Computer modeling of oxygen migration accompanying aluminum production

Abstract

The behavior of oxygen ions in the Al melt under action of a constant electric field was studied by molecular dynamics. The rate of moving up of O 2-ions from the graphite wall to the melt surface increases and the time interval in which the first ion reaches the surface decreases with an increase in O 2-concentration. When the number of ions is less than 90 small ion clusters consisting of only a few oxygen ions are often formed on the Al melt surface. In the case when the number of ions is 90, a vertical chain extending from top to bottom of the molecular dynamics cell is formed. The number of O 2-ions in the surface layer strongly depends on time. Before reaching the surface of the melts, an ion carries out a random motion in the vicinity of the bottom of the basic cell, and reaching the surface the ion moves randomly in a thin surface layer of the cell. Al atomic selfdiffusion coefficient and internal energy of the Al melts increase while O 2-ion selfdiffusion coefficient decreases with increasing the concentration of ions in the system. Modeling has shown that changing the boundary conditions in time can have a significant effect on the behavior of the "Al-O 2--graphite" system with a high content (= 90) of oxygen ions. Since the change in the boundary conditions is quite likely when aluminum melt enters the electrolyte, then during the smelting of aluminum, both relatively slow and rapid processes of oxygen release can occur.

Peculiarities of formation of hydroxonium ion and its small clusters

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