Electric explosion of steel wires for production of nanoparticles: Reactions with the liquid media

Abstract

Electric explosion (EEW) of iron and iron alloy wires (Fe, FeCrNi-ASI 304, and FeNiCo-Kovar) was performed in various liquid media (water, paraffin oil, ethylene glycol, siloxane) by injecting 1.2 × 10−18 J/atom energy. Products were collected separately in coarse and fine fractions and characterized by X-ray diffraction (XRD), scanning, transmission, and high-resolution transmission electron microscopies (SEM, TEM, HRTEM, respectively), Mössbauer spectroscopy, and prompt gamma activation analysis (PGAA). The dominant primary products in the coarse fractions are spherical metallic globuli modified either by direct interactions with the liquid media or by interactions with vaporized decomposition products of the liquid media. Fine fractions are formed in small quantities, and their compositions exhibit broad variety. Considering the morphology of this fraction, condensation is proposed as the dominant process of formation. The Kovar in siloxane case is an exception, and the mass of the fine fraction with decomposition products exceeds that of the metallic component in the coarse fraction. The main emphasis is placed on analysis of products in the fine fractions. In cases using water as the liquid medium, formation of oxide byproducts is dominant, i.e., wüstite is formed with iron, and mixed oxides FeCr2O4, (FeCr)2O3 and CrOOH are formed with FeCrNi steel. The fcc-to-bcc phase transition is also revealed in the latter case. In the case of the EEW process with iron in paraffin oil, the principal byproducts are carbon and carbonaceous residue. The carbonaceous coating layers are formed on the surface of particles, resulting in a core-shell structure, and carbon is also dissolved in the metal to form various carbide phases. For EEW of Kovar in ethylene glycol, the amount of carbonaceous byproducts is moderate, probably due to the formation and removal of gaseous byproducts (CO, CO2). In the Kovar-in-siloxane case, the main products result from decomposition of siloxane, and bcc and fcc metallic components are embedded into the siliceous oxide matrix in minor amounts. The formation of elemental silicon is also detected.A simplified summary scheme of processes is proposed to interpret the possible paths of reactions resulting in the formation of the products identified in EEW.