Showing papers on "Titanium published in 2016"

Selective Laser Melting of Titanium Alloys and Titanium Matrix Composites for Biomedical Applications: A Review†

Abstract: Titanium materials are ideal targets for selective laser melting (SLM), because they are expensive and difficult to machinery using traditional technologies. After briefly introducing the SLM process and processing factors involved, this paper reviews the recent progresses in SLM of titanium alloys and their composites for biomedical applications, especially developing new titanium powder for SLM. Although the current feedstock titanium powder for SLM is limited to CP-Ti, Ti–6Al–4V, and Ti–6Al–7Nb, this review extends attractive progresses in the SLM of all types of titanium, composites, and porous structures including Ti–24Nb–4Zr–8Sn and Ti–TiB/TiC composites with focus on the manufacture by SLM and resulting unique microstructure and properties (mechanical, wear/corrosion resistance properties).

Recent advances in titanium-based electrode materials for stationary sodium-ion batteries

Abstract: Recently, the attention to sodium-ion batteries has been refocused on large-scale energy storage applications, due to sodium's low cost and infinite abundance. Sodium is one of the most abundant elements on earth and exhibits chemical properties similar to lithium. Owing to their superior sodium storage capability especially for excellent safety and stability, Ti-based compounds have been extensively investigated as both cathode and anode materials. Herein we outline the current cathodes and anodes, and emphasize the critical roles of titanium in developing advanced electrodes for sodium-ion batteries. The latest advances and progress in the exploration of Ti-based compounds with various different frameworks such as NASICON, tunnel, MXenes, spinel, and layered structures are systematically reviewed. The straightforward linking of the structure–function–property relationship for Ti-based compounds, especially for layered Na/Ti-containing oxides, is summarized and analyzed. The titanium element plays a critical role in both positive and negative electrodes, i.e., supplying the charge transfer and high safety for anodes and greatly enhancing the structural and cycling stability for cathodes. Based on the bi-functional roles of titanium, a new concept of symmetric Na-ion cells employing layered Na/Ti-containing oxides as bipolar electrodes is proposed and realized. Symmetric Na-ion cells already offered a high voltage and withstood long time charge–discharge processes, demonstrating the practicality beyond the proof of concept. The participation of titanium in sodium-based electrode materials will greatly promote the development of room-temperature sodium-ion batteries towards stationary energy storage.

Transition Metal Nitride Coated with Atomic Layers of Pt as a Low-Cost, Highly Stable Electrocatalyst for the Oxygen Reduction Reaction

Abstract: The main challenges to the commercial viability of polymer electrolyte membrane fuel cells are (i) the high cost associated with using large amounts of Pt in fuel cell cathodes to compensate for the sluggish kinetics of the oxygen reduction reaction, (ii) catalyst degradation, and (iii) carbon-support corrosion. To address these obstacles, our group has focused on robust, carbon-free transition metal nitride materials with low Pt content that exhibit tunable physical and catalytic properties. Here, we report on the high performance of a novel catalyst with low Pt content, prepared by placing several layers of Pt atoms on nanoparticles of titanium nickel binary nitride. For the ORR, the catalyst exhibited a more than 400% and 200% increase in mass activity and specific activity, respectively, compared with the commercial Pt/C catalyst. It also showed excellent stability/durability, experiencing only a slight performance loss after 10,000 potential cycles, while TEM results showed its structure had remained intact. The catalyst's outstanding performance may have resulted from the ultrahigh dispersion of Pt (several atomic layers coated on the nitride nanoparticles), and the excellent stability/durability may have been due to the good stability of nitride and synergetic effects between ultrathin Pt layer and the robust TiNiN support.

Surface thermal oxidation on titanium implants to enhance osteogenic activity and in vivo osseointegration.

Abstract: Thermal oxidation, which serves as a low-cost, effective and relatively simple/facile method, was used to modify a micro-structured titanium surface in ambient atmosphere at 450 °C for different time periods to improve in vitro and in vivo bioactivity. The surface morphology, crystallinity of the surface layers, chemical composition and chemical states were evaluated by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Cell behaviours including cell adhesion, attachment, proliferation and osteogenic differentiation were observed in vitro study. The ability of the titanium surface to promote osseointegration was evaluated in an in vivo animal model. Surface thermal oxidation on titanium implants maintained the microstructure and, thus, both slightly changed the nanoscale structure of titanium and enhanced the crystallinity of the titanium surface layer. Cells cultured on the three oxidized titanium surfaces grew well and exhibited better osteogenic activity than did the control samples. The in vivo bone-implant contact also showed enhanced osseointegration after several hours of oxidization. This heat-treated titanium enhanced the osteogenic differentiation activity of rBMMSCs and improved osseointegration in vivo, suggesting that surface thermal oxidation could potentially be used in clinical applications to improve bone-implant integration.

Activating earth-abundant electrocatalysts for efficient, low-cost hydrogen evolution/oxidation: sub-monolayer platinum coatings on titanium tungsten carbide nanoparticles

Abstract: Most earth-abundant electrocatalysts suffer from negligible activity for the hydrogen oxidation reaction (HOR) and significant overpotentials for the hydrogen evolution reaction (HER) in acidic media. We designed earth-abundant, carbon-supported titanium tungsten carbide (TixW1−xC) nanoparticles decorated with surface Pt coatings ranging from the “single-atom” to the two-monolayer regime. Reactivity studies demonstrated that sub-monolayer Pt coverages are optimal and could activate the exposed metal carbide sites for both HER and HOR at low overpotentials. Specifically, a 0.25 monolayer coverage of Pt improved the exchange current density of Ti0.2W0.8C by more than three orders of magnitude. This catalyst outperformed traditional Pt/C by a factor of 13 on a Pt mass basis, allowing for over a 96% reduction in Pt loadings. Deactivation was not observed after 10 000 cycles between −50 and +600 mV vs. RHE in 1.0 M HClO4, and activity was maintained after 140 000 catalytic turnovers. A technoeconomic analysis revealed that over the catalyst lifetime, this new architecture could reduce materials and energy costs by a factor of 6 compared to state-of-the-art earth-abundant catalysts and a factor of 12 compared to Pt/C.

Rolling-induced Face Centered Cubic Titanium in Hexagonal Close Packed Titanium at Room Temperature

Abstract: Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline hexagonal close packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: 〈0001〉hcp||〈001〉fcc and , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pure-shuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning.

Gold‐Nanoparticle‐Loaded Carbonate‐Modified Titanium(IV) Oxide Surface: Visible‐Light‐Driven Formation of Hydrogen Peroxide from Oxygen

Abstract: Gold nanoparticle-loaded rutile TiO2 with a bimodal size distribution around 10.6 nm and 2.3 nm (BM-Au/TiO2) was prepared by the deposition precipitation and chemical reduction (DP-CR) technique. Visible-light irradiation (λ>430 nm) of the BM-Au/TiO2 plasmonic photocatalyst yields 35 μm H2O2 in aerated pure water at irradiation time (tp)=1 h, and the H2O2 concentration increases to 640±60 μm by the addition of 4 % HCOOH as a sacrificing electron donor. Further, a carbonate-modified surface BM-Au/TiO2 (BM-Au/TiO2-CO32−) generates a millimolar level of H2O2 at tp=1 h with a quantum efficiency (Φ) of 5.4 % at λ=530 nm under the same conditions. The recycle experiments confirmed the stable performance of BM-Au/TiO2.

Influence of iridium oxide loadings on the performance of PEM water electrolysis cells: Part II – Advanced oxygen electrodes

Abstract: The purpose of this research paper is to report on the applicability of micro-sized titanium particles as the support of IrO2 particles at the anode of PEM water electrolysis cells. A PEM single cell containing only 0.1 mg cm −2 of IrO2 as anode catalyst and 50 wt.% metallic Ti achieved 1.73 V at 1 A cm −2 and 80 °C. Such level of performance is similar to those usually obtained with conventional loadings of several mg cm −2 of IrO 2 at the anode side. SEM observations and EIS measurements revealed that the micro-sized titanium particles added to the anodic catalyst layer favor an intimate electrical contact between the catalyst layer and the current collector, and contribute to the reduction of the ohmic resistance of the catalytic layer. A long-term water electrolysis experiment using IrO 2 /Ti as anode material demonstrated a good stability of the MEA over 1000 h of operation. Using such a low IrO 2 loading (0.1 mg cm −2 IrO 2 ), the degradation rate measured at 1 A cm −2 was reduced from 180 μV h −1 (measurement made on pure IrO 2 anode) down to only 20 μV h −1 for the 50 wt.% IrO 2 /Ti anode.

Titanium incorporated with UiO-66(Zr)-type Metal–Organic Framework (MOF) for photocatalytic application

Abstract: A UiO-66-type metal–organic framework (MOF) fabricated with titanium was successfully prepared via a facial modified post-grafting method. The as-prepared samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet-visible adsorption spectroscopy (UV-vis), and photoluminescence spectroscopy (PL) techniques. The introduction of titanium enhanced the optical properties of UiO-66 via the formation of oxo-bridged hetero-Zr–Ti clusters, but led to a sacrifice in crystallinity. The removal of methylene blue (MB) over these samples could be attributed to the dual function of the adsorption and photo-degradation mechanisms. The highest MB removal efficiency of 87.1% was achieved over UiO-66(1.25Ti) under simulated sun-light irradiation.

Analysis and Characterization of the Role of Ni Interlayer in the Friction Welding of Titanium and 304 Austenitic Stainless Steel

Abstract: Joining of commercially pure Ti to 304 stainless steel by fusion welding processes possesses problems due to the formation of brittle intermetallic compounds in the weld metal, which degrade the mechanical properties of the joints. Solid-state welding processes are contemplated to overcome these problems. However, intermetallic compounds are likely to form even in Ti-SS joints produced with solid-state welding processes such as friction welding process. Therefore, interlayers are employed to prevent the direct contact between two base metals and thereby mainly to suppress the formation of brittle Ti-Fe intermetallic compounds. In the present study, friction-welded joints between commercially pure titanium and 304 stainless steel were obtained using a thin nickel interlayer. Then, the joints were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, and X-ray diffractometry. The mechanical properties of the joints were evaluated by microhardness survey and tensile tests. Although the results showed that the tensile strength of the joints is even lower than titanium base metal, it is higher than that of the joints which were produced without nickel interlayer. The highest hardness value was observed at the interface between titanium and nickel interlayers indicating the formation of Ni-Ti intermetallic compounds. Formation these compounds was validated by XRD patterns. Moreover, in tensile tests, fracture of the joints occurred along this interface which is related to its brittle nature.

The roles of different titanium species in TS-1 zeolite in propylene epoxidation studied by in situ UV Raman spectroscopy

Abstract: Titanium silicalite (TS-1) zeolites with different titanium species were synthesized and characterized by ultraviolet (UV)-Raman, ultraviolet visible (UV-Vis) diffuse reflectance spectroscopies and by the NH3 temperature programmed desorption (NH3-TPD) method. The roles of different titanium species in TS-1 samples have been investigated by gas chromatography-Raman spectrometry (GC-Raman) during the propylene epoxidation process. For the first time, a positive correlation was found among the concentration of framework Ti species, the amount of active intermediate Ti-OOH (η(2)) and the conversion of propylene by the in situ GC-Raman technique. The results give evidence that the framework titanium species is the active center and Ti-OOH (η(2)) is the active intermediate. The presence of extra-framework Ti species is harmful to propylene epoxidation. Furthermore, the amorphous Ti species has a more negative effect on the yield of propylene oxide (PO) than the anatase TiO2. The NH3-TPD results reveal that the amorphous Ti species are more acidic and thus should be mainly responsible for the further conversion of PO.

MoS2–Titanium Contact Interface Reactions

Abstract: The formation of the Ti–MoS2 interface, which is heavily utilized in nanoelectronic device research, is studied by X-ray photoelectron spectroscopy. It is found that, if deposition under high vacuum (∼1 × 10–6 mbar) as opposed to ultrahigh vacuum (∼1 × 10–9 mbar) conditions are used, TiO2 forms at the interface rather than Ti. The high vacuum deposition results in an interface free of any detectable reaction between the semiconductor and the deposited contact. In contrast, when metallic titanium is successfully deposited by carrying out depositions in ultrahigh vacuum, the titanium reacts with MoS2 forming TixSy and metallic Mo at the interface. These results have far reaching implications as many prior studies assuming Ti contacts may have actually used TiO2 due to the nature of the deposition tools used.

Structures, preparation and applications of titanium suboxides

Abstract: The crystal structure, physical and chemical properties, and applications of titanium suboxides (TinO2n−1, n = integer greater than one) have recently attracted tremendous attention. In this paper, the structure and physical properties of titanium suboxides are summarized, and recent progress in their synthesis methods and applications in catalysis, environmental, electronic and optoelectronic devices and batteries is reviewed. The presence of two Ti3+ and (n − 2)Ti4+ provides TinO2n−1 with several possible configurations of cations in the crystal, various charge-ordered states and electronic structures which lead to their versatile physical properties, such as conductivity, magnetic and optical properties. A series of TinO2n−1 has been synthesized by redox reduction of different titanium sources of TiO2 and other raw materials. Notably, Magneli phase titanium oxides (typically n is between 4 and 6) have played very important roles in Pt-catalyst support, organic degradation, coatings and supports in various electronic and optoelectronic devices. Undoubtedly, titanium suboxides are expected to become indispensable materials in future.

Heterogeneous titanium catalysts for oxidation of dibenzothiophene in hydrocarbon solutions with hydrogen peroxide: On the road to oxidative desulfurization

Abstract: Titanium centers grafted on hydrophobic silica bearing long chain silanes (octadecyl or octyl) are able to oxidize dibenzothiophene (DBT), as well as simpler sulfides and 2,6-dimethyldibenzothiophene, to the corresponding sulfone in hydrocarbon solution with aqueous hydrogen peroxide in only a slight excess over the stoichiometric amount, without using any surfactant or cosolvent. The productivity per gram of catalyst or per Ti site can be optimized by tuning the silanization of the silica (or using a commercially available silanized silica) and the Ti loading of the catalyst. The catalyst preparation and the oxidation reaction are compatible with the use of an industrial grade aromatic solvent.