Hydrogen Sorption Behavior of Cast Ag-Mg Alloys

Abstract

In this paper, the hydrogen sorption properties of casted Ag-Mg alloys were investigated. The obtained alloys were structurally analyzed by X-ray diffraction (XRD) and observed by scanning electron microscopy (SEM). The study was carried out for four alloys from the two-phase region (Mg) + γ′ (AgMg4) with nominal concentrations of 5 wt. %, 10 wt. %, 15 wt. %, and 20 wt. % Ag, four alloys with nominal compositions equivalent to intermetallic phases: AgMg4, AgMg3, AgMg, and Ag3Mg, one alloy from the two-phase region AgMg + Ag3Mg (Ag60Mg40), and one alloy from the two-phase region AgMg + AgMg3 (Ag40Mg60). The hydrogenation process was performed using a Sievert-type sorption analyzer. The hydride decomposition temperature and kinetic properties of the synthesized hydrides were investigated by differential scanning calorimetry (DSC) coupled with thermogravimetric analysis (TGA). Samples with high magnesium content were found to readily absorb significant amounts of hydrogen, while hydrogen absorption was not observed for samples with silver concentrations higher than 50 at. % (AgMg intermetallic phase).

Dual tuning of the de-/hydrogenation thermodynamics and kinetics of the Mg–Ni alloy by introducing the Ag–H bond: enhanced hydrogen storage properties at moderate temperatures

“…26 Intermetallic phases, such as AgMg and Ag 3 Mg, in Mg-Ag systems can promote the decomposition of MgH 2 and improve thermodynamic properties. 27 Similar to Mg 3 Ag, Mg 4 Ag also exhibits complete reversibility in hydrogenation, resulting in a reduction of the reaction enthalpy to 59.5 kJ mol −1 . 28,29 Reversible reaction can be expressed as,…”

Experimentally Observed Nucleation and Growth Behavior of Mg/MgH2 during De/Hydrogenation of MgH2/Mg: A Review

“…However, its application is limited by its high dehydrogenation temperature (>300 • C) [28][29][30]. Moreover, sluggish hydrogen absorption and desorption kinetics are observed due to the fact that the hydrogen absorption and desorption reactions of the MgH 2 /Mg system involve different gas-solid reaction energy barriers up to 218 kJ/mol, including hydrogen dissociation, hydrogen diffusion, and nucleation and growth processes [29,[31][32][33]. The hydrogen absorption process in metallic Mg has been divided into the following steps [31,[34][35][36][37][38]: (1) physisorption of hydrogen molecules on the surface of metallic Mg; (2) dissociation of hydrogen molecules and chemisorption.…”

Mixing Enthalpies of Liquid Ag–Mg–Pb Alloys: Experiment vs. Thermodynamic Modeling

“…The addition of silver has a positive effect on the properties of Mg-based alloys [ 6 ] since it was found to possess catalytic properties for the dissociation of molecular hydrogen, as well as potential to protect metals from surface oxidation [ 7 ]. For these reasons, and also cognitive motivation, in two of our previous works, we investigated the ability of Mg–Ag alloys produced by mechanical milling [ 8 ] and classical melting and casting [ 9 ] to absorb hydrogen. The addition of Pb to this system is not beneficiary from a density point of view since it rather lowers the gravimetric hydrogen capacity of such alloys.…”