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Aiming at the deficiencies of the three typical "external gettering" systems: metal-oxide equilibrium deoxidation (MED), halide flux deoxidation (HFD) and electrochemical deoxidation (ECD), a novel deoxidation method based on the combination of oxytropic rare earth metal Y and Ca for in-depth deoxidation of Zr-O solid solution was proposed. The thermodynamic properties of the deoxidation method were analyzed, and it was found that the addition of metallic Y could significantly improve the deoxidation ability of the Ca-CaCl 2 system, because Y could form Y-Y 2 O 3 equilibrium to "anchor" the activity of CaO (a CaO) at a very low level. When the activity of Y 2 O 3 (a Y2O3) and a CaO in the flux conforms to a Y2O3 < 18.9 a 3 CaO at 1173 K, the deoxidation mode is thermodynamically feasible. Experiments were conducted to verify the method. The results showed that even if CaO was saturated in CaCl 2 flux, the oxygen content of Zr-O solid solution could still be controlled at the level of less than 100 ppm, thus the "anchoring effect" of Y on a CaO was verified. The oxygen content, phase and microstructure of the reacted Y specimens were analyzed, which suggested that when the ratio of CaO was less than 40 % of its solubility in CaCl 2 flux, the oxygen potential of the system was controlled by Y-O solid solution, and when it was greater than 40 %, the oxygen potential of the system was controlled by Y-Y 2 O 3 equilibrium. [Display omitted] • A novel in-depth deoxidationmethod based on the combination of oxytropic metals Y and Ca was proposed. • The formation of Y-O solid solution and Y-Y 2 O 3 equilibrium can "anchor" a CaO at an extremely low level. • The oxygen content of zirconium can be stably reduced to less than 100 ppm using this deoxidation model. [ABSTRACT FROM AUTHOR]

Thermodynamic properties of zirconium-oxygen (Zr–O) solid solution and its deoxidation by calcium in CaCl 2 molten salt were studied using a chemical equilibration technique. In the temperature range from 1173 to 1373 K, the equilibrium oxygen contents in Zr were measured experimentally under coexistence of Ca and CaO in CaCl 2 molten salt. The oxygen content in Zr was reduced from about 800 ppm to a minimum of less than 100 ppm. Then a CaO sensor — niobium-oxygen (Nb–O) solid solution was employed to equilibrate with Zr–O solid solution to determine the oxygen activity coefficient in Zr–O solid solution. Zr and Nb specimens were submerged in Ca-saturated CaCl 2 molten salt containing different amounts of CaO. CaCl 2 melt was used for a homogeneous reaction and composition. The experimental results shown that Henry's law held and the activity coefficient of oxygen was constant within the concentration range of this study. Based on the result, the standard formation Gibbs free energy of Zr–O solid solution was obtained as a function of temperature: 1/2O 2 (g) = O (in Zr) Δ G Z r − O θ = − 543577 + 64. 3 T (1173−1373K) The p-t-x relationship of the deoxidation system was obtained simultaneously, which make the deoxidation limit and variation trend of oxygen content in Zr–O solid solution predictable and controllable under different conditions. Oxygen distribution coefficient between Zr–O solid solution and Nb–O solid solution was found in agreement with the theoretical value and independent of oxygen potential of the system. • A simple method is used to verify the validity of Henry's law in Zr–O solution. • The formation Gibbs energy of Zr–O solid solution was obtained. • The p - t - x relationship of the deoxidation system was also established. • Oxygen distribution coefficient is independent with external oxygen potential. • The results of this paper can make the deoxidation process of Zr predictable. [ABSTRACT FROM AUTHOR]