FORMATION OF NITRIDES DURING THE INTERACTION OF NITROGEN WITH LIQUID ALUMINUM AND ITS ALLOYS

Procesi littâ, 2025, Vol 3 (161), 23-32

Abstract

The purpose of the presented work is to substantiate the formation of a nitrogen solution in liquid aluminum and silumin. It was believed that the interaction of nitrogen with liquid aluminum occurs directly on the surface of the melt, and in this regard, the question of the possibility of the formation of dispersed nitrides in the volume of the melt during gas nitration arose. Thermodynamic calculations have proven that the reaction of aluminum nitride formation under standard conditions, under which the correction for the surface energy (dispersion) of nitride particles is very small, i.e. the reaction product Al + 0.5N2 = AlN is massive, occurs at any real temperatures. And when forming aluminum nitride of high dispersion, compensation is possible, under certain conditions, of the free energy of the system. It has been calculated at what sizes of dispersed nitrides that may be formed, their surface energy compensates for the change in the free energy of the reaction of aluminum nitride formation under standard conditions. The size of nitrides was determined at certain temperatures at which their formation is thermodynamically probable. The experiments were carried out by creating the conditions of a flow system. That is, on one side of the sample, the pressure of a mixture of nitrogen and hydrogen was created, and on the opposite side, a vacuum. The calculation showed that under standard conditions, the surface energy of nitride will be 8.52•10-3 J/mol and is a small value. The change in the surface free energy of aluminum nitride particles with a size of 1.2•10-9 m at a temperature of 1373 K will be 168605 J/mol, and at a temperature of 1473 K – 82428 J/mol. It was established by X-ray diffraction that under the conditions of a flowing gas-melt system, a nitrogen solution is formed in aluminum, and during the crystallization of the melt, nitrides precipitate. The obtained data correlate with those given in the scientific literature on the interaction of highly reactive metals with nitrogen. It was determined that the process of saturation of the aluminum melt with nitrogen under flowing conditions without crystallization of the melt is reversible, and in stationary systems at temperatures below 2940 K, which corresponds to the negative values of the change in the free energy of the reaction of aluminum nitride formation, the process is irreversible.