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

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 NaF_19.69-KF_25.84-(AlF₃)_54.47 bath at 800 °C 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.