Fracto-Electron Emission During Fracture of Engineering Ceramics

Abstract

An experimental study of the emission of fracto-electrons from engineering ceramics, such as alumina, zirconia, alumina/zirconia and silicon nitride, has been made under ambient atmosphere when they were fractured wi th a Charpy impact machine or by a power press machine. In these experiments, an indenter, made of a hard electro-conductive material, acted as an electrode to collect the emitted electrons; the collected electrons were fed into a high-sensitivity charge amplifier.The resul ts obtained showed that when the test specimen fractur~d, fracto-electrons were emitted. That, this was so, was confirmed by the simultaneous appearance of the electrical and acoustical signals. The total charge collected varied in a range of 10-11 to 10-9 C, depending on the fracture mode, fracture load and the nature the gaseous environment. The fracture surfaces of the specimens were electrified reaching potentials of the order of a few hundred volts. We believe that the origin of the fractoelectrons is the separation of the charges on the fracturing surfaces, which leads to the formation of an electric field and the liberation of exoelectrons which have sufficiently high energies to cause the ionization of the ambient gaseous atoms/molecules.