Powder and its manufacturing method

Abstract

To provide powder which contains carbon, nitrogen, boron and oxygen as constituent elements and contains particles having the same crystal structure as boron nitride with a turbulent structure and which can improve the productivity of hexagonal boron nitride.SOLUTION: One aspect of the present disclosure provides powder which contains carbon, nitrogen, boron, and oxygen as constituent elements and contains particles having the same crystal structure as boron nitride with a turbulent structure and which has a value of A / B of 1.4 or less when, in the Raman spectrum, A is a maximum value of a peak in the range of wave number 1,480 cm-1 to 1,900 cm-1 and B is a maximum value of a peak in the range of wave number 1,000 cm-1 or more and less than 1,480 cm-1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to powders and methods for producing the same, and more particularly to powders containing particles that contain carbon, nitrogen, boron, and oxygen as constituent elements and have the same crystal structure as turbostratic boron nitride, and methods for producing the same. [Background technology]

[0002] Boron nitride powder has lubricity, high thermal conductivity, insulating properties, etc., and is widely used in applications such as solid lubricants, thermally conductive fillers, insulating fillers, etc. In recent years, due to the increasing performance of electronic devices, there is a demand for boron nitride such as the above to have excellent thermal conductivity.

[0003] For example, Patent Document 1 proposes a hexagonal boron nitride powder and a method for producing the same, which, when used as a filler for insulating heat dissipation materials such as resins, can increase the thermal conductivity and withstand voltage (dielectric breakdown voltage) of the resins.

[0004] Hexagonal boron nitride powder is produced, for example, by a production method including a pressure nitriding step in which boron carbide is nitrided in a pressurized nitrogen-containing atmosphere to obtain a nitride, and a decarburization and crystallization step in which the nitride is mixed with a boron source and heat-treated to decarburize and promote crystallization, thereby obtaining hexagonal boron nitride (see, for example, Patent Document 2). The above-mentioned production method aims to improve the decarburization performance in the subsequent step by nitriding boron carbide once. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-116401 [Patent Document 2] International Publication No. 2019 / 073690 Summary of the Invention [Problem to be solved by the invention]

[0006] However, at present, the yield of hexagonal boron nitride produced by the above-mentioned production method is not particularly high.

[0007] An object of the present disclosure is to provide a powder containing particles that contain carbon, nitrogen, boron, and oxygen as constituent elements and have the same crystal structure as turbostratic boron nitride, which can improve the productivity of hexagonal boron nitride, and a method for producing the powder. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present inventors have conducted extensive research and found that, while conventional manufacturing methods employ a method in which the boron carbide nitride obtained in the pressure nitriding step is decarburized and crystallized in a subsequent step, the yield of hexagonal boron nitride is not improved in terms of crystallization in this step, and there is room for improvement. The inventors then discovered that by previously decarburizing the boron carbide nitride in an environment prone to exposure to oxygen, thereby reducing the amount of residual carbon, and adjusting the crystal structure of the nitride to a low crystallinity, it is possible to shorten the firing time in the subsequent crystallization step, thereby improving the productivity of hexagonal boron nitride. Furthermore, the crystal structure of the nitride was found to be highly crystalline at a wavenumber of 1480 cm in Raman spectroscopy. -1 More than 1900cm -1 The maximum value of the peak in the following range, wavenumber 1000 cm -1 More than 1480cm -1 It has also been found that a powder in which the ratio of the maximum value of the peak in the range of less than 1000 nm to the maximum value of the peak in the range of less than 1000 nm is adjusted to be within a predetermined range corresponds well to a raw material powder suitable for improving the productivity of hexagonal boron nitride. The present disclosure is based on this finding.

[0009] One aspect of the present disclosure is a powder containing particles that contain carbon, nitrogen, boron, and oxygen as constituent elements and have the same crystal structure as turbostratic boron nitride, and in a Raman spectroscopy spectrum, -1 More than 1900cm-1 The maximum peak value in the following range is A, and the wavenumber is 1000 cm -1 More than 1480cm -1 When the maximum value of the peak in the range below is taken as B, the value of A / B is 1.4 or less.

[0010] The powder containing particles having the same crystal structure as turbostratic boron nitride, which contain carbon, nitrogen, boron, and oxygen as constituent elements, has a low A / B value. -1 More than 1900cm -1 The peaks in the following range correspond mainly to the in-plane vibration of carbon atoms, which is characteristic of the graphene structure, and are observed when the crystallinity is excellent. -1 More than 1480cm -1 Within this range, peaks corresponding to structural disturbances and defects in graphene, as well as peaks corresponding to hexagonal boron nitride, are observed. That is, the fact that the A / B value is kept low means that the highly crystalline portions of the particles constituting the powder (for example, residual graphite contained in the boron carbide raw material) are sufficiently reduced, and the powder contains a relatively large amount of amorphous matter. This makes the powder suitable as a raw material for manufacturing hexagonal boron nitride to improve productivity.

[0011] The powder may have a carbon content of 4.0% by mass or less and an oxygen content of 5.0% by mass or less. By having the carbon and oxygen contents in the powder within the above ranges, when the powder is used as a production raw material, the carbon and oxygen to be removed are reduced in advance, which makes it possible to further reduce the amount of auxiliary agent used in the subsequent decarburization and crystallization steps and to further reduce the heat treatment time, thereby further improving the productivity of hexagonal boron nitride.

[0012] The powder may have an average particle size of 10 to 100 μm. The particle size of the hexagonal boron nitride can be adjusted by adjusting the particle size of the powder, and when the powder has an average particle size in this range, the performance of the resulting hexagonal boron nitride as a filler can be improved.

[0013] One aspect of the present disclosure provides a method for producing a powder containing particles having the same crystal structure as turbostratic boron nitride, the powder containing carbon, nitrogen, boron, and oxygen as constituent elements, the powder comprising: a pressure nitriding step in which boron carbide powder is sintered at a temperature of 1900 to 2200°C in a pressurized nitrogen atmosphere to obtain a sintered product; and an oxidation step in which the sintered product is heat-treated in an atmosphere having an oxygen partial pressure of 20% or more to obtain a heat-treated product, the oxidation step comprising stirring a mixture containing the sintered product and the heat-treated product.

[0014] The method for producing the powder includes an oxidation step in which the sintered product obtained in the pressure nitriding step is heat-treated in an oxygen-containing atmosphere, and the mixture is stirred during the oxidation step. By stirring the mixture during the oxidation step, the surface area of ​​the sintered product or heat-treated product that comes into contact with oxygen can be varied, thereby sufficiently reducing the carbon content of the sintered product or heat-treated product, reducing highly crystalline components in the powder (e.g., residual graphite contained in the raw material boron carbide), and further suppressing the improvement of crystallinity in the particles that make up the resulting powder. This manufacturing process, which includes such operations, can reduce the A / B value of the resulting powder.

[0015] The temperature of the heat treatment in the oxidation step may be 700 to 1050°C.

[0016] In the above-mentioned production method, the mixture may be stirred using a rotary kiln. When the stirring is performed using a rotary kiln, the powder can be produced more easily than when the mixture is stirred after temporarily stopping heating, as in a batch process. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide a powder containing particles having the same crystal structure as turbostratic boron nitride, which contains carbon, nitrogen, boron, and oxygen as constituent elements, and which can improve the productivity of hexagonal boron nitride, and a method for producing the powder. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following contents.

[0019] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified.

[0020] One embodiment of the powder according to the present disclosure is a powder containing particles having the same crystal structure as turbostratic boron nitride, containing carbon, nitrogen, boron, and oxygen as constituent elements. The powder may be an aggregate of the specific particles described above, and may also contain other particles as long as the spirit of the present disclosure is not impaired. The particles may have the same crystal structure as turbostratic boron nitride (t-BN), and the crystal structure may include, for example, a crystal structure in which some of the elements constituting turbostratic boron nitride are replaced by carbon, or a crystal structure in which carbon is dissolved in a crystal structure consisting of boron nitride. The particles may also include particles of what is called boron carbonitride, or may be particles of what is called boron carbonitride.

[0021] In the particles, the total amount of carbon, nitrogen, boron, and oxygen may be, for example, 95% by mass or more based on the total amount of elements constituting the particles. The composition of the above elements in the particles may be, for example, a carbon content of 0.1 to 5.0% by mass, a nitrogen content of 48 to 56% by mass, a boron content of 37 to 43% by mass, and an oxygen content of 0.1 to 5.5% by mass.

[0022] The crystallinity of the particles constituting the powder is adjusted. In the Raman spectroscopy, the powder has a wave number of 1480 cm -1 More than 1900cm -1 The maximum peak value in the following range is A, and the wavenumber is 1000 cm -1 More than 1480cm -1 When the maximum peak value in the range below is B, the A / B value is 1.4 or less. -1 More than 1900cm -1 The following range includes peaks that correspond to the in-plane vibration of carbon atoms characteristic of graphene or similar structures and are observed when the crystallinity is excellent. In the case of graphene, the peak is at 1580 cm -1 A peak is observed around 1000 cm -1 More than 1480cm -1 In the range of less than 1000 nm, peaks corresponding to structural disorders, defects, etc. in graphene, and peaks corresponding to hexagonal boron nitride are observed.

[0023] The upper limit of the A / B ratio in the powder may be, for example, 1.3 or less, 1.2 or less, 1.1 or less, or 1.0 or less. When the upper limit of the A / B ratio is within the above range, the firing time can be shortened when the resulting powder is used as a raw material, thereby further improving the productivity of hexagonal boron nitride. The lower limit of the A / B ratio in the powder is not particularly limited, but may be, for example, 0.3 or more, 0.4 or more, or 0.5 or more. When the lower limit of the A / B ratio is within the above range, excessive oxidation of the powder can be prevented. The A / B ratio in the powder may be adjusted within the above range, and may be, for example, 0.3 to 1.4, 0.4 to 1.3, or 0.5 to 1.3.

[0024] The A / B value of the powder is measured by the following method. Specifically, first, a cross-sectional sample of the powder is prepared using a cross-sectional sample preparation device. Next, the obtained cross-sectional sample is used as the measurement object, and a Raman spectrum is obtained by measuring it using a Raman spectrometer under the following measurement conditions. In the obtained Raman spectrum, the A / B value at a wavenumber of 1480 cm -1 More than 1900cm -1 The maximum value of the peak A and the wavenumber 1000 cm in the following range: -1 More than 1480cm -1 The maximum value B of the peak in the range less than 10 μm is identified, and the value of A / B is determined. Measurements are performed by performing mapping measurements in 1 μm steps (10 points x 10 points) on an approximately 10 μm square area at the center of the particle observed in the cross-sectional sample, accumulating the spectra for 100 points, and then correcting the baseline derived from fluorescence using a polynomial model to obtain a Raman spectrum. Examples of cross-sectional sample preparation devices that can be used include the "CP-9010" (trade name) manufactured by JEOL Ltd. Examples of Raman spectroscopy devices that can be used include the "XploRA Raman Microscope" (trade name) manufactured by Horiba, Ltd. <Raman spectroscopy measurement conditions> Laser: 532nm (neutral density filter: 10%) Range: 100~4000cm -1 Objective lens: 100x Grating: 1200gr Slit: 100μm Confocal hole: 100 μm Laser polarization: Circular Exposure time: 1 second Number of exposures: 3

[0025] The powder has a reduced carbon and oxygen content. When the powder is used as a raw material for producing hexagonal boron nitride, by reducing the carbon and oxygen to be removed in the powder in advance, it is possible to reduce the amount of auxiliary agents used in the subsequent decarburization and crystallization steps and to reduce the heat treatment time, thereby further improving the productivity of hexagonal boron nitride.

[0026] The upper limit of the carbon content in the powder may be, for example, 4.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less, based on the total amount of the powder. The lower limit of the carbon content in the powder may be, for example, 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, based on the total amount of the powder.

[0027] The oxygen content in the powder may be, for example, 5.0% by mass or less, 4.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less, based on the total amount of the powder. The lower limit of the oxygen content in the powder may be, for example, 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more, based on the total amount of the powder.

[0028] The powder may have a carbon content of 4.0% by mass or less and an oxygen content of 5.0% by mass or less.

[0029] The total carbon and oxygen content of the powder may be, for example, 5.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less, based on the total amount of the powder. The lower limit of the total carbon and oxygen content of the powder is not particularly limited, and may be 0% by mass or more, based on the total amount of the powder, but may be, for example, 0.5% by mass or more, or 1.0% by mass or more.

[0030] In this specification, the carbon, nitrogen, boron, and oxygen contents refer to values ​​measured by the following methods. The carbon content refers to a value measured using a carbon / sulfur simultaneous analyzer. An example of a carbon / sulfur simultaneous analyzer that can be used is the "IR-412" (trade name) manufactured by LECO. The nitrogen content refers to a value determined by titration. Specifically, a sample is first alkaline decomposed with sodium hydroxide, and ammonia is distilled from the decomposed solution using steam distillation and collected in an aqueous boric acid solution. The collected solution is titrated with a normal sulfuric acid solution to determine the nitrogen atom content in the sample. The boron content refers to a value determined by titration. Specifically, a sample is first heated and melted in a platinum crucible, completely dissolved in hydrochloric acid, and then titrated with an aqueous sodium hydroxide solution to determine the boron atom content in the sample. The oxygen content refers to a value measured using an oxygen / nitrogen simultaneous analyzer. As the oxygen / nitrogen simultaneous analyzer, for example, "EMGA-910 type" (product name) manufactured by Horiba Ltd. can be used.

[0031] The powder may have an adjusted particle size. The upper limit of the average particle size of the powder may be, for example, 100 μm or less, 90 μm or less, or 80 μm or less. When the upper limit of the average particle size is within the above range, a hexagonal boron nitride powder prepared using the powder as a raw material can be suitably used for a thin heat dissipation component with a film thickness of about 0.2 mm. The lower limit of the average particle size of the powder may be, for example, 10 μm or more, 15 μm or more, or 20 μm or more. When the lower limit of the average particle size is within the above range, a hexagonal boron nitride powder prepared using the powder as a raw material and a heat dissipation component prepared using the hexagonal boron nitride powder can exhibit high heat dissipation properties. The average particle size of the powder may be adjusted within the above range, for example, 10 to 100 μm, 15 to 90 μm, or 20 to 80 μm.

[0032] The average particle size in this specification is a value obtained by measuring the powder as it is without homogenization, and is the average particle size of primary particles, not including aggregated particles. The above-mentioned powders typically do not include aggregated particles. The average particle size in this specification also refers to the particle size (median diameter, d50) at which the cumulative value of the cumulative particle size distribution on a volume basis is 50%. The average particle size in this specification is measured using a laser diffraction / scattering particle size distribution analyzer in accordance with ISO 13320:2009. Specifically, it is measured by the method described in the Examples section of this specification. Examples of laser diffraction / scattering particle size distribution analyzers that can be used include the "LS-13 320" (instrument name) manufactured by Beckman Coulter.

[0033] The above-mentioned powder can be produced, for example, by the following method. One embodiment of the powder production method is a method for producing a powder containing particles having the same crystal structure as turbostratic boron nitride, containing carbon, nitrogen, boron, and oxygen as constituent elements, and comprising a pressure nitriding step in which boron carbide powder is fired at a temperature of 1900 to 2200°C in a pressurized nitrogen atmosphere to obtain a fired product, and an oxidation step in which the fired product is heat-treated in an atmosphere with an oxygen partial pressure of 20% or more to obtain a heat-treated product. The oxidation step is a step that includes stirring a mixture containing the fired product and the heat-treated product (hereinafter also referred to as a stirring oxidation step).

[0034] In the pressure nitriding step, boron carbide powder is fired at a temperature of 1900 to 2200°C in a pressurized nitrogen atmosphere to obtain a fired product. The fired product may contain boron carbonitride (B4CN4). The lower limit of the firing temperature in the pressure nitriding step may be 1900°C or higher, or may be 2000°C or higher. By setting the lower limit of the firing temperature within the above range, the nitriding of boron carbide can be more fully promoted. Furthermore, the upper limit of the firing temperature may be 2200°C or lower, or may be 2150°C or lower. By setting the upper limit of the firing temperature within the above range, it is possible to prevent the crystallinity of boron carbonitride from becoming too high, which would result in a decrease in production efficiency in the crystallization step, which is a manufacturing process for hexagonal boron nitride powder, when the boron carbonitride is used as a raw material for manufacturing hexagonal boron nitride powder. The firing temperature may be adjusted within the above range, for example, 1900 to 2200°C or 1900 to 2150°C.

[0035] The lower limit of the pressure in the pressure nitriding step may be, for example, 0.6 MPa or more, 0.7 MPa or more, or 0.8 MPa or more. By setting the lower limit of the pressure within the above range, the nitriding of boron carbide can be more sufficiently promoted. The upper limit of the pressure in the pressure nitriding step may be, for example, 1.0 MPa or less, or 0.9 MPa or less. By setting the upper limit of the pressure within the above range, an increase in manufacturing costs can be suppressed. The pressure may be adjusted within the above range, and may be, for example, 0.6 to 1.0 MPa.

[0036] The nitrogen gas concentration in the nitrogen pressurized atmosphere in the pressure nitriding step may be, for example, 95.0% by volume or more, 98.0% by volume or more, or 99.9% by volume or more. By setting the nitrogen gas concentration within the above range, the nitriding of boron carbide can be carried out under milder conditions. The above nitrogen gas concentration is a concentration based on volume under standard conditions. The firing time in the pressure nitriding step is not particularly limited as long as the nitriding proceeds sufficiently, and may be, for example, 6 to 30 hours or 8 to 20 hours.

[0037] In the oxidation step, the fired product is heat-treated in an atmosphere with an oxygen partial pressure of 20% or more to obtain a heat-treated product. In the oxidation step, the carbon content in the fired product is combined with oxygen and removed from the system as carbon dioxide gas, thereby performing a decarburization treatment. In this step, stirring the mixture containing the fired product and the heat-treated product increases the surface area in contact with oxygen, improving the efficiency of the decarburization treatment and, by making the decarburization treatment conditions milder, it is possible to suppress an increase in production costs.

[0038] The atmosphere during the heat treatment in the oxidation step (firing atmosphere) is an atmosphere with an oxygen partial pressure of 20% or more, and may be, for example, air or a mixed gas with an adjusted oxygen partial pressure. From the viewpoint of reducing production costs, the firing atmosphere is air. The oxidation step may be performed in a closed system or an open system, but the system can be adjusted so as to maintain the firing atmosphere. During the oxidation step, air or a mixed gas that satisfies the above-mentioned conditions may be circulated at a rate of, for example, 100 L / min or less. During the oxidation step, air or a mixed gas that satisfies the above-mentioned conditions may be circulated at a rate of, for example, 20 L / min or more, or 30 L / min or more.

[0039] When a mixed gas is used, the lower limit of the oxygen partial pressure may be, for example, 20% or more, 25% or more, or 30% or more. When the lower limit of the oxygen partial pressure is within the above range, the oxidation reaction of carbon in the oxidation step can be further promoted. When a mixed gas is used, the upper limit of the oxygen partial pressure may be, for example, 70% or less, 60% or less, or 50% or less. When the upper limit of the oxygen partial pressure is within the above range, excessive oxidation of the powder can be prevented. When a mixed gas is used, the oxygen partial pressure may be adjusted within the above range, for example, 20 to 80% or 25 to 60%. Note that the oxygen partial pressure in this specification refers to the partial pressure of oxygen under standard conditions in the mixed gas occupying the firing atmosphere, and refers to a value measured by an oxygen concentration meter. For example, the "G1690" (trade name) manufactured by Sakaki Corporation can be used as the oxygen concentration meter.

[0040] The upper limit of the temperature (heating temperature) for the heat treatment in the oxidation step may be, for example, 1050°C or lower, 1000°C or lower, or 950°C or lower. When the upper limit of the heating temperature is within the above range, excessive oxidation can be prevented. The lower limit of the temperature for the heat treatment in the oxidation step may be, for example, 700°C or higher, 750°C or higher, or 800°C or higher. When the lower limit of the heating temperature is within the above range, the reaction in the carbon oxidation step can be further promoted. The heating temperature in the oxidation step may be adjusted within the above range, and may be, for example, 700 to 1050°C, 700 to 1000°C, or 750 to 950°C.

[0041] The stirring operation of the mixture containing the fired product and the heat-treated product in the oxidation step may be performed intermittently or continuously throughout the oxidation step. When the stirring operation is performed intermittently, for example, the heat treatment may be temporarily stopped for the stirring operation.

[0042] The means for stirring the mixture containing the calcined product and the heat-treated product in the oxidation step is not particularly limited, and any means capable of changing the surface of the mixture in contact with the calcination atmosphere may be used. Examples of such means include manual stirring, stirring using a mechanical stirrer, stirring using a fluidized bed, and stirring using a rotary kiln such as a rotary kiln. The mixture may be stirred using a rotary kiln. By using a rotary kiln, the surface in contact with the calcination atmosphere is continuously changed while vibration is applied to the mixture, which can suppress excessive crystallinity and also facilitate the desorption of carbon dioxide gas and the like.

[0043] When a rotary kiln is used, the raw material, that is, the fired product, is fed into the kiln using a screw feeder or the like, and heat treatment can be carried out in a flowing atmosphere in which air or the mixed gas is introduced at a predetermined flow rate.

[0044] The feed rate of the raw material calcined product is not particularly limited, but may be, for example, 5 g / min or more, 10 g / min or more, 20 g / min or more, or 100 g / min or more. The feed rate of the raw material calcined product may be, for example, less than 1000 g / min or less than 800 g / min. When the upper limit of the feed rate is within the above range, the surface of the calcined product can be more sufficiently exposed to oxygen, thereby further improving the production efficiency of hexagonal boron nitride powder using the powder. The feed rate of the raw material calcined product may be adjusted by the inner diameter and length of the kiln furnace, and can be set to, for example, about 3 to 15 volume % of the volume of the kiln furnace.

[0045] The lower limit of the flow rate of air or the mixed gas may be, for example, 10 L / min or more, 20 L / min or more, 30 L / min or more, 40 L / min or more, or 45 L / min or more. By setting the lower limit of the flow rate within the above range, it is possible to ensure a sufficient supply of oxygen while more easily removing carbon dioxide and the like. The upper limit of the flow rate of air or the mixed gas may be, for example, 1000 L / min or less, 950 L / min or less, or 900 L / min or less. Setting the upper limit of the flow rate within the above range can further promote the oxidation reaction of carbon in the oxidation step. The flow rate of air or the mixed gas may be adjusted within the above range, and may be, for example, 10 to 1000 L / min or 20 to 950 L / min.

[0046] The lower limit of the rotation speed of the rotary kiln may be, for example, 0.5 rpm or more, 0.7 rpm or more, or 1.0 rpm or more. By setting the lower limit of the rotation speed within the above range, it is possible to adjust the residence time and prevent excessive oxidation and an increase in production costs. The upper limit of the rotation speed of the rotary kiln may be, for example, 10 rpm or less, 9 rpm or less, or 8 rpm or less. By setting the upper limit of the rotation speed within the above range, it is possible to further promote the reaction in the carbon oxidation step. The rotation speed of the rotary kiln may be adjusted within the above range, and may be, for example, 0.5 to 10 rpm, or 0.7 to 9 rpm.

[0047] The tilt angle of the rotary kiln can be adjusted depending on, for example, the temperature and time of the heat treatment, the feed amount, etc. The tilt angle of the rotary kiln may be, for example, 0.2 to 6°, 0.3 to 5°, or 0.5 to 4°.

[0048] The powder obtained as described above is suitable as a raw material for producing hexagonal boron nitride powder. For example, the powder can be mixed with an auxiliary agent such as a boron source to prepare a raw material composition, and the raw material composition can be heat-treated to generate primary particles of boron nitride, thereby obtaining hexagonal boron nitride powder containing agglomerated particles formed by the aggregation of the primary particles. In other words, the powder can be used as a raw material for producing hexagonal boron nitride powder by desorbing carbon and oxygen contained in the powder as carbon dioxide gas or the like to decarbonize the powder, generating primary particles of a predetermined size, and agglomerating these particles to obtain agglomerated particles. One example of a method for producing hexagonal boron nitride powder includes a step of heating a raw material composition containing the powder and a boron source to generate primary particles of boron nitride and obtain agglomerated particles formed by the aggregation of the primary particles (hereinafter also referred to as a crystallization step).

[0049] The boron source may be boric acid, boron oxide, or a mixture thereof. The mixture heated in the crystallization step may contain known additives.

[0050] In the raw material composition, the blending ratio of the powder and the boron source can be appropriately set according to the molar ratio. When at least one of boric acid and boron oxide is used as the boron source, for example, the boron source may be blended so that the total amount of boric acid and boron oxide is 20 to 300 parts by mass, or the total amount of boric acid and boron oxide is 50 to 250 parts by mass, per 100 parts by mass of the powder.

[0051] The heating temperature at which the mixture is heated in the crystallization step may be, for example, 2000°C or higher, or 2100°C or higher. By setting the lower limit of the heating temperature within the above range, particle growth can be sufficiently promoted. The heating temperature at which the mixture is heated in the crystallization step may be, for example, 2150°C or lower, or 2100°C or lower. By setting the upper limit of the heating temperature within the above range, yellowing of the hexagonal boron nitride powder can be suppressed. The heating temperature may be adjusted within the above range, and may be, for example, 2000 to 2150°C. The heating temperature at which the raw material composition is heated in the crystallization step is preferably lower than the heating temperature of the powder in the nitriding step.

[0052] The crystallization step may be performed under normal pressure (atmospheric pressure) or under pressure exceeding atmospheric pressure (e.g., 50 kPa or higher). When pressure is applied, the pressure may be, for example, 0.5 MPa or lower, or 0.3 MPa or lower. The pressure referred to above is a gauge pressure.

[0053] The heating time in the crystallization step may be 0.5 hours or more, 1 hour or more, or 3 hours or more. By setting the lower limit of the heating time within the above range, particle growth can be sufficiently promoted. The heating time in the crystallization step may be 40 hours or less, 30 hours or less, 20 hours or less, or 10 hours or less. By setting the upper limit of the heating time within the above range, an increase in manufacturing costs can be suppressed. The heating time may be adjusted within the above range, for example, 0.5 to 40 hours, or 1 to 30 hours. Note that the firing time, heating time, etc. in this specification refer to the time (retention time) during which the temperature of the ambient environment of the object is maintained at a predetermined temperature after it has reached that temperature.

[0054] The method for producing hexagonal boron nitride powder may include other steps. Examples of such other steps include a pulverization step and a classification step. In the method for producing hexagonal boron nitride powder, for example, a pulverization step may be carried out after the crystallization step. In the pulverization step, a general pulverizer or crusher can be used. For example, a ball mill, a vibration mill, a jet mill, or the like can be used. In this specification, "pulverization" also includes "crushing." The average particle size of the hexagonal boron nitride powder may be adjusted to 15 to 100 μm by pulverization and classification.

[0055] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. Furthermore, the descriptions of the above-described embodiments can be mutually applied. [Example]

[0056] The present disclosure will be described in more detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0057] Example 1 100 parts by mass of orthoboric acid manufactured by Nippon Denko Corporation and 35 parts by mass of acetylene black (product name: HS100) manufactured by Denka Co., Ltd. were mixed using a Henschel mixer. The resulting mixture was loaded into a graphite crucible and heated in an arc furnace in an argon atmosphere at 2200°C for 5 hours to obtain a fired product containing lumped boron carbide (BC) (pressure nitriding process). The resulting lumps were coarsely crushed using a jaw crusher to obtain a coarse powder. This coarse powder was further crushed using a ball mill equipped with silicon carbide balls (φ10 mm) to obtain a crushed powder. The crushing using the ball mill was carried out at a rotation speed of 20 rpm for 60 minutes. The crushed powder was then classified using a vibrating sieve with 75 μm openings. The fine powder that fell through the sieve was subjected to airflow classification using a Crusseal classifier to obtain a powdered fired product with a particle size of 10 μm or more. The carbon content of the obtained fired product was 10.1% by mass and the oxygen content was 0.2% by mass. The prepared boron carbide powder was subjected to a nitriding treatment in a carbon resistance heating furnace under a nitrogen gas atmosphere at a firing temperature of 2000°C and a pressure of 0.90 MPa for 12 hours.

[0058] The nitrided fired powder was fed into a rotary kiln (inner diameter: 100 mm, length: 1900 mm) at a feed rate of 10 g / min. While air was circulating through the kiln at 45 L / min, the fired product was oxidized by heat treatment at 900°C to obtain a powdered heat-treated product (oxidation step). This heat-treated product was designated as the powder of Example 1. The rotary kiln had an inclination angle of 1° and a rotation speed of 1.0 rpm. The residence time (heating time) of the fired product in the kiln was 90 minutes. The carbon content of the obtained powder was 1.8% by mass, the oxygen content was 1.8% by mass, the boron content was 42% by mass, and the nitrogen content was 54% by mass. The average particle size of the obtained powder was 35 μm.

[0059] <Powder evaluation> The obtained powder was measured by Raman spectroscopy and found to have a wave number of 1480 cm -1 More than 1900cm -1 The maximum value of the peak A and the wavenumber 1000 cm in the following range: -1 More than 1480cm -1The maximum value B of the peak in the range below was determined, and the intensity ratio (value A / B) was determined.

[0060] Example 2 1000 g of the fired material prepared in the same manner as in Example 1 was placed in an alumina crucible and heat-treated in an air atmosphere at 800°C for 1 hour in a muffle furnace. After 3 hours, the temperature was lowered to 150°C, and the powder was stirred so that the heat-treated surface material packed in the crucible and the fired material inside the crucible were interchanged. Thereafter, the powder was further heat-treated in an air atmosphere at 800°C for 1 hour in a resistance heating furnace. The temperature was similarly lowered to 150°C and heat-treated again at 800°C for 1 hour to obtain a powdered heat-treated product (oxidation step). This heat-treated product was designated as the powder of Example 2. The carbon content, oxygen content, and average particle size of the obtained powder were measured in the same manner as in Example 1. The obtained powder was also analyzed by Raman spectroscopy in the same manner as in Example 1 to determine the A / B value. The results are shown in Table 1.

[0061] Example 3 Powder was obtained in the same manner as in Example 1, except that the kiln temperature was changed to 700°C. The carbon content, oxygen content, and average particle size of the obtained powder were measured in the same manner as in Example 1. The obtained powder was also analyzed by Raman spectroscopy in the same manner as in Example 1, and the A / B value was determined. The results are shown in Table 1.

[0062] Example 4 Powder was obtained in the same manner as in Example 1, except that the temperature of the kiln furnace was changed to 1000°C. The carbon content, oxygen content, and average particle size of the obtained powder were measured in the same manner as in Example 1. The obtained powder was also analyzed by Raman spectroscopy in the same manner as in Example 1, and the A / B value was determined. The results are shown in Table 1.

[0063] Example 5 A powder was obtained in the same manner as in Example 1, except that the boron carbide pulverization method was intensified to 150 minutes and boron carbide powder classified into fine powder with an opening size of 32 μm or less was used. The carbon content, oxygen content, and average particle size of the obtained powder were measured in the same manner as in Example 1. The obtained powder was also analyzed by Raman spectroscopy in the same manner as in Example 1, and the A / B value was determined. The results are shown in Table 1.

[0064] Example 6 A powder was obtained in the same manner as in Example 1, except that the method of preparation after pulverization of boron carbide was changed to use boron carbide powder classified using a sieve with a mesh size of 45 μm or more and 212 μm or less. The carbon content, oxygen content, and average particle size of the obtained powder were measured in the same manner as in Example 1. The obtained powder was also analyzed by Raman spectroscopy in the same manner as in Example 1, and the A / B value was determined. The results are shown in Table 1.

[0065] (Comparative Example 1) The powdered fired product (before the oxidation step) obtained in Example 1 was used as the powder of Comparative Example 1. The carbon content, oxygen content, and average particle size of the obtained powder were measured in the same manner as in Example 1. The obtained powder was also analyzed by Raman spectroscopy in the same manner as in Example 1, and the A / B value was determined. The results are shown in Table 1.

[0066] <Performance evaluation as powder raw material> Using the powders obtained in Examples 1 to 6 and Comparative Example 1 as raw materials, hexagonal boron nitride powder was produced and the productivity was evaluated.

[0067] Boric acid was added to the powder and mixed using a Henschel mixer. 2 kg of the mixture was then loaded into a boron nitride crucible and heated from room temperature to 2000°C in a nitrogen gas atmosphere under atmospheric pressure in a resistance heating furnace. Crystallization was then fully promoted at 2000°C to prepare hexagonal boron nitride powder. The amount of boric acid added was the minimum amount necessary to achieve a graphitization index of 2 or less for the hexagonal boron nitride powder obtained by firing at 2000°C. The time required to maintain the temperature at 2000°C (firing time) and the total time required to return the temperature to room temperature (heating time) were the times required for sufficient crystallization at 2000°C. The amount of boric acid added, firing time, and heating time for each of Examples 1 to 6 and Comparative Example 1 are shown in Table 1.

[0068] When the hexagonal boron nitride powder was prepared as described above, the yield of the hexagonal boron nitride powder was evaluated based on the raw material powder, and the production efficiency, taking into account the time required for production (heating time), was evaluated. The results are shown in Table 1. The production efficiency means the value obtained by dividing the yield by the heating time, and is shown in Table 1 as a relative value based on Comparative Example 1.

[0069] [Graphitization index of hexagonal boron nitride powder] The graphitization index of the hexagonal boron nitride powder used to determine the boric acid content was calculated from the results of measurements using powder X-ray diffraction. In the obtained X-ray diffraction spectrum, the integrated intensities of each diffraction peak corresponding to the (100), (101), and (102) planes of the primary particles of hexagonal boron nitride (i.e., each diffraction peak) and its baseline were calculated (arbitrary units) and designated as S100, S101, and S102, respectively. Using the calculated area values, the graphitization index was determined based on the following formula (1): GI=(S100+S101) / S102 … Formula (1)

[0070] [Table 1] [Industrial Applicability]

[0071] According to the present disclosure, it is possible to provide a powder containing particles composed mainly of carbon, nitrogen, and boron and having the same crystal structure as turbostratic boron nitride, which can improve the productivity of hexagonal boron nitride, and a method for producing the powder.

Claims

1. A powder containing particles having the same crystal structure as turbostratic boron nitride, the particles containing carbon, nitrogen, boron, and oxygen as constituent elements, In the Raman spectrum, the wave number is 1480 cm －１ More than 1900cm －１ The maximum value of the peak in the following range is A, and the wave number is 1000 cm －１ 1480cm or more －１ When the maximum value of the peak in the range less than 1.5 is B, the value of A / B is 1.4 or less.

2. 2. The powder according to claim 1, wherein the carbon content is 4.0% by mass or less and the oxygen content is 5.0% by mass or less.

3. 3. The powder according to claim 1, having an average particle size of 10 to 100 μm.

4. A method for producing a powder containing particles having the same crystal structure as turbostratic boron nitride, the particles containing carbon, nitrogen, boron, and oxygen as constituent elements, comprising: a pressure nitriding step of sintering the boron carbide powder at a temperature of 1900 to 2200°C in a pressurized nitrogen atmosphere to obtain a sintered product; an oxidation step of heat-treating the fired product at a temperature of 700 to 1050°C in an atmosphere having an oxygen partial pressure of 20% or more to obtain a heat-treated product; The oxidation step comprises stirring a mixture containing the fired product and the heat-treated product.

5. The method according to claim 4 , wherein the mixture is stirred by a rotary kiln.

Images