(261c) Breakage of Structured Particles: A Comparison between Stress-Strain and Impact Events

The breakage of structured particles is important in the food, automotive, electronic, and ceramic industries. Many of the structured particles created consist of relatively uniform or well-graded primary powder particles designed to have minimal segregation that are then made into larger particles that have intricate structures and designs. The tendency for structured particles to break depends on the strength of the bonds formed between the primary particles as well as on the structure of the larger particles. Breakage also depends on the set of forces that act on a structured particle during a breakage event. A population balance model is a reasonable means to describe breakage events and can be used to examine how breakage might occur. However, current formulations of the population balance model do not include the effects of global structure on breakage. They also do not include the effect of particle scale bond strengths, nor do they include any description of the influence of the different types of stress-strain or impact-induced stresses that are present with the material during processing. There is a difference between the breakage mode when the primary influence of breakage events consists of impact events as compared to stress-strain events.

The goal of this paper is to look at particle scale strength as a function of particle size distribution and then examine the differences in breakage of structured particles during stress-strain events versus impact events. A population balance model is used to determine the breakage selectivity coefficients. These coefficients are then correlated with the mode of breakage (impact versus stress-strain) using FEM models of stress induced by each type of breakage. However, the breakage rate constants are correlated to the strength as a function of the particle size distribution of the primary particles. Combining the breakage pattern computed by FEM analysis of particles with particle scale strength models and the population balance model provides a rich toolset to understand and predict breakage. A set of structured particles (balls, rods, crosses, and grid-shaped) were created from a consistent set of cohesive particles. These particles were then subjected to stress-strain events and impact events. The breakage studied by the population balance model and FEM analysis of structured particles were used to determine the breakage selectivity behavior. A polydisperse particle scale strength law was used to determine strength as a function of the primary particle size which was correlated to the breakage rate constants.