JPH0524849B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a hexagonal boron nitride powder (hereinafter referred to as h-BN) with excellent sintering properties and a method for producing the same, and relates to a raw material powder for producing a boron nitride sintered body and a method for producing the same. It is related to. [Prior Art] h-BN is a white powder that has a hexagonal layered structure similar to graphite, and has various properties. In particular, it has excellent thermal conductivity, electrical insulation, corrosion resistance, lubricity, heat resistance, machinability, etc., and it is used in a wide variety of applications by taking advantage of these properties. Applications as a powder include plastic additives and lubricants, and applications as molded bodies and composite materials include jigs, electrical insulation materials, and mold materials. Various methods have been developed to synthesize h-BN, which has a wide range of uses, but the methods currently used industrially include (1) mixing a mixture of borax and urea in an ammonia atmosphere;
Method of heating synthesis at 800℃ or higher
1610) (2) Method of mixing boric acid or boron oxide and calcium phosphate and heating in an ammonia atmosphere (Special Publication No. 1610-24669) (3) Mixing boric acid and nitrogen-containing compounds (urea, melamine, dicyandiamide, etc.) at 1600℃ The main methods include heating to a higher temperature (Japanese Patent Publication No. 48-14559). (4) There is also a gas phase synthesis method using boron trichloride and ammonia, but due to the high cost of raw materials, this method is limited to manufacturing products for special purposes. (Japanese Patent Publication No. 38-22852) (5) Since crystals do not grow in the method (3) above, in order to improve this drawback, there is a method of growing crystals by adding an alkaline earth metal compound (Japanese Patent Publication No. 41-1989). 18570) has been proposed. (6) Furthermore, as a method for highly purifying h-BN, a method of adding an alkali metal to crude h-BN using boric acid as a raw material and heating it to over 1000℃
26600). In the method (1) above, since the borax in the raw material contains a large amount of sodium, when the temperature exceeds 1000℃, the sodium oxide begins to evaporate, condenses in the cooling section, and is used in the reactor due to the deliquescent nature of sodium oxide. The sodium component must be removed by washing once at a temperature below 1000℃ to avoid damaging the material. Therefore, a cleaning step is required, which complicates the process. In the method (2) above, it is also necessary to remove the added calcium phosphate by pickling. Furthermore, in the method (3) above, high purity products cannot be produced unless the temperature is raised to 1600°C or higher. The method (5) of growing crystals by adding an alkaline earth metal also requires pickling treatment to remove additives, as in (3) above. The method (6) of adding an alkali metal compound to achieve high purity is to synthesize crude h-BN at a temperature of 800℃ or higher, crush it, add an alkali metal compound, and then undergo a molding process at a temperature of 1000℃ or higher. The process is very complicated because it is heated by In this method, the purity of crude h-BN is about 80%, which cannot be said to be high purity, and even in the high purification process, the remaining B ₂ O ₃ is not nitrided and purified, but is removed by evaporation. It's just that. For this reason, the utilization rate of boron as a raw material is extremely low, and it is difficult to say that this is a fundamental solution. Furthermore, as a similar method to the present invention, a method is prepared in which a boron nitride powder is mixed with an alkaline earth metal borate to synthesize a powder for producing a sintered body, and this powder is hot pressed to produce a sintered body (Japanese Patent Publication No. 40124).
In this method of hot pressing by adding a sintering aid to boron nitride powder, the characteristics of the boron nitride powder used as the raw material do not differ from conventional products, and crystals grow in high purity boron nitride, which causes problems during the production of sintered bodies. Anisotropy occurs, and low-crystalline boron nitride has low purity and contains a large amount of sintering aids and impurities, resulting in poor high-temperature properties and cannot provide any fundamental solution. [Problems to be Solved by the Invention] As described above, in order to obtain high-purity h-BN using the conventional techniques, high-temperature heat treatment or complicated steps such as pickling were required. In addition, if the purity is simply increased, crystals will also grow at the same time, and if a sintered body is manufactured using boron nitride powder with large crystals as a raw material, the sintered body will have poor sintering properties and poor strength at high temperatures. I can only get it. As a result of intensive efforts by the present inventors to compensate for the shortcomings of the prior art, they were able to produce an excellent h-BN powder as a raw material for a sintered body, which could not be obtained by conventional methods. An object of the present invention is to provide an h-BN powder with excellent sintered properties and a method for producing the same. According to the present invention, it is possible to obtain h-BN which is highly pure, does not have much crystal growth, has a quasi-graphitic structure, and uniformly contains a fine alkaline earth metal compound as a stabilizer. [Means for solving the problems] The present invention contains an alkaline earth metal in an amount of 0.0001 to 0.1 mol per 1 mol of boron, and has a crystallite size of 8.
~50nm, and the purity of boron nitride is 95% by weight or more, making it a hexagonal boron nitride powder with excellent sintering properties. Such h-BN can be produced by the following method. A mixture of an oxygen-containing boron compound and a nitrogen compound is used as a raw material, and carbonaceous powder and/or
Alternatively, borax is added and heated in a non-oxidizing atmosphere. This produces h-BN powder with high purity and undeveloped crystals, which could not be obtained by conventional methods. Furthermore, an alkaline earth metal compound is uniformly dispersed in the h-BN powder as a stabilizer for boron oxide existing as an impurity or oxygen incorporated into the h-BN crystals. This uniform dispersion of the alkaline earth metal may be performed before or after heating in the non-oxidizing atmosphere, and by this dispersion, h-BN powder with excellent sintering properties can be obtained. The first aspect of the production method of the present invention is to mix an oxygen-containing boron compound and a nitrogen compound, and to prepare an alkaline earth metal for 1 mole of boron in the mixture.
0.0001 to 0.1 mol of an alkaline earth metal compound is added, and 0.005 to 0.1 mol of carbonaceous powder and/or anhydrous borax is added as carbon per mol of boron in the mixture. It is characterized by adding 2.5 to 30% by weight of borax and heating the above mixture in a non-oxidizing atmosphere under normal pressure or reduced pressure. In the second method of the present invention, an oxygen-containing boron compound and a nitrogen compound are mixed, 0.005 to 0.1 mole of carbonaceous powder is added as carbon per mole of boron in the mixture, and the above mixture is mixed under normal pressure. Alternatively, hexagonal boron nitride powder is obtained by heating in a non-oxidizing atmosphere under reduced pressure, and the hexagonal boron nitride powder has an alkaline earth metal content of 0.0001 to 0.1 per mole of boron in the powder.
It is characterized by mixing molar alkaline earth metal compounds. The third method of the invention is to mix an oxygen-containing boron compound and a nitrogen compound, and obtain a carbonaceous powder containing 0.005 to 0.1 mole of carbon per mole of boron in the mixture, and 2.5 to 30% by weight of borax is added as anhydrous borax, and the above mixture is heated in a non-oxidizing atmosphere under normal pressure or reduced pressure to obtain hexagonal boron nitride powder. It is characterized in that 0.0001 to 0.1 mole of an alkaline earth metal compound is mixed as an alkaline earth metal with respect to 1 mole of boron in the powder. A fourth method of the invention is to mix an oxygen-containing boron compound and a nitrogen compound, and add 0.0001 to 0.1 mole of the alkaline earth metal compound as an alkaline earth metal per mole of boron in the mixture, and the oxygen-containing boron compound. 2.5-30% by weight of anhydrous borax based on the compound
After adding borax and heating the above mixture at low temperature in a non-oxidizing atmosphere under normal pressure or reduced pressure to obtain crude hexagonal boron nitride powder, the crude hexagonal boron nitride powder is washed and dried. It is characterized by The fifth invention method is to mix an oxygen-containing boron compound and a nitrogen compound, add 2.5 to 30% by weight of borax as anhydrous borax to the oxygen-containing boron compound, and mix the above mixture under normal pressure or After obtaining a crude hexagonal boron nitride powder by heating at low temperature in a non-oxidizing atmosphere under reduced pressure, the crude hexagonal boron nitride powder is washed and dried, and an alkaline earth is added to each mole of boron in the dry powder. It is characterized by mixing 0.0001 to 0.1 mol of an alkaline earth metal compound as the metal. [Function] Hereinafter, the method for producing h-BN powder which is most suitable as a raw material for a sintered body will be specifically explained in detail along with its function. There are various oxygen-containing boron compounds that are boron sources, but if you take into account the possibility of contamination with impurities, it is appropriate to use boric acid, boric acid dehydrate, ammonium borate, etc. Urea is a nitrogen compound that is a nitrogen source. , melamine, dicyandiamide, cyanuric acid, ammonium chloride, and the like, which can be decomposed and removed at high temperatures are preferred. The mixing ratio of these raw materials must be such that the molar ratio of boron to nitrogen (N/B) is 1 or more. For the purpose of further nitriding the mixture, for example, boric acid and melamine were mixed so that (N/B) = 2 and heated in an ammonia atmosphere.
Boron nitride content is 85% by weight at ℃, 92% at 1500℃
It was in weight%. Moreover, the size of the crystallite at this time was 45 nm in Lc. The purity of the h-BN powder used here is determined by analyzing the N in the synthesized boron nitride using an alkali melting method using a theoretical value of 56.5% of the N content in boron nitride, and converting the analytical value of N (%) to the theoretical value. The value divided by is multiplied by 100 and expressed as a percentage. The crystal structure of boron nitride differs depending on the synthesis conditions. For example, when boron nitride is synthesized in a nitrogen atmosphere using boric acid and urea as raw materials,
Boron nitride is formed at 600°C, but in this case, it has not completely formed into a hexagonal crystal structure, but instead has a structure in which adjacent layers are randomly positioned relative to each other, which is called a turbostratic structure in crystallography. There is. Ordinary crystalline boron nitride has a hexagonal layered structure similar to graphite, and each layer is completely parallel, which is different from boron nitride, which has a turbostratic structure. As the temperature is further raised, the turbostratic structure gradually changes to a hexagonal structure, and at the same time, grain growth and impurities such as boron oxide, ammonium borate, oxygen and carbon in the crystals are removed, and the purity improves. To go.
When the temperature exceeds 1600℃, the primary particle size also increases to 1μm or more, and if heating continues, the purity (N
(value calculated from the analytical value) is 99% or more by weight boron nitride. A method to quantify these crystal structures is to measure the size of crystallites (Japan Society for the Promotion of Science 117
Commission Act). The size of crystallites is expressed by the average thickness in the c-axis direction (Lc) and the average diameter in the a-axis direction (La), and since the (002) peak is the strongest, Lc
It is also more accurate to display it as . When the above-mentioned crystal structure was evaluated by Lc, it was a turbostratic structure at approximately 10 nm or less, a quasi-graphitic structure at approximately 10 to 40 nm, and a completely hexagonal structure at approximately 40 nm or more. Therefore, the quasi-graphitic structure referred to in the present invention is
In terms of Lc, it is approximately 10 to 40 nm of boron nitride. However, this boundary is not clear, and as a powder raw material for a sintered body, the characteristics are most expressed when Lc is 8 to 50 nm. Therefore, the Lc of the raw material powder is 8~
50nm is preferable. As a result of investigating a method for producing high-purity h-BN in which no crystals with Lc size of 20 nm or less are grown at the lowest possible temperature, it was found that the low purity of h-BN is due to B ₂ O that is not completely nitrided. ₃ exists, and crystallites grow because the melting point of B ₂ O ₃ is as low as 450°C, forming a liquid phase, and crystal growth of h-BN via the liquid phase occurs significantly from 1600°C. It became clear that this was because of this. In order to highly purify boron nitride in this way, it is necessary to raise the temperature to 1600° C. or higher in order to evaporate and remove B ₂ O ₃ , and in this case, crystal growth inevitably occurs. From these results, in order to produce h-BN with the desired high purity and no crystal growth, it is necessary to evaporate impurities (B ₂ O ₃ , etc.) and to adjust the temperature at which crystallite growth becomes significant. It is necessary to remove liquid phase components (B ₂ O ₃ , etc.) before reaching . We investigated a processing method that satisfies these conditions. As a result, we found that addition of borax or carbonaceous powder was effective for removing B ₂ O ₃ and the like. First, to explain the effects of borax, borax is anhydrous borax or borax. By adding anhydrous borax or borax, sodium metaborate having a low boiling point of B ₂ O ₃ is produced, which is evaporated and removed at a temperature of 1500° C. or lower, thereby highly purifying h-BN. Unlike sodium oxide, the evaporated sodium metaborate was not deliquescent, so it was trapped and removed in the cooling section, and there was almost no damage to the reaction vessel. The recovered sodium metaborate can be used again as a boron source. Anhydrous borax has a higher melting point (740°C) than boric acid or boron oxide, so it plays the role of a carrier that increases the contact area between the boron raw material and nitriding gas in the nitriding reaction, widening the reaction interface and promoting nitriding. The appropriate amount of borax to be added is 2.5 to 30% by weight of anhydrous borax based on the oxygen-containing boron compound as the raw material. If it exceeds 30% by weight, sodium oxide will also be produced in addition to sodium metaborate, which is not preferable. Furthermore, if it is less than 2.5% by weight, it does not play the role of a filler, so the nitriding rate decreases at temperatures below 1300°C. It is also possible to achieve high purity by adding an alkali metal compound such as sodium carbonate by reacting with B ₂ O ₃ to form sodium metaborate, but the amount added must be increased to prevent the formation of sodium oxide. Since h-BN cannot function as a carrier in small amounts, the purity of h-BN will not improve even if it is treated at temperatures below 1300°C. Carbonaceous powder will be explained as another additive that promotes the evaporation of B ₂ O ₃ . In other words, this is a method of removing B ₂ O ₂ as B ₂ O 2 by reducing B 2 O ₃ with carbonaceous powder. As the carbonaceous powder, any powder ranging from amorphous carbon powder to highly graphitized powder can be used, but amorphous carbonaceous powder is more preferable. The amount added at this time is such that carbon will remain if added in excess, so B ₂ O ₃ in the sample
must be added in an equimolar amount. Therefore, the amount added varies depending on the residual B ₂ O ₃ . If the purity of h-BN is set to the lower limit of 70% by weight produced by the conventional technique, the amount of carbonaceous powder added will be 0.1 mol or less of carbon relative to the boron in the boron compound. Further, if the amount added is less than 0.005 mol, the reducing effect will not appear. Therefore, 0.005 carbon per mole of boron
Additions of ~0.1 mol are suitable. Although carbonaceous powder and borax are similarly effective in promoting nitriding reactions and removing impurities, there is a big difference between the two in terms of grain growth. When borax is used as an additive, it forms a liquid phase at low temperatures, and the h-
As BN growth occurs, the crystallites become larger. Therefore, when using borax, it is necessary to heat it as low as possible to suppress crystal growth. In the present invention, low-temperature heating refers to heating at a temperature at which borax or by-produced sodium metaborate and sodium oxide do not significantly evaporate, and at which boron nitride is highly purified without causing coarse growth. Its temperature is 900-1300℃. Incidentally, the evaporation temperatures of borax, sodium metaborate, and sodium oxide are 1575°C, 1430°C, and 1275°C, respectively. In addition, it is necessary to improve the purity of borax by passing through a washing and drying process. On the other hand, the addition of carbonaceous powder does not form a liquid phase, but on the contrary, it exists as fine particles dispersed in the liquid phase, which lowers the viscosity, lowers the activity of the liquid phase, and suppresses grain growth. It works differently. Therefore, in order to produce h-BN with lower crystallinity, it is preferable to add carbonaceous powder. Furthermore, since the carbonaceous powder is solid and exists between particles, it is preferable that the carbonaceous powder be as fine as possible from the viewpoint of dispersion. From this point of view, if carbonaceous powder and liquid phase forming substances such as borax are used together, borax has a great effect in promoting the low-temperature nitriding reaction, and in addition, carbonaceous powder and h - Interacts to improve contact with BN. In this way, high-purity, low-crystalline h-
Production of BN can be more easily achieved by using carbonaceous powder alone or in combination with carbonaceous powder and borax. Regarding the timing of addition of these additives for grain growth suppression and high purity, since the purpose of carbonaceous powder is to reduce and remove some of the impurity B ₂ O ₃ in the form of B ₂ O ₂ , this reaction It is sufficient if the temperature is lower than 1300℃, which is effective. In other words, when synthesizing h-BN powder using boric acid, its dehydrate, or ammonium borate as a raw material, if the temperature is below 1300℃, it is possible to sinter it to a certain temperature, take it out, and then add carbonaceous powder. be. Of course, the operation is simplest if it is added as a raw material powder. The effect of adding borax at the raw material stage is significant since it partially contributes to the nitriding reaction. If the goal is to simply produce h-BN with high purity or low crystallinity using carbonaceous powder, addition can be done at any time as long as the temperature is 1300°C or lower. Next, addition of an alkaline earth metal compound will be explained. As mentioned above, adding borax or carbonaceous powder is an effective method for removing B ₂ O ₃ , which is an impurity in h-BN, but it is not completely removed in this case either. , a trace amount of B ₂ O ₃ remains. This residual B ₂ O ₃ reacts with moisture in the atmosphere and causes volume expansion. Furthermore, since the melting point of B ₂ O ₃ is as low as 450°C, the higher the content of B ₂ O ₃ when producing a sintered body from h-BN powder, the lower the strength at high temperatures, for example 1000°C. . Therefore, as a result of investigating a method for stabilizing the remaining B ₂ O ₃ in the sintered body and increasing its melting point, it was found that addition of an alkaline earth metal compound is effective. Carbonate compounds of alkaline earth metals are particularly suitable.
For example, by adding calcium carbonate (CaCO ₃ ) and heat-treating it, it can be combined with calcium oxide (CaO).
The following compounds that react with B ₂ O ₃ and have high melting points are CaO・B ₂ O ₃ (melting point 1125℃), 2CaO・B ₂ O ₃ (melting point 1280℃), 3CaO・B ₂ O ₃ (melting point 1454℃), etc. It is converted into a compound that is stable even at high temperatures. The amount of the alkaline earth metal compound added is an amount commensurate with the residual amount of B ₂ O ₃ in the boron nitride produced, but the purity of boron nitride is 95% by weight or more as high purity boron nitride powder, and in this case, impurities Since it is less than 5% by weight, the amount added is as an alkaline earth metal relative to the boron of the oxygen-containing boron compound in the raw material.
It may be 0.1 mole or less. In addition, in the method of obtaining high-purity h-BN without high-temperature heating, which is one of the objects of the present invention, the upper limit of the purity of the boron nitride produced is about 99.95% by weight.
In this case, the amount of the alkaline earth metal compound added to the impurities may be 0.0001 mol or more. By the method described above, h-BN with high purity and excellent high-temperature sintering properties can be produced without developing crystals. Regarding the timing of addition of alkaline earth metals, it is easy to add them in the form of fine carbonates, oxides, hydroxides, etc. during the mixing of raw materials in terms of the manufacturing process. It is also possible to add an alkaline earth metal compound to low-crystalline, high-purity h-BN powder. In this case, the alkaline earth metal compound as an additive must be uniformly mixed with h-BN of fine particle size, and the soluble alkaline earth metal compound (nitrate, etc.) must be dissolved in a solvent and mixed uniformly with h-BN. Then it is effective. Next, as conditions for producing h-BN according to the present invention, first, the atmosphere must be a non-oxidizing atmosphere such as inert gas or ammonia gas in order to prevent oxidation of h-BN. The heat treatment temperature should be above 1300°C, where impurity evaporation becomes active, but below ₁₆₀₀ °C, where crystal growth does not become noticeable. To prevent, 1500 ~
Preference is given to processing at a temperature of 1600°C. Furthermore, if the atmosphere is reduced under reduced pressure during heating, sodium metaborate, an impurity generated when adding borax,
Impurities generated by B ₂ O ₃ or carbonaceous addition
It can facilitate the evaporative removal of B ₂ O ₂ and B ₂ O ₃ . Therefore, if the pressure is reduced at a temperature of 1300°C or higher, where impurity evaporation becomes active, purification can be achieved even more effectively, and the purification processing time can be shortened, reducing energy consumption. Very advantageous. In addition, the final product is produced by crushing and sintering the bulk composite, but usually after crushing, granulation is performed for the purpose of improving filling properties. In this case, the powder is used in a slurry state using a spray drying method. At this time, it is effective to dehydrate and wash the slurry once or several times because the product is uniform and residual impurities such as sodium components or boron oxide can be removed. Of course, since h-BN is hydrophobic, the use of water as a solvent requires a surfactant. Alternatively, using an organic solvent such as an alcohol as a dispersant is highly effective. [Examples] Examples 1 to 8 Examples 1 to 8 and comparative examples produced by the method of the present invention are shown in Table 1. The manufacturing process will be explained using Example 3 as an example. To 1.8 kg of boric acid and 2 kg of melamine, 150 g of anhydrous borax of 200 mesh or less, 20 g of carbon black, and 10 g of calcium carbonate of 200 mesh or less were added and mixed in a V-blender.
This was placed in a graphite crucible with a height of 300 mmH, and after the top was covered, it was heated in a high frequency furnace at 1550 °C in an _N2 atmosphere.
Heat treated for hours. The resulting treated product was pulverized and classified using a jet mill to obtain a fine powder with no crystal growth, boron nitride purity: 97.2% by weight, CaO content: 0.7% by weight, crystallite Lc: 10.2nm. When this product was hot-pressed at 1900°C for 2 hours at a pressure of 200Kg/cm ² to produce a molded product, it had a density of 2.12g/cm ³ and a bending strength at 1000°C of 8.9Kg/mm ² , which is superior to conventional products. A sintered body was obtained. Examples 1 and 6 are examples in which carbonaceous powder is added, Examples 2 and 7 are examples in which anhydrous borax is added, Example 3,
4, 5, and 8 are examples in which both were added. In addition, Examples 6 to 8 used the same raw materials and additives as Examples 1 to 3, heated to 900 °C in a N ₂ atmosphere in a high frequency furnace, then reduced the pressure to 10 ^-1 Torr, and heated to 1550 °C. Heat treatment was performed at ℃ for 1 hour. The obtained h-BN powder was a highly pure product with no developed crystals, and all the sintered bodies obtained by hot pressing had excellent strength at high temperatures. A comparative example is an example in which carbon black is equivalent to 1.03 moles of carbon relative to boron in the raw material, and anhydrous borax is equivalent to 50% by weight of boric acid, but the purity is
It is present in large amounts as impurities, as low as 68% by weight, CaO: 6.4% by weight, Carbon (C): 8.6% by weight, and Na ₂ O: 5.9% by weight.It is not the original white powder of boron nitride, but has a black color, and it is hot pressed. The properties of the sintered body also deteriorated. [Reference example] CaCO ₃ is added to commercially available boron nitride powder with a purity of 97% by weight.
When 1.5% by weight of powder was added and mixed in a ball mill, the fine powder was sintered under the same hot press treatment conditions as in the previous example to produce a sintered body. Density: 1.94 g/cm ³ Bending strength at 1000°C: 3.1 It was Kg/ ^mm2 .

〔Example〕

Examples 9-10 Examples 9-10 are shown in Table 2. In Example 9, 20 kg of carbon black was added to 1.8 kg of boric acid and 2 kg of melamine.
After adding g and mixing with a V blender, the inner diameter
This was placed in a graphite crucible with a diameter of 200 mm and a height of 300 mmH, and after the top was covered, it was placed in a N ₂ atmosphere using a high frequency furnace.
Heat treatment was performed at 1550°C for 1 hour. After crushing the generated lumps, add Ca(NO ₃ ) ₂ to 100 g of boron nitride.
1.2g was added and pulverized and mixed in a ball mill for 30 hours to obtain a fine powder. The properties of this treated product are shown below. Purity of boron nitride: 97.7% by weight Crystallite size (Lc): 15.8nm CaO: 0.4% by weight When this h-BN powder was hot pressed at a pressure of 200Kg/cm ² and 1900℃ for 2 hours, the density: 2.01g A molded product with a bending strength of 4.8 Kg/ ^{mm 2 at} 1000°C was obtained. Next, in Example 10, 1.8 kg of boric acid, 2 kg of dicyandiamide, 25 g of carbon black, and 200 g of anhydrous borax were added.
and then treated in the same manner as in Example 9 to obtain a fine powder. The properties of the obtained h-BN powder are: Boron nitride purity: 98.2% by weight Crystallite (Lc): 22.4nm CaO: 0.4% by weight This h-BN fine powder was heated at a pressure of 200Kg/cm ² and 1900°C.
A molded body was produced by hot pressing for 2 hours, and a molded body having a density of 1.97 g/cm ³ and a bending strength at 1000°C of 6.1 Kg/mm ² was obtained.

【table】

[Table] Examples 11-12 Examples 11-12 are shown in Table 3. In Example 11, 10 g of CaCO ₃ and 150 g of anhydrous borax were added to 1.8 kg of boric acid and 2 kg of melamine, mixed in a V-blender, and then placed in a graphite crucible with an inner diameter of 200 mmφ and a height of 30 mmH, and the top was covered. By high frequency furnace
Heat treatment was performed at 1100° C. for 2 hours in an N ₂ atmosphere. The resulting treated product was a lumpy product with boron nitride purity: 94.3% by weight, crystallite size (Lc): 14.2nm, CaO: 0.7% by weight, and Na ₂ O: 1.2% by weight. This product is crushed,
After dispersing in an aqueous solution containing 2% of an anionic surfactant with an HLB value of 14, such as a polyoxyethylene alkyl ether-based anionic surfactant, stirring and washing, dehydrating and drying using a suction filtration method, boron nitride. Purity: 97.7% by weight CaO: 0.9% by weight Na ₂ O: 0.007% by weight. This h-BN fine powder was heated at a pressure of 200Kg/cm ² and a temperature of 1900°C.
After hot pressing for 2 hours, a molded product with density: 1.96 g/cm ³ and bending strength at 1000°C: 5.3 Kg/mm ² was obtained. Next, in Example 12, 200g of anhydrous borax was added to 1.8Kg of boric acid and 2Kg of melamine, mixed in a V blender, placed in a graphite crucible with an inner diameter of 200mmφ and a height of 300mmH, covered with a top lid, and heated in a high frequency furnace. _N2
Heat treatment was performed at 1200°C in an atmosphere for 2 hours. The resulting treated product was a lumpy product with boron nitride purity: 95.2% by weight, crystallite size (Lc): 22.5nm, and Na ₂ O: 1.6% by weight. This product is crushed,
After separating into an aqueous solution containing 2% of anionic HLB value 14 surfactant and washing with stirring, dehydrating and drying by suction filtration method, this h-BN powder is
1.2 g of Ca(NO ₃ ) ₂ was added to 100 g of BN and pulverized and mixed in a ball mill for 30 hours to obtain a fine powder. The characteristics of this fine powder were as follows: Boron nitride purity: 98.2% by weight Crystallite size (Lc): 22.5nm CaO: 0.4% by weight Na ₂ O: 0.01% by weight. This h-BN fine powder was heated at a pressure of 200Kg/cm ² and a temperature of 1900°C.
As a result of hot pressing for 2 hours, a molded article having a density of 1.98 g/cm ³ and a bending strength at 1000°C of 4.5 Kg/mm ² was obtained.

【table】

〔Effect of the invention〕

The hexagonal boron nitride powder of the present invention has high purity and small crystal grains, and when produced into a sintered body, it has excellent sintered properties and high strength at high temperatures. Such hexagonal boron nitride powder can be easily manufactured at low cost through a simple manufacturing process according to the method of the present invention.

Claims (1)

[Claims] 1. 0.0001 alkaline earth metal per mole of boron.
A hexagonal boron nitride powder containing ~0.1 mol, having a crystallite size of 8 to 50 nm, and having a boron nitride purity of 95% by weight or more, and having excellent sintering properties. 2. Mix an oxygen-containing boron compound and a nitrogen compound, add 0.0001 to 0.1 mole of an alkaline earth metal compound as an alkaline earth metal per mole of boron in the mixture, and further add 1 mole of boron in the mixture. 0.005-0.1 mol of carbonaceous powder as carbon and/or 2.5-30% by weight of anhydrous borax as anhydrous borax is added to the oxygen-containing boron compound as a raw material, and the above mixture is heated under normal pressure or reduced pressure. A method for producing hexagonal boron nitride powder with excellent sintering properties, which comprises heating in a non-oxidizing atmosphere. 3. Mix an oxygen-containing boron compound and a nitrogen compound, and add carbon to 1 mole of boron in the mixture.
0.005 to 0.1 mol of carbonaceous powder is added, and the above mixture is heated in a non-oxidizing atmosphere under normal pressure or reduced pressure to obtain hexagonal boron nitride powder, and the hexagonal boron nitride powder contains A method for producing hexagonal boron nitride powder with excellent sintering properties, which comprises mixing 0.0001 to 0.1 mol of an alkaline earth metal compound as an alkaline earth metal per 1 mol of boron. 4 Mix an oxygen-containing boron compound and a nitrogen compound, and add carbon to 1 mole of boron in the mixture.
0.005 to 0.1 mol of carbonaceous powder, and 2.5 to 30 as anhydrous borax to the raw oxygen-containing boron compound
% by weight of borax is added, and the above mixture is heated in a non-oxidizing atmosphere under normal pressure or reduced pressure to obtain hexagonal boron nitride powder, and 1 mol of boron in the powder is added to the hexagonal boron nitride powder. 1. A method for producing hexagonal boron nitride powder with excellent sintering properties, which comprises mixing 0.0001 to 0.1 mol of an alkaline earth metal compound as an alkaline earth metal. 5. Mixing an oxygen-containing boron compound and a nitrogen compound, adding 0.0001 to 0.1 mole of an alkaline earth metal compound as an alkaline earth metal to 1 mole of boron in the mixture, and anhydrous borax to the oxygen-containing boron compound. After adding 2.5 to 30% by weight of borax as a crude hexagonal boron nitride powder, the above mixture is heated at low temperature in a non-oxidizing atmosphere under normal pressure or reduced pressure to obtain crude hexagonal boron nitride powder. A method for producing hexagonal boron nitride powder with excellent sintering properties, which comprises washing and drying boron powder. 6. Mix an oxygen-containing boron compound and a nitrogen compound, add 2.5 to 30% by weight of borax as anhydrous borax to the oxygen-containing boron compound, and place the above mixture in a non-oxidizing atmosphere under normal pressure or reduced pressure. After heating at low temperature to obtain crude hexagonal boron nitride powder, the crude hexagonal boron nitride powder is washed and dried, and 0.0001 to 0.1 mole of alkaline earth metal is added to 1 mole of boron in the dry powder. A method for producing hexagonal boron nitride powder with excellent sintering properties, which comprises mixing an alkaline earth metal compound.