Microstructural Transformation and Hydrogen Generation Performance of Magnesium Scrap Ball Milled with Devarda’s Alloy

Abstract

A method for magnesium scrap transformation into highly efficient hydroreactive material was elaborated. Tested samples were manufactured of magnesium scrap with no additives, or 5 and 10 wt.% Devarda’s alloy, by ball milling for 0.5, 1, 2, and 4 h. Their microstructural evolution and reaction kinetics in 3.5 wt.% NaCl solution were investigated. For the samples with additives and of scrap only, microstructural evolution included the formation of large plane-shaped pieces (0.5 and 1 h) with their further transformation into small compacted solid-shaped objects (2 and 4 h), along with accumulation of crystal lattice imperfections favoring pitting corrosion, and magnesium oxidation with residual oxygen under prolonged (4 h) ball milling, resulting in the lowest reactions rates. Modification with Devarda’s alloy accelerated microstructural evolution (during 0.5–1 h) and the creation of ‘microgalvanic cells’, enhancing magnesium galvanic corrosion with hydrogen evolution. The 1 h milled samples, with 5 wt.% Devarda’s alloy and without additives, provided the highest hydrogen yields of (95.36 ± 0.38)% and (91.12 ± 1.19)%; maximum reaction rates achieved 470.9 and 143.4 mL/g/min, respectively. Such high results were explained by the combination of the largest specific surface areas, accumulated lattice imperfections, and ‘microgalvanic cells’ (from additive). The optimal values were 1 h of milling and 5 wt.% of additive.

Enhanced Hydrogen Generation from Magnesium–Aluminum Scrap Ball Milled with Low Melting Point Solder Alloy

“…Therefore, for the tested conditions, materials, and ball milling parameters, 1 h appeared to be the optimal time. The existence of the optimal ball milling durations was reported in a number of previous studies for Mg and Al powders [89,92,94]. For all of the compositions, the 2 h kinetic curves had a distinctive acceleration section in the beginning (intervals from 0 to 10-15 min.…”

“…For each sort of sample, three repetitive experiments were carried out to obtain average kinetic curves and standard deviations. For the samples ball milled without additives, the particle sizes were estimated previously [89] using an optical microscope (Bio 6) with a camera (UCMOS 10,000 KPA; 'Altami' LLC, Saint Petersburg, Russia) and 'Altami Studio 3.5' software. The procedure included taking images under brightfield illumination, object (particles) contouring, and calculation of the contour sizes (maximum Feret diameters) using the calibration data.…”

“…The elemental compositions were estimated by the energy-dispersive X-ray spectroscopy (EDX) method. The SEM-EDX analysis was carried out by a scanning electron microscope TESCAN VEGA3 ('Oxford Instruments' PLC, Abingdon, United Kingdom) for all samples except those ball milled without additives whose images were taken previously For the samples ball milled without additives, the particle sizes were estimated previously [89] using an optical microscope (Bio 6) with a camera (UCMOS 10,000 KPA; 'Altami' LLC, Saint Petersburg, Russia) and 'Altami Studio 3.5' software. The procedure included taking images under brightfield illumination, object (particles) contouring, and calculation of the contour sizes (maximum Feret diameters) using the calibration data.…”

Effects of Bi–Sn–Pb Alloy and Ball-Milling Duration on the Reactivity of Magnesium–Aluminum Waste-Based Materials for Hydrogen Production

“…As demonstrated in the previous studies [ 67 , 109 ], prolonged ball milling (2–4 h) combined with a relatively high 20 wt.% of low melting point Wood’s alloy diminished the hydrogen production performance for the samples produced of the same metal scrap. The measured specific surface areas of the original Mg scrap and samples ball milled for 0.5, 1, 2, and 4 h were respectively 2.567, 2.036, 2.022, <0.1, and 0.943 m 2 /g [ 109 ]. This nonmonotonic trend was caused by the microstructural evolution of the samples’ particles affected by competing agglomeration and disintegration processes driven by impacts from steel milling balls.…”

Silver-Assisted Hydrogen Evolution from Aluminum Oxidation in Saline Media

“…Although no visual evidence of silver oxidation and cold welding was observed, the swarf particles were flattened but still too large in size, and the silver particles did not look attached to them. Heavier balls were expected to accelerate the structural evolution of aluminum particles: flattening, accumulation of microstrains and embrittlement, and further progress of two competing processes of fracturing in the hardened regions and agglomeration of the resulting smaller pieces caused by cold welding (first, into flattened lamellar structures, and finally, into compacted equiaxed solid shapes) [ 61 , 103 , 104 , 105 ]. However, in the present study, the base material was represented by quite large pieces, several mm in size.…”