FRACTOEMISSION DURING FRACTURE OF ENGINEERING CERAMICS

An experimental study of the emission of fracto-electrons from engineering ceramics, such as Al2O3, ZrO2, Al2O3/ZrO2, and Si3N4, has been made under ambient atmospheric conditions when they were fractured with an indenter mounted on the arm of a Charpy impact machine or by a power press machine. In these experiments, the 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 results obtained showed that, when the test specimen fractured, fracto-electrons were emitted. This was confirmed by the simultaneous appearance of the electrical and acoustical signals. The total charge collected varied in the range of 10(-11)-10(-9) C, depending on the fracture mode, fracture load, and the nature of the gaseous environment. The fracture surfaces of the specimens were found to be electrified, reaching potentials of the order of a few hundred volts. We believe that the origin of the fracto-emission of electrons is the separation of the charges on the fracturing surfaces, which leads to the formation of an electric field and the liberation of exoelectrons; these electrons are of sufficiently high energies to cause the ionization of the ambient gaseous atoms/molecules.