JPS6054885B2 - Manufacturing method of boron structural material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a boron structural material, and particularly aims to improve the film quality, mechanical properties, and manufacturing yield of boron constituting the boron structural material. It is something.

Boron has a hardness second only to diamond, and is extremely wear resistant, making it a useful material for cutting tools, sliding machine parts, bearings, etc. ti, one→
11VhL-→ノH-ttc, ``It has the excellent characteristic of being the largest in the material that is in the middle of the day.This property means that the propagation speed of the sound wave is the largest in the existing material. However, it is particularly useful as an acoustic material.It is difficult to obtain boron-applied products in the form of dense blocks by methods such as casting or rolling. In most cases, it is used as a composite in which a boron film is formed on a substrate made of a material other than boron by vapor deposition, sputtering, chemical vapor deposition (CVD), or the like.

Among the above-mentioned conventional methods for forming a boron film, the CVD method is considered to be able to obtain the best quality film.

In the CVD method, crystalline (β-rhombohedral, α-rhombohedral, tetragonal) boron, amorphous boron, or a mixture of these can be obtained by changing the production conditions. Amorphous boron is considered to have excellent mechanical properties such as tensile strength. However, commercially available boron fibers often have poor mechanical properties due to pores, inherent strain, microcracks, etc.

Furthermore, when the inventors removed the substrate using an appropriate method, the amorphous boron obtained by these conventional methods was destroyed without exception during the process of removing the substrate. This shows the magnitude of the inherent distortion. The inventors were able to solve these problems of the prior art by chemically vapor depositing amorphous boron in multiple layers on a substrate.

That is, with this method, even if the base is removed, the boron structural material is not destroyed unlike the conventional method, and exhibits excellent mechanical properties and a good appearance. Structural materials made of boron alone from which the substrate was removed were also excellent as acoustic materials, such as cantilevers and diaphragms for speakers. The method of the present invention will be specifically explained below.

To form boron on a substrate by CVD, for example, the substrate placed in a reactor is heated by infrared heating, high frequency heating, resistance heating, electrical heating, etc., and reduced as shown in the following formula. Boron is precipitated by a decomposition reaction.

2BX3+3H2→2B+6HX (X is a halogen element such as Cl, Br, I, etc.)CV
In addition to BX3, the raw material gas used in method D includes boron hydride and the like.

In this boron precipitation reaction, various crystal forms can be obtained depending on factors such as heating temperature, gas pressure, and the amount of raw material gas flowing into the reactor. Next, the substrate was often removed in order to evaluate the mechanical and acoustic properties of the boron film itself. This mainly involved chemical methods. As a substrate, CVD of boron is performed at high temperature (90°C).
Since the process is carried out at temperatures above 0°C, a heat-resistant material is required.

Further, heat-resistant metals such as tantalum, niobium, molybdenum, tungsten, titanium, etc. are advantageous, considering that a substrate with a complicated shape can be obtained and heating by electricity or high frequency is easy. The most distinctive feature of the present invention is the CVD method for obtaining amorphous boron.

In the conventional CVD method, amorphous boron is obtained by depositing boron at a relatively low temperature or by feeding a large amount of raw material gas into a reaction chamber. The first drawback of this method is that the utilization rate of the raw material gas is considerably poor. The second drawback is that if the substrate temperature rises even slightly or foreign matter hits the substrate, abnormal growth of the boron film often occurs, or crystalline boron may grow in some areas, causing external The surface irregularities become larger,
The appearance also deteriorates. This also significantly impairs mechanical strength, as a third drawback. Furthermore, when removing the substrate, most of the boron film is destroyed during this process. These phenomena were the same whether the reaction atmosphere was under reduced pressure or normal pressure. The inventors removed these drawbacks by forming multiple amorphous layers.

It is more preferable that each layer of amorphous material has a thickness of about 3 μm to 15 prrt. If the thickness of a single layer is much thicker than the above range, abnormal growth and local crystalline boron are likely to occur.Multilayer amorphous material The film was created using various methods, but all of them were superior to conventional amorphous films in terms of film quality and appearance.

Among these various methods, methods that have excellent effects on film quality, appearance, etc., and are relatively easy to control conditions will be described. This method basically involves the process of gradually increasing the amount of thermal energy supplied to the substrate on which the boron film is to be formed, while flowing the raw material gas at a constant rate, and once the substrate reaches the set temperature. Sometimes, it consists of a process of cutting off the supply of thermal energy to the substrate, and these two processes are repeated to form a boron film on the substrate.

In view of the quality of the boron film, it is desirable that the maximum temperature in the substrate temperature curve be considerably higher than the temperature when amorphous boron is formed by the conventional method. In the process of gradually increasing the amount of thermal energy supplied to the substrate, boron is deposited on the substrate when the substrate reaches a certain temperature or higher.

When this supply of thermal energy is cut off, the temperature of the substrate drops rapidly and boron deposition on the substrate stops. The boron layer thus deposited on the substrate has a uniform appearance without abnormal growth or local crystallization. However, in this method, the time for depositing boron is short, and therefore the thickness of the boron layer obtained by each deposition is thin. When attempting to form a somewhat thick boron film, the amount of thermal energy supplied to the substrate is gradually increased, and when the substrate temperature reaches the set temperature, the amount of supplied thermal energy is kept constant to maintain the temperature constant. The supply of thermal energy to the substrate can then be cut off. As described above, boron continues to be deposited on the substrate while the substrate temperature is held constant, resulting in a thicker boron coating. The time the substrate is kept at a constant temperature is
It changes naturally depending on the temperature. If the holding time is too long, abnormal growth of boron is likely to occur, so it is desirable to determine the appropriate holding time experimentally in advance. The above method is effective whether CVD is performed under reduced pressure or under normal pressure.

Furthermore, since the substrate temperature can be made higher than in the conventional method, the utilization rate of the raw material gas can be increased. The resulting boron film is amorphous and consists of multiple layers, and has excellent mechanical properties and acoustic properties (such as the speed of sound). The substrate material used in the present invention may be any heat-resistant material, and particularly heat-resistant metals such as tantalum, tungsten, molybdenum, titanium, and niobium are suitable.

Among these, it is more desirable to use tantalum as the base material from the viewpoint of thermal expansion coefficient and the like. Furthermore, the substrate is preferably an alloy of chromium and iron, a boride of this alloy, or tantalum, tungsten, molybdenum, titanium, or niobium coated with chromium or its boride.

The thickness of this boride film is preferably about 0.2 to 10 μm. Various methods can be used for coating, including plating, borening, sputtering, vapor deposition, CVD, etc., but the sputtering method is the best in terms of ease of control. Among the above substrates, an alloy of chromium and iron, a boride thereof, or tantalum coated with chromium or a boride thereof is suitable. The effect of the present invention is to obtain an amorphous boron film with excellent appearance and mechanical properties.

Even when a boron structural material is composed of two layers of crystalline boron and amorphous boron, for example, by forming multiple layers of amorphous boron, the mechanical strength and appearance of this structural material are significantly improved. That is, such cases are also included within the scope of the present invention. Next, an example will be described in comparison with a conventional method.

As the substrate, wire rods with a thickness of 250 μm were used, consisting of five types: tantalum, tungsten, tantalum coated with chromium, tungsten coated with chromium, and tantalum coated with a chromium-iron alloy. These were each placed in a reaction vessel, and a mixed gas of boron chloride (BCl3) and hydrogen (H2) was added at a rate of 250 nt/minute for the former.
The latter was supplied at a rate of 1'/min. Then, electricity is applied to the base to generate heat, and the temperature is raised from room temperature to 1250°C.
The operation of raising the temperature in seconds and then cutting off the current was repeated four times to form a four-layer boron film with a thickness of 20 PTrL on the substrate. When these films were examined by X-ray diffraction, it was confirmed that they were composed of amorphous boron. Regarding the samples obtained as described above, the sample having an amorphous boron film on the substrate and the amorphous boron film from which the substrate was removed had a length of 5Tn.
The specimen was cut into a length of 1.5 m, supported at both ends of the 4-frame span, and a concentrated load was applied to the center, and the mechanical strength was evaluated based on the load at which a crack occurred.

The number of samples was 20 each, and the average value is shown in the table below. The table below also shows the yield when removing the substrate to obtain an amorphous boron vibe. For comparison, the results obtained when a single-layer amorphous boron structural material was manufactured using the conventional method are also summarized in the table below.

As is clear from the results in the table above, it can be seen that according to the method of the present invention, the mechanical strength and the yield of amorphous boron vibes are significantly superior to those using the conventional method.

In addition, in order to evaluate the acoustic properties of amorphous boron, the obtained amorphous boron vibrator was processed into a cantilever for a player, and its properties were evaluated.

As a result, compared to conventional cantilevers, the frequency characteristics
Distortion was also improved by several steps. Furthermore, we attempted to evaluate the properties of a plate made only of boron as a shaker plate, and again we obtained good results. Therefore, the boron structural material obtained by the present invention is suitable for acoustic components such as cantilevers for players and diaphragms for head shell speakers. Boron films with high elastic modulus and low distortion and microclutches also have a wide range of uses as mechanical components.

Claims (1)

[Scope of Claims] 1. In the process of successively stacking boron whose crystalline form is mainly amorphous, the method includes a process of gradually increasing the amount of thermal energy supplied to the supporting substrate, and a process of rapidly cutting off the supply of this thermal energy. A method for producing a boron structural material, characterized by: 2. The method for manufacturing a boron structural material according to claim 1, wherein the supporting base is formed from a metal consisting of tantalum, niobium, titanium, tungsten, or molybdenum. 3. A patent claim characterized in that the supporting substrate is made of tantalum, niobium, titanium, tungsten, or molybdenum coated with chromium, a boride of chromium, an alloy of chromium and iron, or a boride of this alloy. A method for producing a boron structural material according to item 1.