Evolution of phase transition and oxidation of copper in electrical fires

摘要

Based on the theories of low-temperature plasma and metal solidification, the similarities and differences between anode melted marks (AMMs) and cathode melted marks (CMMs) in direct current (DC) short circuits were characterized, and the phase transition and oxidation of copper melted marks were analyzed. These data were used to ascertain which melted marks were suitable for identification of evidence of electrical fire materials. These parameters were assessed using metallographic microscopy, X-ray diffraction, laser micro-Raman spectroscopy, scanning electron microscopy and energy-dispersive spectrometry. The grain size of AMMs was 20-40nm and that of CMMs was 20-35nm at a DC of 600A. The oxygen: copper ratio on the three types of regions of AMM surfaces displayed an inverted U-shaped with increasing DC. The oxygen: copper ratio on rough surfaces was <1.3, on smooth surfaces were <0.8, and in gas holes were <1.2. Furthermore, the ratio on longitudinal sections of CMMs showed a similar trend, and was <0.8. Copper (I) oxide appeared only on the surfaces of SSMs (secondary short-circuited melted marks).