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Correlation between the susceptibility to breakdown and surface properties of thin films on implant titanium alloys Ti-5Al-4V and Ti-6Al-4Fe in Ringer 1 and Ringer 2 solutions of different pH values (6.98, 4.35, 2.5) which simulate the conditions that can appear at the longterm (13,000 hours) contact between implant and tissues were studied in this paper. The passive films are very stable up to +1.8 V; Ti-6Al-4Fe alloy presents pitting attack at a pitting initiation potential of +3.5 V in Ringer 1 solution and at +3.9 V in Ringer 2 solution. The pitting protection potential is about +1.75 V in both solutions; this is a very noble potential. Impedance spectra were modeled with one time constant equivalent electrical circuit, typically for a compact oxide film, for all materials, in all tested solutions. The fitting parameters indicate a long-term stability.

The paper presents the experimental results concerning the performance assessment of electrodeposited epoxy films using electrochemical techniques (electrochemical impedance spectroscopy–EIS and anodic polarization) assisted by microscopical studies. The films were formed during the cathodic and anodic electrodeposition of a modified epoxy resin on carbon steel substrate. The specimens were tested in a normal aerated 3% NaCl solution at room temperature for a total period up to 1500 hours. Analysis of the impedance spectra has established an equivalent electric circuit with two time constants fitted to describe the electrodeposited epoxy film/carbon steel/electrolyte system. The time monitoring of the principal elements from the equivalent electric circuit were used to determine protective properties of the electrodeposited epoxy films. Results show a high performance of electrodeposited epoxy films, characterized by uniformity, insignificant porosity, very low water and ions permeability.

The electrochemical impedance spectroscopy (EIS) has been used for the modelling of the alkyd organic film/carbon steel interface in 3% NaCl solution. Both the dielectric properties of the organic film and the corrosion processes of the metallic substrate were investigated with this method. Analysis of the impedance spectra (Nyquist and Bode plots) and the interpretation with the fitting software developed by Boukamp, established the presence of two time constants in the first 250 immersion hours. One time constant concerning the organic layer describes the electrical and barrier properties of film. The second time constant concerning the substrate represents the corrosion reactions at the film/metal interface. For long immersion periods, after the formation of the conductive pathways in the film and the development of the diffusion processes, are necessary another two time constants concerning these phenomenons. The error magnitude between the measured and calculated data with these electric equivalent circuits is satisfactory. The physical properties obtained from the principal elements of the equivalent electric circuits are in concordance with those obtained from others testing methods.

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This paper will address key issues related to the synthesis, characterization and utilization of inorganic/organic hybrid coatings on TiAlVZr bioalloy to control adsorption at interface and the integration capacity of the implant. To enhance the integration capacity function of the biomaterial is necessary to control the composition and structure via the use of hybrid materials consisting of organic and inorganic biomimetic phases [1,2]. Such composite coatings mimic the structure of natural materials of tissues, in our case hydroxyapatite (HA) by association of bovine serum albumin (BSA) with calcium phosphates matrices. Calcium phosphate coating have been deposited on metal substrates by electrochemical method.

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The purpose of this paper is to characterise the anodic oxide films formed on titanium and two ternary titanium alloys, Ti-15Mo-5Al and Ti-10Mo-10Al in 1%, 10% and 20% hydrochloric acid solutions at 25, 50, and 75°C. The anodic film on titanium in hydrochloric acid is stable between + 0.6 V (SCE) and + 2.0 V (SCE). For our new ternary titanium alloys, the passive film is formed at about + 0.6 V (SCE) and is stable to + 2.0 V (SCE). The anodic polarization curves for alloys differ from the base metal curve, presenting two peaks for the critical passivation current density in the active-passive potential range. At the first current peak (the first critical passivation potential E cr1 ) a porous titanium pentaoxide (Ti 3 O 5 ) is formed. When the potential reaches the second current peak (the second critical passivation potential E cr2 ) the compact and protective titanium dioxide (TiO 2 ) is formed. The impedance spectra exhibit the typical behaviour for a passive film i.e. a near capacitive response illustrated by a phase angle close to - 90 over a wide frequency range. The oxide film on titanium and its alloys in hydrochloric acid solutions exhibits a high resistance and a low capacitance (with the increase of the potential) attributed to the surface roughness decrease as the oxide layer thickens.

The item of the paper is focussed on some bio-compatible coatings for rare earth based permanent magnets, which are used as dental materials for prosthetic devices as retention units. The studied alloy belongs to Nd-Fe-B system with some Dy and Al content. The double-layer coatings had different chemical compositions; first layer: Ag30-Cr70, Co30-Cr70, Stainless Steel and the second layer: titanium nitride (TiN). Data about corrosion behavior, wear resistance and adhesion are presented. The corrosion resistance of these coatings was tested in artificial saliva, using electrochemical potentiostatic and potentiodynamic polarization techniques. The stability in the corrosion media, the localized corrosion susceptibility and the corrosion rates were determined. It resulted that the Nd30-Dy5-Fe-Al0.4-B alloy with Ag30-Cr70 + TiN film is very stable in artificial saliva. The wear behavior of the coatings in different conditions of contact and load was tested, also. The adhesion was determined by scratching test.

In vitro osteoblast culture on Ti-6Al-7Nb bioalloy was characterized in this paper. Also, the corrosion resistance of titanium and its Ti-6Al-7Nb bioalloy in Ringer solutions were determined as an aspect of their biocompatibility. Human osteoblast proliferation and viability are very good. Cell effort to adhere on metallic support is visualized by some morphologic changes of the osteoblasts. Cytotoxicity effects of Ti-6Al-7Nb alloy appeared after 48 culture hours and decreased in time, demonstrating a very good biocompatibility. In Ringer solution of different pH values (2.5; 6.9 and 8.9), titanium and Ti-6Al-7Nb alloy presented self-passivation, very large passive potential range, very low passive current densities, confirming a compact, protective, stable layer. The very low corrosion rates and ion release values prove a near imperceptible toxicity. In Ringer solution, open circuit potentials of titanium and its Ti-6Al-7Nb alloy tend to electropositive values, attesting a process of passivity increase by thickening.

The aim of this work is to investigate the long term (3000 exposure hours) tendency of passive layers on titanium to breakdown in Tani-Zucchi and Carter-Brugirard artificial saliva undoped and doped with chloride and fluoride ions. The non-uniformity of the saliva pH (from 7.88 to 5.73 and extreme case 2.15) was simulated. The following techniques were used: potentiostatic, potentiodynamic and linear polarization, the monitoring of the open circuit potentials vs. exposure time and atomic force microscopy. The breakdown (pitting) potential at about +2.9 V and the re-passivation potential at +2.4 V in Tani-Zucchi artificial saliva were determined. So, the pitting protection potential is very noble and can not be reached in human body.