Jornal de Desenvolvimento de Drogas
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Differential Electrostatic Interactions between Granular Species in a Simple Hopper Chute Geometry

Saurabh Sarkar, Janet Cho and Bodhisattwa Chaudhuri

This article presents the findings from an experimental investigation assessing the role of different variables in determining electrostatic charges on a binary granular assembly in a simple hopper-chute set up. Several popular theories describing the generation and subsequent mitigation of static charges is reviewed and the experimental results are discussed in the light of those theories. A detailed discussion is provided on the significance of several variables considered important in the study performed under conditions representative of typical pharmaceutical manufacturing. A simple probability based model is presented which accounts for eventful contacts in a binary mixture. The theoretical arguments presented in the paper, backed by statistical analysis, lend insight into well-known but poorly understood phenomena. It is demonstrated that tribocharging of granular assemblies made of a single species on a given surface was observed in accordance with their work function difference. Mitigation of this generated charge increased linearly with concentration of addition of a second species before plateauing off at higher concentrations. The extent of charge reduction depends on interplay between the work function and hygroscopicity, and the number of contacts between the species involved.