Surface modification of titanium by chemical and thermal methods – electrochemical impedance spectroscopic studies

The surface modification of untreated, alkali treated and alkali heat treated titanium has been investigated by electrochemical impedance spectroscopic technique. The substrates were treated with 10M NaOH aqueous solutions and subsequently heat treated at 600°C, a thin sodium titanium layer was formed on their surfaces. Thus, the treated substrates formed a dense and uniform bone-like apatite layer on their surfaces in simulated body fluid (SBF) solution. This indicates that the alkali and heat treated titanium bond to living bone through the bonelike apatite layer formed on their surface in the body. Electrochemical impedance spectroscopic (EIS) experiments were performed in SBF solution as a function of immersion time. Data of EIS were taken for untreated and the results revealed the formation of one additional layer along with the barrier layer. In case of alkali treated sample, titania gel layer alone dissolves completely and forms apatite and barrier layers, whereas, the alkali and heat treated samples showed three layers namely apatite, gel and barrier layers. The nature of these layers has been obtained by fitting the EIS data to suitable equivalent electrical circuit models. The alkali heat treated titanium results in the faster apatite nucleation and growth on the surface. Immersion in SBF solution exhibited higher apatite film resistance compared to alkali treated and untreated titanium substrate.