Electrochemical Formation of Nd-Fe Alloys in Molten LiF-CaF₂-NdF₃

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Figure 10. XRD patterns of samples D, E, and F prepared by the

potentiostatic electrolysis of Fe plate electrodes in molten LiF-CaF2-NdF3

(0.50 mol%) at 1123 K. Electrolysis conditions: D = 0.10 V for 5 min, E =

0.10 V for 5 min and 0.25 V for 30 min, and F = 0.10 V for 5 min and

0.40 V for 30 min.

14.

15.

16.

17.

3+

E1 = E Nd

Nd —

RT

ln aNd,1 = 0.19 V

3F

3+

E Nd

Nd —

RT

ln aNd,2 = 0.28 V

3F

E2 =

18.

[3]

19.

20.

[ 4]

where ENd3+/Nd = 0.18 V (the result of Fig. 5), T = 1123 K, R =

8.314 J K−1 mol−1, and F = 9.64 × 104 C mol−1. The experimental

results obtained herein are consistent with the calculated equilibrium

potentials.

Conclusions

In the present study, as a fundamental study for recycling, the

electrochemical Nd-alloying behavior of Fe was investigated in a

molten LiF-CaF2-NdF3 (0.3 or 0.5 mol%) system at 1123 K. From

the open-circuit potentiometry of a Mo electrode, the equilibrium

potential of Nd3+/Nd was determined to be 0.18 V (vs Li+/Li).

Liquid Nd-Fe alloy formation occurred rapidly through potentiostatic electrolysis at 0.10 V, and majority of the 100-μm-thick Fe

plate electrode was alloyed after 60 min. In contrast, the rate of

formation of solid Nd2Fe17 alloy was significantly slow at 0.25 V.

However, once the liquid Nd-Fe alloy formation was established,

Nd2Fe17 could be readily formed through the anodic dissolution of

Nd. Based on the open-circuit potentiogram of an Fe electrode

alongside SEM, EDX, and XRD analysis, the equilibrium potentials

of coexistence states of liq. Nd-Fe + Nd2Fe17 and Nd2Fe17 + Fe

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