JPS61111904A - Production of hexagonal boron nitride - Google Patents

Abstract

PURPOSE:To produce a hexagonal boron nitride having high purity in one step from a raw material, by heating a mixture of borax and melamine in an intert gas atmosphere, and washing the reaction product with a dilute mineral acid and then with water. CONSTITUTION:A mixture of crushed borax and melamine is put into a crucible, and heated in an electric oven at 1,100-2,200 deg.C for about 1hr under the flow of nitrogen gas. The reaction product is subjected to the repeated washing with a dilute mineral acid (e.g. 5% hydrochloric acid) and decantation until the pH of the washed liquid becomes <=1, stirred for about 30min, decanted, subjected to the repeated washing with water and decantation until the pH of the washed liquid becomes 5-7, and filtered. The precipitate is washed with methanol and dried in vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing hexagonal boron nitride. More specifically, the present invention relates to a method for directly producing hexagonal boron nitride by reacting borax and melamine.

(Prior Art) Boron nitride is a type of fine ceramics, and can be broadly classified into amorphous boron nitride, cubic boron nitride, and cubic boron nitride. Regarding orthogonal boron nitride, the conventional method
Calcium phosphate is added to boric anhydride and ammonia to produce amorphous boron nitride at a reaction temperature of about 900°C, by-products and additives are removed with hydrochloric acid, and further heat-treated at about 1800°C to obtain macrogonal boron nitride. That is, hexagonal boron nitride is produced from raw materials through two stages of reaction and heat treatment.

(Problems to be Solved by the Invention) An object of the present invention is to produce hexagonal boron nitride from raw materials in a single reaction.

(Means for Solving the Problems) As a result of various studies regarding the above object, the present inventors set reaction conditions in a method of reacting borax and melamine, and further performed post-treatment of the obtained reaction product. It was discovered that high purity hexagonal boron nitride could be obtained by improving the method, and the method of the present invention was developed.

In the method of the present invention, borax and melamine are reacted as raw materials. The reaction is thought to proceed as shown in the following equation.

3Na2B407+2C3N3(NF2)3-1→12
BN +3Na20 + 6CO2+ 6H20 The borax used is most preferably anhydrous, but it may be hydrated.

Regarding the amount of borax and melamine used, in order to convert all the borax into boron nitride, it is desirable to use 2 moles or more of melamine per 3 moles of borax, as shown in the above formula. However, it is not particularly limited.

The reaction is carried out in an inert gas under normal or elevated pressure. Nitrogen, helium, argon, etc. are used as the inert gas.

In the process of the invention, the reaction temperature is at least 110
Temperature range above 0℃ and below 2200℃, preferably 12
It is in the range of 00 to 2000°C. If the temperature is below 1100°C, amorphous boron nitride is produced, and if it exceeds 2200°C, the yield of hexagonal boron nitride decreases, which is not preferable.

The reaction product from the above reaction contains unreacted raw materials and by-products. These unreacted raw materials and by-products are mostly soluble in water, so washing the reaction product with warm or boiling water yields fairly purified orthogonal boron nitride. However, the purity is 80-90%. %, which is still not sufficient.In particular, the by-product sodium oxide exhibits strong basicity and is difficult to sufficiently remove by washing with water alone.

The main feature of the method of the present invention is that the reaction product obtained under the above reaction conditions is treated as follows.

That is, the reaction product is washed with a mineral acid and then with water to obtain hexagonal boron nitride.

The mineral acids used are hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. Among them, hydrochloric acid, sulfuric acid, or a mixture of both give the best results. The concentration of mineral acid used is 0.1~
10%, preferably 1-5%.

Washing is carried out using such a mineral acid until the pH of the washing liquid becomes 1 or less. Then, washing with water is carried out until the pH of the washing liquid becomes 5 to 7.

The methods of washing with mineral acid and washing with water are not particularly limited, and the cleaning may be performed so that each washing solution has a pH within the above range. For example, the reaction product is suspended in an aqueous solution of dilute mineral acid of the above concentration, stirred, filtered,
If necessary, it is further washed with a dilute mineral acid solution until the pH becomes 1 or less. Then, there is a method in which P is separated and the F mass is filtered as it is or suspended in water and washed with water until the pH of the washing solution becomes 5 to 7.

In the present invention, the reaction product may be washed with water and then dried; however, after washing with water, the reaction product may be further washed with a low-boiling organic solvent such as methanol, ethanol, inglobil alcohol, acetone, methyl ethyl ketone, etc., and then dried under normal pressure or By drying under reduced pressure, high-purity hexagonal boron nitride fine powder can be obtained in good yield.

(Action and Effect of the Invention) Borax and melamine are heated to at least 1100°C and 22°C.
The reaction product obtained in one step of the reaction by heating in a temperature range of 0.000C or lower is washed with dilute mineral acid until the pH reaches 1 or less, and then washed with water until the pH reaches 5 to 7 to remove almost all unreacted raw materials and by-products. can be completely removed to obtain high purity hexagonal boron nitride fine powder.

Therefore, the method of the present invention is extremely excellent as a method for providing high-purity hexagonal boron nitride fine powder, which is highly desired especially as an electronic material, a refractory material, or a lubricant.

(Example) Next, the present invention will be specifically explained with reference to Examples.

Example 1 In a 280 cc boron nitride crucible with a lid, crushed anhydrous borax was placed at 60.4 cc. and melamine 113.
5? After adding the mixture, put the crucible into an electric furnace,
The crucible was heated at 1500° C. for 1 hour in an electric furnace while flowing nitrogen gas at a rate of 400 ml per minute.

After the reaction, the reaction product was left to cool in nitrogen overnight, the reaction product was placed in a beaker, and 5% hydrochloric acid was added to the reaction product in the beaker. Washing and decantation were repeated to adjust the pH of the washing solution.
After reducing the pH to 1 or less, the solution was stirred for about 30 minutes, decanted, ion-exchanged water was added, and stirring and decantation were repeated to bring the pH of the washing solution to 6, which was then sent to each house. Furthermore, after washing the precipitate twice with methanol,
As a result of drying at 00°C for 2 hours, a white powder of 27.051- was obtained.

This substance was confirmed to be hexagonal boron nitride by infrared analysis and X-ray analysis. Moreover, it was confirmed by electron micrograph that the particles had a particle size of 1 to 5 microns. The purity of boron nitride obtained by elemental analysis was 99.6%. In addition, the yield of boron nitride based on the borax used was 9
It was 0.6%.

Example 2 In the method carried out in Example 1, instead of 5% hydrochloric acid,
Using 5% sulfuric acid and performing an experiment in the same manner as in Example 1, the purity was 99.6%, the particle size was 1 to 5 microns, and the yield was 90%.
．． 2% hexagonal boron nitride powder was obtained.

Reference Example In the method carried out in Example 1, after the reaction, the reaction product was left to cool overnight, the reaction product was placed in a beaker, boiling water was added to the reaction product, water washing and decantation were repeated three times, and then door to door delivery was carried out. As a result of drying the precipitate under reduced pressure at 100°C for 2 hours,
The obtained white powder was subjected to elemental analysis and confirmed to be boron nitride with a purity of 878%.

Claims (2)

[Claims] (1) After heating a mixture of borax and melamine in an inert gas atmosphere at a temperature range of at least over 1100°C and up to 2200°C, the reaction product obtained is heated until the pH of the cleaning solution becomes 1 or less. Wash with acid, then p of the washing solution.
A method for producing hexagonal boron nitride, characterized by washing with water until H becomes 5 to 7. (2) The method according to claim 1, wherein the dilute mineral acid is dilute hydrochloric acid and/or dilute sulfuric acid.