Electrochemical hydriding of nanocrystalline Mg-Ni-X (X = Co, Mn, Nd) alloys prepared by mechanical alloying and spark plasma sintering

Abstract

In this work, MgNi26, MgNi26Mn10, MgNi26Co10 and MgNi26Nd10 alloys were prepared by mechanical alloying (MA) and subsequent spark plasma sintering (SPS). Mechanical alloying leads to a grain refinement and increases the concentration of lattice defects. SPS technology provides a compact material but with high porosity, consequently creating a high internal surface area within the volume of sample. The combination of the MA and SPS techniques produces a promising material in terms of fast hydriding kinetics and a high content of absorbed hydrogen. All samples were electrochemically hydrided in a 6 mol/L KOH solution at 80 °C for 480 min. The microstructures of the alloys were characterized by scanning electron microscopy and energy dispersive spectrometry. The phase compositions were characterized by X-ray diffraction, and the total hydrogen content in the hydrided pellets was measured using an inert gas fusion analyser. The dehydriding process was studied by thermogravimetry and mass spectrometry. The highest total amount of hydrogen was absorbed by the MgNi26Nd10 alloy, nearly 1.8 wt%. The main hydriding product was the binary hydride MgH2. The results of the mass spectrometry analysis reveal a significant reduction in the temperature of hydrogen evolution from magnesium hydride, probably due to the formation of fine microstructures of the hydrogenated alloys and catalytic effect of Ni. The decomposition temperature was reduced by more than 200 °C as compared to the commercial MgH2.