Pitting of Al and Al–Si alloys in KSCN solutions and the effect of light

Improvements of Corrosion Resistance and Antibacterial Properties of Hydroxyapatite/Cupric Oxide Doped Titania Composite Coatings on Degradable Magnesium Alloys

The excellent biocompatibility of calcium phosphate (CaP) coatings makes them widely used in magnesium (Mg) alloy orthopedic implant materials. However, the porous morphology of CaP coatings limits their corrosion resistance. A cupric oxide (CuO) doped titania (TiO₂) sol-gel coating is prepared on a porous hydroxyapatite (HA) coating. According to electrochemical test results, the HA/CuO-TiO₂ coating obtains a current density of 6 × 10^-4 mA/cm², lower than that of the Mg alloy (2.6 × 10^-2 mA/cm²). The hydrogen evaluation of the HA/CuO-TiO₂ coating is only 1/12 that of the Mg alloy after immersion for 7 days. In addition, the HA/CuO-TiO₂ coating has an antibacterial rate of 99.5 ± 0.4% against Staphylococcus aureus, significantly higher than that of the HA coating (19.8 ± 0.3%) and HTC0 coating (38.4 ± 0.5%). The CuO doped composite coating has no adverse effect or cytotoxicity on cell proliferation (cell viability ≥79.6%). Hence, the HA/CuO-TiO₂ composite coating is useful for enhancing the corrosion resistance and antibacterial properties of Mg alloys while ensuring cytocompatibility. The HA/CuO-TiO₂ coated AZ60 Mg alloy can meet the requirements of clinical application.

Influence of UV light irradiation on the corrosion behavior of electrodeposited Ni and Cu nanocrystalline foils

Influence of ultraviolet (UV) light irradiation on the corrosion behavior of electrodeposited Ni and Cu nanocrystalline foils in 3.5% NaCl solution was studied by means of electrochemical methods, electron work function (EWF) analysis, and characterization with atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the influence of solar light on corrosion of the metals was non-negligible, which could be very different for different materials. The UV light irradiation resulted in an increase in corrosion resistance of the Cu foil but showed an opposite influence on that of the Ni foil. Based on surface state analysis, it was concluded that the UV irradiation altered the surface oxide films. The UV light induced the formation of Cu₂O on Cu, which is more stable and compacted than naturally formed CuO film. However, the UV light accelerated the formation of Ni₂O_3, which is loose, porous and brittle, compared to naturally formed NiO on Ni. The changes in oxide films were responsible for the opposite variations in the corrosion behavior of the Cu and Ni nanocrystalline foils caused by the UV light irradiation.

Effect of Ag Addition on the Electrochemical Performance of Cu10Al in Artificial Saliva

In this work we proposed to evaluate the corrosion resistance of four different alloys by electrochemical techniques, a binary alloy Cu10Al, and three ternary alloys Cu10Al-xAg (x = 5, 10, and 15 wt.%) to be used like biomaterials in dental application. Biomaterials proposed were tested in artificial saliva at 37°C for 48 h. In addition, pure metals Cu, Al, Ag, and Ti as reference materials were evaluated. In general the short time tests indicated that the Ag addition increases the corrosion resistance and reduces the extent of localized attack of the binary alloy. Moreover, tests for 48 hours showed that the Ag addition increases the stability of the passive layer, thereby reducing the corrosion rate of the binary alloy. SEM analysis showed that Cu10Al alloy was preferably corroded by grain boundaries, and the Ag addition modified the form of attack of the binary alloy. Cu-rich phases reacted with SCN⁻ anions forming a film of CuSCN, and the Ag-rich phase is prone to react with SCN⁻ anions forming AgSCN. Thus, binary and ternary alloys are susceptible to tarnish in the presence of thiocyanate ions.