, a mixed gas of 1 part by volume of boron trichloride (BCl ₃ ) and 3 parts by volume of hydrogen (H ₂ ) was flowed into the reaction vessel at a rate of 1 per minute for 3 minutes. At this time, the pressure inside the reactor was controlled to 100 Torr by operating a rotary pump and valves. As a result, an amorphous boron layer with a thickness of about 55 μm was formed on the graphite substrate. The diameter of the sample obtained in this way is measured using a laser beam.
Ten 19 mm discs were cut, and the graphite substrate was then removed to obtain boron thin plates. The yield and various properties of the boron thin plate obtained here are summarized in Table 1 as Sample 1. Thereafter, Samples 2 to 16 shown in Table 1 were prepared in the same manner as described above, with the pressures of the substrate and reactor being constant, and the heating temperature, the film thickness of chromium, titanium, etc. being varied. (However, samples No. 12 to 16 are comparative examples.)

【table】

[Table] From the above results, by forming a chromium or chromium boride layer on graphite and then forming a titanium or titanium boride layer on top of this, using as a substrate on which boron is deposited,
A boron thin plate with improved yield and higher elastic modulus than before can be obtained, and can be used particularly for diaphragms of speakers and microphones to improve the high frequency characteristics of the diaphragms.

Claims (1)

[Claims] 1. A chromium layer or a chromium boride layer is formed on graphite, and then a titanium or titanium boride layer is formed on the substrate using a chemical vapor deposition method ( (CVD method) to deposit boron, then remove the substrate,
A method for producing a boron thin plate, characterized by obtaining a boron thin plate. 2 The thickness of the chromium or chromium boride layer is
2. The method for producing a thin boron plate according to claim 1, wherein the thickness is from 0.5 microns to 10 microns. 3. The method for producing a boron thin plate according to claim 1, wherein the thickness of the titanium or titanium boride layer is from 0.2 microns to 15 microns.