Many industrial operations with powders result in particle surface melting, sintering, deformation and reaction at the inter-particle contact points. These phenomena are due to high temperatures, compression forces, the presence of moisture and/or liquids and subsequent solid-phase crystallization, and the formation of different chemical species. These processes are associated with a relative volume change of the bulk powder and result in agglomeration (usually desired) and caking (not desired).

The dilatometer is an instrument that allows one to measure small volume changes and is used routinely to measure the expansion coefficient of solid materials. During the present research, a dilatometer was modified to be used with powders and procedures were developed to employ it as a tool to detect the above phenomena. Examples are given to show the application of the method to powder processing such as fluidization [1] and storage of powders [2].

This work was extended lately to the micro-level containing two powder particles and the solidifying bridge between them. The study includes the observation and measurement of the strength of microscopic bridges between particles and, is yielding, for the first time, insight into the formation and development of structures that determine the properties of larger powder entities such as clumps, aggregates, granules and tablets [3].

References

1. Tardos, G.I. and R. Pfeffer, “Reaction Induced Agglomeration and Defluidization of Fluidized Beds", Powder Technology, 85, pp 29-35, (1995).

2. Purutyan, H., G. I. Tardos and B. H. Pittenger, “Understanding and Avoiding Caking of Bulk Powders”, pp. 22-29, Chemical Engineering Progress (CEP), May, (2005).

3. Tardos, G.I., L. Farber, D. Bika and J. N. Michaels, “Morphology and Strength development in solid and solidifying inter-particle bridges”, Chapter 28 in “Granulation and coating of fine particles”, A. Salman, M. Hunslow and J.K.S. Seville, Editors, Elsevier, (2006).