409 J. Indian Chem. Soc., Vol. 94, April 2017, pp. 409-417 Steady state kinetics of formation of oxide films on niobium and tantalum metals in malic acid electrolyte at different temperatures Naveen Verma*, Jitender Jindal and Krishan Chander Singh Department of Chemistry, Maharshi Dayanand University, Rohtak-124 001, Haryana, India E-mail : vermanaveen17@gmail.com Manuscript received online 30 November 2016, accepted 10 December 2016 Abstract : Steady state kinetic data from anodic polarization of niobium and tantalum metals under galvanostatic con- ditions have been obtained over wide range of temperatures and at different current densities in malic acid electrolyte. The obtained data has been analyzed in the light of various theories of ionic conduction. The value of constant A in Guntherschulze and Betz equation is temperature dependent while B is independent of temperature. The constant A is also dependent on the nature of the electrolyte. The data indicates the temperature independent Tafel slope which rules out the applicability of the single barrier theory of Cabrera and Mott. The data has been analyzed in terms of Dignam’s equation. The effects of current density and temperature in aqueous electrolyte on various parameters of Dignam’s equation have been examined. Keywords : Tantalum, niobium, malic acid, Tafel slope. Introduction Anodization is an electrolytic passivation process which involves the production of oxide film on the metallic sub- strate 1,2 . It removes electrons from the substrate causes oxidation of anode. In the process of anodic oxidation, the electrode kinetic feature of surface is the critical one. It is extremely complicated to develop anodic oxide film on metal under high field strength because of the vicinity of metal/oxide and oxide/solution interface at which transfer processes must happen. Galvanostatic 3–5 , potentiostatic anodization 6–9 and the sequence of both 4 are the techniques for anodic oxide film growth on metals. The parameters highly influence the oxide film characteristics are the type and concentration of electrolytic solution, electrolytic pH, temperature of electrolyte and the applied current density or voltage 10,11 . Galvanostatic anodization is better than potentiostatic anodization due to the fact that, in later, the current de- creases abruptly until the leakage current pre-dominates or recrystallization begins. In the steady state galvanostatic anodization, the po- tential increases steadily with time due to the formation of the anodic oxide layer 12 . Because of this behavior, elec- tric field inside the film formed, remains constant. In this way, all anodic current density is used in the film forma- tion in states of high field. According to the Guntherschulze and Betz model 13 , high field ionic conduction equation for kinetics of growth of film on metals is represented by ln i = ln A + BE (1) where i = flux density of ionic species i.e. current den- sity, E = electric field strength in the film and A and B are the constants. Various different models, additionally proposed, to clarify the growth kinetics of the oxide film formation by different researchers. Cabrera and Mott model clarify that the Tafel slope must be proportional to temperature. Young, Vermilyea and others disagreed with Cabrera Mott model; the discovered Tafel slope must be independent of the temperature 14 . Numerous efforts have been proposed to consider the growth kinetics of anodic oxide film formation on diffe- rent valve metals by investigators 15–17 . In this section, we examine the development of anodic oxide film on niobium and tantalum metals at different current densities and tem- peratures in aqueous electrolyte such as malic acid. The behavior of Tafel slope and selective consideration of dif-