The hydrogen absorption-desorption performances of Mg-Co-X ternary alloys with BCC structure

To improve hydrogenation properties of Mg-Co binary alloys that were developed by the present authors, ternary Mg₅₀Co₄₅X ₅ alloys (X = Fe, Cu and Pd) were synthesized by ball milling. The formation of the BCC phase in the ternary alloys was verified by means of a XRD Rietveld analysis and TEM observation. The BCC lattice parameters of Mg ₅₀Co₄₅X₅ (X = Fe, Cu and Pd) were found to be smaller than that of Mg₅₀Co₅₀. Fe addition to Mg ₅₀Co₅₀ alloy improved the hydrogen absorption capacity to 2.59 mass% at 373 K. The Pd and Cu added alloys showed a desorption isotherm for which the desorption capacity was up to 0.2 mass% at 373 K in the pressure range of 0.01-5.0 MPa. In situ DSC measurements revealed that the hydrogen absorption and desorption reactions of all the ternary alloys studied were reversible at the first thermal cycle. A series of ternary Mg ₅₀Co_50-yCu_y (y = 5, 7, 9, 10) BCC alloys were synthesized by ball milling. It was found that Mg₅₀Co ₄₁Cu₉ had the highest hydrogen absorption content (2.0 mass%) among these alloys at 373 K, while it desorbed 0.3 mass% hydrogen at the same temperature under vacuum.