Abstract
Tribo-electrification due to collisions of glass beads onto an aluminum plate was studied by measuring the current generated by the electrification of glass beads. When the tangential velocity component upon impact was relatively low, the current was always positive. However, at a higher tangential velocity, the current changed from positive to negative as the collisions continued. When the tangential velocity component was changed abruptly, the current changed its polarity according to the tangential velocity component, suggesting that the polarity of current was determined only by the tangential velocity. It was further shown that the property of metal surface affects the polarity of current. When we used a target which was left under atmospheric conditions for a day, the positive current generated by the collisions gradually decreased with time and eventually becomes negative. Two independent experiments supported that the polarity change found in this study was not related to surface oxidization.
The effect of water molecules adsorbed on the target surface was investigated by thermally desorbing the water from the target. Desorption at a higher temperature resulted in a sharper decrease in the current, which suggests that the water molecules adsorbed on the target surface was one of the main factors which led to the polarity change in current generated by the tribo-electrification.
