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Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment.

In this study, the effect of the recycling process and copper particle incorporation on virgin and recycled pellet HDPE were investigated by thermo-chemical analysis, mechanical characterization, and antibacterial analysis. Copper particles were added to pellet HDPE, virgin and recycled, using a tabletop single screw extruder. Some copper particles, called copper nano-particles (Cu-NPs), had a spherical morphology and an average particle size near 20 nm. The others had a cubic morphology and an average particle size close to 300 nm, labeled copper nano-cubes (Cu-NCs). The thermo-chemical analysis revealed that the degree of crystallization was not influenced by the recycling process: 55.38 % for virgin HDPE and 56.01% for recycled HDPE. The degree of crystallization decreased with the addition of the copper particles. Possibly due to a modification in the structure, packaging organization, and crystalline ordering, the recycled HDPE reached a degree of crystallization close to 44.78% with 0.5 wt.% copper nano-particles and close to 36.57% for the recycled HDPE modified with 0.7 wt.% Cu-NCs. Tensile tests revealed a slight reduction in the tensile strength related to the recycling process, being close to 26 MPa for the virgin HDPE and 15.99 MPa for the recycled HDPE, which was improved by adding copper particles, which were near 25.39 MPa for 0.7 wt.% copper nano-cubes. Antibacterial analysis showed a reduction in the viability of E. coli in virgin HDPE samples, which was close to 8% for HDPE containing copper nano-particles and lower than 2% for HDPE having copper nano-cubes. In contrast, the recycled HDPE revealed viability close to 95% for HDPE with copper nano-particles and nearly 50% for HDPE with copper nano-cubes. The viability of S. aureus for HDPE was lower than containing copper nano-particles and copper nano-cubes, which increased dramatically close to 80% for recycled HDPE with copper nano-particles 80% and 75% with copper nano-cubes.

The increase in longevity worldwide has intensified the use of different types of prostheses for the human body, such as those used in dental work as well as in hip and knee replacements. Currently, Ti-6Al-4V is widely used as a joint implant due to its good mechanical properties and durability. However, studies have revealed that this alloy can release metal ions or particles harmful to human health. The mechanisms are not well understood yet and may involve wear and/or corrosion. Therefore, in this work, commercial pure titanium and a Ti-6Al-4V alloy were investigated before and after being exposed to a simulated biological fluid through tribological tests, surface analysis, and ionic dissolution characterization by ICP-AES. Before exposure, X-ray diffraction and optical microscopy revealed equiaxed α-Ti in both materials and β-Ti in Ti-6Al-4V. Scratch tests exhibited a lower coefficient of friction for Ti-6Al-4V alloy than commercially pure titanium. After exposure, X-ray photoelectron spectroscopy and surface-enhanced Raman spectroscopy results showed an oxide film formed by TiO2, both in commercially pure titanium and in Ti-6Al-4V, and by TiO and Al2O3 associated with the presence of the alloys. Furthermore, inductively coupled plasma atomic emission spectroscopy revealed that aluminum was the main ion released for Ti-6Al-4V, giving negligible values for the other metal ions.

Ti-based alloys as porous materials with low elastic modulus has been recently developed due to the evident need to avoid the stress shielding problems related to stiffness mismatch related to human bone. In this work, Ti-30Nb-13Ta-2Mn alloy as porous material was obtained by powder metallurgy using (NH4)2(CO3) as space-holder. Powders and space-holder were mixed together and compacted with 400 MPa stress. (NH4)2(CO3) particles were removed from the compacts during sintering at 1250 °C for 3 h in Ar atmosphere. The porosity and active area of the porous electrode were estimated by using Archimedes methods and BET analysis. In addition, the surface analysis was carried out by SEM and XRD. Finally, electrochemical measurements such as open circuit potential curves, polarization curves and electrochemical impedance spectroscopy were carried out in a simulated blood plasma fluid called Ringer’s solution at 37 ºC. Results revealed foams with heterogeneous pore distribution in diameter as well as length. The electrochemical results showed that the corrosion potential was shifted to more negative values and the anodic and cathodic current were increased as a function of exposure time. On the other hand, impedance analysis displayed an impedance of the de Levie associated to the anodic response in parallel with an interfacial impedance attributed to cathodic response. Additionally, an evolution of the passive oxide layer as a function of exposure time was observed, which was mainly formed at the pore walls and, the cathodic reaction related to the oxygen reduction reaction took place mainly outside the pore. Reference E. Orazem and B. Tribollet, Electrochemical Impedance Spectroscopy, 2nd Edition, John Wiley & Sons, Inc. Hoboken, New Jersey (2017) 322-332. O.E. Barcia, E. D’Elia, I. Frateur, O.R. Mattos, N. Pébère, B. Tribollet, Application of the impedance model of de Levie for the characterization of porous electrodes, Electrochimica Acta 47 (2002) 2109-2126.

Development of titanium foams with low elastic modulus has increased its scientific and technological relevance due to the evident need to avoid the stress shielding problems related to stiffness mismatch with respect to bone. In this work we studied the synthesis and characterization of foams of pure Ti which present high potential for biomedical applications. Foams were obtained using NaCl (40, 50 and 60 %v/v), with particle size ranging from 150 to 350 mm, as space-holder. Powders and space-holder were mixed together and compacted under 200 to 800 MPa stress. NaCl particles were removed from the green compacts by submerging samples in distilled water at 60 °C (5 cycles of 4h). The green compacts were sintered at 1300 °C for 3 h in Ar atmosphere. Ti-based foams were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, optical microscopy. In addition, electrochemical impedance spectroscopy (EIS) measurements were performed under potentiostatic conditions at the corrosion potential in Ringer solution. Results showed that Ti-based foams with tailored heterogeneous pore distribution may be obtained using space holder method. Using theoretical models the elastic modulus of foams was estimated between 10 and 25 GPa. The experimental EIS data revealed a CPE behavior of the foams for all exposure time studied. Not significant effect was observed in the impedance modulus at low frequency range (|Z|LF) for low compaction stress. However, the |Z|LF decreased markedly for higher compaction stress, which could be related to the increase of the stress raiser. From our results, we conclude that foams with 50 and 60 % of porosity are potential bone replacement materials due to their stiffness closer to human bone value. Ackowledgements: The authors are grateful to Fondecyt Grant 1160604 and 1161444