Triboluminescence and Triboelectrification by the Motion of Mercury Over Glass Coated with Scintillator Dyes

The conversion of mechanical energy into electrical energy and light (triboelectrification and tr iboluminescence) by the movement of mercury over glass surfaces coated with scintil lator compounds was investigated. The motion of mercury over the coated glass involves the bu i ld-up of potential differences in excess of 20V; the na ture of these triboelectric potentials differs signif icantly from those observed in the absence of scintil lator coating. Twelve scintil lator compounds were investigated with the observed luminescence being characteristic of the coating material. Interracial processes can generate potentials of vary ing magnitude, and from a fundamenta l aspect, these vol tage-producing interracial processes involve energy conversion. Scinti l lator compounds are characterized by a relat ively efficient conversion of one form of energy into another; that is, in the usual experimenta l situation, the kinetic energy of high energy particles is converted into light energy. The study was concerned with the electrification, i.e. the separation of electrical charges, which occurs upon rubb ing together dissimilar materials, a process termed "triboelectrification" or sometimes "static electrification." The related optical phenomenon is called tr iboluminescence (1), the emission of light when certain materials are rubbed or certain crystals are crushed. It has been known for a long time that triboelectrification and tr iboluminescence occurs when mercury moves over a glass surface in the presence of inert gases. For example, Picard (2) in 1675 observed a "whitish glow" in a Torricelli barometer. He at t r ibuted this to some "phosphors" ostensibly present as impurities. The explanat ion that is in general agreement with present thinking, namely, that a static electric charge builds up, was first put forth by Huksbee (2) in 1705. Recent workers in this field have observed chemical reactions in a triboelectric discharge (3, 4) and have studied the spectra of light generated by the relative motion of contiguous surfaces of mercury and glass (5-7). In related experiments, contact electrification potentials as high as 100V have been measured (8). While many details of the basic mechanism remain obscure, the process involves charge separation at the mercuryglass interface with the subsequent charge recombinat ion reaction being energetic enough (>20 eV) to pro* E l e c t r o c h e m i c a l Soc ie ty S t u d e n t Member . ** E l e c t r o c h e m i c a l Soc ie ty A c t i v e Member .