Synergistic enhancement of sinterability and corrosion resistance of ZnCr2O4 spinel by TiO2 addition for carbon-free aluminum electrolysis

Abstract ZnCr2O4 is a corrosive-resistant spinel with potential as a sidewall material candidate for advanced carbon-free aluminum electrolysis. However, synergistic enhancement of sinterability and corrosion resistance of ZnCr2O4 is still a challenge. To address this issue, ZnCr2O4 bulks were sintered by using TiO2 as additive, and their corrosion performance was evaluated in the electrolysis of NaF19.69-KF25.84-(AlF3)54.47 bath at 800 oC by both static and dynamic corrosion experiments. The results showed that the doped Ti4+ was located in the octahedral space of ZnCr2O4, and the formed cation vacancies at B-site of spinel promoted the sinterability. The spinel with 10 wt.% TiO2 showed the highest density which was composed of the main phase Zn(Cr, Ti)2O4 and the second phase Cr2Ti5O13. The compact spinels can resist the penetration of electrolyte and further reduce the dissolution of Zn(Cr, Ti)2O4. Consequently, the corrosion rate significantly decreased from 0.028 cm·a-1 for ZnCr2O4 to 0.016 cm·a-1 for 10 wt.% TiO2 added spinel. Based on the experimental analyses and ab initio thermodynamics calculations, the corrosion mechanism of the obtained spinels was revealed. The as-introduced strategy for performance synergy improvement of ZnCr2O4 spinel is expected to allow successful application of new materials in the promising electrolytic cell and other severe corrosion environments.