Microstructure and Electrochemical Characterization of Ti-Sn Binary Alloys for Dental Applications.

This work investigated the microstructure and corrosion behaviors of Ti-Sn alloys with x wt% Sn (x = 5, 10, 15, and 20) for dental applications. The microstructures of commercially pure titanium (cp-Ti) and Ti-Sn alloys were characterized by X-ray diffractometry, optical microscopy, and transmission electron microscopy. The Vickers hardness of the Ti-Sn alloys was compared to that of cp-Ti. The corrosion behaviors of Ti-Sn alloys were tested in 0.9% NaCl solution at 37 °C using open circuit potential, potentiodynamic polarization, AC impedance, and galvanic corrosion tests. Ti-Sn alloys had a hexagonal close-packed structure and their microstructures were transformed from the equiaxed structure with irregular grain boundaries to the martensitic structure as the content of Sn in Ti-Sn alloys increased by over 15 wt%. Among the sample groups, Ti-15Sn and Ti-20Sn alloys exhibited better Vickers hardness values. Ti-Sn alloys had better corrosion resistance than cp-Ti. Ti-15Sn, which showed narrow martensitic bands, exhibited the highest corrosion resistance properties in AC impedance measurements due to its higher resistance and better capacitive parameters. Among the tested groups, the galvanic coupling of Ti-15Sn with cp-Ti showed higher corrosion potentials and lower current densities, which indicates that there was higher corrosion resistance.

Osteoconductivity of Binary Titanium Alloys with Different Micro/Nanoporous Surfaces.

The surface characteristics and osteoconductivity were evaluated for the micro/nanoporous surfaces of titanium (Ti) alloys prepared by micro-arc oxidation (MAO) and hydrothermal treatment (HT) of binary Ti-5 wt% A alloys (A = Au, Mn, Nb, and Pd). Surface properties were analyzed using X-ray diffractometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The osteoconductivity was evaluated by measuring the total protein, ALPase activity, and osteocalcin production. The surface morphologies of MAO/HT specimens mainly affected on their osteoconductivity. Total proteins on Ti alloys (MAO/HT) were slightly lower than that on commercially pure Ti (MAO/HT) after incubation of MG-63 osteoblast-like cells for 14 days. However, better ALPase activity and osteocalcin production were observed on MAO/HT-treated Ti­5Mn, Ti­5Nb, and Ti­5Pd than that on cp-Ti (MAO/HT) after 14 days. Especially, Ti­5Mn (MAO/HT) showed a significant increase of ALPase activity due to its well grown micro/nano structure. Meanwhile, very small nanorods on Ti­5Au (MAO/HT) affected negatively to ALPase activity and osteocalcin production.

Surface Characterization and Osteoconductivity Evaluation of Micro/Nano Surface Formed on Titanium Using Anodic Oxidation Combined with H2O2 Etching and Hydrothermal Treatment.

In this study, surface characteristics and osteoconductivity were investigated for the micro/nanostructured oxide layers fabricated on titanium using anodic oxidation (ANO), chemical etching (Et), and hydrothermal treatment (HT). Commercially pure titanium (CP-Ti) disks were anodic-oxidized using DC-type power supply in 1 M phosphoric acid electrolyte (P-ANO group). These specimens were further chemically etched using 30% H2O2 solution at 60 °C for 10 min (P-ANO-Et group). The P-ANO-Et-HT group was fabricated by hydrothermally treating the P-ANO-Et specimens in phosphorus-containing alkaline solution at 190 °C for 8 hrs. The P-ANO group showed a porous surface that was evenly covered with micro- and sub-micro pores. The size of these pores was decreased in the P-ANO-Et group. The P-ANO-Et-HT group showed a porous surface that was covered with nano-sized crystallites. Anatase TiO2 structure was observed in P-ANO-Et-HT group. The results of XPS demonstrated that the P-ANO-Et-HT group had a well-crystallized TiC2 structure, while the P-ANO and P-ANO-Et groups had an amorphous and phosphate-containing structure. Hydrophilicity of the P-ANO-Et-HT group was the highest. After MG63 osteoblast-like cells were cultured on the specimens for 3 hrs, SEM images of the cells cultured on P-ANO-Et-HT group specimens showed low initial adhesion. However, the osteoconductivity of these specimens increased more rapidly compared to that of the micro-structured surfaces. These results could be applied to fabricate titanium implants with an optimum micro/nano-surface for enhancing their osteoconductivity.

Effect of Nb on the Microstructure, Mechanical Properties, Corrosion Behavior, and Cytotoxicity of Ti-Nb Alloys.

In this paper, the effects of Nb addition (5-20 wt %) on the microstructure, mechanical properties, corrosion behavior, and cytotoxicity of Ti-Nb alloys were investigated with the aim of understanding the relationship between phase/microstructure and various properties of Ti-xNb alloys. Phase/microstructure was analyzed using X-ray diffraction (XRD), SEM, and TEM. The results indicated that the Ti-xNb alloys (x = 10, 15, and 20 wt %) were mainly composed of α + ß phases with precipitation of the isothermal ω phase. The volume percentage of the ω phase increased with increasing Nb content. We also investigated the effects of the alloying element Nb on the mechanical properties (including Vickers hardness and elastic modulus), oxidation protection ability, and corrosion behavior of Ti-xNb binary alloys. The mechanical properties and corrosion behavior of Ti-xNb alloys were found to be sensitive to Nb content. These experimental results indicated that the addition of Nb contributed to the hardening of cp-Ti and to the improvement of its oxidation resistance. Electrochemical experiments showed that the Ti-xNb alloys exhibited superior corrosion resistance to that of cp-Ti. The cytotoxicities of the Ti-xNb alloys were similar to that of pure titanium.

Massive Transformation in Titanium-Silver Alloys and Its Effect on Their Mechanical Properties and Corrosion Behavior.

In order to investigate the relationship between phase/microstructure and various properties of Ti-xAg alloys, a series of Ti-xAg alloys with Ag contents ranging from 5 to 20 wt% were prepared. The microstructures were characterized using X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All of the Ti-xAg alloys showed a massive transformation from the ß-Ti to αm phase, which has a different crystal structure from that of the matrix phase, but it has the same composition as the matrix α-Ti phase. As a result of solid-solution strengthening of α-Ti and massive transformation phase, the Ti-xAg showed better mechanical properties than the commercially pure titanium (cp-Ti). Electrochemical results showed that the Ti-xAg alloys exhibited improved corrosion resistance and oxidation resistance than cp-Ti.

Preparation of MoO3/MoS2/TiO2 composites for catalytic degradation of methylene blue.

Metastable hexagonal MoO3 microrods were grown from bulk MoS2 and used as support materials for MoS2 and TiO2 nanoparticles. The hybrid composites that consisted of MoO3, MoS2, and TiO2 were prepared at a low temperature using the one-step synthesis method. The crystallinity and morphology of the MoO3/MoS2/TiO2 composites that were prepared using HNO3 and titanium tetraisopropoxide were compared with those of the MoO3/MoS2 composites that were prepared without titanium tetraisopropoxide. Titanium isopropoxide facilitated the formation of the MoO3 microrods from the oxidation of the bulk MoS2. The desired MoO3/MoS2/TiO2 composites were obtained using 0.5 g of bulk MoS2, 3-4 ml of HNO3, and 0.367 ml of titanium tetraisopropoxide. The MoO3/MoS2/TiO2 composites that were treated with ultrasonic waves showed rapid degradation of the methylene blue solution (2 x 10(-4) M) in the dark and good photocatalytic ability under ultraviolet light irradiation. The decomposition of methylene blue depended on the composition of the composite.

Fabrication of nanopore YSZ from YSZ and ZnO mixture.

Porous Yttria Stabilized Zirconia (YSZ) with macropore and nanopore was fabricated from sintering and leaching the mixture of YSZ and different types of ZnO. When we used nano-sized crystalline particle, porous YSZ with submicron pores was obtained. In the case of the spherical 30 nm to 100 nm ZnO particles obtained from hydrolysis of zinc acetate in methanol, 2 approximately 10 nm sized pores was observed in the YSZ. From the results, it was suggested that crystalline ZnO particles grew up while the spherical noncrystalline ZnO particles were enclosed in YSZ matrix in the sintering process.

A study on electric conductivity of phosphoric acid supported on nano-pore rice husk silica in H2/Pt/H3PO4 / RHS/Pt/O2 fuel cells.

PEMFC (Polymer Electrolyte Membrane Fuel Cell) is widely considered as an energy conversion system from the chemical energy of hydrogen to electric energy. But, hydrogen fuel obtained from hydrocarbons has trace amount of carbon monoxide which is a potential poison for platinum electrode at the cell operating temperature approximately 100 degrees C and it becomes a huddle for the general usage of PEMFC. On the other hand PAFC (Phosphoric Acid Fuel Cell) operates at a higher temperature and the platinum electrode oxidizes carbon monoxide poison while there is a leakage problem of the liquid phase. To combine the advantages of two fuel cells, the electrolyte systems of phosphoric acid supported silica on ceramics are recently being tested. In this study, we investigated the nm pore rice husk silica as a support for phosphoric acid and tested the electric conductivity of the silica plate and the characteristics of a prototype fuel cell H2/Pt/H3PO4 / RHS/Pt/O2 at 100-200 degrees C. The conductivity of H3PO4/RHS was 8 mS cm(-1) above 175 degrees C under 200 torr H2O. In the fuel cell, the apparent conductance of the electrolyte from I-V characteristics was 2.45 mS/cm at 160 degrees C under 1 atm H2 and air at present.