Anodisation of copper in thiourea-containing acid solution - Part II. In situ transversal imaging observations. Kinetics of anodic film growth

The formation of anodic films during the anodisation of copper, at differen t applied potentials E, in aqueous 0.5 M sulphuric acid containing differen t amounts of dissolved thiourea was investigated following the corroding el ectrode profile by on line in situ imaging. For E < 0.07 V (vs. SCE) the el ectro-oxidation of thiourea to formamidine disulphide and the electrodissol ution of copper to Cu(I)-thiourea complexes, including the formation of a p olymer-like Cu(I)-thiourea complex (film I), take place. For E > 0.07 V, th e main reactions are the electro-decomposition of formamidine disulphide an d Cu(I)-thiourea complexes yielding a copper sulphide-containing film (film II) and the electrodissolution of copper as aqueous Cu(II) ions through fi lm II. The relative contribution of these processes depends on thiourea con centration in the solution, the applied electric potential and anodisation time. The growth kinetics of films I and II were determined from the evolut ion of the average film height [h] obtained from in situ imaging. The kinet ics of him I fit a parabolic rate law, whereas those of film II approach a linear [h] versus anodisation time relationship. The rupture of film II ass ists the localised corrosion of copper. Likely physical mechanisms for the formation of these anodic films are discussed. (C) 2001 Elsevier Science B. V. All rights reserved.