PHYSICAL BEHAVIOR OF WATER-ATOMIZED IRON POWDERS - EFFECTS OF RELATIVE-HUMIDITY AND PARTICLE-SIZE

A study has been completed to determine the effects of particle size a nd atmospheric relative humidity on the behavior of a loose water-atom ized iron powder. Measurements obtained with both a Hall flowmeter and an Arnold Density Meter indicated that the apparent density (AD) of o ne particular lot of water-atomized iron powder varied systematically with particle size and relative humidity (RH). As the particle size of a powder fraction is increased, its apparent density declined. Above a certain 'threshold' humidity level, both the AD and flow time of the as-received powder and its size fractions changed significantly. The effects of threshold humidity on both of these variables were irrevers ible. The behavior of the iron powder as a function of increasing RH h as been found to be related to the amount of adsorbed water vapor and ultimately to the start of corrosion on the particle surfaces. The Arn old Density Meter is most suitable for obtaining a complete set of AD measurements for a powder and its size fractions over the entire spect rum of relative humidity.