JPS6149247B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a pipe-shaped boron structural material, and particularly aims to improve the film quality and mechanical properties of boron constituting the boron structural material, and to improve the manufacturing yield of the boron structural material. It is. Boron has a hardness second only to diamond, and has extremely high wear resistance, making it a suitable material for cutting tools, sliding machine parts, bearings, and the like. Additionally, it has an excellent characteristic of having the highest specific elastic modulus (elastic modulus/density) among currently known materials. This property means that the propagation speed of sound waves is the highest among existing materials, making it 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. For this reason, in the production of various boron-applied products, in most cases, materials such as vapor deposition, sputtering, or chemical vapor deposition (hereinafter referred to as CVD) are used on substrates made of materials other than boron. It is used as a composite with a boron film formed on a substrate made of a material other than boron. Composite structural materials made by such conventional methods do not pose any major problems when used in products that utilize the hardness of boron and its excellent wear resistance. However, this poses a very serious problem in acoustic materials such as speaker diaphragms and cartridge cantilevers that utilize the large specific modulus of elasticity. In other words, the density and elastic modulus of the composite are greatly influenced by the properties of the substrate, and the inherent properties of boron are thereby greatly reduced. on the other hand,
Although there have been many attempts to separate boron from the substrate through chemical or physical treatments, distortion occurs due to differences in coefficient of thermal expansion between the deposited boron film and the substrate, resulting in cracks in the boron film. It has been difficult to obtain a boron film with sufficient mechanical strength at a high yield. In order to eliminate the drawbacks of such conventional methods, the inventors used a wire made of a metal selected from tantalum, niobium, molybdenum, tungsten, and titanium, and coated the surface with chromium or chromium boride. It has been found that it is effective to deposit boron to a desired thickness to form a substrate and then chemically vapor deposit boron onto this substrate. The method of the present invention will be specifically explained below. A method for forming boron on a substrate using the CVD method is to heat the substrate placed in a reactor using methods such as infrared heating, high-frequency heating, or energization.
Boron is precipitated by 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, or I.) In addition to BX ₃ , boron hydrogen compounds are also available as raw material gases used in the CVD method. Further, in this boron precipitation reaction, various crystal forms can be obtained depending on the heating temperature, the amount of raw material flowing into the reactor, etc. Among various crystal forms, β-rombohedral, tetragonal, or amorphous boron is preferable in order to obtain a boron film that is dense and has excellent mechanical properties. Next, the substrate is dissolved and removed by a chemical method,
A pipe made mainly of boron is obtained. As a liquid having such a chemical action, a liquid mainly containing hydrofluoric acid can be considered. A particularly effective solution is one in which bromine, chlorine, iodine, a compound of two or more of these (such as iodine trichloride or iodine monochloride), or a mixture thereof is dissolved in absolute alcohol. Boron is the metal used to form the base.
Tantalum, niobium, molybdenum, titanium, and tungsten are preferable because CVD is performed at high temperatures (1000° C. or higher) and the substrate can be easily heated by electricity. Among these materials, tantalum, molybdenum, and tungsten, which are less susceptible to hydrogen embrittlement, are more desirable because CVD is performed in a hydrogen stream. In addition, in order to reduce the thermal strain between the deposited boron film and the substrate, the thermal expansion coefficient of boron (approximately 8×10 ^-5 /
Tantalum (approximately 7 to 8×10 ^-5 /°C) and titanium (approximately 8×10 ^-5 /°C) are more desirable. The main point of the method of the present invention is that chromium or chromium boride is deposited on a wire made of the above-mentioned metal by electroplating, CVD, or sputtering, and then coated to a desired thickness to form a base. There is a particular thing. Thereafter, boron is deposited on the substrate, and the substrate is further selectively dissolved to obtain a pipe-shaped structural material made of boron. In the past, there have been cases in which the boron film has been destroyed during the selective dissolution process, and the mechanical properties of the resulting boron structural material have been poor. The method of the present invention provides significant improvements in these respects. When a chrome plate or the like is used as a substrate, the substrate itself deforms due to the high temperature during CVD, and cracks occur in the boron film at the end of boron CVD due to its large thermal expansion coefficient. The same was true when bulk chromium boride was used as the substrate. In other words, from the above, the reason why a lump of chromium or chromium boride is used as a substrate for boron CVD is because of the thermal and mechanical properties such as the coefficient of thermal expansion between boron and chromium or chromium boride. This is not desirable due to the difference in Therefore, in order to exhibit the effects of the present invention, the thickness of the chromium or chromium boride layer covering the metal wire naturally has a desirable thickness.
This desired thickness also depends on the thickness of the metal. When the metal is, for example, linear tantalum with an outside diameter of 200 to 300 microns, the desired thickness of the chromium or chromium boride layer is 20 microns or less. If it is too thick, cracks will easily occur in the boron film, and if it is about 0.1 micron, the improvement effect of the present invention will not be clearly recognized. The most desirable coating layer thickness in this case is 0.5~
It was 2.0 microns. The effects of the present invention are even greater when tantalum is used as the metal wire. This is thought to be due to the fact that the coefficient of thermal expansion is close to that of boron and the degree of hydrogen embrittlement is relatively small. Chromium was coated onto the substrate by electroplating, sputtering, or CVD using chromium iodide as a raw material. The results were almost the same regardless of the chromium coating method used. Approximately 3 chrome coated 250 micron thick tantalum wire
It was coated to a micron thickness and then boron was chemically vapor deposited on top. The cross section of the obtained material was as shown in the figure. In the figure, 1 is a tantalum wire,
2 is a boron layer. No. 3 was examined by X-ray diffraction and was found to be a chromium boron compound layer. 4 is a void. This indicates that the chromium coated on tantalum is converted to boride during boron CVD. Note that the voids 4 may not be clearly recognized by microscopic observation of the cross section. From the above, the effects of the present invention are exhibited when the substrate is coated with chromium because, firstly, the coefficient of thermal expansion of chromium or chromium boride is larger than that of boron, and the chromium boride layer The fact that voids as shown in the figure are likely to be formed between the boron layer and the boron layer;
Secondly, it is thought that this may be related to the fact that certain chromium borides have relatively weak bonds with boron (therefore, the above-mentioned voids are likely to occur). Therefore, the thermal strain existing between the substrate and boron is alleviated by the void,
This reduces cracks in the pipe-shaped boron structural material and improves its manufacturing yield. A chromium boride layer on metal can be formed by depositing chromium on the metal and then reacting a boron halide with the chromium, or by CVD from chromium iodide and boron halide, or by depositing chromium boron on the metal. It may also be formed by sputtering. As a result of observing the cross sections of structures made by these methods, no difference could be recognized from the chromium boride layer when chromium was used as the coating material. As described in detail above, according to the conventional method, the boron film may be destroyed during CVD of boron, or
However, the mechanical properties of pipe-shaped boron structures made of simple boron were poor on average, but the method of the present invention has improved them in all respects. . More details will be explained in Examples. A tantalum wire with a diameter of 250 microns and a length of 800 mm was prepared. After degreasing and cleaning the tantalum wire, chromium was deposited thereon by a direct current sputtering method to form a chromium layer of about 2 microns. Next, a tantalum wire coated with a chromium layer is heated by applying electricity.
The temperature was maintained at 1250°C, and a mixed gas of 1 part by volume of boron trichloride (BCl ₃ ) and 3 parts by volume of hydrogen (H ₂ ) was flowed through it at a rate of 1 per minute for 2 minutes. This resulted in a boron layer approximately 50 microns thick. The sample thus prepared was cut into a length of 5 mm using a Yag laser, etc., and immersed in a solution of 50 g of bromine dissolved in 200 ml of commercially available anhydrous methanol to remove tantalum and chromium borides. Dissolved. At this time, boron does not dissolve. The dimensions of the resulting pipe were an inner diameter of 250 microns, an outer diameter of 350 microns, and a length of 5 mm. As a result of investigating by X-image diffraction,
The crystalline form was mainly β-rombohedral. Next, the bending strength of this pipe was measured. The measurement was made with a beam length of 4 mm, with both ends in the form of support beams,
It was calculated from the load when the pipe broke by adding a load W. As a result, the yield of pipes was 74% through the process of dissolving and removing the substrate from samples cut to 5 mm, and the average bending strength of the 20 pipes obtained was 403 g. The results are summarized as Sample 1 in the table below. Samples 2 to 2 shown in the table below were prepared in the same manner as in the above example.
I made 12 and researched them as well. The method for coating tantalum wire with chromium or chromium boride is as follows. For sample 2, chromium was formed to a thickness of about 4 microns by direct current sputtering. For samples 3 and 4, iron was deposited using a DC sputtering method to a thickness not exceeding 1000 angstroms, and then chromium plating was performed to form a chromium layer with a thickness of 5 microns and 8.5 microns, respectively. For samples 5, 6, and 7, chromium was first deposited using the DC sputtering method, and then the tantalum wire was energized to red-hot to react with boron trichloride.
Chromium boride layers were formed with thicknesses of 3 microns, 5 microns, and 5 microns, respectively. Samples 8, 9,
For Nos. 10, 11, and 12, the tantalum wires were energized to red hot, and a mixed gas of chromium iodide, boron trichloride, and hydrogen was brought into contact with them to produce wires of 4.5 microns, 5 microns, 5 microns, 5 microns, and 18, respectively. A micron-thick chromium boride layer was formed.
The thickness of the boron film formed on the chromium layer or chromium boride layer by the CVD method was 47 to 53 microns. The temperature at which boron is deposited, the yield of boron pipes obtained by melting the substrate, the average bending strength, and the crystal form examined by X-ray diffraction are summarized in the table below. The average bending strength is the average value of 20 samples. For comparison, without coating the tantalum wire with chromium, immediately after coating it with boron by CVD method, 50±3
It was deposited to a micron thickness. The boron deposition temperature, yield, average bending strength, and crystal form at that time are also summarized in the table below. The average bending strength is sample 20
This is the average value for the number of books or, if less than that, the number of books.

[Table] As is clear from the results in the above table, according to the method of the present invention, the yield of boron pipes is high and the average bending strength thereof is also high. In comparative examples, even if the yield is good to some extent, the average bending strength of the resulting boron pipe is small (Sample 15), and even if the average bending strength is high, the yield is poor (Sample 13). . Of course, there are many bad things about all of them. Above, we have described an example using tantalum wire, but we have confirmed through experiments that the same results as above can be obtained regardless of the shape of the substrate or the underlying metal of the substrate (molybdenum, niobium, titanium, tungsten). did.

[Brief explanation of the drawing]

The drawing shows a cross section of an example of a sample obtained by forming a chromium layer on a tantalum wire and further chemically vapor depositing boron by the method of the present invention. 1...Tantalum wire, 2...Boron layer, 3...Chromium boron compound layer, 4...Void.

Claims (1)

[Claims] 1 A layer of chromium or chromium boride is formed on a wire made of a metal selected from tantalum, molybdenum, niobium, titanium, and tungsten to form a base, and a layer of chromium or chromium boride is formed on the base by chemical vapor deposition. A method for manufacturing a boron structural material, which comprises forming a boron layer and then dissolving and removing the base to obtain a pipe-shaped structural material made of simple boron. 2. The method for manufacturing a boron structural material according to claim 1, wherein a boron layer is formed on the substrate by chemical vapor deposition while the substrate is heated. 3. The method for producing a boron structural material according to claim 1, characterized in that the metal wire is energized to generate heat, and in this state a boron layer is formed on the substrate by chemical vapor deposition. 4. Production of a boron structural material according to claim 1, characterized in that a boron layer whose main crystalline form is β-rombohedral, tetragonal or amorphous is formed on a substrate by chemical vapor deposition. Method.