Studies of post-production ageing effects in atomised aluminium powder

The evolution of hydrogen gas from the reaction between a series of atomise d aluminium powder samples and 2.5 M HCl was monitored over time. The patte rn of hydrogen evolution in each case was similar in that after an initial period of slow gas production there was a rapid increase followed by slow g as production again. These studies also showed differences in the time take n to reach maximum hydrogen evolution for similarly aged powders. Lower pur ity aluminium powder (99.7 vs. 99.93%) or samples with a higher proportion of smaller particles reached the maximum rate of hydrogen evolution more qu ickly. Changes in the time taken to reach maximum gas evolution were also n oted for all the powders as they aged; the time to reach a maximum generall y increasing with time after atomisation. However, for each powder a short regression occurred between ca. 21 and 35 d. This suggests that changes con tinue to take place in the surface layer of the aluminium particulates long after atomisation has taken place.