Phase equilibria in the ternary system Gd–Fe–Zn and electrochemical hydrogenation of the phases

Chem. Met. Alloys 11 (2018) 27-33

https://doi.org/10.30970/cma11.0381

Nataliya Chorna, Nataliya Sagan, Oksana Zelinska, Vasyl Kordan, Anatoliy Zelinskiy, Volodymyr Pavlyuk

The interaction of the components in the ternary system Gd–Fe–Zn was investigated for the first time using X-ray powder diffraction and energy-dispersive X-ray analysis. The isothermal section of the phase diagram at 500°C was constructed over the whole concentration range. The existence of the ternary compound Gd₂Fe₂Zn₁₅ (Th₂Zn₁₇-type, space group R‑3m, а = 0.90025(10) nm, с = 1.3160(3) nm) was confirmed at 500°C in the Gd–Fe–Zn system. A new ternary compound ~Gd₁₃(Fe,Zn)₅₈ (Gd₁₃Zn₅₈-type, space group P6₃/mmc, а = 1.4306(5) nm, с = 1.4000(2) nm) was obtained. The efficiency of electrochemical hydrogenation of the binary phases GdZn, GdZn₂, GdFe₂ and the solid solutions on their basis was studied in Ni‑MH battery prototypes. GdZn_1‑xFe_x with cubic CsCl-type structure reversibly absorbs 0.006 Н/f.u. when x = 0, and 0.009 H/f.u. when x = 0.04. GdZn_2‑xFe_x with orthorhombic KHg₂-type structure absorbs 0.012 Н/f.u. when x = 0, and 0.016 H/f.u. when x = 0.06. GdFe_2‑xZn_x with cubic MgCu₂-type structure absorbs the largest amount of hydrogen, that is 0.023 Н/f.u. when x = 0, and 0.027 H/f.u. when x = 0.06. The influence of composition, crystal structure and chemical activity of the studied electrode materials in alkaline media on their hydrogen capacity and electrochemical characteristics is discussed.

Isothermal section of the Gd–Fe–Zn phase diagram at 500°С.

Keywords

Phase equilibria / Intermetallic compound / Solid solution / Electrochemical hydrogenation / Ni‑MH battery