The flat blades are smaller in size than the angled blades. Therefore the hold-up increased due to a reduction in the total blade area available for powder transport when using this blade configuration. Blade configuration #3 was composed of the angled and flat blades, with a 1/3 blade configuration that alternated the orientation of the blades by directing the flow forward and then backwards. This alternating configuration, in the second third of the impeller, was expected to increase the recirculation of the powder and, thus, the hold-up. For blade configurations #4 and #5, the use of the small blades in the impeller substantially decreased the amount of powder that could be transported through convection by the impeller. The alternating blade configuration in configuration #5 also created substantial recirculation in the second half of the impeller yielding the highest hold-up.