JPH01160811A - Production of hexagonal boron nitride - Google Patents

Abstract

PURPOSE:To obtain at a low cost the subject high-purity boron nitride little containing water-soluble boron compound, large in specific surface area, by dispersing hexagonal boron nitride powder in water to eliminate the water-soluble boron compound contained followed by drying under a specified condition. CONSTITUTION:Hexagonal boron nitride powder is dispersed in water or hot water to eliminate the water-soluble boron compound contained followed by drying under such as condition as to satisfy the relationship: (a/2)+b<=100 [a is drying time; b is drying temperature ( deg.C)]. The boron nitride thus obtained is such that the amount of boron in the extraction water when leached by boiling with pure water is <=100mug/g-boron nitride and the specific surface area >=5m<2>/g. In cleaning said powder with water, addition of a surfactant and/or water-soluble organic solvent as the dispersant will allow the cleaning effect to be enhanced, therefore being preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to hexagonal boron nitride, and in particular, it is an object of the present invention to provide hexagonal boron nitride containing less water-soluble boron compounds.

[Prior Art] Hexagonal boron nitride (hereinafter referred to as BN) powder is white, has a layered structure similar to graphite, and has various properties. Especially thermal conductivity and electrical insulation.

It has excellent chemical stability, slipperiness, and heat resistance, and it is used in a wide variety of applications by taking advantage of these properties. Plus Dec additive for use as a powder.

It is often used as a lubricant.

Recently, with advances in electronic technology, there has been an increasing demand for high-purity BN for use as fillers and additives that utilize the heat resistance and electrical insulation properties of I3N.

In addition, cubic boron nitride (
c-BN) is used as this raw material. High purity is required for UN as a raw material for c-BN. Further, when making cr3N, BN is molded in advance, but if the density of this molded product is low, there are disadvantages such as a decrease in the yield of c-UN.

Conventional methods for producing high-purity BN can be broadly classified into the following two methods.

(1) A method of evaporating or decomposing impurities by heating to a high temperature (invention described in JP-A No. 58-60603 and invention described in JP-A-58-181708).

(2) A method of obtaining highly pure N from boron trichloride and ammonia using the following formula.

13CC3+NH3→BN+3HC(!...
(1) [Problems to be Solved by the Invention] According to the method (1), impurity oxygen components can be decomposed and volatilized and removed by heating BN at a high temperature. However, when processing a small amount of sample with a thin packed bed, the oxygen component can be easily removed by thermal convection and diffusion outside the sample packed bed, but when processing a large amount, it remains in the packed bed in a gaseous state and solidifies during the cooling process. It precipitates as an impurity on the BN surface or between particles.

For this reason, the method (+) is difficult to process in large quantities and is expensive in terms of energy costs due to high temperature processing.

Furthermore, in the method (2) of producing high-purity BN from BCl23 and NH5, high-purity BN can be obtained, but highly crystalline BN is difficult to obtain, and there are disadvantages in that it is inferior in insulation and thermal conductivity. Hydrolyzability is also greater than that of crystalline BN. In addition, there is a drawback that manufacturing costs increase when industrially mass-produced.

In order to solve the above problems, the inventors
No. 76904 discloses a BN powder containing less water-soluble boron compounds and a method for producing the same. However, as a result of subsequent research by the inventors, it was found that a small particle size is effective in increasing the bulk density of a BN molded article.

In other words, in the drying step, which is the final step in the production of boron nitride that contains few water-soluble boron compounds, BN purified by washing is slightly hydrolyzed, but the degree of hydrolysis becomes smaller as the particle size of the BN powder becomes smaller. Therefore, the larger the specific surface area, the more difficult it is to make fine N powder highly pure. The formula for the hydrolysis of BN is as follows.

2BN+3H20→B t Os + 2 N H3・
...(2) BN+3HtO→H3B Os + N H
3...(3) [Means for solving the problem] Therefore, in order to obtain BN with a small particle size and a small amount of water-soluble boron compounds, the present invention requires: ① Appropriate dispersion of water-soluble boron compounds on the surface. We have discovered that it is necessary to thoroughly wash and remove using a chemical and water, and (1) dry at a low temperature and in a short time in order to suppress hydrolysis to a small amount, leading to the present invention.

That is, the gist of the present invention is that the specific surface area is 5ff.
Boron power in extracted water when boiled with fine and pure water of 79 or higher 'I0Ou9/9-BN or lower High purity crystalline BN
If the amount of water-soluble boron in the water from which BN is boiled and leached is 100 μg/9-I3N or less, it is hexagonal boron nitride with few water-soluble boron compounds. Next, the manufacturing method involves dispersing hexagonal nitride borium powder in water, repeatedly washing and removing water-soluble boron compounds, and then drying for a[
time].

This is a method for producing hexagonal boron nitride containing less water-soluble boron compounds, characterized by drying under conditions satisfying -10b≦100, where the drying temperature is b['c].

[Function] The amount of water-soluble boron is determined by boiling and leaching BN with pure water and quantifying the amount of boron in the extract, and it is desirable that the water-soluble boron is 100μ9#-BN.

If the amount exceeds 100 μy/g-BN, not only the yield of c-BN will be poor, but also the strength of the resulting product will be poor. Preferably, the water-soluble boron content is 50μ9/9-BN or less.

The particle size is indicated using the specific surface area as an index.

It is desirable that the specific surface area of the high purity BN powder is 5 it/g or more. When it is smaller than 5 m'/y, the molded bulk density becomes small and the yield of c-BN decreases. Preferably 7m'/
g or more.

The manufacturing method of the present invention will be explained in detail.

I3N usually contains 1 to 20% oxygen as an impurity. This oxygen combines with boron and exists as boron oxide, and sometimes boron oxide is hydrated and exists as boric acid.

These boron oxides or boric acids are very easily soluble in water. Therefore, hexagonal BN with less water-soluble boron compounds
When attempting to obtain these substances, it is effective to wash and remove these easily soluble substances with water.

In order to effectively wash and remove water-soluble boron compounds,
The crystalline BN powder needs to be well dispersed in water or hot water. BN powder is difficult to wet with water and will not be dispersed in water as it is, and therefore cleaning operations will not proceed easily. When dispersing in water, it is effective to use a dispersant. As a dispersant, (1) HL B (l1hydrophile-L
Anionic, nonionic, or cationic surfactant having an ipophile balance) value in the range of IO to 16.

(2) Alternatively, an aqueous solution of a water-soluble organic solvent can be used.

As surfactants, those exhibiting an HLB value <10 to 16 have a high cleaning effect, such as polyoxyethylene (5) sorbitan monostearate, polyoxyethylene (4) sorbitan trioleate, polyoxyethylene Glycol 400 monooleate, triethanolamine oleate, polyoxyethylene (9) nonylphenol.

Polyethylene glycol 400 monooleate.

Triethanolamine oleate, polyoxyethylene (9) nonylphenol, polyethylene glycol 40
0 monolaurate, polyoxyethylene (4) sorbitan molaurate, etc. can be used.

The concentration of the surfactant is preferably in the range of o,oot to 5% by weight. The reason for this is that if the amount exceeds 5% by weight, there is no difference in the dispersion effect even if more than 5% by weight is added, and it is economically undesirable to add too much. Moreover, if it is less than 0,001% by weight, the effect will not be sufficiently expressed.

Methyl alcohol is a water-soluble organic solvent.

Alcohols such as ethyl alcohol, glycol, and glycerin, as well as acetone, acetylacetone, ethylamine, acetaldehyde, and phenol can be used.

Among water-soluble organic solvents, methyl alcohol and ethyl alcohol are the most suitable because of their cost and ease of use. I3N
The method for dispersing the powder into the cleaning solution is to first disperse the 3N powder in a water-soluble organic solvent such as methyl alcohol or ethyl alcohol to form a highly concentrated slurry, and then add it to the cleaning water to reduce the amount of alcohol used. The dispersibility was also very good. Moreover, the combination of a water-soluble a-solvent and a surfactant is even more effective.

Although the temperature of the cleaning solution is not specified, soluble boron compounds are effectively dissolved at high temperatures. Further, by sufficiently stirring the slurry in which the BN powder is dispersed, dissolution can be effected in a short time and effectively, so it is desirable to sufficiently stir the slurry.

The thinner the slurry concentration during cleaning, the greater the cleaning effect, but there is an optimal range from an economic standpoint. The upper limit is I3N 5
0% by weight slurry. If it becomes thicker than this, stirring will not be done uniformly and sufficiently, and friction with the stirring impeller and container wall will increase, causing impurities to be mixed in.

Although there is little positive reason to specify the lower limit, it is preferably up to 2.5% by weight from the economic point of view.

For stirring the slurry, the most effective method can be adopted depending on the shape of the cleaning device, such as normal stirring, high-speed stirring, or dispersion based on shear force. The operation at this time may be either a continuous method or a batch method.

It is effective to dehydrate the slurry after washing. Dehydration includes centrifugal dehydration, vacuum dehydration, pressure dehydration, natural sedimentation dehydration,
Alternatively, any method such as filtration, suction filtration, or pressure filtration may be used.

Further, it is more effective to repeatedly wash the BN powder after dehydration.

In order to obtain BN powder with less water-soluble boron compounds, it is necessary to carefully perform the final serpentine step.

That is, although most of the soluble boron compounds from the BN powder are removed by thorough washing, I3N is hydrolyzed during drying and the soluble boron compounds increase.

This tendency is particularly strong for fine powders with a specific surface area greater than 5N2/9.

In the drying process, hydrolysis of BN must be suppressed as much as possible. In order to suppress the hydrolysis of BH, it is desirable that 1+b≦100, where the drying time is a [hour] and the drying temperature is b ['C].

When (-+b) becomes larger than 100, that is, when the drying temperature becomes high or the drying time becomes long,
Water-soluble boron compounds increase.

Preferably -+b≦80.

If the above conditions are satisfied, the drying method is not specified. Hot air drying, hot air drying 1 normal drying, vacuum drying.

Various drying methods such as cold drying can be used.

The BN purified in this manner is particularly suitable as a C-BN raw material because it contains significantly less water-soluble boron compounds, has a high purity that cannot be obtained by conventional methods, and has a small particle size.

Furthermore, the present invention is an industrially extremely advantageous method in that it is possible to produce high-purity BN by a wet method instead of a dry method. The obtained high-purity I3N containing less water-soluble boron can be fully applied to new fields that will be developed in the future.

[Example] (Purification by washing was performed using BNs with different specific surface areas than in the example.

) A 0.5% aqueous solution 5θ of an ethylene alcohol-based anionic surfactant having an I L 13 value of 14 was heated to 90° C., 250 g of BN powder was dispersed therein, and the mixture was maintained for 1 hour while stirring. Vacuum filter the slurry to obtain a cake. Thereafter, the cake was redispersed in water, stirred and washed, and vacuum filtered to obtain a cake. This procedure was repeated twice.

The cake was dried with hot air at 60°C for 24 hours to obtain BH powder.

The amount of boron in the extraction water of the BN powder thus obtained at 100°C was determined.

Further, as a comparative example, the same cake was dried with hot air at 1006C for 24 hours, and the amount of extracted boron was determined in the same manner.

The results are shown in Table 1.

As is clear from Table 1, the method of the present invention makes it possible to obtain fine BN powder in which the Bfi in the extraction water is loOppm or less.

(Example 2) High purity BH powders with different specific surface areas were produced according to Example 1, and the powders were molded at a surface pressure of 1 ton/cR''. The molded bulk density and molding workability are shown in Table 2. .

Table 2: Boron 91 in extracted water at 1100°C As is clear from the table, the I3N powder according to the present invention has an increased molded bulk density and is easy to mold.

(Example 3) BH powder with a specific surface area of 9.61"/9 was washed in the same manner as in Example 1 to obtain a cake. This cake was dried under different drying conditions, and the amount of extracted boron was measured in the same manner. .

The results are shown in Figure 1. The numbers inside indicate the amount of boron extracted from the powder obtained under each drying condition. It is clear from the figure that fine BH powder with an extracted boron content of 1100 pp or less can be obtained by the method of the present invention.

(Example 4) BH powder having a specific surface area of 6.5 m'/9 was washed according to Example 1 to obtain a cake after washing with water four times. This cake was dried using a vacuum dryer at 50°C for 7 hours. The amount of boron in the extraction water of the thus obtained [3N powder at 100° C. was determined to be 9 μg/g-BN.

[Effects of the Invention] As is clear from the above explanation, in the present invention, by lowering the content of the water-soluble boron compound, c-
It has the effect of improving the yield of BN and also improving the strength of the obtained product.

Furthermore, according to the present invention, the particle size of hexagonal boron nitride can be reduced and the specific surface area can be increased, making it possible to increase the density of the BN molded body and lower manufacturing costs compared to conventional ones. effective.

[Brief explanation of the drawing]

FIG. 1 shows the third method of manufacturing hexagonal boron nitride according to the present invention.
It is a graph showing the results of measuring the amount of extracted boron in Examples. Figure 1b; Kokugikun U Haruma (h)

Claims (1)

[Claims] After dispersing hexagonal boron nitride powder in water or hot water and washing and removing water-soluble boron compounds, drying time is a [hour].
When the drying temperature is b [℃], the amount of boron in the extracted water when the boron nitride obtained by drying is dried under conditions satisfying a/2+b≦100 and leached by boiling with pure water is 1
00μg/g-BN or less, and the specific surface area is 5m^
2/g or more. A method for producing hexagonal boron nitride.