Effects of Oxidization and Adsorbed Moisture on Time Change in Tribo-electrification of Powder Particles [Translated]^†

Abstract

Tribo-electrification between aluminum target and grass beads has been studied experimentally based on the current generated by the electrification of grass beads. Effect of tangential velocity of impact on the current is investigated. As far as the velocity is low enough, the current shows positive value. However, for higher velocity, the current changes from positive to negative as the time elapses. Sudden increase or decrease in the velocity gives a respective current corresponding to each velocity. The fact means that the polarity of the current is solely determined by the tangential velocity as far as the target is not exchanged. Preservation conditions of the metal target affect on the polarity of the current. If the target is preserved in atmospheric condition for a day, positive current is generated firstly, decreased with time elapsed and finally negative current is generated. Two different experiments support that the polarity change found in this study is not related to the surface oxidization. Effect of water molecules adsorbed on the target surface has been investigated through heat treatment of the target. Higher temperature of the treatment causes the sharper decrease in the initial current, which suggests that the water molecules adsorbed on the target surface causes the change in the polarity of the tribo-electrification. Contact potential difference between particles and target also changes by heat treatment of the target.

Water Vapor Adsorption Effect on Silica Surface Electrostatic Patterning

“…1,8 A persistent problem is the difficulty to produce repeatable and previsible electric potential patterns 9,10 that cannot be solved unless the underlying charge-bearing species, transport phenomena, and chemical reactions are wellunderstood. This undesirable situation is well-documented in the literature, [9][10][11][12][13][14][15][16] and it requires new efforts for the speciation of charge carriers in insulators, as well as their quantification. 16 This problem has been addressed recently, and new proposals have been put forward by different authors.…”

“…Even after a few centuries of research by distinguished authors, electrostatic charging of insulators is still poorly known, and it often goes out of control because the identity of charge carriers is not known, in nearly every case in the laboratory or in a practical situation. , A persistent problem is the difficulty to produce repeatable and previsible electric potential patterns , that cannot be solved unless the underlying charge-bearing species, transport phenomena, and chemical reactions are well-understood. This undesirable situation is well-documented in the literature, − and it requires new efforts for the speciation of charge carriers in insulators, as well as their quantification . This problem has been addressed recently, and new proposals have been put forward by different authors. − Three different mechanisms for contact electrification were recently emphasized by McCarty and Whitesides: electron transfer for contact between metals or semiconductors, ion transfer for contact involving materials that contain mobile ions, and asymmetric partitioning of hydroxide ions between adsorbed layers of water for contact involving nonionic and insulating materials .…”