Healing of bifilm defects is commercially pure zinc

This study explores whether bonding can form between the two layers of a bifilm defect in commercially pure Zn melt. The defect was simulated by keeping two ZnO layers in contact with each other and the trapped atmosphere between them in the liquid alloy for 1–100 minutes. Changes in the layers’ composition and structure were analysed. Findings indicate that the bifilm layers can gradually bond or ‘heal’. The process begins with the growth of ZnO, followed by its transformation into ZnAl2O4, which consumes the oxygen in the trapped atmosphere. Subsequently, the formation of AlN consumes nitrogen. During this phase, bonding between the oxides occurs at some points. Ultimately, the formation of Al2O3 from ZnAl2O4 results in extensive bonding between the two oxide layers. A straightforward mass balance calculation confirmed that even a low Al concentration in the Zn melt – less than 0.004 wt%—is sufficient for these reactions to occur.