CS243893B1 - Process for producing boron nitride powder - Google Patents

Abstract

The solution relates to a method for producing powdered boron nitride with high particle surface activity, good sinterability, and a high degree of particle structural organization. The method is carried out in two stages, of which in the first stage 5 to 20% by weight of a hexagonal modification of powdered boron nitride is added to the mixture and the mixture is annealed in this stage without access of air at a temperature of 80 to 240 °C for 1 to 6 hours, after which the mixture is ground to a grain size of 15 to 150 >um. In the second stage 0.5 to 15% by weight of a powdered metal of the iron or platinum group or their mixture or oxides of these metals, e.g. nickel oxide, is added to the mixture. Then the mixture is annealed at a temperature of 750 to 1,350 ° Celsius for 1 to 6 hours in an ammonia atmosphere.

Description

(75)

Author of the invention DUFEK VLADIMÍR ing. (PRAGUE) HUBÁČEK MILAN ing., BEROUN (54) Production method of boric nitride powder

The present invention relates to a process for the production of boron nitride powder having a high surface activity of particles, good sinterability, and a high degree of structural arrangement of the particles. The process is carried out in two stages, in which, in the first stage, 5-20% by weight of hexagonal modification of boron nitride powder is added to the mixture and the mixture is annealed at 80 to 240 ° C for 1 to 6 hours in the absence of air, after which the mixture is ground to a particle size of 15 to 150 µm. In a second step, 0.5-15% by weight of an iron or platinum group powder or a mixture thereof or oxides of these metals, e.g. nickel oxide, is added to the mixture. The mixture is then calcined at 750 to 1350 ° C for 1 to 6 hours in an ammonia atmosphere.

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of boron nitride powder having a high surface activity of particles, good sinterability, and a high scab structure.

The simultaneous production of boron nitride powder is carried out in two alternatives, one of which is to heat the raw materials to high temperatures of about 1800 ° C and the other to heat to low temperatures of 700 to 1200 ° C. The heating of the raw materials to high temperatures results in boron nitride having a high degree of structural arrangement, with a relatively low specific surface area, and thus a low surface activity. When the raw materials are heated to low reaction temperatures, boron nitride is obtained with the desired high specific surface area and hence a high surface activity, but with a low degree of structure, referred to as the turbostratic form. In addition, the boron nitride obtained contains a certain amount of residual oxygen which reduces its utility parameters.

According to the overriding requirements for the resulting properties, a suitable process for the production of boron nitride from raw materials such as boric acid, boron oxide, borates and borides, exceptionally elemental boron or boron halide, respectively, is chosen. its derivatives treated with nitrogen, ammonia, cyanides, ammonium salts or other nitrogen compounds, including some organic compounds such as urea, melamine and others. In order to improve the sinterability, small amounts of additives are added to the raw material mixture, especially necessary in the manufacture of metallurgical ceramics.

These disadvantages are avoided by the process for producing boron nitride powder for processing into metallurgical ceramic products, from a crystalline boric acid starting material, a nitrogen-containing organic substance, e.g. urea, and an additive according to the invention.

SUMMARY OF THE INVENTION The process is carried out in two stages, in which, in the first stage, 5-20% by weight of hexagonal boron nitride powder is added to the mixture and the mixture is annealed in this stage without air at 80 to 240 ° C. ° C for 1 to 6 hours. Thereafter, the mixture is milled to a particle size of 15 µm to 150 µm and in the second stage 0.5 to 15% by weight of an iron or platinum group metal powder or a mixture thereof or an oxide of these metals, eg nickel oxide, is added to the mixture. The mixture is then calcined at 750 to 1350 ° C for 1 to 6 hours in an ammonia atmosphere.

An advantage of the boron nitride process of the present invention is that hexagonal boron nitride particles are uniformly dispersed throughout the volume of reactants in which the crystalline nuclei of the intermediate are formed in a two-stage annealing process wherein the final product has a high specific surface characterizing the sinterability of boron nitride.

In addition to the technical advantages, in particular in the high degree of structural arrangement of the particles with a large specific surface area of the product, the process according to the invention also brings economic advantages, in particular in reducing the energy consumption of boron nitride production.

Example

According to an exemplary embodiment, a tear ring was produced for use in horizontal continuous steel casting. Crystalline boric acid in a 1: 2 mixture of urea was used as the raw material. The urea additive has a positive effect on soothing the formation of the intermediate. After addition of 8% by weight hexagonal modification of boron nitride powder, the mixture was heated to 80 ° C and this temperature was raised to 240 ° C over 2 hours. In this heating, the surface of the hexagonal modification of boron nitride was coated with an urea borate-type intermediate. Then the mixture was pulverized to a predominant grain size fraction of 100 µm above 90%.

In the second step, 3% by weight of nickel powder with a particle size below 0.045 mm was added, after which the mixture was calcined at 1,150 ° C for 2 hours in a split ammonia environment. An epitaxial growth of the new phase on the surface of hexagonal boron nitride occurred and a significant increase of the 2 -1 specific surface area of the resulting product up to 10 m g. The obtained product consisted of boric nitride powder containing 42% nitrogen, 66% boron and only 2% oxygen and showed good sinterability. The tear ring produced from said boron nitride had very good resistance to sudden temperature changes, a high degree of structural arrangement. Available raw materials are used in the production and failure-free production has been achieved in tear-off applications, which has had a positive effect on the productivity of horizontal continuous steel casting.

The process for producing the boron nitride powder according to the invention is suitable for producing a raw material for making compact bodies such as crucibles, tear-off rings for continuous casting, but also for obtaining a raw material suitable for phase transformations into crystalline modifications with high hardness. Furthermore, boron nitride produced by the process of the invention is suitable for direct use as a high temperature lubricant as well as a dielectric and the like.

Claims (1)

BEFORE THE INVENTION Process for producing boron nitride powder for processing into metallurgical ceramic products, starting from a raw material consisting of crystalline boric acid, a nitrogen-containing organic substance, such as urea, and an additive, characterized in that it is carried out in two stages, of which 5-20% by weight of hexagonal boron nitride powder is added to the mixture and the mixture is calcined at 80 to 240 ° C for 1 to 6 hours in the absence of air at this stage, after which the mixture is ground to a grain size of 15 to 150 µm and 0.5 to 15% by weight of an iron or platinum group powder or a mixture thereof or an oxide of these metals, e.g. nickel oxide, is added to the mixture, followed by calcination at 750 to 1350 ° C for 1 to 6 hours in the atmosphere ammonia.