Analysis of a Simple Test Device for Tribo-Electric Charging of Bulk Powders

We have developed a simple device to characterise the tribo-electric charging propensity of powders. A sample of around one gram of powder is shaken in a container by reciprocal strokes in a horizontal direction. The electric charge on the powder is quantified by a Faraday cup before and after shaking. In this paper, we analyse the operation of this simple test device by investigating the behaviour of a-lactose monohydrate (a-LM), hydroxy propyl cellulose (HPC) and a 50 :50 binary mixture (by mass) of these two powders with various container surfaces commonly used in the pharmaceutical industry. The experiments are carried out in controlled environmental conditions and using different shaking times and frequencies of 10, 20 and 30 Hz. The experimental results show that the saturated charge is independent of the shaking frequency. Furthermore adhered particles coating the inner surface of the shaking container decrease the net amount of charge generated by up to 50%.