FRACTOEMISSION DURING FRACTURE OF ENGINEERING CERAMICS

An experimental study of the emission of fracto-electrons from enginee ring ceramics, such as Al2O3, ZrO2, Al2O3/ZrO2, and Si3N4, has been ma de under ambient atmospheric conditions when they were fractured with an indenter mounted on the arm of a Charpy impact machine or by a powe r press machine. In these experiments, the indenter, made of a hard el ectro-conductive material, acted as an electrode to collect the emitte d electrons; the collected electrons were fed into a high-sensitivity charge amplifier. The results obtained showed that, when the test spec imen fractured, fracto-electrons were emitted. This was confirmed by t he simultaneous appearance of the electrical and acoustical signals. T he total charge collected varied in the range of 10(-11)-10(-9) C, dep ending on the fracture mode, fracture load, and the nature of the gase ous environment. The fracture surfaces of the specimens were found to be electrified, reaching potentials of the order of a few hundred volt s. We believe that the origin of the fracto-emission of electrons is t he separation of the charges on the fracturing surfaces, which leads t o the formation of an electric field and the liberation of exoelectron s; these electrons are of sufficiently high energies to cause the ioni zation of the ambient gaseous atoms/molecules.