Mechanism of Oxygen-Chlorine Potential Interaction During the Ca/Y-Mediated Solid-State Deoxidation of Zirconium

Zirconium (Zr) is a strategic metal resource whose performance is significantly degraded by high oxygen content. The external gettering process is an effective approach for in-depth deoxidation of Zr. In this study, the deoxidation behavior of Zr in the Ca-Y-CaCl₂ external gettering system was investigated by adjusting the chlorine potential through YCl₃ addition. The change of oxygen potential and its synergistic control mechanism during the variation of chlorine potential were systematically examined. The results demonstrated that with increasing chlorine potential, the system undergoes a sequence of reactions: chlorination of Ca, formation of metallic Y, formation of YOCl, dissolution of Y₂O₃, and formation of YCl₃, ultimately reaching a three-phase equilibrium of Y-YOCl-YCl₃. During this process, the oxygen content of Zr fluctuates notably, which is primarily attributed to the shift in the oxygen-transfer medium from Ca to Y. This transition changes the oxygen potential control mechanism from indirect Y-Ca control to direct Y control. After reaching equilibrium at 1173 K for 72 h, the equilibrium oxygen content of Zr initially remains stable with increasing chlorine potential, then gradually decreases, eventually reaching 20 ppmw. This trend is consistent with the mutual interaction of oxygen potential and chlorine potential. The findings provide important theoretical insights into the interaction between oxygen and chlorine potentials in deoxidation systems, elucidate the multi-element synergistic mechanism for oxygen control, and contribute to the design of efficient deoxidation systems.