Cavitation milling

Felmet, K. Olsofsky, M. Robertson, S. Starbuck, C. Tom, J. Tung, H.-H. Wang, J. An evaluation of cavitation milling to achieve particle size reduction of active pharmaceutical ingredients. AIChE Annual Meeting, Reno, Nevada, November, 2001. 

For removal of surface contamination, rust scale, mill scale, and other bound moieties by wet or dry abrasion (including surface layers of metal itself) by wet or dry abrasion, erosion, and/or cavitation processes... 

Wear impact plastic deformation makes some constituents more susceptible to corrosion. Cracks brittle constituents, tears apart ductile constituents to form sites for crevice corrosion, hydraulic splitting. Supplies kinetic energy to drive abrasion mechanism. Pressurizes mill water to cause splitting, cavitation, and jet erosion of metal and protective oxidized material. Pressurizes mill water and gases to produce unknown temperatures, phases changes, and decomposition or reaction products from ore and water constituents. Heats ball metal, ore, fluids to increase corrosive effects. 

This also implies that the main mechanism for crystal breakage is individual crystal breakage in the cavitation field rather than particle-particle interaction, which is more common for most wet-milling operations. The breakage constant of about 0.03 gm/hr per (gm/liter, watt) was found to hold for a number of small molecule organic compounds tested in the fluidized bed crystallizer system. 

Addle and Helmly (1989) measured the cavitations parameter against specifrc speed for a number of dredging pumps. Their work is represented in Figure 8-18. Tables 8-7 and 8-8 also show certain calculations for the design of mill discharge pumps. 

TABLE 8-7 Recommendations for Impeller Diameter, Speed, Specific Speed Number, and Cavitations Parameter for Rubber-Lined Mill Discharge Pumps (U.S. Units)... 

Other interesting processes include cryocrushing (Chakraborty et al., 2005) and ultrasonication (Zhao et al., 2007). Cryocrushing consists of pretreating libers with a laboratory beater PFI-type mill and lieezing the liber aqueous suspension with liquid nitrogen. The libers are nanolibrillated by the mechanical action of a cast iron mortar and pestie. In ultrasonication, ultrasound waves are applied to the liber aqueous suspension, and fibrillation is accomplished by the creation and collapse of microbubbles by acoustic cavitation. 

Pressurizes mill water to cause splitting, cavitation, and jet erosion of metal and protective oxidized material. 

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