How tribo-electric charges modify powder flowability - 2016

The presence of electrostatic charges inside a powder is known to influence drastically thematerial flowing properties.The triboelectric charges produced at the contacts between the grains and at the contacts between the grainsand the container produces electrostatic forces.On the one hand, the triboelectric effect is useful for many applications, but on the otherhand, the triboelectrification causes complications.Unfortunately, the triboelectric effect is still poorly understood, even at the fundamental level.The difficulties are related to the non-equilibrium character of the tribolectectric dynamic and to the variety of mechanisms behind this effect.Moreover, reproducible electrostatic measurements are difficult to perform.We developed an experimental device dedicated to the measurement of powder triboelectric properties.This device measures the ability of a powder to charge electrostatically during a flow in contact with a selected material.This measurement is performed at controlled hygrometric conditions.We present the results of an experimental study involving different powders and granular materials.The relation between the powder electrostatic properties, the hygrometryand the flowing behavior is analyzed.