Powder testing equipment is used to measure the static and dynamic properties of powders for pharmaceutical, coating, and other solid-particulate applications. Powders are collections of solid particles that are surrounded by air or fluid. The variability of a powder is a function of its physical properties, environmental factors, and changes to individual particles. In terms of physical properties, powder testing equipment can be used to measure attributes such as angularity, elasticity, hardness, porosity, size, shape, and texture. Environmental factors for powder analysis include moisture content, external pressure, and vibration. Changes to individual powder particles are caused by factors such as agglomeration, attrition, chemical composition, and electrostatic charge.
Powder testing equipment is used to examine powders in conditioned, variable flow, compact or consolidated, and aerated states. Typically, powder testing begins after a full powder-conditioning cycle is complete. To determine whether the powder has the proper rheology, the basic flowability energy (BFE) is determined. Measured in millijoules (mJ), BFE is the energy to displace a constant volume of conditioned powder at a specific flow pattern and flow rate. Samples are measured with either the constant mass method, or one of several conditioned volume procedures. Powders that are in a non-conditioned state are measured according to stability index (SI), flow rate index (FRI), compaction index, or aeration ratio (AR). Test programs are available with most powder testing equipment.
Selecting powder testing equipment requires an understanding of parameters other than flow energy (BFE). Stability index (SI) refers to the ratio between test samples where a stable powder has a value on one. Flow rate index (FRI) measures changes to BFE when the flow rate of a standard test is reduced by a factor of 10. Powders with a high FRI are often difficult to process because their flow energies and flow behavior are variable. Powder testing equipment is also used to measure the aeration ratio (AR), a value that may range from less than 1.5 to more than 1000. By definition, this ratio is the factor by which BFE is reduced when a powder sample is aerated fully. Powder testing equipment that measures aeration indicates how air passes through a powder mass, and indicates the necessary bed disturbance for air to penetrate the powder.