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The FT4 is supplied with a variety of accessory kits, including the Aeration Control Unit, which allows fine control of air flow through powders under test to evaluate fluidisation behaviour. The bulk properties of powders are affected by the presence of entrained air which fills the spaces between particles. The removal or addition of this air can radically change the flow properties of a powder - often by a factor of 100 or even 1000. When aerated, the contact between particles is reduced and less energy is required to cause flow. For some powders, complete separation of individual particles results in fluidisation when the powder behaves as a fluid. This reduction of flow energy is described by the Aeration Ratio (AR), which can be measured automatically using the Aeration Control Unit on the instrument.

The Aeration Control Unit is under the direct control of the FT4's control system allowing the following types of automated testing, with no operator involvement:

• Aeration or fluidisation assessments to determine response to increasing levels of aeration - up to fluisation velocities where appropriate
• De-aeration testing to determine how readily a given powder releases entrained air following aeration
• Permeability profiles derived from measurements of pressure drop across a powder bed at varying levels of consolidation stresses

With an operating range down to a velocity of 0.02mm/s, this Unit also delivers the high degree of control at very low rates that is essential for characterising powders sensitive to the addition of a very small quality of air.

For more information on the FT4 Powder Rheometer, please visit the Freeman Technology website.