KINETIC ANALYSIS OF THE FORMATION OF BRASS NANOPARTICLES PRODUCED DURING EVAPORATION BY A CONTINUOUS HIGH-ENERGY ELECTRON BEAM

Kinetic estimates of the predominant formation of Cu₅Zn₈ γ-brass nanoparticles among intermetallic phases during evaporation of copper and zinc by a continuous beam of high-energy electrons followed by rapid vapor condensation in a stream of inert argon gas have been carried out. The calculated dependence of the change in the free energy of the mixing of zinc and copper components in the binary system, taking into account the addition to the formation of a new surface during crushing into nanoparticles, on the composition and particle size has a minimum that overlaps the concentration range on the Cu ‒ Zn phase diagram corresponding to γ- and β-brass; There is a vertical shift in the graph of the dependence of the free energy of mixing towards smaller (modulo) values with a decrease in the size of nanoparticles from 126 to 5 nm due to an increase in the surface contribution. It is shown that the dependence of the change in free energy on the composition of the Cu ‒ Zn mixture reflects the thermodynamics of mixing and does not determine the choice of the crystalline phase. The classical theory of nucleation is used to explain the phase composition, taking into account the interphase surface energy at the solid-embryo‒supercooled liquid-cluster interface. Calculations of the change in the free energy of crystal nucleation were carried out with the introduction of effective interphase energy for β-brass, additionally taking into account the energy costs of establishing a long-range subcutaneous order and the contribution of antiphase boundaries. The critical radii and energy nucleation barriers for γ-and β-brass nanoparticles are calculated and it is determined that with increasing supercooling of the cluster at the moment of crystallization, the critical radii and barriers decrease, and the nucleation barrier for γ-brass is significantly lower than for β-brass, due to lower energy costs for formation structure and absence of the need to establish a long-range sublattice order. The estimates obtained are in qualitative agreement with experimental data and explain the predominant formation of the γ-phase among the intermetallic phases of brass under conditions of rapid condensation.

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