DE1087578B - Process for the production of boron nitride - Google Patents

Description

GERMAN

The invention relates to a method for producing boron nitride. There are different procedures known for the production of boron nitride, but none is completely satisfactory for large-scale production. For example, some processes can only be carried out in batches, while others can only be carried out for very high temperatures or using expensive or dangerous compounds can be. In most of the known processes the yield is poor and the product does not show the desired purity.

The aim of the present invention is to provide a method for the production of boron nitride at relatively allow low temperature, with one in high yield a product with a better degree of purity receives.

The inventive method for the production of boron nitride is that melamine with Boric acid converts the resulting reaction product at a temperature of at least 600 ° C Exclusion of oxygen heated and boron nitride isolated. Optionally, melamine can be mixed with boric acid Mix when dry and heat this mixture to at least 600 ° C.

The term “boric acid” is also understood to mean its anhydride.

The reaction between melamine and boric acid can take place in hot aqueous solution, and under Under these conditions, a solid reaction product is obtained by evaporation or by precipitation from the solution obtain. That is either from the aqueous solution or from the mixture of dry substances dissipating reaction product is made in the absence of oxygen and preferably in a nitrogen atmosphere heated to at least 600 ° C for the production of boron nitride.

According to the invention, if a mixture of melamine and boric acid is heated in powder form, the relative mixing ratio of boric acid to melamine on that for the production of melamine borate theoretically necessary stoichiometric amount. The boric acid is used in a ratio of 0.5 to 3 mol applied per mole of melamine. The two compounds are intimately mixed with one another and under Exclusion of oxygen and preferably heated to 600 ° C. under nitrogen until the evolution of gas stops.

The invention will be explained in more detail by means of a few examples.

example 1

Powdered melamine and powdered boric acid become 1.5 moles of boric acid per mole of melamine mixed together. The mixture is used in process for the production of boron nitride

Applicant:

Union Carbide Corporation,
New York, NY (V. St. A.)

Representative: Dr.-Ing. F. Wuesthoff, 'Dipl.-Ing. G. Pulse

and DipL-Chem. Dr. rer. nat. E. Frhr. v. Bad luck man,

Patent Attorneys, Munich 9, Schweigerstr. 2

Claimed priority:
V. St. v. America December 11, 1957

Bucket Miller King, Berea, Ohio (V. St. A.),
has been named as the inventor.

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A covered graphite crucible is given to exclude oxygen from the mixture in granulated Coke is embedded. The reaction mixture is then heated to 950 to 1000 ° C. for 2 hours. The resulting boron nitride product was a soft sintered lump that was 24.7% of the starting mix weighed.

Example 2

Powdered melamine and powdered boric acid are 2.25 moles of boric acid per mole of melamine mixed together. The mixture is placed in an open graphite container and placed in a nitrogen atmosphere. 30 Heated to 1000 ° C for a further 30 minutes and to 1800 ° C for a further 30 minutes. The reaction product, a porous, cream-colored mass was recognized as boron nitride by X-ray diffraction. One Overall analysis showed a content of 43.1% boron, 55.7% nitrogen and 0.1% Carbon. The yield was 85%> theory.

According to another embodiment of the invention, boric acid and melamine are hotter in water Solution reacted together, leaving a concentrated solution of boric acid near the Boiling point is maintained and melamine is added practically in the amount necessary for the formation of Melamine borate is theoretically necessary. Then you can water from the resulting solution remove by evaporation to dryness or cool the solution to precipitate the reaction product

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and decant the water. The finely divided reaction product is placed in a suitable container and, in the absence of oxygen, to at least 600 ° C heated. This form of implementation is described in the following example.

Example 3

Melamine is added in a ratio of 1 mol of melamine to a hot aqueous solution of boric acid to 0.5 moles of boric acid. The solution is evaporated to dryness and the solid reaction product is pulverized and placed in a covered steel container. This container is used to exclude air in coke and Sand embedded and heated to 800 ° C for 8 hours. The resulting fine creamy white powder was through X-ray diffraction recognized as boron nitride.

A boron nitride prepared according to this example was coated in the same manner as in Example 2 1800 ° C heated. The analysis of the product showed a content of 43.6% boron, 52.8% nitrogen and 0.23% carbon.

Example 4

Melamine is added in a ratio of 2 moles of boric acid to a hot aqueous solution of boric acid 1 mol of melamine, the solution is evaporated to dryness, the reaction product is pulverized and then heated to 600 ° C. for 28 hours in the absence of oxygen. You get a white one Boron nitride containing 35.9% boron, 42.6% nitrogen and 0.5% carbon. Although the speed of response at 600 ° C is much lower than at 800 ° C, forms at this temperature Boron nitride.

Example 5

Powdered boric acid and powdered melamine were mixed with each other in a molar ratio of 3 moles of boric acid mixed to 1 mole of melamine and heated to 950 ° C. for 2 hours with the exclusion of oxygen. the Analysis of the boron nitrite showed a content of 38.6% boron, 41.6% nitrogen and 0.43% carbon. yield 92 per cent of theory.

Example 6

Melamine is added to a hot aqueous solution of boric acid in a molar ratio of 3 moles of boric acid to 1 mole of melamine. The solution is evaporated to dryness, the reaction product is pulverized and then heated to 800 ° C. for 3 hours with the exclusion of oxygen. Boron nitride is obtained in 91% yield with a content of 34.5% boron, 41.6% nitrogen and 1.61% by volume of carbon.

Of the implementation forms described, the so-called "dry process" is preferred

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Claims (4)

Patent claims: 1. Process for the production of boron nitride, characterized in that melamine is used with Reacts boric acid in a molar ratio of 0.5 to 3 moles of boric acid per mole of melamine, whereupon the reaction product is heated to at least 600 ° C. in the absence of oxygen and boron nitride isolated. 2. The method according to claim 1, characterized in that that one finely divided melamine and finely divided boric acid in the dry state intimately mixes with each other and reacts. 3. The method according to claim 1, characterized in that melamine with boric acid in aqueous Reacts solution, whereupon the solution is evaporated to dryness and the residue is heated. 4. The method according to claim 1 to 3, characterized in that the reaction product in heated under a nitrogen atmosphere. © t 009 588/381 8.60