Boron structure and boron powder of high purity

Abstract

A boron structure body includes boron having each concentration of Ti, Al, Fe, Cr, Ni, Co, Cu, W, Ta, Mo and Nb being 0.1 ppmw or less and having a thickness of 0.8 to 5 mm. The boron structure body may have a tubular shape, and when used as a doping agent, a ratio of .sup.11B that is an isotope may be 95 mass % or more. The boron structure body can be easily crushed, and a high-purity boron powder having an average particle diameter of 0.5 to 3 mm and having each metal impurity concentration of 0.3 ppmw or less can be obtained.

Claims

1. A boron structure body comprising boron having each concentration of titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium being 0.1 ppmw or less, and having a thickness of 0.8 to 5 mm.

2. The boron structure body according to claim 1, having a tubular shape.

3. The boron structure body according to claim 1, having a density of 2.2 g/cm.sup.3 or more.

4. The boron structure body according to claim 1, wherein a ratio of .sup.11B as an isotope of boron is 95 mass % or more.

5. A boron structure body to claim 1, having a total metal impurity concentration of 0.1 ppmw to 0.9 ppmw.

6. A boron powder comprising a crushed material of the boron structure body according to claim 1, having an average particle diameter of 0.5 to 3 mm, and having each concentration of titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium being 0.3 ppmw or less.

7. The boron powder according to claim 6, wherein the each concentration of titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium is 0.2 ppmw or less.

8. A boron powder having an average particle diameter of 0.5 to 3 mm, and having each concentration of titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium being 0.3 ppmw or less.

9. The boron powder according to claim 8, wherein the each concentration of titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium is 0.2 ppmw or less.

10. The boron powder according to claim 6, having an average particle diameter of 0.7 mm or more.

11. The boron powder according to claim 10, wherein the average particle diameter is 0.8 mm or more.

12. The boron powder according to any one claim 6, wherein a content of a boron fine powder having a particle diameter of less than 0.5 mm is 40 mass % or less.

13. A method of making the boron structure body, comprising: feeding a boron halide represented by BX.sub.3, wherein X is chlorine, bromine or iodine but is not fluorine, together with hydrogen to a heated metal substrate; reducing the boron halide and depositing boron on the metal substrate, wherein contamination due to diffusion of metal substrate components during deposition is suppressed by adjusting a thickness of deposited boron on the metal substrate to a specific thickness; and obtaining a boron structure body by removing the metal substrate after the deposition, wherein the boron structure body comprises boron and titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium, each having a concentration of 0.1 ppmw or less, wherein the boron structure body has a thickness of 0.8 to 5 mm.

14. The method according to claim 13, further comprising crushing the boron structure body.

Description

EXAMPLES

(1) In order to describe the present invention more specifically, examples are given below, but the present invention is in no way limited to those examples. In the following examples and comparative examples, thickness, metal impurity concentration, density and ratio of a .sup.11B isotope in a boran structure body, and average particle diameter, metal impurity concentration and ratio of a fine powder having a particle diameter of less than 0.5 mm in a boron powder were evaluated in the following manner.

(2) (Thickness of Boron Structure Body)

(3) In a tubular boron structure body after removal of a metal care wire, a distance between a tube inner wall surface (surface having been in contact with the metal core wire) and a tube outer wall surface (growth surface) was measured using a vernier caliper. Measurement was carried out at 5 or more points, and the maximum value was taken as a thickness of the boron structure body.

(4) (Metal Impurity Concentration of Boron Structure Body)

(5) From the boron structure body, a sample of about 1 g was taken out, and it was dissolved in nitric acid. Then, concentrations of metals (titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium) in a solution in which boron had been completely dissolved were measured by ICP-MS.

(6) (Density of Boron Structure Body)

(7) The density was determined by an Archimedes method.

(8) (Ratio of .sup.11B Isotope in Boron Structure Body)

(9) A powder obtained from the boron structure body was measured by a mass spectrometer to determine ratios of .sup.11B and .sup.10B.

(10) (Average Particle Diameter of Boron Powder)

(11) The boron powder was classified by a sieve, then a histogram was prepared, and from a cumulative volume of particles, a median diameter was determined.

(12) (Metal Impurity Concentration of Boron Powder)

(13) The metal impurity concentrations of the boron powder were measured in the same manner as in the measurement for the boron structure body. For crushing, a hammer with a head of stainless steel was used.

(14) (Ratio of Fine Powder Having Particle Diameter of Less than 0.5 mm in Boron Powder)

(15) After deposition of boron, a metal core wire was removed, and than a ratio of a weight of a fine powder having a particle diameter of less than 0.5 mm to a weight of a boron structure body was determined.

Experimental Example 1

Experimental Example 1-1

(16) A bell jar type reactor in which a diameter of a bottom part was 30 cm, a height of a straight barrel part was 30 cm, and a height from a bottom plate to a ceiling part was 50 cm was prepared. A tungsten core wire having a diameter of 2 mm and a length of 200 mm was stood up in the reactor in such a manner that the core wire was in an inverted U shape. The air in the reactor was replaced with nitrogen, and thereafter, the nitrogen was replaced with hydrogen. The core wire was electrically heated to 1200° C., and a mixed gas in which commercial BCl.sub.3 having each concentration of titanium, aluminum, iron, chromium, nickel, cobalt, copper, tungsten, tantalum, molybdenum and niobium being 0.1 ppmw or less and H.sub.2 were mixed in such a manner that the H.sub.2/BCl.sub.3 molar ratio became 5 was allowed to flow at 10 L/min, thereby forming a boron layer in a prescribed thickness on the tungsten wire. The resulting boron rod was taken out, and using a treatment solution consisting of anhydrous methanol and bromine (bromine concentration: 200 g-bromine/liter), the core wire part was removed, thereby obtaining a tubular boron structure body. The structure body was composed of crystalline boron, and its thickness, metal impurity concentrations and density were measured. The results are set forth in Table 1. This structure body was manually crushed with a hammer (made of stainless steel) to obtain a boron powder. This powder was washed with a mixed solution of nitric acid and hydrofluoric acid, then washed with water and dried. A part of the resulting boron powder was collected, and an average particle diameter, metal impurity concentrations, and a ratio of a fine powder having a particle diameter of less than 0.5 mm were measured. The results are set forth in Table 2.

Experimental Examples 1-2 to 1-5

(17) By changing the boron deposition time, the thickness of the boron structure body was changed. A thickness, metal impurity concentrations and a density of the boron structure body in each experimental example were measured. The results are set forth in Table 1. The resulting boron structure body was crushed and washed in the same manner as in Experimental Example 1-1. A part of the resulting boron powder was collected, and an average particle diameter, metal impurity concentrations, and a ratio of a fine powder having a particle diameter of less than 0.5 mm were measured. The results are set forth in Table 2. From Table 1 and Table 2, it can be seen that when the thickness of the boron structure body was in the range of 0.8 to 5 mm, a boron powder having an average particle diameter of 0.5 to 3 mm, containing a small amount of a fine powder and having a high purity was obtained by crushing the structure body.

(18) Experiment Nos. 1-1 and 1-5 are comparative examples. When the thickness of the boron structure body was small (Experiment No. 1-1), the boron structure body was excessively fragmentated, and a boron powder having a desired particle diameter could not be obtained. When the thickness of the boron structure body was large (Experiment No. 1-5), contamination with large amounts of impurities derived from peripheral devices and the core wire took place, and since the crushing was difficult, contamination with impurities derived from the hammer took place, and the particle diameter of the powder also became too large.

Experimental Example 2

Experimental Examples 2-1 to 2-5

(19) Experimental examples wee carried out in the same manner as in Experimental Example 1, except that the tungsten core wire was changed to a tantalum core wire. A thickness, metal impurity concentrations and a density of the boron structure body in each experimental example are set forth in Table 1. An average particle diameter, metal impurity concentrations, and a ratio of a fine powder having a particle diameter of less than 0.5 mm in the boron powder are set forth in Table 2. As can be understood from Table 1 and Table 2, the relationship between the thickness of the boron structure body and the metal impurity concentrations of the boron powder showed the same tendency as in the use of the tungsten core wire. Experiment Nos. 2-1 and 2-5 are comparative examples.

(20) TABLE-US-00001 TABLE 1 Boron structure body Thick- ness of Exper- structure Den- iment body Metal impurity concentration of boron structure body (ppm w) sity No. (mm) Ti Al Fe Cr Ni Co Cu W Ta Mo Nb (g/ml) 1-1.sup.※ 0.5 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 1-2 1.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 1-3 2.2 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 1-4 4.6 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 1-5.sup.※ 8 3 2 25 3 31 1 12 250 5 3 8 2.37 2-1.sup.※ 0.5 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 2-2 1.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 2-3 2.2 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 2-4 4.6 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2.37 2-5.sup.※ 8 1 3 83 2 18 2 25 4 780 47 41 2.37 .sup.※Experiment Nos. 1-1, 1-5, 2-1 and 2-5 are comparative examples.

(21) TABLE-US-00002 TABLE 2 Boron powder Ratio of fine powder with Average particle Exper- particle diameter of iment diameter less than 0.5 Metal impurity concentration of boron powder ppm w) No. (mm) mm (mass %) Ti Al Fe Cr Ni Co Cu W Ta Mo Nb 1-1.sup.※ 0.2 92 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 1-2 0.8 35 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 1-3 1.5 11 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 1-4 2.3 7 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 1-5.sup.※ 6.6 1 3 3 105 33 49 10 15 250 5 3 8 2-1.sup.※ 0.2 92 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2-2 0.7 38 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2-3 1.6 10 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2-4 2.4 6 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2-5.sup.※ 7.2 1 2 3 188 39 61 15 35 4 780 47 41 .sup.※Experiment Nos. 1-1, 1-5, 2-1 and 2-5 are comparative examples.

Experimental Example 3

(22) An ether complex of commercial BF.sub.3 having a .sup.11B isotope ratio of 80.1 mass % that was a natural ratio and anisole (C.sub.6H.sub.5OCH.sub.3) was formed, and by means of a reaction distillation column for carrying out chemical exchange reaction of the complex with BF.sub.3 and distillation, BF.sub.3 having a high ratio of .sup.11B was obtained by concentration.

(23) A ratio of .sup.11B in the resulting BF.sub.3 was measured by a mass spectrometer, and as a result, the ratio of .sup.11B was 97 mass %. This BF.sub.3 was gasified and introduced into a container having been heated to 250° C. together with sublimed AlCl.sub.3 gas while adjusting flow rates in such a manner that the molar ratio between the BF.sub.3 gas and the AlCl.sub.3 gas became 1:1, and vapor phase reaction was carried out, thereby obtaining BCl.sub.3. A ratio of .sup.11B in the BCl.sub.3 obtained above was measured by a mass spectrometer, and as a result, the ratio of .sup.11B was 97 mass %.

(24) This BCl.sub.3 was subjected to hydrogen reduction in the same manner as in Experimental Example 1-1, thereby forming a boron structure body. The resulting boron structure body was composed of crystalline born and had a density of 2.37 g/cm.sup.3. Regarding a powder obtained from the structure body, ratios of .sup.11B and .sup.10B were measured by a mass spectrometer, and as a result, the ratio of .sup.11B was 97 mass %. From the boron structure body having a thickness of 2 mm, a boron powder having a particle diameter in the range of 0.8 to 2.5 mm and having an average particle diameter of 1.6 mm was obtained in a yield of 94% based on the boron structure body. Concentrations of Ti, Al, Fe, Cr, Ni, Co, Cu, W, Ta, Mo and Nb in the boron powder were each 0.1 ppmw less that was the detection limit.