Contact Charging Between a Borosilicate Glass and Nickel

Abstract

The charging of borosilicate glass spheres rolling on clean nickel has been studied under controlled conditions of cleanliness, humidity, and gas pressure. Strong evidence indicates the process of charge transfer to be a type of contact electrification akin to that operating between two metals. The observed charging is, however, influenced by other factors. The amount of charge acquired increases with surface areas in contact and hence with distance rolled until other factors intervene. The rate of charging depends on rolling speed and surface conductivity of the borosilicate glass, while the maximum equilibrium charge depends on the pressure of the ambient gas. The gas pressure effect is shown to be caused by electrical discharge of the highly charged sections of the borosilicate glass to the metal, as suggested by E. W. B. Gill, and this causes a minimum equilibrium charge to occur about 1 mm air pressure, as observed by D. E. Debeau. The effect of transverse electrical fields reported by E. W. B. Gill and G. F. Alfrey is negligible for low surface conductivity but becomes important at higher surface conductivity, in particular above 40 percent relative humidity at 20°C.