Structural features of ultrafine powders, generated in conditions of wire electrical explosion

Abstract

During several decades the question of the presence or absence of Laplace compression in particles less than 0.1 microns, has been discussed. A consequence of this compression could be an increase of X-ray density in small particles. The study of the structure of final products of wire electrical explosion (ultrafine powders, UFP) has shown that their X-ray density is lower than for metals in a stable massive condition. It is shown that the metals (Al, Cu), not having polymorphic modifications are characterized by a specific defect type-static displacement of atoms concerning X-ray density, lowered up to 0.1-0.2%. In the case of polymorphism of UFP metals, the crystal modifications with lowered density are stabilized: iron as /spl gamma/-Fe, tungsten as /spl beta/-W. As regards formation of chemical compounds, oxide UFPs are also formed with lowered X-ray density (/spl gamma/-Al/sub 2/O/sub 3/, TiO/sub 2/).