Current Understanding of Ti Anodisation: Functional, Morphological, Chemical and Mechanical Aspects

Abstract

This paper provides an overview of the current understanding of the Ti anodisation process. As compared to other valve-metals, Ti exhibits several significant differences regarding its anodisation behaviour, the most important one being the marked semiconducting character of its anodic oxide. In the first part of this paper, a general introduction to anodisation processes is given and theoretical models describing the growth kinetics, breakdown and internal stress development in anodic oxide films are presented. In the second part, the peculiarities of Ti regarding the anodisation behaviour are discussed extensively. In particular, the influence of the main experimental parameters (metal substrate, electrolyte and growth rate) on both the anodisation process and the functional, morphological, chemical and mechanical characteristics of the anodic films is reviewed.This review intends to provide an overview of the current understanding of the process of Ti anodisation. Anodisation has been used for almost eighty years, primary in the field of corrosion science, as a simple and efficient way of producing thick protective oxide coatings on the so-called 'valve-metals' (Al, Ta, Ti, Nb, Zr, Hf and W) and their alloys. Anodisation is a very peculiar oxidation process in that it relies on the migration of ions across solid films over rather large distances, typically up to several hundreds of nanometres, the migration being promoted by very high electric fields of the order of 10 7 ' joris.proost@uclouvain.be 117 Brought to you by | Purdue University Libraries Authenticated Download Date | 5/28/15 6:56 PM

Application-wise nanostructuring of anodic films on titanium: a review

“…where i is the formation current density, i 0 its initial value, b a high field constant (in cm/V) and E the field strength, equal to the ratio between potential drop across the film, DU, and film thickness, d. [12] Concerning specifically titanium, scientific interest towards its oxidation has grown exponentially in the last decade, as proved by the rapid increase in the number of articles dealing with titanium anodising (Figure 1). This is due to constant improvements in the knowledge and control of anodising processes that led À and are still leading À to new oxide morphologies, compositions and functionalities, thereby expanding the area of possible application of anodic titanium oxides.…”

“…Both an inward oxide growth and an outward oxide growth are usually considered, due to field-assisted ion migration under high field conditions, with a slight predominance of O 2¡ charge carriers across the oxide to reach the metal surface where Ti 4C cations are produced. [12] The process is often performed under galvanostatic conditions À application of a constant current impulse, in the range of few mA/cm 2 up to hundreds of mA/cm 2 , until the desired cell voltage or a determined charge is reached À or by a potential sweep, with anodising rates generally in the range 1 V/s to 1 V/min. In both cases, a period of maintenance and stabilisation can be applied at a constant cell voltage: this step is particularly important when the production of nanotubular oxides is desired, as described in more details in Section 2.2.…”

Effect of etching on the composition and structure of anodic spark deposition films on titanium

“…Titanium anodizing is a consolidated technology that is used to produce the formation on the metal of an oxide film, always based on the titanium dioxide (TiO 2 ) formation but with different thickness, crystal structure, morphology and composition depending on process parameters [1,2]. This treatment is particularly spread in biomedical applications, where the favourable combination of mechanical properties, durability and biocompatibility of titanium and its alloys make them particularly suitable for dental and orthopaedic implants, as well as for ostheosynthesis devices [3,4].…”

Anodic oxidation of titanium: from technical aspects to biomedical applications

“…Generally speaking, oxide thickness increases with cell voltage, as already mentioned. Moreover, several possible morphologies can be produced, which depend not only on cell voltage, but also on the composition of the electrolytic solution in which the electrodes are immersed (34).…”