I am trying to distinguish different zirconia powders based upon flowability. The goal is to determine a method for determining if the powders will flow in a pressurized hopper.

I have tried a Hall flowmeter and the powder does not flow. I had to place a 10mm opening Hall flowmeter on a shake plate to get flow times. The flow times do not represent what is observed in the pressurized hopper. I have measured particle size, bulk density, and surface area and cannot find a strong connection. The particles are D50 ~15micrometers and I cannot observe a difference in the distribution just by looking at the data.

What else can I look at to help distinguish between powders? Also with particle size how much effect could a difference of 1 or 2 microns in the D50 value have on flowability and/or a 0.5% increase in submicron particles? ■