JP2015182936A - High-purity boron and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which enables production of high-purity simple boron through simple procedures.SOLUTION: A method of producing simple boron by reducing boric acid anhydride (BO) with an active metal includes a step 1 of mixing boric acid anhydride with an active metal, a step 2 of sintering the resultant mixture at 200-550°C for 1-5 h and a step 3 of raising the temperature of the resultant sintered body to a temperature at least 50°C higher than the melting point of the active metal and effective for the reduction reaction and carrying out the reduction reaction for 0.5-2.0 h.

Description

  The present invention relates to a method for producing simple boron.

  Boron (B) is a semiconductor element belonging to Group III in the periodic table, and is used as a raw material for glass, preservatives, abrasives, pharmaceuticals, deoxidizers in metal smelting, alloy additives, and refractory metal borides. Used. In addition, high-purity boron is particularly important as a dopant for a semiconductor substrate or a material for a Co—Fe—B sputtering target used for a ferromagnetic layer of a TMR (tunnel Magneto-Resistance) element.

Boron is a substance that has a high melting point of 2080 ° C. and a boiling point of 2550 ° C., which is difficult to purify. J. et al. Since Gay Lussac et al. Reduced boric anhydride with potassium in an iron vessel, various purification methods have been proposed. The process for producing simple boron is roughly divided into the following four types.
(1) Reduction of borax (Na ₂ B ₄ O ₇ ) and boric anhydride (B ₂ O ₃ ) with an active metal.
(2) The boron halide is reduced with an active metal.
(3) The boron chloride is reduced with hydrogen.
(4) Deposit on the cathode by molten salt electrolysis.

  Boron easily reacts with oxygen and nitrogen at high temperatures and easily forms borides with various metals, so that it is difficult to obtain high purity by any method (Non-patent Document 1). ).

As a method for reducing boric acid described in (1) with an active metal, a “magnesium reduction method” (Non-patent Document 2) is known. The method is as follows. The boron mineral is reacted with HCl and boron is extracted in the form of boric acid. There are three types of boric acid: normal boric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), and pyroboric acid (H ₂ B ₄ O ₇ ). When normal boric acid is heated to 373K, metaboric acid is generated by a dehydration reaction, and when heated to 413K, a condensation reaction occurs along with the dehydration reaction to generate pyroboric acid. When metaboric acid and pyroboric acid are heated to 413 K or more, anhydrous boric acid (B ₂ O ₃ ) is generated. When Mg is added to B ₂ O ₃ and heated to about 1273 K for reduction, brown amorphous boron having a purity of 90 to 92% is obtained.

  As a method for further increasing the chemical purity of the obtained boron, Non-Patent Document 2 describes a “zone purification method”. This is a method in which a boron raw material rod is heated in an inert gas using a high frequency, or heated by using an electron beam in a vacuum to be melted and purified. In addition, it is described that an “electrolytic purification method” can also be employed.

Kazuo Akashi and Ichiro Egami, “Manufacture of simple boron by molten salt electrolysis”, Institute of Industrial Science, University of Tokyo, Production Research 15 (11), p427-435, 1963 , Toshiaki Shishido, Shigeru Okada, "Methods for producing boron and borides", "Basics and applications of boron and borides and related substances", CMC Publishing, p153-155, 2008

Conventionally, it has been difficult to obtain high-purity boron by a method of reducing borax (Na ₂ B ₄ O ₇ ) or boric anhydride (B ₂ O ₃ ) with an active metal, and to obtain high-purity boron. A complicated operation such as a zone melting method is required, and the cost is high. There is also room for improvement in purity. Then, this invention makes it a subject to provide the method which can manufacture a high purity simple substance boron with a simple procedure. Another object of the present invention is to provide high-purity boron that has not been achieved by conventional manufacturing methods.

The present inventor has conducted extensive studies to solve the above-mentioned problems. As a result, when reducing boric anhydride (B ₂ O ₃ ) with an active metal, a boric anhydride (B It was found that the adhesion between ₂ O ₃ ) and the active metal was improved and the subsequent reduction reaction was promoted.

The present invention completed on the basis of the above knowledge is, in one aspect, a method for producing simple boron by reducing boric anhydride (B ₂ O ₃ ) with an active metal, wherein the boric anhydride and the active metal are combined. Step 1 for mixing, Step 2 for sintering the obtained mixture at a temperature of 200 to 550 ° C. for 1 to 5 hours, and a temperature higher than the melting point of the active metal by 50 ° C. or more And a step 3 in which the reduction reaction is carried out for 0.5 to 2.0 hours.

  In one embodiment of the method according to the invention, the active metal is selected from elemental calcium and elemental magnesium.

  In another embodiment of the method according to the invention, the active metal is elemental calcium and the reduction reaction is carried out at 889-1039 ° C.

  In yet another embodiment of the method according to the invention, the active metal is elemental magnesium and the reduction reaction is carried out at 699-849 ° C.

  In a further embodiment of the method according to the invention, steps 2 and 3 are carried out in a graphite crucible.

  In another aspect, the present invention provides elemental boron in which the total concentration of impurities Na, Mg, Al, Si, Ca, and Fe is 5 mass ppm or less.

  In one embodiment of elemental boron according to the present invention, the concentration of Na is less than 0.1 ppm by mass.

  In another embodiment of the elemental boron according to the present invention, the Mg concentration is less than 0.1 mass ppm.

  In still another embodiment of the elemental boron according to the present invention, the concentration of Al is 0.5 mass ppm or less.

  In still another embodiment of the elemental boron according to the present invention, the concentration of Si is 1.0 mass ppm or less.

  In still another embodiment of the elemental boron according to the present invention, the concentration of Ca is less than 0.5 ppm by mass.

  In yet another embodiment of the elemental boron according to the present invention, Li, Be, F, Na, Mg, P, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Each concentration of Th and U is below the detection limit.

  In still another embodiment of the elemental boron according to the present invention, the concentration of C is 200 ppm by mass or less.

  In still another embodiment of the elemental boron according to the present invention, the concentration of O is 300 mass ppm or less.

According to the present invention, when producing simple boron by a method of reducing boric anhydride (B ₂ O ₃ ) with an active metal, the purity is remarkably high without performing a complicated operation such as a zone melting method. Single boron is obtained. The simple boron according to the present invention is useful, for example, as an electronic device material that requires high purity.

An example of the flowchart of the manufacturing method of the simple substance boron concerning this invention is shown. An example of the temperature rising profile at the time of implementing the manufacturing method of the elemental boron which concerns on this invention is shown.

In one aspect, the present invention provides a method for producing elemental boron by reducing boric anhydride (B ₂ O ₃ ) with an active metal. In one embodiment of the simple boron production method according to the present invention, Step 1 of mixing boric anhydride and active metal, and then sintering the resulting mixture at a temperature of 200 to 550 ° C. for 1 to 5 hours. Step 2 and then Step 3 in which the obtained sintered body is heated to a temperature higher by 50 ° C. or more than the melting point of the active metal and subjected to a reduction reaction for 0.5 to 2 hours.

  From the viewpoint of obtaining high purity simple boron, it is preferable to use as high purity boric anhydride as the raw material as possible. Therefore, it is preferable to use those having a purity of 99.9% by mass (3N) or higher, excluding C, N, O, S and H which are gas components, and those having 99.99% by mass (4N) or higher are used. It is more preferable to use 99.999 mass% (5N) or more. The purity here is a value calculated from the impurity concentration measured by a GDMS (Glow Discharge Mass Spectrometry) method.

  The form of boric anhydride to be used is not particularly limited, but is preferably a powder form, which facilitates uniform mixing with the active metal. For example, a powder having a D50 (particle size with a cumulative weight particle size distribution with a cumulative value of 50%) of about 100 to 200 μm may be used.

  The active metal serving as a reducing agent is not particularly limited as long as it has a reducing action on the boric anhydride. For example, simple substance Ca, simple substance Mg, simple substance Ti, simple substance Li, simple substance Na, simple substance K, Single Rb, Single Be, Single Sr, Single Ba, Single Zr, Single Hf, Single Rare Earth (Single Sc, Single Y, Single La, Single Ce, Single Pr, Single Nd, Single Pm, Single Sm, Single Eu, Single Gd , Simple substance Tb, simple substance Dy, simple substance Ho, simple substance Er, simple substance Tm, simple substance Yb, simple substance Lu), simple substance Zn, and simple substance Al. Among these, simple Ca, simple Zn and simple Mg are preferable from the viewpoint of easy separation from the reducing agent and economical efficiency. These can also be used independently and can also be used in combination of 2 or more types.

  From the viewpoint of obtaining high-purity elemental boron, it is preferable to use an active metal having a purity as high as possible. Therefore, it is preferable to use those having a purity of 99.9% by mass (3N) or higher, excluding C, N, O, S and H which are gas components, and those having 99.99% by mass (4N) or higher are used. It is more preferable to use 99.999 mass% (5N) or more. The purity here is a value calculated from the impurity concentration measured by a GDMS (Glow Discharge Mass Spectrometry) method.

  The form of the active metal to be used is not particularly limited, but a powder form is preferable because it can be easily mixed with boric anhydride evenly. For example, a powder having a particle size with a D50 (particle size with a cumulative weight particle size distribution with a cumulative value of 50%) of about 10 mm or less, typically with a D50 of about 5 to 9 mm may be used.

  In step 1, the boric anhydride and the active metal are mixed. Although there is no particular limitation on the mixing method, from the viewpoint of preventing contamination, mixing is performed in an inert atmosphere such as Ar, or at least the surface in contact with the mixture is pBN, Ta, graphite, and the surface is a dense dense surface. Mix in a container made of a heat-resistant material that does not react with the raw materials, such as quartz or dense alumina with a smooth surface and does not easily cause contamination, typically in a container made entirely of these materials. Is preferred. Moreover, it can typically carry out by mixing a powdery boron oxide and a powdery active metal. Further, since the reduction reaction is easily promoted, it is preferable to prepare a uniform mixture by stirring or the like.

  Moreover, it is preferable from the viewpoint of obtaining simple boron having a high purity that the mixing of both is performed with the amount of the reducing agent slightly less than the reaction equivalent. Specifically, the amount of Ca or Mg is preferably 0.80 to 0.98 times, more preferably 0.9 to 0.95 times the reaction equivalent.

  In step 2, the mixture obtained in step 1 is sintered. By sintering, the adhesion between boric anhydride and the active metal is improved, and the subsequent reduction reaction is promoted. This makes it possible to produce single boron having a high purity in a high yield. It also contributes to improving yield. Since sintering does not proceed if the sintering temperature is too low, sintering must be performed by heating the mixture to 180 ° C. or higher. The sintering temperature is preferably 180 ° C. or higher, more preferably 200 ° C. or higher. On the other hand, if the sintering temperature is too high, volatilization of the active metal is promoted, and an effective sintered body cannot be obtained. Is preferable, and it is more preferable to set it as 550 degrees C or less.

  Moreover, since sintering will not fully advance when sintering time is too short, it should be 1 hour or more, and it is preferable to set it as 1.5 hours or more. On the other hand, if the sintering time is too long, the active metal volatilizes, so it should be 5 hours or less, and preferably 4 hours or less.

  Here, the sintering time refers to the time during which the mixture stays in the temperature range of 200 to 550 ° C. Therefore, when staying in the temperature range before and after reaching the holding temperature, the time is also taken into consideration. For example, in the example of the temperature rise profile shown in FIG. 2, the “Ca” line reaches 200 ° C. 32 minutes after the start of the temperature rise, then rises to 550 ° C., and then at 550 ° C. for 1 hour. After being held, the temperature rises further after 2 hours and 30 minutes from the start of the temperature increase. In this case, since the total stay in the temperature range of 200 to 550 ° C. is 1 hour and 58 minutes, the sintering time is calculated as 1 hour and 58 minutes. In addition, the “Mg” line reaches 200 ° C. 30 minutes after the start of the temperature rise, and after that, after being held at 200 ° C. for 1 hour 30 minutes, the temperature is further raised to exceed the temperature of 550 ° C. Since it takes 2 hours and 2 minutes, the total temperature stays in the temperature range of 200 to 550 ° C. for about 3.5 hours, so the sintering time is 3 hours and 32 minutes.

  In addition, as a matter to be noted during sintering, sintering is performed in an inert atmosphere such as Ar in order to prevent contamination, and at least the surface in contact with the mixture is contaminated with pBN, Ta, graphite, or the like. It is preferable to sinter in a sintering vessel made of a material that does not easily cause these factors, typically in a sintering vessel made entirely of these materials.

In step 3, the obtained sintered body is reduced to generate simple boron. The reduction reaction at this time can be expressed, for example, as B ₂ O ₃ + 3Ca → 2B + 3CaO when simple substance Ca is used as the reducing agent. Although the temperature of the mixture at the time of carrying out the reduction reaction varies depending on the type of active metal, it is preferably 50 to 200 ° C. higher than the melting point of the active metal, and 70 to 160 ° C. higher than the melting point of the active metal. More preferably. If the temperature is lower than this range, the reduction reaction does not proceed sufficiently. If the temperature is higher than this range, the volatilization amount of the active metal increases and the reduction reaction does not proceed easily. It is. From the viewpoint of promoting the reduction reaction and safety, the pressure in the container during the reduction reaction is preferably 300 to 500 torr (weakly reduced pressure atmosphere). For example, when elemental Ca is used as the active metal, the reduction reaction is preferably performed at 889 to 1039 ° C., more preferably at 899 to 999 ° C. Moreover, when using single-piece | unit Mg as an active metal, it is preferable to perform a reductive reaction at 699-849 degreeC, and it is more preferable to carry out at 719-809 degreeC.

  When the reduction reaction time is too short, the reduction does not proceed sufficiently. On the other hand, when the reduction reaction time is too long, contamination from the oxide formed by the reaction between the produced B and the reducing material may increase. 0.0 hours are preferable, and 1.0 to 1.5 hours are more preferable. Here, the reduction reaction time in the present invention refers to the time during which the temperature of the mixture stays in a temperature region higher than the melting point of the active metal by 50 ° C. or more.

  For example, in the example of the temperature rise profile shown in FIG. 2, the temperature rise of the “Ca” line starts at 889 ° C., which is 50 ° C. higher than 839 ° C., which is the melting point of Ca. After 3 hours and 28 minutes, the temperature was raised to 900 ° C., held for 1 hour, cooled in the furnace, and returned to 889 ° C. again after 4 hours and 32 minutes from the start of the temperature rise. In this case, from the definition of the reduction reaction time described above, the reduction reaction time is calculated as 1 hour 4 minutes. In the “Mg” line, the temperature reaches 699 ° C., which is 50 ° C. higher than the melting point of Mg after 649 ° C., 4 hours and 54 minutes after the temperature starts, and then reaches 800 ° C. After the temperature rises, it is held for 1 hour, cooled in the furnace, and returned to 699 ° C. again after 6 hours 49 minutes from the start of the temperature rise. In this case, from the above-described definition of the reduction reaction time, the reduction reaction time is calculated as 1 hour 55 minutes.

  Further, the reduction reaction is preferably carried out in a container having the same material as the sintering reaction from the viewpoint of preventing contamination.

  The transition from the sintering process to the reduction process is preferably carried out continuously without lowering the temperature. This is because once the temperature is lowered to room temperature after the sintering step or taken out from the reaction vessel, production efficiency is reduced and unexpected side reactions and contamination may occur. If the rate of temperature rise at the time of transition is too slow, the reducing material may volatilize before the reduction reaction proceeds, leading to a decrease in yield, whereas if it is too early, the reaction proceeds without the raw material or crucible being sufficiently heated. Therefore, it is preferably 1 to 30 ° C./min, more preferably 5 to 30 ° C./min.

  According to the present invention, by adopting the above-described manufacturing method, high purity single boron can be obtained without performing complicated operations such as zone melting method, raw material purity, heat treatment conditions, and contamination prevention. According to the preferable production conditions in which the concentration is strictly controlled, it is possible to obtain elemental boron in which the total concentration of impurities Na, Mg, Al, Si, Ca and Fe is 5 mass ppm or less, and preferably the total concentration is Single boron having 3 mass ppm or less can be obtained, and more preferably, single boron having a total concentration of 2 mass ppm or less can be obtained.

  According to one embodiment of elemental boron produced according to the present invention, the concentration of Na is less than 0.1 ppm by weight.

  According to one embodiment of elemental boron produced according to the present invention, the concentration of Mg is less than 0.1 ppm by weight.

  According to one embodiment of the elemental boron produced according to the present invention, the concentration of Al is 0.5 mass ppm or less.

  According to one embodiment of the elemental boron produced according to the present invention, the concentration of Si is 1.0 mass ppm or less.

  According to one embodiment of the elemental boron produced according to the present invention, the concentration of Ca is less than 0.5 ppm by mass.

  According to one embodiment of elemental boron produced according to the present invention, Li, Be, F, Na, Mg, P, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Each concentration of Th and U is below the detection limit. The detection limit value of each element is shown in Table 5 described in the examples.

  In one embodiment, the elemental boron according to the present invention can have a C concentration of 200 ppm by mass or less, preferably 150 ppm by mass or less, more preferably 100 ppm by mass or less. For example, it can be 50-200 mass ppm, and typically can be 90-150 mass ppm.

  In addition, in one embodiment, the elemental boron according to the present invention can have an O concentration of 300 ppm by mass or less, preferably 200 ppm by mass or less, more preferably 100 ppm by mass or less. For example, 50 to 300 ppm by mass, and typically 80 to 200 ppm by mass.

  In the present invention, impurity concentrations other than gas components (C, N, O, S, H) are measured by a GDMS (Glow Discharge Mass Spectrometry) method. The concentrations of oxygen (O), nitrogen (N) and hydrogen (H) are measured by inert gas melting-infrared absorption method (in the examples, TCH-600 manufactured by LECO was used). The concentration of carbon (C) and sulfur (S) is measured by a combustion-infrared absorption method (in the examples, LE-CO CS-444 was used).

  High-purity boron can be used, for example, as a dopant for a silicon semiconductor or a material for a Co—Fe—B sputtering target used for a ferromagnetic layer of a TMR element.

Examples for better understanding of the present invention and its advantages will be described below, but the present invention is not limited to these examples.
Except for carbon (C), nitrogen (N), oxygen (O), hydrogen (O), and sulfur (S), which are gas component elements, the analytical value of each element concentration is a GDMS (Glow Discharge Mass Spectrometry) method ( V. G. Scientific VG-9000), and for the analysis of gas component elements, oxygen (O), nitrogen (N) and hydrogen (H) were analyzed by LECO oxygen nitrogen analyzer (model TCH). -600) for carbon (C) and sulfur (S) using a carbon sulfur analyzer (model CS-444) manufactured by LECO.

(Comparative example 1: no sintering process)
1000 g of boric anhydride powder (particle size: D50 = 150 μm) with a purity of 99.9% by mass, excluding C, N, O, S and H, which are commercially available gas components, 0.95 times the reaction equivalent 1641 g of in-house purified gas components C, N, O, S, and H, which are 99.9% by mass of pure calcium powder (particle size: D50 = 5-9 mm), were substituted with Ar. After stirring and mixing so as to be uniform in the glove box, the obtained mixture was charged into a graphite crucible. The inside of the crucible was placed in an Ar atmosphere and heated to 900 ° C. at a temperature rising rate of 7.5 ° C./min, and the temperature was maintained for 1.0 hour to carry out a reduction reaction. After the reduction reaction, the furnace was cooled while maintaining the Ar atmosphere. The sintering time at this time was about 47 minutes according to the definition described above. The reduction reaction time at this time was 1 hour 4 minutes according to the definition described above. After dissolving the impurities in hydrochloric acid, the amount of simple boron obtained by filtration and washing with pure water was 244 g, which was lower in yield than the invention examples described later. Table 1 shows the analysis results of impurity elements of boric anhydride and simple calcium used as raw materials, and simple boron produced. Reductant Ca remained as much as 65 mass ppm, and the crucible material and Ca reacted without reacting with B ₂ O ₃ , so that the crucible material C was contaminated. As a result, the C concentration became 540 mass ppm. Further, since the sintering is insufficient, the reduction of the material of B ₂ O ₃ is insufficient, O was as high as 2500 mass ppm.

(Comparative Example 2: No reducing agent Mg sintering step)
1000 g of boric anhydride powder (particle size: D50 = 150 μm) with a purity of 99.9% by mass, excluding C, N, O, S and H, which are commercially available gas components, 0.95 times the reaction equivalent 995 g of in-house refined gas components C, N, O, S and H excluding 99.9% by mass of pure magnesium powder (particle size: D50 = 5 to 9 mm) substituted with Ar After stirring and mixing so as to be uniform in the glove box, the obtained mixture was charged into a graphite crucible. The inside of the crucible was placed in an Ar atmosphere and heated to 800 ° C. at a temperature increase rate of 7.5 ° C./min, and the temperature was maintained for 1.0 hour to carry out a reduction reaction. After the reduction reaction, the furnace was cooled while maintaining the Ar atmosphere. The sintering time at this time was about 47 minutes according to the definition described above. The reduction reaction time at this time was 1 hour 33 minutes according to the definition described above. After dissolving the impurities in hydrochloric acid, the amount of simple boron obtained by filtration and washing with pure water is 238 g, which is lower in yield than the invention examples described later. Table 2 shows the analysis results of impurity elements of boric anhydride and simple magnesium used as raw materials, and simple boron produced. A large amount of Mg as a reducing agent remained at 74 ppm by mass, and the crucible material and Mg reacted without reacting with B ₂ O ₃ , thereby being contaminated by C as the crucible material. As a result, the C concentration was 450 mass ppm. Further, since the sintering is insufficient, the reduction of the material of B ₂ O ₃ is insufficient, O was as high as 3200 mass ppm.

(Invention Example 1)
1000 g of boric anhydride powder (particle size: D50 = 150 μm) with a purity of 99.9% by mass, excluding C, N, O, S and H, which are commercially available gas components, 0.95 times the reaction equivalent 1641 g of in-house purified gas components C, N, O, S, and H excluding 99.9% by mass of pure calcium powder (particle size: in the range of 5 to 9 mm) were replaced with Ar. After stirring and mixing so as to be uniform in the glove box, the obtained mixture was charged into a graphite crucible. The inside of the crucible is in an Ar atmosphere, heated to 550 ° C. at a temperature rising rate of 6.1 ° C./min, maintained at that temperature for 1 hour, and then sintered to 900 ° C. at a temperature rising rate of 5.83 ° C./min. The reduction reaction was carried out by heating and holding for 1 hour. The temperature rising profile at this time is shown in FIG. 2 (refer to the “Ca” line in the graph). After the reduction reaction, the heater power of the furnace was turned off and the furnace was cooled while maintaining the Ar atmosphere. The sintering time at this time was 1 hour 58 minutes according to the definition described above. The reduction reaction time at this time was 1 hour 4 minutes according to the definition described above. After dissolving the impurities in hydrochloric acid, 295 g of simple boron obtained by filtration and washing with pure water was obtained. Table 3 shows the analysis results of impurity elements of boric anhydride and simple calcium used as raw materials, and simple boron produced. The obtained single boron was remarkably higher in purity than Comparative Example 1.

(Invention Example 2)
1000 g of boric anhydride powder (particle size: D50 = 150 μm) with a purity of 99.9% by mass, excluding C, N, O, S and H, which are commercially available gas components, 0.95 times the reaction equivalent 995 g of in-house refined gas components C, N, O, S, and H with a purity of 99.9% by mass excluding C, N, O, S, and H (particle size: in the range of 5-9 mm) were replaced with Ar After stirring and mixing in a glove box, the resulting mixture was charged into a graphite crucible. The inside of the crucible was placed in an Ar atmosphere, heated to 200 ° C. at a heating rate of 400 ° C./h, maintained at that temperature for 1 hour and 30 minutes, sintered, and then heated at a heating rate of 171 ° C./h (2.85 ° C./h). min) to 800 ° C. and maintained at the temperature for 1 hour to carry out a reduction reaction. The temperature rise profile at this time is shown in FIG. 2 (see the “Mg” line in the graph). After the reduction reaction, the heater power of the furnace was turned off and the furnace was cooled while maintaining the Ar atmosphere. The sintering time at this time was 3 hours and 32 minutes according to the definition described above. The reduction reaction time at this time was 1 hour 55 minutes according to the above-mentioned definition. After dissolving the impurities in hydrochloric acid, 295 g of simple boron obtained by filtration and washing with pure water was obtained. Table 4 shows analysis results of impurity elements of boric anhydride and simple magnesium used as raw materials and simple boron produced. The purity of the obtained elemental boron was significantly increased as compared with Comparative Example 1.

(Detection limit)
Table 5 shows the detection limit of each element.

Claims (14)

A method for producing elemental boron by reducing boric anhydride (B ₂ O ₃ ) with an active metal, wherein Step 1 of mixing the boric anhydride and the active metal, and then the resulting mixture is 200- Step 2 of sintering at a temperature of 550 ° C. for 1 to 5 hours, and then reducing the temperature of the obtained sintered body to a temperature higher than the melting point of the active metal by 50 ° C. or more for 0.5 to 2.0 hours And performing step 3.   The method according to claim 1, wherein the active metal is one or two selected from elemental calcium and elemental magnesium.   The process according to claim 1, wherein the active metal is elemental calcium and the reduction reaction is carried out at 889-1039 ° C.   The process according to claim 1, wherein the active metal is elemental magnesium and the reduction reaction is carried out at 699-849 ° C.   The method as described in any one of Claims 1-4 which implements the process 2 and the process 3 in the crucible made from a graphite.   Elementary boron whose total concentration of impurities Na, Mg, Al, Si, Ca and Fe is 5 mass ppm or less.   The elemental boron according to claim 6, wherein the concentration of Na is less than 0.1 ppm by mass.   The elemental boron according to claim 6 or 7, wherein the Mg concentration is less than 0.1 ppm by mass.   The elemental boron according to any one of claims 6 to 8, wherein the concentration of Al is 0.5 ppm by mass or less.   The elemental boron according to any one of claims 6 to 9, wherein the concentration of Si is 1.0 mass ppm or less.   The elemental boron according to any one of claims 6 to 10, wherein the concentration of Ca is less than 0.5 ppm by mass. Li, Be, F, Na, Mg, P, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, The concentrations of Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Th, and U are below the detection limit. The simple substance boron as described in any one of 11.   The elemental boron according to any one of claims 6 to 12, wherein the concentration of C is 200 mass ppm or less.   The elemental boron according to any one of claims 6 to 13, wherein the concentration of O is 300 mass ppm or less.

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