Luminescence during the anodization of zirconium

Abstract

In this paper, we have presented our recent investigation of luminescence during the anodization of zirconium in oxalic acid and 12-tungstosilicic acid water solutions. For the first time we have measured weak anodic luminescence (galvanoluminescence GL) during the anodization of zirconium and found strong influence of sample surface pretreatment, as well as of the current density, on luminescence intensity. Increased roughness of zirconium samples and higher anodization current density result in more intense GL. Spectral characterization of GL showed that there are wide GL bands present mostly in the range from 400 nm to 825 nm. As the anodization voltage approaches the breakdown voltage (about 380 V in oxalic acid and 480 V in 12-tungstosilicic acid), a large number of microdischarges appear superimposed on the GL. XRD and EDX measurements show that the main elements of the coating formed in oxalic acid are Zr and O, with ZrO 2 as dominant crystalline phase. The main elements of the coating formed by PEO process in 12-tungstosilicic acid are Zr, O, and W. The coating is partly crystallized and mainly composed of ZrO 2 and WO 3. The elements present in PEO microdischares indicate that plasma is generated in microchannels filled with anodic gas with water vapor during the anodization of zirconium in 12-tungstosilicic acid. During PEO in oxalic acid additional zirconium plasma is generated in micro channels across the oxide layer. © 2012 Elsevier Ltd.