Enhanced Centrifuge-Based Approach to Powder Characterization: Establishment of a Size-Linked Effective Hamaker Constant Distribution

Many types of manufacturing processes involve powders and are affected by powder behavior. It is highly desirable to implement tools that allow the behavior of bulk powder to be predicted based on the behavior of only small (milligram-scale) quantities of powder. Such descriptions can enable engineers to significantly improve the performance of powder processing and formulation steps. An enhancement to the centrifuge technique was proposed for this purpose.

 

Simulations of the centrifuge technique were performed by calculating the removal of a simulated rough powder containing spheres with sinusoidal surface protrusions and intrusions from both nominally-flat surfaces and surfaces with well-defined indentations. The size distribution of the powder was based on an experimentally-determined distribution from a commercial silica powder. It was discovered that the adhesion of the rough spherical powder could be described in terms of an equivalent powder of smooth spherical particles with a size-dependent ‘effective’ Hamaker constant distribution.

 

Experimental validation of the simulation technique was performed with a silica powder dispersed onto nominally-flat stainless steel surfaces with no engineered surface features. The observed adhesion and removal of powder from the plates in the centrifuge was used within the simulation procedure to show its application to real systems. It was determined that the behavior of the rough, spherical powder could be represented with great accuracy by the expected behavior of an equivalent smooth, spherical powder with a size-dependent effective Hamaker constant distribution. In this manner, the roughness effects and size variations of a real powder are captured in this one distributed parameter (effective Hamaker constant distribution) which provides a substantial improvement to the existing technique. This can lead to better optimization of powder processing by allowing the behavior of topographically-complex powders to be described in terms of topographically-simple equivalent ones.