Electrification due to the separation of materials

Most dielectric materials acquire an electrostatic charge when brought into contact with, and then separated from, a dissimilar material. If the contacting materials are identical, electrification is observed when the two bodies are asymmetrically rubbed together. Electrification is also obtained if a dielectric material, such as mica, is simply cleaved into two parts. Since dielectric materials are good insulators, charge accumulated on a dielectric body decays very slowly. Charge retention on dielectric materials usually represents a nuisance (shocks, dust collection, etc.) or a hazard (explosion of fuels, powders, etc.). On the other hand, the motion of small dielectric particles can be controlled via an electric field if the particles acquire an electrostatic charge by contact and separation from other materials. The ability to manipulate charged particles with an electrostatic force is utilized in the electrophotographic copying process, spray painting, and separation of ores.