Electrical Characterisation of Powders

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United Kingdom

Experience in powder handling industry have shown that some powders exhibit flow problems when transported through pipes and hoppers, and also the tendency of particles to adhere to conveyor belts and machinery. These problems have been thought to be the cause of electrostatic charge build up on the powder particles. In some cases it has been observed that two almost identical powders will behave differently, one may cause flow and other problems whilst the second may be quite acceptable.

The aim of this short study was to measure a few electrical properties of some powders which caused problems and to compare them with those similar powders which did not give rise to any problems. The properties studied were:-

(i) Tribocharging characteristics of the powders.

(ii) Resistivity as a function of pressure.

(iii) Dielectric constant and spectroscopic analysis.

The tribocharging behaviour of the powders was studied by passing small quantities through different tubes, for example, copper, aluminium, perspex etc , and measuring the charge generated as a function of powder velocity and tube length. The magnitude and polarity of charge acquired by the powder determines the nature and severity of the problem.

The resistivity and dielectric constant both play a role in determining the build up of charge and rate of discharge. The higher the resistivity of a powder the longer it takes for the charge to leak away from it. The greater the dielectric constant the higher the charge it would acquire. Both these parameters were measured and compared for different powders. Spectroscopic analysis such as infra-red spectra of the powders were also compared.