Synthesis of AlH3 by a Ball-Milling Solid-Phase Chemical Reaction and Its Hydrogen Desorption Properties

The synthesis of AM, with LiAlH4 and AlCl3 was done by ball-milling solid phase chemical reaction under H-2 atmosphere. The effects of different milling times (4-20 h) on the solid state chemical reaction and dehydrogenation properties of the milled mixture were investigated comprehensively using X-ray diffraction (XRD), thermal analysis (TG-DSC), mass spectroscopy (MS), scanning electron microscopy (SEM), and dehydrogenation measurements. The milled reaction was found to proceed as follows: 3LiAlH(4) + AlCl3 -> 4AlH(3) + 3LiCl. The reaction was almost complete after milling for 20 h and amorphous AlH3 was formed. With an increase in milling time dehydrogenation kinetics was improved resulting in hydrogen desorption at a temperature lower than 100 degrees C. The maximum desorbed hydrogen capacities reached 2.6%-3.6% (w), which is close to the theoretical capacity of 4.85% (w) for the reaction. A decrease in the maximum desorbed hydrogen capacity can be attributed to the formation of LiCl center dot H2O and also to the decomposition of AlH3 during the milling process.