JPH0647446B2 - Boron Nitride Manufacturing Method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing boron nitride, and more particularly to a method for producing boron nitride in which hexagonal type crystals are greatly developed.

[Conventional technology]

Conventionally, as an industrial production method of boron nitride, boric acid, boric anhydride or borax, and a mixture of an organic compound that generates ammonia by thermal decomposition of dicyandiamide, melamine, urea, or the like, or A method in which boric acid is granulated with a filler having a large specific surface area such as calcium phosphate and heated in an ammonia stream is used. In this method, it is difficult to retain the reaction surface of boric acid or borax that is nitrided at a temperature above its melting point, and the reaction rate is low, which prevents the production batch from increasing in size and the reaction is slow. Slow heating is required, and the reaction does not proceed if rapidly heated, so the reaction time cannot be shortened by rapid heating. Further, this method has a problem that the obtained boron nitride is blackened or the nitriding is uneven due to carbonization of melamine or the like.

On the other hand, boric acid or boric anhydride and melamine are mixed and water is further added to form a boron nitride precursor, which is heated in an inert atmosphere. Since it reacts completely, there is no melamine carbonization due to subsequent heating, and the heating residue of the precursor remains only boron nitride, and all other components are vaporized,
It was found that high-purity and high-purity boron nitride can be easily obtained.

[Problems to be solved by the invention]

Therefore, after conducting various studies on the above method,
The ratio of the boron atom (B) to the nitrogen atom (N) of boric acid or boric anhydride and the organic cyclic compound having an NH ₂ group (B
/ N ratio), in a non-oxidizing gas atmosphere, 700 to 2
It was found that there was a difference in crystallinity after heating at 300 ° C. For example, when the organic cyclic compound having an NH ₂ group is melamine, boric acid or boric anhydride and melamine are B
/ N: mixed in the range of 1/3 to 2/1, but B / N:
When the amount of boric acid or anhydrous boric acid is around 1/2, boron nitride having good hexagonal crystallinity can be obtained, and when the amount of melamine is large, an amorphous turbostratic boron nitride can be easily formed.
If there is a large amount of boron nitride having this amorphous disordered layer structure, the obtained boron nitride has a small crystal and is unstable, so that it easily reacts with water, air, etc. and is easily decomposed and oxidized. However, if the amount of boric anhydride as a raw material is increased, the crystallinity is improved but the yield of boron is lowered, and the boron oxide remaining in the product must be removed, which is economically disadvantageous.

As a solution to this problem, it is conceivable to add an alkali metal oxide or an alkaline earth metal oxide conventionally known as a crystallization accelerator for boron nitride, but these are NH ₂ -containing organic cyclic compounds such as melamine. It has stronger alkalinity than that of, and interferes with the precursor formation reaction at room temperature. However, it has been found that addition of an alkali metal compound or an alkaline earth metal compound as a carbonate promotes crystallization of boron nitride at a high temperature of 700 to 2300 ° C. without hindering the above reaction.

The present invention has been completed based on the above new findings, and is derived from boric acid or boric anhydride and an organic cyclic compound having an NH ₂ group, and has good crystallinity and is stable to water and air, and is boron nitride. It aims at providing the method of manufacturing.

[Means for solving problems]

The present invention has been made to achieve the above object,
The gist thereof is that boric acid or boric anhydride, an organic cyclic compound having an NH ₂ group are mixed with an alkali metal or alkaline earth metal carbonate and water, and the mixture is dried or calcined. 700-2 under non-oxidizing gas atmosphere
It is a method for producing boron nitride which is heated at 300 ° C.

[Specific Structure and Action of Invention]

Among boric acid or boric anhydride used in the present invention, as orthoboric acid, metaboric acid or tetraboric acid can be used.

Moreover, the organic cyclic compound having an NH ₂ group is preferably one that does not melt during the heating reaction of boron nitride.
For example, melamine, ammeline, ammelide, melam, melem, melon, cyanomelamine, guanylmelamine, and the like. The reason why it is desirable not to melt is that foaming occurs when heated, the decomposed gas does not easily escape, carbonization easily occurs due to insufficient decomposition, and the purity of boron nitride decreases.

Typical examples of the alkali metal or alkaline earth metal carbonates include lithium carbonate and calcium carbonate, but bicarbonates such as sodium hydrogen carbonate and double carbonates such as dolomite (MgCO ₃ · CaCO ₃ ). Good. The carbonate preferably has low solubility in water, and when dissolved, the pH of the solution is preferably lower than the pH of the aqueous solution of the organic cyclic compound having NH ₂ .

The amount of the above-mentioned alkali metal carbonate or alkaline earth metal carbonate added is preferably 0.5 wt% or more, more preferably 1.0 wt% or more as an oxide with respect to the obtained boron nitride. If it is less than 0.5 wt%, there is no effect. Further, the effect increases as the added amount increases, but if it exceeds 10 wt%, the effect of the added amount decreases, and it is not economical considering the case of removing the added amount in the subsequent process.

Now, using boric acid (H ₃ BO ₃ or HBO ₂ ) or boric anhydride (B ₂ O ₃ ) and melamine (C ₃ N ₆ H ₆ ),
The case of producing boron nitride will be described.

To add an alkali metal carbonate or an alkaline earth metal carbonate (hereinafter referred to as “carbonate”), these carbonates are crushed in advance and then added to a mixture of boric acid or boric anhydride powder, melamine powder and water. After adding or mixing with any of the above components, other components may be added and mixed. It is desirable to pulverize these carbonates in advance and uniformly mix them.

Alternatively, a water-soluble oxide or chloride may be added to and dissolved in boric acid or a mixture of boric anhydride, melamine and water, and carbon dioxide may be blown into the mixture to form a carbonate.

By the above mixing, C ₃ N ₃ (NH ₂ —H _{3) in which} the nitrogen atom of the NH ₂ group of melamine and the hydrogen atom of boric acid are hydrogen-bonded.
A precursor having a molecular formula of BO ₃ ) ₃ is obtained. After drying or calcining this, it is placed in a non-oxidizing gas atmosphere for 7
By firing at a temperature of 00 to 2300 ° C., water- and boron-stable boron nitride rich in hexagonal crystals and having good crystallinity can be obtained.

If the firing temperature is lower than 700 ° C., it is difficult to generate boron nitride, and even if it exceeds 2300 ° C., the generated boron nitride does not change and is not economical.

Incidentally, in the present invention, nitrates, sulfates and the like may be considered in place of the above carbonates, but of these, the solubility in water is low, for example, when calcium sulfate is used, a crystal growth effect is recognized, but drying, temporary Grilled or 700
Corrosive gas is generated when firing at a high temperature of ℃ or more, which is not preferable.

It is not clear why the addition of alkali metal or alkaline earth metal carbonates improves the crystallinity of BN, but the addition of these compounds produces a low melting point substance which melts, It is presumed that BN dissolves in it and grows into a large crystal when it recrystallizes.

Also, by adding water and mixing, boric acid and NH
A precursor in which an organic cyclic compound having two groups is bonded is obtained, and the precursor is calcined and fired, so that the boron yield is high and the boron nitride production yield is high.

The present invention will be described below with reference to Examples and Comparative Examples.

〔Example〕

Boric acid powder: 18.6 g, melamine powder: 12.6 g,
Calcium carbonate powder: 3.1 g was sampled in an alumina pot, water: 1 was further added, and the alumina pot was rotated to mix the contents for 10 hours. The well-mixed slurry-like mixture was poured into a stainless steel plate and dried at 250 ° C. The dried and solidified mixture was lightly crushed, put into an alumina crucible, heated to 1000 ° C. in a horizontal annular furnace while flowing nitrogen gas at a flow rate of 5 / min, and held for about 1 hour, and then cooled. The cooled sample was taken out, crushed and sieved with 100 mesh, and part of it was measured for crystallinity (according to Gakshin Carbon Material 117 Committee) Lc by X-ray method, and part was subjected to thermogravimetric analysis in air. did. As a result, the crystallinity Lc
= 120Å, the oxidation starting temperature was 800 ° C. Water was added to the obtained powder sample, but no gas was generated and no ammonia odor was observed.

[Comparative example]

Same as Example except that no calcium carbonate was added.

When the cooled sample was ground in air, it had an ammonia odor and gas generation was observed by adding water. Also, the crystallinity Lc = 60Å, the oxidation start temperature is 70
At 0 ° C., the crystal of boron nitride was undeveloped as compared with the examples,
It was shown to be unstable to water and air (oxygen).

〔The invention's effect〕

As described above, according to the method of the present invention, boric acid or a mixture of boric anhydride and an organic cyclic compound having an NH ₂ group and water is heated to obtain a high boron yield and a hexagonal-rich crystallinity. It is an excellent method that can produce boron nitride that is stable in water and air.

Claims (1)

[Claims] 1. Boric acid or boric anhydride, and an organic cyclic compound having an NH ₂ group are mixed with an alkali metal or alkaline earth metal carbonate and water, and the mixture is dried or calcined. 700 to 230 in an oxidizing gas atmosphere
A method for producing boron nitride, which comprises heating at 0 ° C.