On some peculiarities of electrochemical oxidation of Ti and Ti6Al6V alloy

Andrzej Sadkowski 1Janusz Kamiński 2Malgorzata Lewandowska 2Magdalena I. Walczak 1

1. Polish Academy of Sciences, Institute of Physical Chemistry, Kasprzaka 44/52, Warszawa 01-224, Poland
2. Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland

Abstract

Electrochemical oxidation is commonly used in industrial practice, e.g. as a method for coloring of the metal surface and modification of its properties. However, the process of oxide film formation is still not fully understood. Ti and Ti6Al4V electrodes were examined with various electrochemical methods in conditions of anodic film formation in 1M H2SO4. The influence of metal microstructure on the process of oxidation was found. Good conditions for anodizing were available only after etching electrodes surface in HNO3/HF solutions revealing fresh, active metal surface ready to hydrogen intake. Etched microcrystalline Ti electrodes presented different interference colors at various crystallites seen under optical microscope while nanocrystalline anodized surfaces were colored uniformly. Rest potential of both etched and anodized electrodes drifted in long runs to reversible hydrogen electrode potential.

The process of anodic film formation in the voltage range of 10V – 95V examined with cyclic voltammetry (CV) was clearly stepwise with oxidation state attained at lower voltage preserved and only superadded in subsequent scan to higher voltage limit. CV tests in broad voltage range disclosed sharp current spikes possibly related to phase transition in interfacial region. There was not clear difference in electrochemical characteristics of anodized Ti and Ti6Al4V electrodes.

Electrochemical impedance (0.1 Hz – 100 kHz) showed that the electrodes with “native oxide” presented ohmic resistance component of several ohms typical for metal/electrolyte interface and oxide layer resistance of the order of 107 Ohm while oxides formed electrochemically presented properties typical for semiconductor/electrolyte interface without clearly distinct ohmic resistance and at least three relaxation times. This character was preserved for many days for electrodes stored in laboratory atmosphere.

 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium D, by Andrzej Sadkowski
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 13:44
Revised:   2009-06-07 00:44