Acoustic propagation and multiple scattering in powders

Abstract

Determination of the material properties of powders is critical in very many industries yet crucial transformations such as the transition from a free-flowing powder to a caked powder defy quantitative measurement. In particular, distinguishing between the onset of caking (so that it may be prevented, for example) and consolidation or segregation of powders which have not caked is very difficult. We present here calculations of the acoustic properties of free flowing powders based on scattering theory (Alba, 2004), together with model calculations for caked and consolidated powders within which an effective stiffness has developed (Coghill 2011, Makse 2004). These calculated values are compared with the measured acoustic properties of silica powders demonstrating that acoustic measures such as the velocity of sound and the attenuation of sound (insertion loss) are highly effective in distinguishing between caking and consolidation. Alba. 2004, Chapter 10 of “Concentrated dispersions, theory, experiments, and applications,“ edited by P. Somasundaran and B. Markovic, American Chemical Society (ACS) Symposium Series 878. Coghill and Giang, Powder Technol. 208, 694–701, 2011. doi:10.1016/j.powtec.2010.11.040. http://dx.doi.org/10.1016/j.powtec.2010.11.040. Makse, Gland, Johnson, and Schwartz, Phys. Rev. E70, 1–19, 2004. doi:10.1103/PhysRevE.70.061302.