JPS6259506A - Production of boron nitride - Google Patents

Abstract

PURPOSE:To produce stable boron nitride, by blending boric acid or boric anhydride and an NH2 group-containing organic cyclic compound with a carbonate of alkali metal or alkaline earth metal and water, drying or calcining the blend and heating the blend in a nonoxidizing gas atmosphere at a specific temperature. CONSTITUTION:Powder of boric acid such as orthoboric acid, metaboric acid, etc., is blended with powder of an NH2 group-containing organic cyclic compound such as melamine, ammeline, ammelide, etc., powder of an alkali metallic carbonate or of an alkaline earth metallic carbonate such as lithium carbonate, calcium carbonate, etc., and water to give a slurried mixture. The mixture is dried or calcined at about 250 deg.C, ground and heated in a nonoxidizing gas atmosphere such as N2 gas, etc., at 700-2,300 deg.C, to give boron nitride having improved crystallizability rich in hexagonal system and stability to water and air in high boron yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing boron nitride, and more particularly, to a method for producing boron nitride with largely developed orthogonal crystals.

[Conventional technology]

Traditionally, boron nitride has been produced industrially by heating a mixture of boric acid, boric anhydride, or borax and an organic compound that generates ammonia through thermal decomposition such as dicyandiamide, melamine, or urea, or A method is used in which the powder is granulated with a filler having a large specific surface area such as calcium phosphate, and then heated in an ammonia stream.

In this method, it is difficult to maintain the y-responsive surface of boric acid or borax that is nitrided at temperatures above their respective melting points, and the reaction rate is also low, which prevents the production batch from increasing in size.
In addition, since the reaction is slow, heat removal is required, and rapid heating prevents the reaction from proceeding, so rapid heating cannot shorten the reaction time. Furthermore, this method uses carbonization of melamine, etc.
There are also problems that the obtained boron nitride is blackened and the nitridation is non-uniform.

On the other hand, a method in which boric acid or boric anhydride is mixed with melamine, etc., water is added to form a boron nitride precursor, and this is energized in an inert atmosphere is that melamine is kept at room temperature during m1M formation. Because the reaction is complete, there is no melamine carbonization due to subsequent heating, and only boron nitride remains after heating the precursor, and all other components are vaporized, resulting in high yield and high purity boron nitride. I learned that it is easy to obtain.

[Problem that the invention seeks to solve]

Therefore, after conducting various research on the above method 9, I found that
The ratio of boron atoms (B) to nitrogen atoms (N) in boric acid or boric anhydride and an organic cyclic compound having an NH2 group (B
/N ratio) in a non-oxidizing gas atmosphere.
It was found that a difference occurred in crystallinity after heating at 300°C. For example, when the organic cyclic compound having an NH2 group is melamine, boric acid or boric anhydride and melamine are
/N: //, mixed in the range of 3 to 2//, but B/
N: / / With a border around 2, if there is a large amount of boric acid or boric anhydride, hexagonal crystalline boron nitride can be obtained, and if there is a large amount of melamine, boron nitride with an amorphous turbostratic structure can be easily formed. . When there is a large amount of boron nitride with this amorphous turbostratic structure, the obtained boron nitride has small crystals and is unstable, so it easily reacts with water, 9-gas, etc., and easily decomposes and oxidizes (
-Mau. However, if the amount of boric anhydride used as a raw material is increased, although the crystallinity is improved, the boron yield decreases, and the boron fermentation remaining in the product must be removed, which is economically disadvantageous.

As a solution to this problem, it has been considered to add alkali metal oxides or alkaline earth metal oxides, which are conventionally known as crystallization promoters for boron nitride. It is highly alkaline compared to Celsius and prevents precursor formation reactions at room temperature. However, it has been found that a) when a potassium metal compound or an alkaline earth metal compound is added as a carbonate, the crystallization of boron nitride is promoted at a high temperature of 700 to 2300° C. without interfering with the above reaction.

The present invention was completed based on the above-mentioned new findings. The purpose of the present invention is to provide a method for producing stable boron nitride.

[Means for solving problems]

The present invention has been made to achieve the above objects,
The gist is that boric acid or boric anhydride, an organic cyclic compound having an NH2 group, an alkali metal or alkaline earth metal carbonate, and water are added and mixed, and after drying or calcining, a A method for producing boron nitride involves heating at 700 to 300°C in an oxidizing gas atmosphere.

[Specific structure and operation of the invention]

Of the boric acid or boric anhydride used in the present invention, any of orthoboric acid, metaboric acid, and tetraboric acid can be used as the boric acid.

Further, the organic cyclic compound having an NH2 group desirably does not melt during the heating reaction of boron nitride.

Examples include melamine, ammeline, ammelide, melam, melem, melon, cyanomelamine, guanylmelamine, and the like. The reason why it is desirable not to melt is that it foams when heated, makes it difficult for decomposed gas to escape, is easily carbonized and turns black due to insufficient decomposition, and lowers the purity of boron nitride.

In addition, carbonates of alkaline or alkaline earth metals include, for example, lithium carbonate and calcium carbonate, but also bicarbonates such as bicarbonate (MgCOa-CaCOa), etc. A double carbonized salt may also be used. The carbonate desirably has a low solubility in water, and when dissolved, the pH of the solution is desirably lower than the pH of the aqueous solution of the organic cyclic compound having NHz.

The amount of the above-mentioned alkali metal carbonate or alkaline earth metal carbonate to be added is (7,jwt% or more, particularly preferably i0wtchi or more. In addition, the effect increases as the amount added increases, but if it exceeds 0 wt%, the effect of the increased amount will be small. Considering the case where the amount added is removed in the subsequent process, Not economical.

Now, a case will be described in which boron nitride is produced using boric acid (HsBOa゛ or) IBO2> or boric anhydride (BzOs) and melamine (C8N6H6).

Alkali metal carbonates or alkaline earth metal carbonates (
To add these carbonates (hereinafter referred to as carbonates), these carbonates are crushed in advance and then added to a mixture of boric acid or boric anhydride powder, melamine powder, and water, or
After mixing with any of the above components, other components may be added and mixed.

It is desirable to crush these carbonates in advance and mix them uniformly.

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

The above mixture reacts with Cal'La (NH2-Ha
A precursor having the molecular formula BOa)a is obtained.

After drying or calcining this, it is heated to 700~. When fired at a temperature of 2300°C, boron nitride with good crystallinity rich in hexagonal crystals and stable in water and air can be obtained.

If the firing temperature is less than 700°C, boron nitride will not be produced.
Even if the temperature exceeds 2300° C., the amount of boron nitride produced remains uneconomical.

In the present invention, nitrates, sulfates, etc. can be considered as substitutes for these carbonates, but among these, if calcium sulfate, which has a low solubility in water, is used, a crystal growth effect is observed, but drying, Calcined or 700
This is not preferable since corrosive gas is generated during firing at a high temperature of .degree. C. or higher.

It is not clear why the addition of alkali metal or alkaline earth metal carbonates improves the crystallinity of KBN, but the addition of these compounds produces a low melting point substance that melts, and the BN does not dissolve into it. It is presumed that the crystals will grow into large crystals when they recrystallize.

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

〔Example〕

Boric acid powder Nino 62, melamine powder: /', 2. gf
1 Calcium carbonate powder: 3. /f was collected in an alumina pot, water: /l was further added, and the alumina pot was rotated to mix the contents for 10 hours. Pour the thoroughly mixed slurry-like mixture into a stainless steel vat,
It was dried at 0°C. This dry and solidified mixture was lightly crushed, placed in an aluminum crucible, heated in a horizontal annular furnace to 1,000°C while flowing nitrogen gas at a flow rate of 3 t/m, held for about 7 hours, and then cooled. did. Take out the cooled sample, crush it, sieve it with No. 00 Melesh, and measure a portion of it by X-ray method to determine the crystallinity (according to Jakushu Carbon Materials 7/7 Committee VC) L
C was measured and a portion was subjected to thermogravimetric analysis in air.

As a result, the degree of crystallinity was L c =/0OA, and the oxidation initiation temperature was g00°C. Water was added to the obtained powder sample, but no gas was generated and there was no ammonia odor.

[Comparative example]

The procedure was the same as in Example except that calcium carbonate was not added.

When the cooled sample was crushed in air, there was an ammonia odor, and when water was added, gas was generated. In addition, the crystallinity L e = A Oh - oxidation start temperature was 700°C, indicating that the crystals of boron nitride were less developed than in the examples and were unstable to water and air (oxygen). .

〔Effect of the invention〕

As described above, the method of the present invention uses boric acid or anhydrous boron and NH! By heating a mixture of an organic cyclic compound having a group and water, ? This method is capable of producing boron nitride with high boron yield, hexagonal crystallinity, and stability in water and air.

Claims (1)

[Claims] Boric acid or boric anhydride and an organic cyclic compound having an NH_2 group are mixed with alkali metal or alkaline earth metal carbonate and water, and after drying or calcining, under a non-oxidizing gas atmosphere, A method for producing boron nitride, which comprises heating at 700 to 2300°C.