Arc Synthesis, Crystal Structure, and Photoelectrochemistry of Copper(I) Tungstate.

A little-studied p-type ternary oxide semiconductor, copper(I) tungstate (Cu2WO4), was assessed by a combined theoretical/experimental approach. A detailed computational study was performed to solve the long-standing debate on the space group of Cu2WO4, which was determined to be triclinic P1. Cu2WO4 was synthesized by a time-efficient, arc-melting method, and the crystalline reddish particulate product showed broad-band absorption in the UV-visible spectral region, thermal stability up to ∼260 °C, and cathodic photoelectrochemical activity. Controlled thermal oxidation of copper from the Cu(I) to Cu(II) oxidation state showed that the crystal lattice could accommodate Cu2+ cations up to ∼260 °C, beyond which the compound was converted to CuO and CuWO4. This process was monitored by powder X-ray diffraction and X-ray photoelectron spectroscopy. The electronic band structure of Cu2WO4 was contrasted with that of the Cu(II) counterpart, CuWO4 using spin-polarized density functional theory (DFT). Finally, the compound Cu2WO4 was determined to have a high-lying (negative potential) conduction band edge underlining its promise for driving energetic photoredox reactions.

Solute lean Ti-Nb-Fe alloys: An exploratory study.

In this study, we explored the Ti-Nb-Fe system to find an optimal cost-effective composition with the lowest elastic modulus and the lowest added Nb content. Six Ti-(31-4x)Nb-(1+0.5x)Fe ingots were prepared and Nb was substituted with Fe, starting at Ti-31Nb-1.0Fe and going up to Ti-11Nb-3.5Fe (wt%). The ingots were subjected to cold rolling, recrystallization and solution treatment, followed by water-quenching (WQ), furnace cooling (FC) or step-quenching to 350°C, which caused massive formation of isothermal ω phase. All the water-quenched alloys displayed athermal ω phase, which is apparently the result of fully collapsed ß phase. The Fe content improved the compressive strength of the alloys. In the FC alloys, substitution with Fe favored the formation of α phase instead of ω phase, giving rise to a solute-rich ß phase with a lattice parameter of 0.3249nm. Among the FC alloys, the lowest modulus of 83±4GPa was obtained in the Ti-19Nb-2.5Fe alloy, which exhibited fine and well dispersed α precipitation and absence of ω phase. DSC experiments indicated that the experimental alloys showed varying phase stability during heating.

Reducing Staphylococcus aureus growth on Ti alloy nanostructured surfaces through the addition of Sn.

ß-type Ti alloys containing Nb are exciting materials for numerous orthopedic and dental applications due to their exceptional mechanical properties. To improve their cytocompatibility properties (such as increasing bone growth and decreasing infection), the surfaces of such materials can be optimized by adding elements and/or nanotexturing through anodization. Because of the increasing prevalence of orthopedic implant infections, the objective of this in vitro study was to add Sn and create unique nanoscale surface features on ß-type Ti alloys. Nanotubes and nanofeatures on Ti-35Nb and Ti-35Nb-4Sn alloys were created by anodization in a HF-based electrolyte and then heat treated in a furnace to promote amorphous structures and phases such as anatase, a mixture of anatase-rutile, and rutile. Samples were characterized by SEM, which indicated different morphologies dependent on the oxide content and method of modification. XPS experiments identified the oxide content which resulted in a phase transformation in the oxide layer formed onto Ti-35Nb and Ti-35Nb-4Sn alloys. Most importantly, regardless of the resulting nanostructures (nanotubes or nanofeatures) and crystalline phase, this study showed for the first time that adding Sn to ß-type Ti alloys strongly decreased the adhesion of Staphylococcus aureus (S. aureus; a bacteria which commonly infects orthopedic implants leading to their failure). Thus, this study demonstrated that ß-type Ti alloys with Nb and Sn have great promise to improve numerous orthopedic applications where infection may be a concern.

Ti-Mo alloys employed as biomaterials: effects of composition and aging heat treatment on microstructure and mechanical behavior.

The correlation between the composition, aging heat treatments, microstructural features and mechanical properties of ß Ti alloys is of primary significance because it is the foundation for developing and improving new Ti alloys for orthopedic biomaterials. However, in the case of Ti-Mo alloys, this correlation is not fully described in the literature. Therefore, the purpose of this study was to experimentally investigate the effect of composition and aging heat treatments on the microstructure, Vickers hardness and elastic modulus of Ti-Mo alloys. These alloys were solution heat-treated and water-quenched, after which their response to aging heat treatments was investigated. Their microstructure, Vickers hardness and elastic modulus were evaluated, and the results allow us to conclude that stabilization of the ß phase is achieved with nearly 10% Mo when a very high cooling rate is applied. Young's modulus was found to be more sensitive to phase variations than hardness. In all of the compositions, the highest hardness values were achieved by aging at 723K, which was attributed to the precipitation of α and ω phases. All of the compositions aged at 573K, 623K and 723K showed overaging within 80h.

High resolution transmission electron microscopy study of the hardening mechanism through phase separation in a beta-Ti-35Nb-7Zr-5Ta alloy for implant applications.

beta-Ti alloys are highly attractive metallic materials for biomedical applications due to their high specific strength, high corrosion resistance and excellent biocompatibility, including low elastic modulus. This work aims to clarify the hardening mechanism of a beta-Ti-Nb-Zr-Ta alloy using different characterization techniques. Ingots (50 g) of Ti-35Nb-7Zr-5Ta (wt.%) alloy were arc furnace melted in an Ar((g)) atmosphere, homogenized, hot rolled, solubilized and finally aged at several temperatures from 200 to 700 degrees C for 4 h. Microstructure characterization was performed using X-ray diffraction, optical microscopy, scanning and high resolution transmission electron microscopy (HR-TEM). The 4 h aging showed that the highest hardness values were found when aged at 400 degrees C and the HR-TEM images confirmed splitting of spots on the Fourier space map, which indicated the presence of a coherent interface between separated phases (beta and beta') and explains the hardening mechanism of the alloy. Through geometric phase analysis analysis, using the HR-TEM image, the localized strain map showed 5-10 nm domains of the beta and beta' phases. The combination of suitable values of yield strength, hardness and low Young's modulus makes Ti-35Nb-7Zr-5Ta alloy suitable for medical applications as a metallic orthopedic implant.