JP7066169B2 - Method for Producing Cubic or Hexagonal Boron Nitride - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) October 25, 2017 Published by the Japan Society for High Pressure Pressure, Proceedings of the 58th High Pressure Discussion Meeting, High Pressure Science and Technology Vol. 27 (2017) Special Issue (2) November 8-10, 2017 Sponsored by the Japan Society for High Pressure Pressure, 58th High Pressure Discussion Meeting, Nagoya University (Furumachi, Chitose-ku, Nagoya City) (3) Published November 14, 2017 (for recording) USB) International Workshop on UV Materials and Devices IWUMD 2017 Abstracts (4) Held from November 14th to 18th, 2017, International Workshop on UV Materials, University of Tokyo, Centennial Hall, Kyushu University, Centennial Hall, Kyushu University Chome 1-1) (5) New Diamond Issued on November 20, 2017, Abstracts of the 31st Diamond Symposium (6) November 20-22, 2017, New Diamond 31st Diamond Symposium (Kansai Gakuin University Nishimiya Uegahara Campus) (7) Published December 11, 2017 (USB for recording), ICON-2DMAT 2017 (The 3 ▲ rd ▼ International Science on 2D Materials) and Technology), Proceedings (8) Held from December 11th to 14th, 2017, ICON-2DMAT 2017 (The 3 ▲ rd ▼ International Conference on 2D Technical Society), Science Technology), School of Science (21 Nanyang Link Singapore 637371)

The present invention relates to a method for producing cubic or hexagonal boron nitride.

Among the boron nitrides, low ^- density hexagonal sp2 type layered compounds, boron nitride (hBN), and high-density cubic boron nitride (cBN) are industrially used. hBN is known as a heat-resistant material / heat insulating material, and cBN is known as an ultra-hard material next to diamond. In recent years, these hBNs and cBNs are also based on excellent properties as wide-gap semiconductors.

hBN is industrially produced by reduction nitriding treatment using boron oxide and carbon as raw materials (see, for example, Patent Document 1). The cBN is produced by high-temperature and high-pressure treatment of an alkali metal or alkaline earth metal boronitride together with hBN (see, for example, Non-Patent Document 1 and Non-Patent Document 2). In particular, in the production of cBN, hBN used as a raw material and a boronitride of an alkali metal or an alkaline earth metal are expensive, so that the production cost of cBN is high. It is desirable to develop a method for producing cBN at a lower cost. Further, it is industrially advantageous if hBN and cBN can be produced separately from the same raw material by simply changing the production conditions.

On the other hand, it is known that rhombic symmetric boron nitride (rBN) is produced using NaBH ₄ and NH ₄ Cl (see, for example, Non-Patent Document 3). According to Non-Patent Document 3, rBN can be obtained by reacting NaBH ₄ and NH ₄ Cl prepared at a molar ratio of 1: 1 at a temperature of 1 atm and 900 ° C., from rBN to hBN. We conclude that the conversion is difficult.

Japanese Unexamined Patent Publication No. 60-155507

T. Taniguchi et al., J. Mol. Cryst. Growth, 222,549-557,2001 T. Taniguchi et al., J. Mol. Cryst. Growth, 303,527-529,2007 T. Sato, Proc. Japan Acad. , 61, Ser. B, 459-463, 1985

From the above, it is an object of the present invention to provide a method for inexpensively producing single crystal powders of cubic boron nitride (cBN) and hexagonal boron nitride (hBN). A further object of the present invention is to provide a method for inexpensively producing single crystal powders of cBN and hBN in which the abundance ratio of boron isotopes is controlled, which enables the production of cBN and hBN separately.

The method for producing a single crystal powder of boron nitride made of cubic boron nitride (cBN) or hexagonal boron nitride (hBN) according to the present invention is a method of producing a borohydride powder of a Group 1 element and ammonium halide. Including the step of reacting the raw material powder containing the powder, in the raw material powder, the borohydride of the Group 1 element is 1.25 or more and 1.75 or less in terms of molar ratio with respect to the ammonium halide. The raw material powder is reacted in a temperature range of 1000 ° C. or higher and 2500 ° C. or lower under a pressure of 3 GPa or higher and 10 GPa or lower, thereby solving the above-mentioned problems.
The hydrogenated boride of the Group 1 element may be a material selected from at least one selected from the group consisting of NaBH ₄ , LiBH ₄ , KBH ₄ and CsBH ₄ .
The ammonium halide may be a material selected from at least one selected from the group consisting of NH ₄ Cl, NH ₄ Br, NH ₄ I and NH ₄ F.
The boron nitride is cubic boron nitride (cBN), and the reaction step is to combine the raw material powder with P (GPa)> T (° C.) /465 + 0.79 (where T is 1000 ° C. ≦ T). The reaction may be carried out under a temperature and pressure satisfying (° C.) ≤ 2500).
In the reaction step, the raw material powder may be reacted in a temperature range of 1450 ° C. or higher and 1700 ° C. or lower under a pressure of more than 4.75 GPa and 5.5 GPa or lower.
The boron nitride is hexagonal boron nitride (hBN), and the reaction step is to combine the raw material powder with P (GPa) <T (° C.) / 465 + 0.79 (where T is 1000 ° C. ≦ T (where T is 1000 ° C. ≦ T). The reaction may be carried out under a temperature and pressure satisfying (° C.) ≤ 2500).
In the reaction step, the raw material powder may be reacted in a temperature range of 1250 ° C. or higher and 1700 ° C. or lower under a pressure of 3.75 GPa or higher and 4.75 GPa or lower.
The hydrides of the Group 1 element are elemental substances hydrides enriched with boron isotopes in 10B (concentration rate is 95% or more), and hydrides enriched with boron isotopes in 11B (concentrations). The rate may be 95% or more) alone, or any combination of these.
The proportion of the boron isotope in the boron nitride may match the proportion of the boron isotope in the hydrogenated boride of the Group 1 element.
The product obtained in the above reaction step may be further treated with a solvent to further include the step of removing the second phase.
The raw material powder may contain a reaction inhibitor.
In the reaction step, the raw material powder may be reacted for a time of 10 minutes or more and 24 hours or less.
A belt-type high-pressure device may be used for the reaction step.
The single crystal powder may have a particle size in the range of 50 μm or more and 1 mm or less.
The single crystal powder may have a particle size in the range of 100 μm or more and 400 μm or less.

According to the production method of the present invention, a raw material powder containing a hydrogenated boride powder of a Group 1 element and a powder of ammonium halide is used, both of which are easy to obtain and inexpensive to produce. The cost can be reduced. Further, in the raw material powder, the hydrogenated boride of the group 1 element is contained so as to have a molar ratio of more than 1 with respect to ammonium halide, so that a relatively large size single crystal made of boron nitride is formed. High-purity powder can be produced. In addition, it is possible to make cubic or hexagonal boron nitride by simply controlling the reaction conditions. In addition, since the abundance ratio of the boron isotope in the raw material becomes the abundance ratio of the boron isotope in the obtained boron nitride as it is, it is easy to control the abundance ratio of the boron isotope.

The figure which shows the relationship between pressure and temperature for making cubic boron nitride and hexagonal boron nitride separately. The figure which shows typically the high pressure cell provided with the capsule used for the production of the single crystal powder of boron nitride which is an embodiment of this invention. The figure which shows typically the belt type high pressure apparatus used for manufacturing the single crystal powder of boron nitride which is an embodiment of this invention. The figure which shows the optical micrograph of the sample of Example 1. The figure which shows the XRD pattern of the sample of Example 2. The figure which shows the XRD pattern of the sample of Example 8. The figure which shows the optical micrograph of the sample of Example 10. SIMS profile of B isotope element of sintered body of Example 10 The figure which shows the Raman spectrum of the sample of Examples 1 and 10. The figure which shows the Raman spectrum of the sample of Example 1 and 10-12. The figure which shows the Raman spectrum of the sample of Examples 7 and 13-15. The figure which shows the relationship between the abundance ratio of the boron isotope of cBN and Raman shift obtained from FIG. The figure which shows the relationship between the abundance ratio of the boron isotope of hBN and Raman shift obtained from FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same elements are given the same numbers, and the description thereof will be omitted.

In the present invention, a single crystal powder composed of cubic boron nitride (cBN) and hexagonal boron nitride (hBN) will be focused on, and a method for producing the single crystal powder will be described.

cBN belongs to the cubic system, belongs to the F4￣ (￣ represents the overline on 4) 3m space group (space group 216 of International Talbes for Crystallography), and the crystal parameters and atoms shown in Table 1. Occupy the coordinate position. The crystal structure parameters are, for example, G.I. Will et al., Journal of the Less-Common Metals, 117, 61, 1986.

In addition, hBN belongs to the hexagonal system, is a sp2 type layered compound, belongs to the P6 ₃ / mmc space group (space group No. 194 of International Talbes for Crystallography), and has crystal parameters and atomic coordinates shown in Table ² . Occupy a position. The crystal structure parameters are, for example, R.I. S. It is disclosed by Peace, Acta Crystallogica, 5,356,1952.

In Tables 1 and 2, the lattice constants a, b, and c indicate the length of the axis of the unit cell, and α, β, and γ indicate the angle between the axes of the unit cell. Atomic coordinates indicate the position of each atom in the unit cell.

In the present invention, in addition to cBN / hBN containing no dopant, the ratio of B and N changes, or other elements (for example, a part of N is O (oxygen), C (carbon), Si (silicon)). , Be (berylium), etc.) changes the lattice constant, but the crystal structure and the atomic position given by the site occupied by the atom and its coordinates are such that the chemical bond between the skeleton atoms is broken. It is intended that those that do not change significantly are also cBN / hBN. In the present invention, the results of X-ray diffraction and neutron diffraction of the target substance are calculated from the lattice constant and atomic coordinates obtained by Rietbelt analysis in the space group of F4 ￣ 3 m or P6 ₃ / mmc. If the length of the chemical bond in Table 1 or 2 is within ± 5% of that calculated from the lattice constant and atomic coordinates of the crystal shown in Table 1 or Table 2, it can be determined that the crystal structure is the same. If the length of the chemical bond exceeds ± 5%, the chemical bond may be broken and another crystal may be formed. As another simple determination method, the main peaks of X-ray diffraction of the cBN crystal or the hBN crystal (for example, about 5 with strong diffraction intensity) may be compared with that of the target substance.

From this point of view, in the present invention, cBN or hBN has the same crystal structure as the crystal structure of cBN or hBN, respectively, and the molar ratio of cBN or hBN itself to B and N is from the stoichiometric composition. It also includes those that are misaligned and those in which a part of B and N is replaced with another element (for example, O, C, Si, Be, etc.). In particular, if the element in which a part of B and N is replaced is Be, Si, or the like, it functions as a dopant, so that it can also function as a semiconductor material.

According to the present invention, the above-mentioned powder consisting of a single crystal of boron nitride, which is cBN or hBN, reacts a powder of a borohydride of a Group 1 element with a raw material powder containing a powder of ammonium halide. Manufactured by steps. Specifically, in the raw material powder, the hydrogenated boride of the Group 1 element is contained so as to have a molar ratio of more than 1 with respect to ammonium halide, and the raw material powder is contained at a temperature of 1000 ° C. or higher and 2500 ° C. or lower. In the range, the reaction is carried out under a pressure of 3 GPa or more and 10 GPa or less.

The inventors of the present application have described the above-mentioned temperature range and pressure of a hydride of a Group 1 element (MBH ₄ : M is a Group 1 element) and an ammonium halide (NH ₄ X: X is a halogen element). It has been found that if the reaction is carried out below, the following compound decomposition reaction can occur and a single crystal powder of boron nitride, which is cBN or hBN, can be produced.
MBH ₄ + NH ₄ X → BN + MX + 4H ₂

Even more surprisingly, according to the above formula, the hydride of the Group 1 element and the ammonium halide may be 1: 1 in molar ratio, but in reality, the hydrogen of the Group 1 element is hydrogen. Using a raw material powder in which the borohydride is made to have a molar ratio of more than 1 with respect to ammonium halide not only promotes the reaction, but also has a particle size in the range of 50 μm or more and 1 mm or less. It was found that a large single crystal powder could be obtained. The upper limit is not particularly limited, but may be 3 or less in consideration of reactivity and the amount of raw material powder used. In fact, in the raw material powder in which the borohydride of the Group 1 element and the ammonium halide have a molar ratio of 1, the metathesis reaction does not proceed even if the conditions are scrutinized, and it is cBN or hBN. No single crystal powder of boron nitride was obtained. That is, it can be said that the inventors of the present application have repeated various experiments and found a unique combination and mixing ratio of raw materials that allow the metathesis reaction to proceed under a predetermined temperature range and pressure.

If the temperature is lower than 1000 ° C. and 3 GPa, the above-mentioned metathesis reaction does not proceed. Further, when the temperature exceeds 2500 ° C. and 10 GPa, the above-mentioned metathesis reaction proceeds, but a special device is required, which is industrially unfavorable.

The group 1 element borohydride is a material selected at least from the group consisting of NaBH ₄ , LiBH ₄ , KBH ₄ and CsBH ₄ . These hydrogenated borides are easily available and can allow the metathesis reaction to proceed. Of these, NaBH ₄ is preferable from the viewpoint of reaction efficiency.

Further, if the production method of the present invention is adopted, the abundance ratio (ratio) of boron isotopes in the hydride of Group 1 elements becomes the isotope abundance ratio (ratio) of boron in the obtained boron nitride. Since there is a match, a single crystal powder of boron nitride with a controlled amount of boron isotope is obtained. From this point of view, the hydrides of Group 1 elements are elemental hydrides enriched with boron isotopes in ¹⁰ B (concentration rate is 95% or more), and enriched with boron isotopes in ¹¹ B. The borohydride (concentration rate is 95% or more) alone or any combination thereof may be used. If the enrichment rate is 95% or more, the effect of isotope enrichment is ensured.

The abundance ratio of boron isotopes ¹⁰ B and ¹¹ B in hydrogenated boride, which does not control the abundance ratio of boron isotopes, is 2: 8. When such a hydrogenated boride is used, the abundance ratio of the boron isotopes ¹⁰ B and ¹¹ B in the obtained boron nitride is 2: 8. However, if a boron isotope-enriched borohydride alone is used in ¹⁰ B, a boron isotope-enriched monocrystal powder of boron in ¹⁰ B can be obtained, and boron isotope-enriched hydrogenation in ¹¹ B. When the boro compound alone is used, a single crystal powder of boron nitride enriched with boron isotope in ^11B can be obtained. Further, if the borohydride enriched with boron isotope in ¹⁰ B and the borohydride enriched with boron isotope in ¹¹ B are used in a desired ratio, ¹⁰ B and ¹¹ B are desired. A single crystal powder of boron nitride having an abundance ratio can be obtained.

Ammonium halide is a material selected at least from the group consisting of NH ₄ Cl, NH ₄ Br, NH ₄ I and NH ₄ F. These ammonium halides are easily available and can allow the metathesis reaction to proceed. Of these, NH ₄ Cl is preferable from the viewpoint of reaction efficiency.

In the raw material powder, it is preferable that the hydrogenated boride of the Group 1 element is contained so as to have a molar ratio of more than 1 and less than 2 with respect to ammonium halide. Within this range, a single crystal powder of boron nitride can be produced. More preferably, the hydrogenated boride of the Group 1 element is contained so as to have a molar ratio of 1.25 or more and 1.75 or less with respect to ammonium halide. This makes it possible to reliably produce a single crystal powder of boron nitride.

All of the raw materials may be used as powder, but in this case, the raw material is a powder having a particle size of 100 nm or more and 500 μm or less. If the particle size is in this range, the progress of the metathesis reaction is promoted. More preferably, the raw material powder is preferably a powder having a particle size of 200 nm or more and 200 μm or less. In the specification of the present application, the particle size is a volume-based median diameter (d50) measured by a microtrack or a laser scattering method.

Further, the raw material powder may contain a reaction inhibitor. The reaction inhibitor is not particularly limited as long as it can be diluted in order to suppress heat generation, and examples thereof are sodium chloride (NaCl) and cesium chloride (CsCl). The amount contained in the raw material powder is in the range of 10% by weight or more and 75% by weight or less. Within this range, the metathesis reaction proceeds.

The raw material powder is held in a pressure resistant capsule that is durable even under the above temperature range and pressure. The pressure-resistant capsule is made of a material that does not react with the raw material powder, but is preferably made of molybdenum (Mo). The bulk density of the raw material powder held in the capsule is preferably 1.3 g / cm ³ or more and 3.0 g / cm ³ or less. By setting the filling factor to satisfy such bulk density, the metathesis reaction between the powders can be promoted.

Whether or not the obtained boron nitride powder is a single crystal can be determined by a single crystal X-ray structure diffraction method, but simply, when observed with an optical microscope or the like, the powder has a self-shaped shape. For example, it can be determined that a single crystal powder has been obtained.

Next, the production of a single crystal of boron nitride will be described.
FIG. 1 is a diagram showing the relationship between pressure and temperature for making cubic boron nitride and hexagonal boron nitride separately.

As shown in FIG. 1, the phase boundary between cubic boron nitride (cBN) and hexagonal boron nitride (hBN) uses temperature (T (° C.)) and pressure (P (GPa)). It has been reported that P = T / 465 + 0.79 (for example, O. Fukunaga, Diamond Relat. Meter., 9, 2000, 7).

If the above relational expression is used, in the step of reacting, the relational expression between the temperature (T (° C.)) and the pressure (P (GPa)) is P> T / 465 + 0.79 (however, 1000 ≦ T ≦ 2500). When satisfied, a single crystal powder consisting of cBN is obtained. More preferably, the raw material powder may be reacted in a temperature range of 1450 ° C. or higher and 1700 ° C. or lower under a pressure larger than 4.75 GPa and 5.5 GPa or lower. As a result, a single crystal powder composed of cBN and having a relatively large particle size in the range of 100 μm or more and 1 mm or less (preferably 100 μm or more and 400 μm or less) can be obtained.

If the above relational expression is used, in the step of reacting, the relational expression between the temperature (T (° C.)) and the pressure (P (GPa)) is P <T / 465 + 0.79 (however, 1000 ≦ T ≦ 2500). When satisfied, a single crystal powder consisting of hBN is obtained. More preferably, the raw material powder may be reacted in a temperature range of 1250 ° C. or higher and 1700 ° C. or lower under a pressure of 3.75 GPa or higher and 4.75 GPa or lower. As a result, a single crystal powder composed of hBN and having a relatively large particle size in the range of 100 μm or more and 1 mm or less (preferably 100 μm or more and 400 μm or less) can be obtained.

In the step of reacting, it is preferable to react in the above-mentioned temperature range and pressure range by using the relational expression shown in FIG. 1 from the viewpoint of discriminating that cBN and hBN can be easily separated. However, depending on the conditions, cBN and hBN can be created separately even if the relational expression shown in FIG. 1 is not satisfied. For example, in Examples 4 and 6 described later, although the relational expression shown in FIG. 1 is not always satisfied, hBN single crystal powder has been successfully produced.

The reaction time is not particularly limited, but, as an example, the above-mentioned raw material powder is used for 10 minutes or more and 24 hours or less. If it is less than 10 minutes, the above-mentioned metathesis reaction may not be sufficient, and even if it is carried out for more than 24 hours, the reaction does not proceed any further, which is inefficient.

Any device can be used for the reaction step as long as the above temperature conditions and pressure conditions are satisfied, but for example, a belt type high pressure device is preferable. The belt-type high-voltage device not only satisfies the above conditions, but can also be mass-produced and is practical.

Here, exemplary, a case where a high-pressure cell provided with a capsule filled with raw material powder is used and the reaction is performed by a belt-type high-pressure device is shown.

FIG. 2 is a diagram schematically showing a high-pressure cell provided with a capsule used for producing a single crystal powder of boron nitride according to an embodiment of the present invention.

FIG. 2A is a perspective view of the high-voltage cell, and FIG. 1B is a cross-sectional view of the high-voltage cell. The high-pressure cell 1 includes a cylindrical pyrophyllite 11, two steel rings 12A and 12B arranged in the cylinder of the pyrophyllite 11 so as to be in contact with the upper side and the lower side of the inner wall surface of the cylinder, and a steel ring 12A. , A cylindrical carbon heater 15 arranged on the central axis side of the 12B, a pressure-resistant heat-resistant capsule 16 arranged inside the carbon heater 15, and a raw material powder 17 filled inside the pressure-resistant heat-resistant capsule 16. The gap between the pyrophyllite 11 and the carbon heater 15 is filled with the filling powder 13, and the gap between the carbon heater 15 and the pressure resistant capsule 16 is also filled with the filling powder 14.

In FIG. 2, a hydrogenated borohydride powder 18 enriched with a ¹⁰ B isotope of a Group 1 element and a powder 19 of a hydride enriched with an ¹¹ B isotope of a Group 1 element are contained in a pressure resistant capsule 16. And the raw material powder 17 in which the powder 20 of ammonium halide is mixed are filled.

After spreading the filling powder 14 on the inner bottom of the cylindrical carbon heater 15 whose one end side is closed with a disk-shaped lid, the pressure-resistant heat-resistant capsule 16 is arranged coaxially in the cylindrical carbon heater 15. The gap between the pressure-resistant heat-resistant capsule 16 and the inner wall surface of the carbon heater 15 is filled with the filling powder 14, and the filling powder 14 is further spread on the upper part of the pressure-resistant heat-resistant capsule 16, and then the other end side is disk-shaped. Seal with a lid.

The cylindrical carbon heater 15 is arranged coaxially in the tubular pyrophyllite 11, and then the filling powder 13 is filled in the gap between the carbon heater 15 and the inner wall surface of the pyrophyllite 11. .. Examples of the filling powders 13 and 14 include NaCl + 10 wt% ZrO ₂ .

Next, the steel ring 12A is pushed so as to be embedded in the filling powder 13 on the upper side of the inner wall surface of the pyrophyllite 11, and another steel ring is embedded in the filling powder 13 on the lower side of the inner wall surface of the pyrophyllite 11. Push in 12B. As described above, the high-pressure cell 1 in which the raw material powder 17 is filled in the pressure-resistant heat-resistant capsule 16 can be obtained.

FIG. 3 is a diagram schematically showing a belt-type high-pressure device used for producing a single crystal powder of boron nitride according to an embodiment of the present invention.

A conductor 26A and 26B made of a thin metal plate are brought into contact with a predetermined position between the cylinders 27A and 27B of the belt type high voltage device 21 and between the anvils 25A and 25B, and the present invention will be described with reference to FIG. The high-voltage cell 1 is arranged. Next, pyrophyllite 28 is filled between these members and the high-voltage cell 1.

The anvils 25A and 25B and the cylinders 27A and 27B are moved to the high pressure cell 1 side to pressurize the high pressure cell 1 so as to satisfy the above conditions. In a pressurized state, it may be heated so as to satisfy the above conditions and held for a predetermined time.

Although a single crystal powder of boron nitride is obtained in this way, the resulting product may be treated with a solvent to remove the second phase following the reaction step. This can improve the purity of boron nitride in the product. The product may contain a halide (MX) of Group 1 elements as the second phase, as shown in the above reaction equation. The second phase can be easily dissolved and removed by washing the product with a solvent such as water or ethanol. In particular, when MX is NaCl, it can be easily dissolved and removed with water. When water is used, it is preferable to heat it to a temperature of 50 ° C. or higher and 90 ° C. or lower, preferably 75 ° C. or higher and 85 ° C. or lower, because dissolution and removal are promoted.

In this way, a single crystal powder of boron nitride, which is the cBN or hBN of the present invention, can be obtained. For example, when boron nitride is cBN, it has a hardness next to that of diamond, so that a single crystal powder can be used as an abrasive grain. When boron nitride is hBN, the single crystal powder can be used as a heat radiating material or a heat insulating material because it has high thermal conductivity and excellent heat resistance and heat insulating properties. In particular, ¹⁰ B-concentrated boron nitride has a high heat dissipation effect.

Both cBN and hBN are known as wide-gap semiconductors, and according to the production method of the present invention, they are relatively large single crystal powders having a size of at least several hundred μm at low cost. , Can be used for sensors, etc.

Since ¹⁰ B has a large neutron scattering cross section and neutron absorption capacity is enhanced, ¹⁰ B-concentrated boron nitride single crystal powder can be used as a neutron beam shielding material and a neutron beam detector.

The single crystal powder may be used as it is, or may be processed into a plate shape or the like if necessary. For example, since each hBN single crystal powder has a thin plate shape, it may be mixed with a resin such as plastic and cured to form a plate shape. This functions as a heat dissipation board and a heat insulating board.

Alternatively, a single crystal powder may be molded and sintered to obtain a large sintered body. For example, when the boron nitride is cBN, the sintered body may be processed into a cutting tool, and when the boron nitride is hBN, the sintered body may be used as a heat dissipation substrate or a heat insulating substrate.

Prior to sintering, it is preferable to adjust the particle size of the raw material product (cBN / hBN containing / not containing the second phase), and the single crystal powder is a powder satisfying the range of 10 nm or more and 10 μm or less. Adjust the particle size until it becomes. This makes it possible to manufacture a hard material which is a dense sintered body. More preferably, the particle size is adjusted until the reaction product becomes a powder satisfying the range of 50 nm or more and 5 μm or less. As a result, it is possible to produce a hard material which is a sintered body which is dense and whose grain growth is suppressed. For the particle size adjustment, a wet or dry ball mill, jet mill, or the like may be used, and classification such as sieving may be performed.

In the sintering of cBN, a molded product (which may be molded into pellets or the like or may be filled in a container) is placed in a stable region of cBN specified in FIG. 1 in a temperature range of 1500 ° C. or higher and 2000 ° C. or lower. Sinter with. Within this temperature range, sintering proceeds. More preferably, the molded body is sintered in a temperature range of 1800 ° C. or higher and 2000 ° C. or lower under a pressure of 8 GPa or higher and 10 GPa or lower. Within this temperature range and under this pressure, it is possible to produce a hard material which is a dense sintered body while suppressing grain growth. The sintering time depends on the size of the molded product, but is exemplifiedly in the range of 10 minutes or more and 1 hour or less. Any device can be used for sintering, but for example, a belt type high pressure device is preferable. The belt-type high-voltage device not only satisfies the above conditions, but can also be mass-produced and is practical.

On the other hand, in the sintering of hBN, a molded product (which may be molded into pellets or the like or may be filled in a container) is sintered in a temperature range of 1200 ° C. or higher and 2000 ° C. or lower. After molding, it may be sintered in a normal atmosphere furnace, but it may be sintered under pressure in the stable region of hBN specified in FIG. 1 using a belt-type high-pressure device, a hot press, a hot hydrostatic pressure press (HIP), or the like. May be sintered. Sintering is preferably carried out in a reducing atmosphere, such as in a nitrogen atmosphere.

In the step of sintering, a material selected from the group consisting of TiN, WC, WN, TaC, Co, Ni and Cr may be added to the product. These function as a sintering aid and can provide a hard material which is a denser sintered body. The amount to be added is preferably less than 10% by weight. From the viewpoint of control, the addition of the sintering aid to the product is preferably used by directly mixing the product and the sintering aid, but the member to which the product is contacted / filled ( For example, a material similar to the sintering aid is used for the capsule material), and it is also intended to be sintered as it is.

Next, the present invention will be described in detail with reference to specific examples, but it should be noted that the present invention is not limited to these examples.

[Examples 1 to 9]
In Examples 1 to 9, using a belt-type high-pressure device provided with the high-pressure cells shown in FIGS. 2 and 3, NaBH ₄ is used as the borohydride of the Group 1 element and NH ₄ Cl is used as the ammonium halide. Boron nitride (cBN or hBN) single crystal powder of the present invention was produced from the raw material powder under various pressure and temperature conditions.

NaBH ₄ (manufactured by Sigma-Aldrich, the abundance ratio of boron isotopes ( ¹⁰ B: ¹¹ B) was 2: 8 of the natural ratio) and NH ₄ Cl (manufactured by Wako Pure Chemical Industries, Ltd.) in molar ratio. , 6: 4 to prepare a raw material powder. It was confirmed that the particle size of the raw material powder was 100 nm or more and 500 μm or less. The mixing was carried out in a glove box filled with nitrogen gas (concentrations of _H2O and _O2 were controlled to 1 ppm or less).

This raw material powder is filled in a cylindrical pressure-resistant heat-resistant capsule (16 in FIG. 2) made of Mo (molybdenum) whose one end is closed with a disk-shaped lid, and then the other end is a disk-shaped Mo. Sealed with a made lid. At this time, the bulk density at the time of filling was 1.4 g / cm ³ . Next, filling powder (NaCl + 10 wt% ZrO ₂ ) is spread on the inner bottom of a cylindrical carbon heater (15 in FIG. 2) whose one end is closed with a disk-shaped lid, and then the pressure-resistant heat-resistant capsule is cylindrical. The filling powder (NaCl + 10wt% ZrO ₂ ) is filled in the gap between the pressure-resistant heat-resistant capsule and the inner wall surface of the carbon heater, and the filling powder is further placed on the upper part of the pressure-resistant heat-resistant capsule. After spreading (NaCl + 10 wt% ZrO ₂ ), the other end side was sealed with a disk-shaped lid.

Next, after arranging the cylindrical carbon heater coaxially in the tubular pyrophyllite, the filling powder (NaCl + 10 wt% ZrO ₂ ) is filled in the gap between the carbon heater and the inner wall surface of the pyrophyllite. ) Was filled.

Next, the steel ring was pushed into the filling powder on the upper side of the inner wall surface of the pyrophyllite, and another steel ring was pushed into the filling powder on the lower side of the inner wall surface of the pyrophyllite. As described above, a high-voltage cell (1 in FIG. 2) was produced.

The high pressure cell was placed at a predetermined position in the belt type pressurizing device shown in FIG. The high pressure cell was pressurized to the pressure values shown in Table 3. Next, under pressure, the mixture was heated at the temperatures shown in Table 3. In this state, the temperature and pressure were maintained for 30 minutes. As a result, the raw material powder was reacted at high temperature and high pressure.

The temperature and pressure were returned to normal temperature, and the product inside the pressure-resistant heat-resistant capsule was taken out. The product was then treated in water heated to 80 ° C. As a result, NaCl adhering to the product was dissolved and removed. The products thus obtained are referred to as samples of Examples 1 to 9, respectively.

The samples of Examples 1 to 9 were observed with an optical microscope (SZX12, manufactured by Olympus Corporation) and identified by powder X-ray diffraction (XRD, RINT2200, manufactured by Rigaku Corporation). The results are shown in FIGS. 5 and 6. The Raman spectra of the samples of Examples 1 to 9 were measured by a Raman spectroscope (PDPX, manufactured by Photon Design Co., Ltd.). The results are shown in FIGS. 9 to 11.

[Comparative Example 1]
In Comparative Example 1, a raw material powder containing NaBH ₄ as a borohydride of a Group 1 element and NH ₄ Cl as an ammonium halide using a belt-type high-pressure device provided with the high-pressure cells shown in FIGS. 2 and 3. Therefore, an attempt was made to produce a single crystal powder of boron nitride (cBN) at a pressure of 5 GPa and a temperature of 1500 ° C. Comparative Example 1 is the same as that of Example 1 except that the molar ratios of NaBH ₄ and NH ₄ Cl are different, and thus the description thereof will be omitted. Similar to Example 1, the sample of Comparative Example 1 was observed with an optical microscope, and the XRD pattern was measured.

[Comparative Example 2]
In Comparative Example 2, using the belt-type high-pressure device provided with the high-pressure cells shown in FIGS. 2 and 3, boron nitride (boron nitride) (from the raw material powder of hBN as a raw material and NaBH ₄ as a catalyst at a pressure of 5 GPa and a temperature of 1500 ° C. An attempt was made to produce a single crystal powder of cBN). Comparative Example 2 is the same as Example 1 except that NaBH ₄ and hBN are mixed so as to have a molar ratio of 2: 8 to obtain a raw material powder, and thus the description thereof will be omitted. The hBN was prepared in the same manner as in Non-Patent Document 2. Similar to Example 1, the sample of Comparative Example 2 was observed with an optical microscope, and the XRD pattern was measured.

[Comparative Example 3]
In Comparative Example 3, using the belt-type high-pressure device provided with the high-pressure cells shown in FIGS. 2 and 3, boron nitride was prepared from a raw material powder of hBN as a raw material and NH ₄ Cl as a catalyst at a pressure of 5 GPa and a temperature of 1500 ° C. An attempt was made to produce a single crystal powder of (cBN). Comparative Example 3 is the same as Example 1 except that NH ₄ Cl and hBN are mixed so as to have a molar ratio of 2: 8 to obtain a raw material powder, and thus the description thereof will be omitted. The hBN was prepared in the same manner as in Non-Patent Document 2. Similar to Example 1, the sample of Comparative Example 3 was observed with an optical microscope, and the XRD pattern was measured.

The above Examples / Comparative Examples are shown in Table 3 for simplicity, and the results will be described.

FIG. 4 is a diagram showing an optical micrograph of the sample of Example 1.

In FIG. 4, one square has a length of 1 mm. According to FIG. 4, it was found that the powder size of the sample of Example 1 had a large particle size having a range of 50 μm or more and 1 mm or less, more specifically, 100 μm or more and 400 μm or less. Further, it was found that each of the powders had an automorphic shape and was a single crystal. Although not shown, it was confirmed that the samples of Examples 2 to 9 had the same size and were single crystals.

FIG. 5 is a diagram showing an XRD pattern of the sample of Example 2.
FIG. 6 is a diagram showing an XRD pattern of the sample of Example 6.

According to FIG. 5, the XRD pattern of the sample of Example 2 mainly matched the XRD pattern of cBN (JCPDS No. 25-1033). Although some peaks indicating hBN were observed, it is determined that 95 vol% or more of the products are cBN. Although not shown, the XRD patterns of the samples of Examples 1 and 3 all matched the XRD pattern of cBN, and no peak indicating the hBN phase or the impurity phase was observed. From this, based on the phase boundary line shown in FIG. 1, the relational expression between the temperature (T (° C.)) and the pressure (P (GPa)) is P> T / 465 + 0.79 (however, 1000 ≦ T ≦). It was found that if 2500) was satisfied, a single crystal powder consisting of cBN could be obtained.

FIG. 6A shows the XRD pattern of the sample of Example 8 before washing with water (80 ° C.), and FIG. 6B shows the XRD pattern of the sample of Example 8 after washing. According to FIG. 6, it was shown that NaCl, which is an impurity, is easily dissolved and removed by water. According to FIG. 6B, the XRD pattern of the sample of Example 5 matched the XRD pattern of hBN (JCPDS No. 34-0421), and no peak showing an impurity phase was observed. Although not shown, the XRD patterns of the samples of Examples 4 to 7 and Example 9 also matched the XRD pattern of hBN, and no peak showing an impurity phase was observed. From the results of Examples 5 and 7 to 9, the relational expression between the temperature (T (° C.)) and the pressure (P (GPa)) is P <T / 465 + 0.79 based on the phase boundary line shown in FIG. However, it was found that a single crystal powder composed of hBN can be obtained when (1000 ≦ T ≦ 2500) is satisfied.

Although not shown, the XRD pattern of the sample of Comparative Example 1 did not have a peak showing cBN, and it was found that the metathesis reaction did not proceed. From this, in order to proceed with the metathesis reaction, it is essential that the raw material powder contains a hydrogenated boride of a Group 1 element in a molar ratio of more than 1 with respect to ammonium halide. It has been shown.

Although not shown, the XRD pattern of the sample of Comparative Example 2 matched the XRD pattern of cBN, and no peak indicating the hBN phase or the impurity phase was observed. Further, the sample of Comparative Example 2 was a powder having a size of about 5 μm according to the observation with an optical microscope.

The XRD pattern of the sample of Comparative Example 3 mainly matched the XRD pattern of hBN, a peak showing cBN was partially observed, and it was determined that about 5 vol% of the product was cBN. Further, the sample of Comparative Example 3 was a powder having a size of about 5 μm according to the observation with an optical microscope.

For the sake of simplicity, the main production phases of the samples of Examples 1 to 9 and Comparative Examples 1 to 3 are summarized in Table 4.

From these, in order to obtain a single crystal powder made of cBN / hBN having a size of 50 μm or more, preferably 100 μm or more, a powder of a borohydride of a Group 1 element and a powder of ammonium halide are used. It was shown that it is preferable to use the raw material powder contained therein.

[Examples 10 to 15]
In Examples 10 to 15, the Na ¹⁰ BH ₄ and the boron isotope enriched to ¹⁰ B as the hydride of the Group 1 element by using the belt type high pressure apparatus provided with the high pressure cells shown in FIGS. 2 and 3. / Or from the raw material powder of Na ¹¹ BH ₄ enriched with boron isotope to ¹¹ B and NH ₄ Cl as ammonium halide, the single crystal powder of boron nitride (cBN or hBN) of the present invention under various pressure and temperature conditions. Manufactured.

As Na ¹⁰ BH ₄ enriched with boron isotope to ¹⁰ B, Na ¹⁰ BH ₄ (manufactured by Katchem, ¹⁰ B enrichment by manufacturer analysis (electron spin resonance method (ESR)) was 98% or more). As Na ¹¹ BH ₄ enriched with boron isotope in ¹¹ B, Na ¹¹ BH ₄ (manufactured by Katchem, ¹⁰ B enrichment by manufacturer analysis (electron spin resonance method (ESR)) was 99% or more) was used. , The composition shown in Table 5 was mixed, and the reaction was carried out at the pressure and temperature shown in Table 5. Since the detailed procedure is the same as that of the first embodiment, the description thereof will be omitted. The products thus obtained are referred to as samples of Examples 10 to 15, respectively.

Similar to Example 1, the samples of Examples 10 to 15 were observed with an optical microscope, and the XRD pattern and Raman spectrum were measured. Further, the sample of Example 10 was sintered by the belt type pressurizing device of FIGS. 2 and 3. Specifically, the sample of Example 10 is boiled and purified in aqua regia (nitric acid: hydrochloric acid = volume ratio 1: 1) at 150 ° C., further purified with distilled water, and then filled in a hexagonal boron nitride (hBN) capsule. Then, it was sintered at 2000 ° C. for 15 minutes under a pressure of 10 GPa. The obtained sintered body had a size of 6 mm in diameter and 1 mm in thickness. The concentration distribution of boron isotopes in the depth (thickness) direction of this sintered body was investigated by secondary ion mass spectrometry (SIMS: IMS-7f, manufactured by CAMECA). These results are shown in FIGS. 7 to 12.

The above examples are shown in Table 5 for simplicity, and the results will be described.

FIG. 7 is a diagram showing an optical micrograph of the sample of Example 10.

According to FIG. 7, it was found that the size of the powder of the sample of Example 10 had a large particle size having a range of 50 μm or more and 1 mm or less. Further, it was found that each of the powders had an automorphic shape and was a single crystal. Although not shown, it was confirmed that the samples of Examples 11 to 15 had the same size and were single crystals.

Although not shown, the XRD patterns of the samples of Examples 10 to 12 all matched the XRD patterns of cBN, as in FIG. In addition, the XRD patterns of the samples of Examples 13 to 15 all matched the XRD patterns of hBN, as in FIG. 6 (B). From these, it was shown that the method of the present invention can be adopted to prepare a single crystal powder made of cBN and a single crystal powder made of hBN, as in Examples 1 to 9.

FIG. 8 shows the SIMS profile of the B isotope element of the sintered body of Example 10.

According to FIG. 8, it was found that the sintered body of Example 10 was cBN enriched with ¹⁰ B ( ¹⁰ B enrichment rate was 96%) from the surface to the depth direction. Furthermore, although there is a slight error, it is suggested that the abundance ratio of boron isotope in Na ¹⁰ BH ₄ enriched with boron isotope in ¹⁰ B used as a raw material is substantially reflected in the sample after the reaction. Was done.

FIG. 9 is a diagram showing Raman spectra of the samples of Examples 1 and 10.
FIG. 10 is a diagram showing Raman spectra of the samples of Examples 1 and 10-12.
FIG. 11 is a diagram showing Raman spectra of the samples of Examples 7 and 13 to 15.

The Raman spectrum of the sample of Example 1 has peaks near 1060 cm ^-1 and 1310 cm ^-1 , and the Raman spectrum of the sample of Example 10 peaks near 1080 cm ^-1 and 1330 cm ^-1 . And showed a clear peak shift. Since the sample of Example 1 uses a raw material containing a boron isotope at a natural ratio, the abundance ratio of the boron isotope in the obtained cBN single crystal powder is also the natural ratio ( ¹⁰ B: ¹¹ B = 2). : 8). On the other hand, the sample of Example 10 is a cBN single crystal powder enriched with ¹⁰ B as described above, and the abundance ratio of the boron isotope is ¹⁰ B: ¹¹ B = 9.6: 0.4. .. The peak shift suggests that the greater the abundance ratio of ¹⁰ B, the shorter the wavelength side, and the larger the abundance ratio of ¹¹ B, the longer the wavelength side, based on the difference in the abundance ratios of the boron isotopes.

FIG. 9 shows in detail the peaks in the vicinity of 1050 to 1080 cm ^-1 . As described above, assuming that the abundance ratio of the boron isotope used as the raw material is reflected substantially as it is, the abundance ratio of the boron isotope in the samples of Examples 1 and 10 to 12 ( ¹⁰ B: ¹¹ B). Are 2: 8, 9.6: 0.4, 0.1 to 0: 9.9 to 10 and 5: 5, respectively. Here, focusing on the Raman shift, peaks appear in the order of Example 11, Example 1, Example 12, and Example 10 from the long wavelength side to the short wavelength side, and the abundance ratio of ¹⁰ B is large. The abundance ratio of / ^11B was matched in ascending order.

FIG. 10 shows in detail the peaks in the vicinity of 1350 to 1390 cm ^-1 . In FIG. 10, the Raman spectrum shown by a thick line is a spectrum of hBN in which the boron isotope is a natural ratio obtained with reference to Non-Patent Document 2. Again, as described above, assuming that the abundance ratio of the boron isotope used as the raw material is reflected substantially as it is, the abundance ratio of the boron isotope in Examples 7, 13 to 15 ( ¹⁰ B: ¹¹ B). ) Are 2: 8, 9.6: 0.4, 0.1 to 0: 9.9 to 10 and 5: 5, respectively. Here, focusing on the Raman shift, peaks appear in the order of Example 14, Example 7, Example 16, and Example 13 from the long wavelength side to the short wavelength side, and the abundance ratio of ¹⁰ B is large. The abundance ratio of / ^11B was matched in ascending order.

From the above, it was shown that the peak of the Raman spectrum shifts to the short wavelength side as the abundance ratio of ¹⁰ B increases and to the long wavelength side as the abundance ratio of ¹¹ B increases in both cBN and hBN.

FIG. 12 is a diagram showing the relationship between the abundance ratio of the boron isotope of cBN obtained from FIG. 10 and the Raman shift.
FIG. 13 is a diagram showing the relationship between the abundance ratio of the boron isotope of hBN obtained from FIG. 11 and the Raman shift.

As shown in FIG. 12, it was found that the abundance ratio of boron isotopes in cBN has a linear relationship with Raman shift. As shown in FIG. 13, it was found that the relationship between the abundance ratio of boron isotopes in hBN and Raman shift is a substantially linear relationship, although it is arched.

From this, by investigating the Raman shift for arbitrary cBN and hBN samples, it is possible to determine the abundance ratio of boron isotopes in those samples from the above linear relational expression, and the boron isotopes in cBN / hBN. It has been shown that a method of identifying the abundance ratio of cannabinol can be provided.

According to the production method of the present invention, a single crystal powder made of boron nitride can be produced inexpensively and with high purity, and cubic or hexagonal boron nitride can be produced separately, or the abundance ratio of boron isotopes is controlled. Boron nitride can be produced. Since the boron nitride single crystal powder thus obtained functions as an ultra-hard material, it is preferable for grinding / cutting tools (for example, drills, end mills, bobs, milling cutters, lathes, pinion cutters, etc.), and the machining tool industry. , Used in the processing industry, processing equipment industry, etc. Further, since the boron nitride single crystal powder thus obtained has a relatively large size, it can be used as a wide-gap semiconductor. Since the boron nitride single crystal powder thus obtained has a controlled abundance ratio of boron isotopes, it is used as a neutron beam shielding material and a neutron beam detector.

1 High-voltage cell 11 Pyrophyllite container (cylinder)
12A, 12B Steel Ring 13,14 Filling Powder (NaCl + 10wt% ZrO ₂ )
15 Carbon Heater 16 Pressure Resistant Heat Resistant Capsule 17 Raw Material Powder 18, 19 Group 1 Elemental Hydroboride Powder 20 Ammonium Halogen Powder 21 Belt Type High Pressure Device 25A, 25B Anvil 26A, 26B Conductor 27A, 27B Cylinder 28 Pyro Philite (for filling)

Claims (15)

A method for producing a single crystal powder of boron nitride.
The boron nitride is cubic boron nitride (cBN) or hexagonal boron nitride (hBN).
Including the step of reacting a raw material powder containing a powder of a hydrogenated boride of a Group 1 element with a powder of ammonium halide.
In the raw material powder, the hydrogenated boride of the Group 1 element is contained so as to have a molar ratio of 1.25 or more and 1.75 or less with respect to the ammonium halide.
A method of reacting the raw material powder in a temperature range of 1000 ° C. or higher and 2500 ° C. or lower under a pressure of 3 GPa or higher and 10 GPa or lower. The method according to claim 1, wherein the hydrogenated boride of the Group 1 element is a material selected from at least one selected from the group consisting of NaBH ₄ , LiBH ₄ , KBH ₄ and CsBH ₄ . The method according to claim 1 or 2, wherein the ammonium halide is a material selected at least from the group consisting of NH ₄ Cl, NH ₄ Br, NH ₄ I and NH ₄ F. The boron nitride is cubic boron nitride (cBN).
In the reaction step, the raw material powder is reacted under a temperature and pressure satisfying P (GPa)> T (° C.) / 465 + 0.79 (where T satisfies 1000 ° C. ≤ T (° C.) ≤ 2500). , The method according to any one of claims 1 to 3 . The method according to claim 4, wherein the reaction step is to react the raw material powder in a temperature range of 1450 ° C. or higher and 1700 ° C. or lower under a pressure of more than 4.75 GPa and 5.5 GPa or lower. The boron nitride is hexagonal boron nitride (hBN).
In the reaction step, the raw material powder is reacted under a temperature and pressure satisfying P (GPa) <T (° C.) / 465 + 0.79 (where T satisfies 1000 ° C. ≤ T (° C.) ≤ 2500). , The method according to any one of claims 1 to 3 . The method according to claim 6, wherein the reaction step is to react the raw material powder in a temperature range of 1250 ° C. or higher and 1700 ° C. or lower under a pressure of 3.75 GPa or higher and 4.75 GPa or lower. The hydrides of the Group 1 element are elemental substances hydrides enriched with boron isotopes in 10B (concentration rate is 95% or more), and hydrides enriched with boron isotopes in 11B (concentrations). The method according to any one of claims 1 to 7, wherein the rate is 95% or more) alone or a combination thereof. The method according to any one of claims 1 to 8 , wherein the ratio of the boron isotope in the boron nitride is the same as the ratio of the boron isotope in the hydrogenated boride of the Group 1 element. The method according to any one of claims 1 to 9 , further comprising a step of treating the product obtained in the reaction step with a solvent to remove the second phase. The method according to any one of claims 1 to 10 , wherein the raw material powder contains a reaction inhibitor. The method according to any one of claims 1 to 11, wherein the reaction step is a reaction of the raw material powder for a time of 10 minutes or more and 24 hours or less. The method according to any one of claims 1 to 12, wherein the reaction step uses a belt-type high-pressure device. The method according to any one of claims 1 to 13, wherein the single crystal powder has a particle size in the range of 50 μm or more and 1 mm or less. The method according to claim 14, wherein the single crystal powder has a particle size in the range of 100 μm or more and 400 μm or less.

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