Cold Gas-Dynamic Spray for Catalyzation of Plastically Deformed Mg-Strips with Ni Powder

Abstract

Magnesium hydride (MgH₂) has received significant attention due to its potential applications as solid-state hydrogen storage media for useful fuel cell applications. Even though MgH₂ possesses several attractive hydrogen storage properties, it cannot be utilized in fuel cell applications due to its high thermal stability and poor hydrogen uptake/release kinetics. High-energy ball milling, and mechanically-induced cold-rolling processes are the most common techniques to introduce severe plastic deformation and lattice imperfection in the Mg/MgH₂. Furthermore, using one or more catalytic agents is considered a practical solution to improve both the de-/rehydrogenation process of MgH₂.These treatments are usually dedicated to enhance its hydrogen storage properties and deduce its thermal stability. However, catalyzation of Mg/MgH₂ powders with a desired catalytic agent using ball milling process has shown some disadvantages due to the uncontrolled distribution of the agent particles in the MgH₂ powder matrix. The present study has been undertaken to employ a cold gas-dynamic spray process for catalyzing the fresh surfaces of mechanically-induced cold-rolled Mg ribbons with Ni powder particles. The starting Mg-rods were firstly heat treated and forged 200 times before cold rolling for 300 passes. The as-treated ribbons were then catalyzed by Ni particles, using cold gas-dynamic spray process. In this catalyzation approach, the Ni particles were carried by a stream of Ar gas via a high-velocity jet at a supersonic velocity. Accordingly, the pelted Ni particles penetrated the Mg-substrate ribbons, and hence created numerous micropores into the Mg, allowed the Ni particles to form a homogeneous network of catalytic active sites in Mg substrate. As the number of coating time increased to three times, the Ni concentration increased (5.28 wt.%), and this led to significant enhancement of the Mg-hydrogen storage capacity, as well as improving the de-/rehydrogenation kinetics. This is evidenced by the high value of hydrogen storage capacity (6.1 wt.% hydrogen) and the fast gas uptake kinetics (5.1 min) under moderate pressure (10 bar) and temperature (200 °C). The fabricated nanocomposite MgH₂/5.28 wt.% Ni strips have shown good dehydrogenation behavior, indicated by their capability to desorb 6.1 wt.% of hydrogen gas within 11 min at 200 °C under 200 mbar of hydrogen pressure. Moreover, this system possessed long cycle-life-time, which extended to 350 h with a minimal degradation in the storage and kinetics behavior.

Keywords: catalyzation; cold-spray technology; cycle-life-time; de/rehydrogenation kinetics; severe plastic deformation.

Figure 1

(a) During hydrogen-RBM of Mg doped with 5.5 wt.% Ni powders, a ball-powder-ball collision occurs. In (b) and (c), FE-SEM micrographs of the cross-sectional view of the powders obtained after 6 h and 12.5 milling, respectively, are shown. The FE-SEM micrographs of the powders milled for 50 and 100 h, respectively, are shown in (d,e), respectively.

Figure 2

(a) Induction melting furnace hosted the Mg-rods, (b) forging process, (c) cold rolling process, (d) schematic illustration of drawing a Mg bar, using two-drum cold roller machine, (e) warm pressing, (f) original Mg-rod (i), Mg-strip obtained after forging at 400 °C for 200 times (ii), (iii) final product after re-cold rolling for 10 passes. Final product of Mg ribbons obtained after 300 passes of cold rolling, and (g) array of snipped Mg-strips ready for coating with Ni powders, using cold spray technique.

Figure 3

(a) The cold-rolled Mg ribbons (1) were placed and fixed on stainless steel plate by clips (2); (b) two-movable jaws (3) were used to fix the ribbons that was aligned perpendicular (5) to the cold spray (CS) gun nozzle (6). In the image above (c), the Mg-ribbons have been coated three times with Ni powders. To ensure straightening, the uncoated Mg-strips were wrapped in balance papers and put in a two-jaw style vise for 16 h (d), and then CR for 10 times (e).

Figure 4

(a) Cold-spray experimental set up, and (b) schematic presentation of the coating CS process of Mg-ribbons, using supersonic Ni powder particles. The subsonic and supersonic zones within the nozzle gun are depicted in the figure (b).

Figure 5

XRD patterns of the raw Mg-rods before and after cold rolling are shown in (a,b), respectively.

Figure 6

FE-HRTEM image of (a) the starting Mg-rods and (b) the corresponding FE-HRTEM image of Mg-rods drawn for 300 passes of cold rolling.

Figure 7

Low magnification BFI of raw Mg-rods obtained after cold rolling for (a) 0 passes and (b) 10 passes. The low magnification FE-SEM micrograph of Mg-rods obtained after 100 passes is displayed in (c), where the STEM of the rods drawn for 300 passes of CR is shown in (d).

Figure 8

Schematics (a,c,e) and FE-SEM micrographs of Ni powders (b,d,f) pelted into Mg-substrate strips.

Figure 9

FE-HRTEM with atomic resolution of a selected zone of Mg-strip coated with 3 Ni powder layers, using the cold spray process. The FE-HRTEM with atomic resolution of a selected zone of Mg-strip coated with 3 Ni powder layers, using the cold spray process is presented in (a). The corresponding image of scanning transmission electron microscope (STEM) is presented in (b).

Figure 10

Scanning electron images (SEIs) of Mg-strips coated with Ni powder particles (a) 1-time, (d) 2-times, and (g) 3-times. The corresponding EDS elemental maps for Mg in the samples coated 1-, 2-, and 3-times are presented in (b), (e) and (h), respectively. The Ni-EDS maps of the CS samples obtained after 1-, 2-, and 3 coatings are presented in (c), (f), and (i), respectively.

Figure 11

HP-DSC thermograms of (a) the as-received Mg rods, as-cold rolled rods, as-cold rolled that were cold sprayed with Ni powders 3-times and (b) Mg-rods that were cold rolled 300 times and then cold sprayed with Ni powders 1-, 2-, and 3-times. The HP-DSC thermograms measured with different heating rates, k (10, 11, and 12 °C/min) of cold rolled Mg-rods for 300 times and then cold sprayed with Ni powders for 3 times are displayed in (c) together with Arrhenius plot of hydrogenation (d). The He-atmospheric pressure DSC thermograms measured with different k values (5, 10, 20, 30, and 40 °C/min) of cold Mg-rods that were cold rolled 300 times and then cold sprayed with Ni powders for 3 times are presented in (e).

Figure 12

The HP-DSC thermograms measured with different heating rates, k (10, 11, and 12 °C/min) of cold rolled Mg-rods for 300 times and then cold sprayed by Ni powders for 3 times are displayed in (a) together with Arrhenius plot of hydrogenation (b). The He-atmospheric pressure DSC thermograms measured with different k (5, 10, 20, 30, and 40 °C/min) of cold rolled Mg-rods for 300 times and then cold sprayed with Ni powders for 3 times are presented in (c).

Figure 13

Hydrogenation kinetics of the as-received Mg-rods, Mg-rods that were cold rolled for 300 passes, Mg-rods that were cold rolled for 300 passes and then cold sprayed with Ni powders 1-, 2-, 3 times; and ball-milled MgH₂/5.5 wt.% Ni obtained after 50 h of milling. The measurements were conducted at 150 °C/10 bar.

Figure 14

Hydrogen released kinetics of raw Mg-rods; Mg-rods that were cold rolled for 300 passes, Mg-rods that were cold rolled for 300 passes and then cold sprayed with Ni powders 1-, 2-, 3 times; and ball-milled MgH₂/5.5 wt.% Ni obtained after 50 h of milling. The measurements were conducted at 200 °C/200 mbar.

Figure 15

XRD patterns of Mg-strips that were cold rolled for 300 passes and then cold sprayed with Ni 3 times after completion of the (a) hydrogenation and (b) dehydrogenation measurements.

Figure 16

Cycle-life-time of Mg-strips that were cold rolled for 300 passes and then cold sprayed with Ni 3-times.