(54l) Triboelectric Charge of Spherical Glass Particles Against Metal Pipeline

These days, powders are used in many ways such as in food, pharmacies, and the chemical industry. Usually, powders are highly charged when friction or collision occurs. This electrostatic charging phenomenon may lead to problems including inter-particle cohesion, particle-wall adhesion, a production efficiency decrease.

This experiment is mainly on how much the electrostatic charge (charge to mass ratio, q/m [C/kg]) of glass particles are affected by the size of powder and air pressure. A spiral air type apparatus that evaluates the q/m on particles and two different sizes of spherical glass beads were used in this experiment. The apparatus mainly consists of four parts; an air apply part for controlled air duration and pressure, a powder apply part for setting the deserved amount of powder (1 g in this experiment), a metal pipe line part for generating the tribocharge, and a cyclone part for collecting and evaluating the q/m of the powder that passed through the pipe line. During the experiment, the metal pipe line was grounded electrically.

As the result, in all of the tests, all glass particles were shown as positively charged. This agrees with the triboelectric series between metals and glass particles due to the work function. The smaller particles (50 % volume-average, D50: 100 mm) had a larger q/m than the larger one (180 mm) with good reproducibility. For example, at 0.3 MPa, the smaller had an average of 95.4 nC/g while the larger had an average of 80.6 nC/g. This is because the total surface area of all of the smaller beads combined is greater than the total of the larger ones. The q/m increased as the supplied spiral air pressure increased, in the order of 47.8 nC/g (0.1 MPa), 61.2 nC/g (0.15 MPa), 67.4 nC/g (0.2 MPa), 74.4 nC/g (0.25 MPa), and finally, 80.6 nC/g (0.3 MPa) when the larger powder (180 mm) was used. The more the supplied spiral air pressure, the chances of collision and the force of the contact increases.