A great attention has been recently given to improve the existing hydrogen production technologies or to find new methods for hydrogen production. There are different types of methods available to produce hydrogen, such as biological processes, renewable energy sources [2] -[4] , catalytic steam reforming of natural gas, naphtha and other hydrocarbons, partial oxidation of hydrocarbons, gasification of coal and biomass resources and electrolysis of water [5] -[7] .

Metal particles such as Ni, Fe, V, Mn, Ti, Ag, Ca, Zn, Zr, Al, and their corresponding alloys can be potentially used to produce hydrogen through catalyst (water-soluble inorganic salts) assisted reactions in water [8] . Some lightweight meta-metals or their hydrides can produce hydrogen through reactions with water. In this method, the theoretical hydrogen production rates are as follows: 1 g of sodium borohydride gives 2.4 L of hydrogen; 1 g of aluminum gives 1.244 L with bayerite/boehmite formation; 1 g of magnesium gives 0.95 L, and Al and Mg hydrides give respectively 2.24 L and 1.88 L of hydrogen. Compared to other systems, aluminium has favorable features, such as cost-effectiveness, non-reactivity at normal conditions, easy storability, safety during transportation, and non-toxicity.

Several researchers have investigated various aluminum activation processes, such as treatment with iodine vapor, reaction at supercritical conditions, treatment of the metal surface with NaOH or KOH solutions, surface contact with activator metals (mercury, gallium, indium) and metal-alloys (gallium-indium eutectics) [9] -[11] . Activator metals remove the alumina layer and generate fractures on the aluminum core which is a potential way to enhance the reactivity of the aluminum. The mercury usage is creating health hazards and environmental problems. The gallium-indium eutectics seem to be the best choice to activate aluminum particle reactions with water.

Bennett and Pinnel [12] investigated the reactions of solid aluminum with liquid water and examined its products using X-ray diffraction, thermo-gravimetric and differential thermal (TG-DTA) analysis. Sheindlin and Zhuk [13] investigated the commercial possibility of hydrogen production using aluminum and its alloys. Wang et al. [10] analyzed the aluminum-based hydrogen production methods, their limitations and challenges for commercialization. Soler et al. [14] reported on the production of hydrogen using aluminum and aluminum alloys with aqueous alkaline solutions. Sarou-Kanian et al. [15] studied the low temperature reactivity of aluminum nano-powders with liquid water.

Kravchenko et al. [16] investigated the reaction of water with aluminum-based metal composites doped with gallium (Ga), indium (In), zinc (Zn), or tin (Sn) for hydrogen generation, using X-ray diffraction, DTA, and energy dispersive analysis (EDAX). Parmuzina and Kravchenko [17] demonstrated the method of aluminum activation by liquid eutectics Ga-In (70:30) and Ga-In-Sn-Zn (60:25:10:5) (galinstan), and the dispersion of the obtained specimens up to a particle size of <0.25 mm, leading to reactions with water and hydrogen production. The reaction temperature alters the resultant compounds and hydrogen yield [12] . As the reactions occur between water and aluminum at 50˚C to 100˚C, the reaction product is noticed as “pseudoboehmite”, which contains more hydroxyl ions than corresponding to A1OOH, i.e., the compound may vary from 1.5 to 2.5 H₂O per A1₂O₃.

At 25˚C, (Bayerite-β Al₂O₃∙3H₂O, formation)

At 90˚C, (Boehmite-α Al₂O₃∙H₂O, formation)

Ilyukhina et al. [18] investigated mechanochemical activation of aluminum using gallam metals which is processed in a high-energy ball mill.

In the present study, we have chosen the galinstan (Ga-In-Sn-Zn-60:25:10:5) eutectic, which gives optimized performances over Ga-In eutectics [17] . In this paper, we have addressed some of the associated problems in this aluminum activation method, and mainly the dependency of hydrogen production rate and yield on aluminum particle sizes, aluminum and galinstan eutectic content, and reaction temperature. The paper gives further explanation on the aluminum activation and its reaction with water. The paper also examines the effects of Al particles specific surface area and galinstan eutectic content on hydrogen production rate and yield.

We have examined three compositions of mixtures in this study, 85% Al-15% galinstan eutectics, 90% Al-10% galinstan eutectics and 95% Al-5% galinstan eutectics by mass. The galinstan eutectic composition is fixed as Ga-In-Sn-Zn (60:25:10:5). As the temperature of the activated-aluminum particle is increased by means of lighting, cracks are initiated and propagate. This is demonstrated in Figure 1. Hugo and Hoagland [19] reported that the ductile materials exhibit brittle fracture behavior because of interactions between the solid metal and the adsorbed liquid atoms. The liquid metal embrittlement may be caused either by tensile decohesion or enhanced shear. Such an action is explained by the effect of adsorptive decrease in solid strength under the physico- chemical influence of the medium. This effect is called Rebinder effect. The rate of liquid gallium penetration at the boundaries of the grains in the aluminum polycrystal can reach 0.55 to 30 µms⁻¹ at temperatures close to ambient [9] . These overall effects make the aluminum particles being readily reactive with water.

Three micron-sized Al particles are considered in the present study, namely 30 µm, 60 µm, and 350 µm. The hydrogen release rate is estimated at the temperatures of 30˚C, 50˚C, and 90˚C. Figure 2 shows the reaction rate and the hydrogen release rate of the activated aluminum mixtures with water at 30˚C. Figures 3-6 display the plots for the hydrogen release per gram of aluminum versus time for three mixture compositions.