Electrochimica Acta 130 (2014) 477–487 Contents lists available at ScienceDirect Electrochimica Acta j ourna l ho me page: www.elsevier.com/locate/electacta Characterization of electrical discharges during spark anodization of zirconium in different electrolytes Janaina S. Santos a , Sherlan G. Lemos b , Wesley N. Gonc ¸ alves c , Odemir M. Bruno c , Ernesto C. Pereira a,∗ a Universidade Federal de São Carlos, P.O.Box 676, São Carlos, Brazil b Universidade Federal da Paraíba, P.O.Box 5093, João Pessoa, Brazil c Universidade de São Paulo, P.O.Box 369, São Carlos, Brazil a r t i c l e i n f o Article history: Received 18 November 2013 Received in revised form 10 March 2014 Accepted 11 March 2014 Available online 22 March 2014 Keywords: Zirconium Oxide coatings Anodic film Spark anodization a b s t r a c t The evolution of the electrical discharges parameters during spark anodization of metallic Zr under gal- vanostatic regime have been investigated by image analysis in phosphoric and oxalic acid electrolytes. The experiments were recorder using a high-speed video camera during the entire anodization with a resolution of 1.7 ms for determination of discharge lifetime and a standard resolution of 33 ms (real-time imaging) for determination of the average area and discharge population density. The discharge behavior was dependent of the current density, electrolyte composition and anodization time. During breakdown process, sparks discharges are progressively turned to micro-arcs, which can be seen by enlargement of discharge area, gradual increase of lifetime and reduction of discharge population density. A factorial design was used to estimate the effects of experimental conditions on the discharge behavior. The current density and electrolyte composition were the most important factors that affected the discharge popula- tion density. The anodization time and the electrolyte composition were the main factor that influenced the discharge area and lifetime. In comparison with the voltage vs. time curve, the results demonstrate important features of the process and the changes of the electrical discharges characteristics during the experiments. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The anodization under high electric field is known, in the lit- erature, as Spark Anodizing, Plasma Electrolytic Oxidation (PEO) and Micro Arc Oxidation (MAO). This method is normally used for production of coatings in valve metals, such as Zr, Ti, Al and Ta, due to the formation of a thick oxide layer, rigidly adhered to the metal substrate, promoting corrosion resistance, thermal and wear protection [1–4]. This process is characterized by a series of simultaneous events such as voltage oscillations, oxygen evolution, local oxide crystallization and internal stress [5]. Besides, the for- mation of pores can occur if the electrolyte is oxide-dissolving [5]. The presence of a large number of short-lived electrical discharges at the electrode surface is also observed and it is associated to the localized electric breakdown of the growing oxide [1,5]. The breakdown is a complex phenomenon that influences the oxide properties. The anodic oxides obtained from valve metals have been ∗ Corresponding author. E-mail address: ernesto@ufscar.br (E.C. Pereira). investigated since 50’s, at the time, for development of new mate- rials for capacitors [6–8]. Several models have been proposed in the literature in order to explain the electrolytic breakdown observed during the growth of the anodic oxides from valve metals, such as electron avalanche [9–11], mechanical breakdown [12,13] and pit formation [13–16]. However, due its complexity, there is not a generally accept complete mechanistic overview of the break- down phenomenon in valve metal oxides. For this reason, studies are still being done in order to understand the fundamental aspects of breakdown [1,17,18]. In recent years, imaging techniques have been used to char- acterize the microdischarges parameters during the anodization of different metals such as Al, Ti, Mg and Ta under DC and AC regime [19–25]. Based on these studies, several mechanisms have been proposed to explain the electric breakdown phenomenon and the influence of the electrical microdischarges on morphology and microstructure of anodic films. Moreover, some authors suggest the modification of the morphology and microstructures properties of the oxide films by controlling the sparking during the process [22]. In order to investigate the relation between the growth of the oxide and the microdischarges during AC PEO of aluminium in alkaline http://dx.doi.org/10.1016/j.electacta.2014.03.052 0013-4686/© 2014 Elsevier Ltd. All rights reserved.