A Walgreen Lecture

Granular Electrostatics

Troy Shinbrot
Rutgers University

Charged particle clouds frequently generate spectacularly devastating dust explosions in granular processing plants, and similarly sand becomes strongly electrified by helicopters traveling in desert environments, producing hazardous conditions. Likewise, sandstorms in the desert are well known to produce strong particle charging and consequent electrical disturbances. The issue of granular charging even has implications for missions to the Moon and to Mars, where charged dust degrades solar cell viability and clings to spacesuits, limiting the lifetime of their joints.

Despite the wide-ranging importance of granular charging, even the simplest aspects of its causes remain elusive. Thus several careful studies have confirmed (1) that identical materials - such as grains of sand in the desert - charge one another on contact, and (2) that insulating materials - which by definition have no free charge carriers to perform the task - transfer large amounts of charge. In this talk, we describe recent experimental and computational results demonstrating a novel mechanism by which identical fluidized grains can charge one another. We define optimal conditions for this charging to occur, and we describe several outstanding charging paradoxes that remain.