V. I. Lyashenko

CATALYTIC SYNTHESIS OF GRAPHITE-LIKE BORON NITRIDE

It is well-known [1, 2] that lithium compounds have a strong effect on the process of formation of boron nitride by the carbothermal method from highly dispersed charges produced by the dissolution method. It is therefore interesting to examine the effect of these compounds on the formation and ordering of the structure of boron nitride in other methods of preparation.Investigations were carried out into the process of nitriding boron and a mixture of boric acid with soot in the presence of lithium compounds. Initial substances were amorphous boron with a purity of 98.6, boric acid of ChDA grade, grade 514 soot, grade ChDA lithium carbonate and hydroxyl, and dried nitrogen and ammonia. Charges were prepared by mixing the components by the dried method. The ratio of the boric acid and soot in the charges was constant (7:2), and the concentration of the addition was varied in the range from 1 to 58% (by mass). Nitriding was carried out in the temperature range 800–1500°C in a gas flow with an optimum speed of 2 litres/h. Temperature was measured with a platinum-platinum/rhodium thermocouple and regulated using an Sh-4501 device. Nitriding products were examined by chemical and x-ray analysis and also electron microscopy.

Crystallization of boron nitride from solution in a lithium borate melt

We have investigated the reaction between disordered (turbostratic) boron nitride and lithium carbonate under a nitrogen atmosphere using x rays and electron microscopy. Lithium borate and cyanamide were found to be the reaction products at a temperature of 650°C. Spontaneous crystallization of highly, ordered graphitic boron nitride occurs from solution in a melt of lithium borates at 1000°C. Three-dimensional ordering and crystal size increase with elevation of the temperature to 1450°C.

Effect of lithium on structure formation of graphite-like boron nitride with carbothermal synthesis

Formation of a graphite-like boron nitride structure during carbothermal analysis in the presence of lithium compounds in a stream of nitrogen or ammonia is studied by electron microscopy, x-ray, and chemical methods. A marked reduction in the formation temperature for graphite-like boron nitride with a highly ordered structure is observed and chemical aspects of the process are discussed.

On the interaction of the detonation-synthesized ultradisperse diamond and turbostratic boron nitride

The results are given of the electron-microscopic studies of the initial powders of ultradisperse diamonds with the tBN coating and after sintering of these powders both in the initial state and with coating. The possibility has been found of the interaction of the initial components in the course of sintering to form diamond-like phases.