Studies of Mechanochemically Activated Aluminum Powders for Generating Hydrogen from Water

Commercially available aluminum PA-4 and ASD-1 powders were mechanochemically activated by Ga-In-Sn or Ga-In-Sn-Zn eutectic alloys (5 wt.%) and graphite (1-3 wt.%) in a mixer type ball mill. Subsequently, they were pressed (P = 4 MPa) into the pellets used to generate hydrogen from water via the hydrolysis process. X-ray diffraction study of the milled PA-4 powder revealed the presence of four phases, including aluminum, graphite, and two In-Sn intermetallic compounds (In3Sn and In1-xSnx, were x approximate to 0.04). SEM morphological characterization of the surfaces of the prepared pellets showed the presence of clear interfaces between the grains of aluminum. The quantitative analysis by EDX showed a uniform distribution of the activating additives over the pellet surface, where the graphite was also partly aggregated. Studies on the hydrolysis kinetics of Al-based pellets demonstrated that it readily proceeds at temperatures of >= 5 degrees C. At the same time, the efficiency of hydrogen generation depends on the amount of the added graphite, particle size of aluminum powders, duration of their mechanochemical treatment, and the hydrolysis temperature. The introduction of graphite and eutectic alloys into the aluminum powders during their mechanochemical treatment significantly accelerate the hydrolysis process. Besides, the process is faster, the more graphite is added. The obtained values of the hydrogen evolution rate and hydrogen yield during the hydrolysis of pellets from finer ASD-1 powder exhibit significantly superior performance compared to pellets' hydrolysis from coarser PA-4 powder. Increased duration of aluminum powders mechanochemical treatment from 1 to 4 h results in a significant increase in the hydrolysis rate of the prepared pellets and hydrogen yield. The rise of hydrolysis temperature from 5 to 25 degrees C lead to an increase in the hydrolysis rate during its active stage.