JPS62100404A - Production of pulverous hexagonal boron nitride having high purity - Google Patents

Abstract

PURPOSE:To produce fine powder of hexagonal boron nitride having high purity and optional particle size by heating fine powder of crude hexagonal boron nitride at an appropriate temp. and under appropriate pressure in nonoxidizing atmosphere, then heating at an appropriate temp. under reduced pressure. CONSTITUTION:Fine powder of crude hexagonal boron nitride synthesized at ca. 800-1,200 deg.C is heated at 1,200-1,800 deg.C under >=20Torr in nonoxidizing atmosphere. By this treatment, the particle size is grown to some degree obtaining boron nitride having 100Angstrom -5mum primary particle size depending on the temp., and impurities such as B-O-N, etc., are transformed to BN and B2O3. Then, BN, etc., are removed by heating at 1,600-2,000 deg.C under <=20Torr in nonoxidizing atmosphere. By this method, fine powder of hexagonal boron nitride having high purity and primary particle size controlled to desired particle size is obtd. by removing impurities such as B2O3, etc., by evaporation without causing the growth of particle size.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing hexagonal boron nitride (hereinafter referred to as 'l'-h-BN), which involves controlling the -order particle size and purity. It's about getting the technology you can.

[Conventional technology]

h-BN is white and has a hexagonal layered structure similar to graphite, and has various characteristics. In particular, it has excellent thermal conductivity, electrical insulation, corrosion resistance, lubricity, heat resistance, and machinability, and these properties can be used for a wide variety of applications.
1 is there. Applications as a powder include plastic additives and lubricants, and as molded bodies and composite materials, it can be used as a therapeutic agent.
It is used as electrical insulation material, mold material, etc.

Various methods have been devised to synthesize h-BN, which has a wide range of uses, but the method currently used in the T industry is: (1) A mixture of borax and urea is synthesized in an ammonia atmosphere at 80%
A method of heating to below 0℃ (Japanese Patent Publication No. 38-161O), (2) Mixing boric acid or boron oxide and calcium phosphate,
(3) A method of heating boric acid and a nitrogen-containing compound (urea, melamine, ammonium chloride, dicyandiamide, etc.) to 1600°C or higher (Patent IQ448-14559), (4) A method of nitriding with ammonia, Method of vapor phase synthesis.

etc. are the main ones.

(5) Furthermore, h-BN number with a purity of about 90@star%,''- a method of adding a fulkaline metal compound and heating it to 100°C or less to improve the purity to 99 tons% or less ( Special Publication No. 47-26600).

[Problem that the invention seeks to solve]

”-Method (1) is to produce crude BN at about 900°C, remove alkaline content by washing with water, and then heat it in a non-oxidizing atmosphere for 1 hour.
It is highly purified by reheating to 600°C to 2000°C to evaporate and remove impurities. High purification process h-BN particles undergo crystal growth and have a primary particle size of 1 to 5 pLm.

Similarly, the methods described in Section 2 (2) and (3) also have the drawback that grain growth occurs during the high purification process, making it impossible to arbitrarily control grain a.

Next, method (4) is different from methods (1) to (3),
Because of the gas phase synthesis method, it is possible to obtain -BN with high purity and a fine particle size, but since boron pentachloride as the N material is expensive, there is a drawback that the manufacturing cost is high.

In addition, in the method (5) of adding an alkali metal compound to the crude BN for high purification, it is possible to obtain h-BN with finer grains than the h-BN obtained by the production methods (1) to (3). However, there were drawbacks such as the fact that the added alkali metal adhered to the synthesis furnace, making it undesirable during production.

The present invention is directed to the -
- It is an object of the present invention to provide a method for producing h-BN in which the IIT function is to control the size of the secondary particle diameter to a certain degree ψ.

[Means to solve problems]

As a result of extensive research to supplement the conventional technology, the inventors of the present invention have developed a technology that can control the granulation diameter with a purity of 95% by weight or more.

The motivation for developing this technology was to improve the purity of h-BN.
The main point lies in the discovery that high purity can be achieved without causing grain growth if the process is carried out at a reduced pressure F of 0 Torr or less. In other words, if the grain growth and purification processes of h-BN are performed independently, high-purity h-BN with various primary particle diameters can be obtained.
can be easily manufactured. Since h-BN grows with the heat treatment temperature, after it has grown to the desired primary particle size, by proceeding with the heat treatment while keeping the atmosphere below 20 Torr, high purity can be achieved while suppressing the growth of crystal grains. High purity h-B with a particle size of 91.
N can be ftJ.

The method of highly purifying h-BN while controlling the secondary particle diameter according to the present invention will be described in more detail. Crude h-BN, which is a raw material, is usually synthesized at 800°C to 1200°C, and its crystals are not completely hexagonal but have a turbostratic structure. The size of crystal f- Lc (7
The value measured by the method according to the materials of the Carbon Materials 117 Committee Ll Association) is small, ranging from 50 to 100 particles, and the -order particle size S is also fine, around 100 particles. The purity was determined from nitrogen analysis in the sample and was in the range of 50 to 95%. Most of the impurities were # elements, and the existing forms of ammonium borate, boron oxide, etc. were identified by X-ray diffraction.

As a method for removing these impurities, a method of evaporating them as steam through heat treatment is adopted. However, impurities generated a liquid phase during the heat treatment, and as h-BN became highly purified, crystallites also grew, and the secondary particle size also increased. For example, crude h-B synthesized from borax and urea at 900℃
When N (1190 tonxing% pure, L e = 150 people) was washed with water to remove alkaline content and heated, L c grew to about 1000 people at 1800°C. No growth of crystallites was observed at temperatures below F. A similar tendency was observed when crude h-BN synthesized from boric acid, dicyandiamide, etc. was used. At this time, h-BNNi degree is 9
At 9.21 TjM-%, the particle size was 3 μm.

In this way, when trying to obtain h-BN with high purity, the primary particles also grow, so it was not possible to obtain h-BN with high purity with the primary particle diameter desired by the name of the experiment.

As a result of studies17 to solve this problem, it was found that there was a need for a method to rapidly remove impurities that carve the liquid phase, which is the cause of grain growth. Removal power U: If heat treatment is performed under reduced pressure, the evaporation rate of impurities will be high and grain growth will not occur. It has become clear that grain growth hardly occurs when the pressure is reduced to 20 Torr or higher.

However, the Japanese h-
BN at 1200℃ to 180℃ at a pressure of 20Torr or more
Even after heat treatment at 0°C, the purity did not reach 95% or higher. The reason for this is that crude h-BN contains a large amount of resistant element in the form of intermediates such as B-0-N, and is contained in -BN, so it cannot be heated during heat treatment under reduced pressure. It seems likely that it could not be removed.

It is necessary to generate grain J&length to some extent under normal pressure, convert intermediates such as 11-0-N into BN and B2O3, and remove them by evaporation. By heating to 1200°C to 1800°C at a pressure of 20 Torr or more (usually normal pressure), BN is made into BN having a particle diameter in the range of lOOλ to 5 m depending on the temperature, and then Impurities such as B20 in BN are evaporated and removed by heating to 1600° C. to 2000° C. under reduced pressure of 20 Torr or higher.

If high purity is achieved in this way, various −・Next $1″L
High purity h-BN with r-diameter can be obtained.

The temperature of 20 Torr or higher in the grain growth process is 20 Torr.
The range below r is the range in which grain growth occurs, and grain growth begins at 1200°C, and when the temperature exceeds 1800°C, grain growth decreases by 1.

Next, the reduced pressure conditions in the first stage of impurity removal are such that the non-oxidizing atmosphere such as N2 is 20 Torr or higher. However, when impurities such as 8203°NI (3, Go, etc.) come out during heating, the temperature may become higher than 20 Torr inside the packed layer, but if the non-oxidizing atmosphere is 20 Torr or higher, the impurity The removal speed 1■ to the outside is also large, and the grain J&length is suppressed.

The heating temperature under reduced pressure of 20 Torr or less is preferably higher than the grain growth process temperature. This range is preferably 1,600° C. or below (- is preferable) at which impurities can be completely removed, and the limit must be below the temperature at which the graphite used as the container and BN react to form B4C, and is 2,000° C. or below.

〔Example〕

Examples 1 to 4 1.0 kg of anhydrous borax and 2.0 kg of urea were mixed and treated in an ammonia atmosphere at 900'OX for 2 hours, followed by washing with water to remove the sodium content (BN purity 91.3 city U%). , -order particle size 130 people) was filled into a graphite crucible, and N
1200℃ and 1400℃ under normal pressure in two atmospheres, respectively.
, l 600 '011 After holding at 1800°C for 1 hour,
After maintaining the atmosphere under a reduced pressure of 0.1 Torr, 1aoo
Heat treatment was performed for 2 hours at 'c. The results are shown in Table 1. As is clear from Table 1, it was possible to produce 11-BN having various crystal grains with high purity IN of less than 1% in 95 tons.

Comparative Example-1 Crude h-BN produced by the same method as Example-1 was mixed with 0. 1 soo'c, 2 o'clock ff under reduced pressure of ITOrr! 1
After 8 treatments, the purity was 93% by weight and the particle size was 160.

Comparative Example-2 Crude hB produced by the same method as Example-1
N lid N2 atmosphere atmospheric pressure at 1100℃ lh
r After heat treatment, 0. ITorr (7) M pressure C18
00" Purity was 94.2 after 0XZhr heat treatment.
The particle size was 210 people in city v%.

〔Effect of the invention〕

Inventiveness? J: allows the particle size of highly purified h-BN to be controlled to a desired value, making it possible to produce h-BN that can be widely used in various applications.

Claims (1)

[Claims] 1. In a non-oxidizing atmosphere of 20 Torr or more, crude hexagonal boron nitride fine powder is heated at a temperature of 1200°C to 1800°C, and then heated to 20Torr.
1600°C to 20°C in a non-oxidizing atmosphere below rr
A method for producing high-purity hexagonal boron nitride powder, the method comprising heating to 00°C.