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The development of a biodegradable metallic implant demands a precisely defined degradation profile and adequate mechanical properties. Mg has been proposed for this purpose but it has an excessively high corrosion rate and insufficient yield strength. In the present work pure Mg mechanically reinforced by a powder metallurgy (Mg(PM)) route and treated with KF was used. The effect of chlorides, at the physiological level, on four fluoride conversion coatings (F-CC) formed on Mg(PM) was evaluated comparatively. The behavior of Mg(PM) during fluoride treatments (0.01 M-0.3 M fluoride-containing solutions) before and after the addition of chlorides (8 g L-1 NaCl) was investigated by conventional corrosion techniques and by scanning electrochemical microscopy (SECM) complemented with SEM observations and EDX analysis. Results showed that the composition and the microstructural characteristics of the F-CCs as well as their corrosion behavior change with KF concentration and immersion time. Treatments in the 0.01 M-0.1M KF range prove to be effective to protect Mg(PM) against corrosion in the absence of chlorides while higher KF solution concentration (0.3 M) adversely affects the corrosion resistance of this metal. In the presence of chloride ions the F-CCs progressively lose their fluoride content and their corrosion resistance at a rate that depends on the treatment conditions. Such temporary corrosion protection is appropriate for biodegradable implants.

A study has been performed to select optimum process conditions (temperature, pH, reagent concentration, reaction kinetics, deposition time, etc.) in gold deposition on Si(n) from sulphite/thiosulphate electrolytic baths. Gold deposits have been obtained by electrochemical techniques such as constant potential, constant current, cyclic voltammetry and pulsating overpotential, in diffusional regime or by charge transfer control, at two pH values (6 and 9) and two temperatures (30 and 50°C). The surface morphology of the Au deposits was studied by scanning electron microscopy (SEM), the preferred orientation and average size of the Au electrodeposited particles on n-Si substrates were obtained by X-ray diffraction (XRD), and qualitative and semiquantitative analysis of the gold sample was performed by energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). The surface sulphur content was much lower or almost zero for gold samples obtained at pH 9 compared to those obtained at pH 6. However, when the different methods were compared at pH 6, both cyclic voltammetry and pulsating overpotential deposition led to deposits with a low or zero sulphur content. The results also show that various morphologies with different grain sizes can be obtained without the addition of additives.

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