Pressure-Temperature-Humidity-Time
Powders and granular materials are unique in terms of industrial materials in that they can remember their stress and environmental history. In other words, a powder can change depending on how it is handled and stored. For example, if a powder is stored in an industrial tote containing a 1 ton mass, the gas in the powder will be removed (compressibility) and the powder particles may form large particles (agglomerates) due to the pressure acting on the particles. If stored long enough in this way, the powder may actually become a solid (caking). When the pressure is removed, the powder may or may not go back to its original condition before storage.
