Cu-Al-Ni based alloys, although are included in the category of inferior non-precious alloys, are still widely used in many countries, unofficially accepted in absence of some international standards, especially due to their low cost, the satisfactory tolerance and perhaps to their aspect, similar to that of the gold-based alloys. Contrary, in many countries the cooper-based alloys are not accepted as biomaterials, especially due to their high citotoxicity.The corrosion behaviour of copper-based alloys (Gaudent and NPG+2) in simulated saliva was studied by potentiodynamic polarization and by electrochemical impedance spectroscopy (EIS). Were established the main parameters of the corrosion process. The keeping of these alloys in solution reduces the intensity of the corrosion process but not the influence the type of the corrosion. In all cases a pitting corrosion was evidenced. The obtained results were completed with microstructure observation and SEM analysis. It was found that both alloys present (the) similar corrosion rates, so the alloying of the copper-based alloy with gold 2% (NPG+2) does not have a significant effect on the corrosion process.Present paper made a comparative study of two cooper-based dental alloys: NPG+2 (non-precious gold) (Alba Dent, USA) and Gaudent (IMNR, Romania) with the composition presented in the Table 1, regarding the corrosion behaviour and also attempt to elucidate the copper dissolution mechanism in artificial saliva. The corrosion medium was an artificial aerated saliva (CarterBrugirard AFNOR/NF (French Association of Normalization) having the composition: NaCl -0.7 g/L, KCl -1.2 g/L, Na 2 HPO 4 H 2 O -0.26 g/L, NaHCO 3 -1.5 g/L, KSCN -0.33 g/L, carbamide -1.35 g/L , and pH = 8.The two alloys have a similar biphasic composition: α-phase and eutectoid γ'. As one can be seen in Figure 1, the difference between the two alloys is that the eutectoid γ' is lamelar in Gaudent and globular in NPG+2.The corrosion type and the influence of the time period of immersion in solution for the studied alloys were analyzed on the basis of cyclic polarization curves. These curves were recorded both for samples with freshly polished surface and for samples maintained seven days in artificial saliva. In Figures 2 a) and b) are presented the cyclical polarization curves for Gaudent and NPG+2 alloys. The structure of the salt deposits on the Gaudent surface after electrochemical treatment is better evidenced by scanning electron microscopy in Figure 3.Gaudent and NPG+2 alloys are very susceptible to pitting corrosion in artificial saliva, the process taking place at relative small over-potentials and with high corrosion current densities. Using two electrochemical methods (polarization resistance and EIS) it was found that both alloys present the similar corrosion rates , so the alloying of the copper-based alloy with gold 2% does not have a significant effect on the corrosion process. The type of corrosion do not modifies by maintaining

Titanium possesses an excellent corrosion resistance in biological environments because the titanium dioxide formed on its surface is extremely stable. When aluminium and vanadium are added to titanium in small quantities, the alloy achieves considerably higher tensile properties than of pure titanium and this alloy is used in high stress-bearing situations. But these metals may also influence the chemostatic mechanisms that are involved in the attraction of biocells. V presence can be associated with potential cytotoxic effects and adverse tissue reactions. The alloys with aluminium and iron or with aluminium and niobium occur to be more suitable for implant applications: it possesses similar corrosion resistance and mechanical properties to those of titanium-aluminium-vanadium alloy; moreover, these alloys have no toxicity.In this paper, pure Ti, Ti-6Al-7Nb and Ti-6Al-4Fe were studied. The implant materials were prepared by chemical treatment consisting in immersion in 10M aqueous NaOH solution at 60º C for 24 hours. After the attack, were washed with distilled water and dried at 40°C during 24 hours.Data about mechanical behaviour are presented. The mechanical behaviour was determined using optical metallography (Figure 1), tensile strength ( Figure 2) and Vickers microhardness.For the electrochemical measurements a conventional three-electrode cell with a Pt grid as counter electrode and saturated calomel electrod (SCE) as reference electrode was used. AC impedance data were obtained at open circuit potential using a PAR 263 A potentiostat connected with a PAR 5210 lock-in amplifier. The amplitude of the AC potential was 10 mV and single sine wave measurements at frequencies between 10 -1 and 10 5 Hz were performed for each sample. The spectra were interpreted using the non-linear least square fitting procedure.The ESEM and EDAX observations were carried out with an environmental scanning electron microscope Fei XL30 ESEM with LaB6-cathode attached with an energy-dispersive electron probe X-ray analyzer (EDAX Sapphire) For the cross section of passive layer, the sample was sputter-coated with gold for analysis. After 3 days of immersion in simulated body fluid the nucleation of the bone growth was observed on the implant surface (Figure 3).It resulted that the tested oxide films presented passivation tendency and a very good stability and no form of local corrosion was detected. The electrochemical behaviour of these films is described by an equivalent circuit with two time constants. The mechanical data confirm the presence of an outer porous passive layer and an inner compact and protective passive layer. EIS confirms the mechanical results. The thicknesses of these layers were measured. SEM photographs of the surface and EDX profiles for the samples illustrate the appearance of a microporous layer made up of an alkaline titanate hydrogel. It can be observed that the Na concentration is bigger just under the surface and starts to decrease as is analysed deeper in the passive layer. The apatite-forming abili...

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Titanium alloys possess attractive properties for biomedical applications where the most important factor is biocompatibility. Between the titanium alloys, the Ti-6Al-4V has been successfully applied for biomedical applications [1], because it possesses sufficient strength and ductility for use as human body implants [2].Aluminium is an alpha phase stabilizer and Vanadium a beta phase stabilizer, in consequence the titanium alloys with Al and V have a two-phase alpha-beta structure. The alpha-beta alloys can be mechanically processed and heat-treated to obtain improved mechanical properties. Futher studies have shown that the release of both Al and V ions from the alloy might cause long-term health problems, such as osteomalacia, neuropathy and Alzheimer diseases [3,4]. V presence can be associated with potential cytotoxic effects and adverse tissue reactions and Al produces potential neurological disorders. For this reason, recently, other alloys have been developed to decrease the aluminium concentration (and one of these is Ti-5Al-4V) or to replace vanadium (and one of these is Ti-6Al-3.5Fe). The iron is also beta-phase stabilizer and the resulted alloy has a two-phase alphabeta structure with added advantage of nontoxicity.It is well known that surface sensitive properties like corrosion and hardness are dependent on the chemical composition of the surface. In this paper Ti, Ti-5Al-4V and Ti-6Al-3.5Fe with the composition presented in the Table 1 were evaluated; the microstructure and microhardness were determined.From metallographic photos (Fig.1) can be observed that both titanium alloys, Ti-5Al-4V and Ti6Al-4Fe have an alpha-beta structure. Aluminium is an alpha phase stabilizer while V and Fe are beta phase stabilizers. The beta phase appears dark and the alpha phase light. Alpha phase was the dominant phase in these alloys.From Vickers microhardness measurements can be concluded that the alloys formed a hard layer on their surface which greatly improves their wear resistance in comparation with titanium. As the load increases, the values of microhardness are increasing (the layer became more compact). With a load of 200 grams it can be seen that the microhardness is decreasing which mean that the indenter reach the base metal. From the corresponding depth of penetration, it was found that passive film on the implant surface has a two-layer structure: a thin barrier-type inner layer (about 3 µ) and a porous outer layer (about 1.5 µ).The proposed model for the passive layer formed on the surface of the implants, deduced from the metalographical observations and microhardness measurements is shown in figure 2. The results were confirmed by mechanical approach, in terms of two-layer model of the oxide film, consisting of a thin barrier type inner layer and a porous outer layer. The pronounced porous outer layer is

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006