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Fu T.,Xi'an Jiaotong University | Fu T.,Xi'an University of Science and Technology | Liu B.,Xi'an Jiaotong University | Dong B.,Xi'an Jiaotong University | And 3 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

A low modulus near (type titanium alloy (Ti-25Nb-3Zr-2Sn-3Mo, or TLM alloy) was subjected to hydrothermal treatments with a urea solution at different temperatures followed by heat treatment. The surface structure, the chemical composition, adhesion and hydrophilicity of the treated TLM alloy were investigated by SEM, XRD, XPS, Rockwell-C indentation test and contact angle measurement. The results show that nanosheet films of ammonium titanate can be formed at 105 and 120°C , while the nanoparticle film of anatase TiO2 containing Nb2O5 is formed at 150°C on the alloy surface. The subsequent annealing heat treatment at 400°C can decompose the ammonium salts and crystallize titania. The obtained oxide films have a good adhesion. The duplex treatment has enhanced the hydrophilicity of the TLM alloy, and it would be good for its biocompatibility. Copyright © 2014, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.

Fu T.,Xi'an Jiaotong University | Alajmi Z.,Xi'an Jiaotong University | Yang S.Y.,Xi'an Jiaotong University | Zhou Y.M.,Xi'an Jiaotong University | And 2 more authors.
Journal of Sol-Gel Science and Technology | Year: 2014

Pure and Ag-containing TiO2 films (Ag/Ti = 3.3 at.%) are coated on plasma nitrided 316L stainless steel by sol-gel method for biomedical applications. The addition of Ag does not cause obvious change in TG-DSC curves of the dried gels. The rough surface generated by plasma nitriding and the addition of Ag improve structural integrity of the TiO2 films. X-ray diffraction reveals N loss and oxidation of the nitride layer during calcination treatment, and peaks of Ag or its oxides are not detected. X-ray photoelectron spectroscopy analysis indicates that Ag presents as metallic state in the film. Water contact angles of the coating samples decrease with UV irradiation treatment. The potentiodynamic polarization tests in a Ca-free Hank's balanced salt solution show that the TiO2 coated samples have decreased corrosion resistance due to N loss and oxidation of the nitride layer. The methods for crystallization of TiO2 gel layers with minimized or avoided structural changes of the nitride layer will be tried in order to improve corrosion resistance of the duplex treated 316L stainless steel. © 2013 Springer Science+Business Media New York.

Fu T.,Xi'an Jiaotong University | Shen Y.,City University of Hong Kong | Alajmi Z.,Xi'an Jiaotong University | Wang Y.,Xi'an Jiaotong University | And 2 more authors.
Ceramics International | Year: 2014

Ag-containing TiO2 films (Ag/Ti=3.3, 9.1 at%) were sol-gel coated on NiTi alloy that had been surface roughened by the NaOH-HCl treatment for antibacterial application. Thermal analyses of the dried gels reveal that the addition of 9.1 at% Ag lowers the anatase-rutile transformation temperature from 618 to 586 °C. Morphological observation shows that surface roughening and silver addition improve structural integrity of the TiO2 films. X-ray diffraction reveals that the addition of Ag does not obviously change crystallinity of the anatase films. X-ray photoelectron spectroscopy results indicate metallic nature of Ag in the film and complete coverage of the films on the roughened alloy substrate. Microindentation test exhibits that the Ag-TiO2 film on the roughened substrate has higher cohesive strength than that on the polished substrate. The potentiodynamic polarization test in a Ca-free Hank's balanced salt solution demonstrates good protection of the TiO2 and Ag-TiO2 films for the alloy substrate. Ultraviolet light illumination for 3 h can increase surface hydrophilicity of the coated NiTi samples by reducing contact angles from >65° to <20°. © 2014 Elsevier Ltd and Techna Group S.r.l.

Jia B.,Beijing Institute of Technology | Song W.,Beijing Institute of Technology | Tang H.,State Key Laboratory of Porous Metal Materials | Mao X.,Northwest Institute for Nonferrous Metal Research | Ning J.,Beijing Institute of Technology
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

The hot deformation behavior of Ti600 alloy at deformation temperatures ranging from 25 to 800 ℃ and strain rates of 10-4 and 10-3 s-1 was studied by isothermal compression on a WDW-300 electronic universal testing machine. GW-1200A controller and high-temperature furnace were used to provide an accurate temperature control and measurement during testing. The true stress-true strain curves of Ti600 alloy were obtained. The results show that the flow stress of Ti600 alloy does not change obviously with the increasing of strain rate at lower temperatures (25 and 300 ℃), while it increases with the increasing of strain rate at higher temperatures (600 and 800 ℃), and the flow stress decreases with the increasing of temperature at the same strain rate. Based on the experimental results of true stress-true strain curves of Ti600 alloy at different temperatures, a modified Inoue Katsuro constitutive model was established to explore the flow stress of Ti600 alloy at elevated temperatures. A good agreement between the model predictions and the experimental results is derived, which verifies the reliability of the model. The fracture mode of Ti600 alloy at room temperature after the quasi-static compression was analyzed using scanning electron microscopy (SEM) and results show that the alloy is mainly of brittle fracture with some ductile fracture in the local region of the fracture surface.

Liu J.-K.,Shanxi University | Liu J.-K.,Central South University | Zheng Z.-S.,Central South University | Zheng Z.-S.,State Key Laboratory of Porous Metal Materials
Applied Mathematics and Mechanics (English Edition) | Year: 2014

An efficient high-order immersed interface method (IIM) is proposed to solve two-dimensional (2D) heat problems with fixed interfaces on Cartesian grids, which has the fourth-order accuracy in the maximum norm in both time and space directions. The space variable is discretized by a high-order compact (HOC) difference scheme with correction terms added at the irregular points. The time derivative is integrated by a Crank-Nicolson and alternative direction implicit (ADI) scheme. In this case, the time accuracy is just second-order. The Richardson extrapolation method is used to improve the time accuracy to fourth-order. The numerical results confirm the convergence order and the efficiency of the method. © 2014, Shanghai University and Springer-Verlag Berlin Heidelberg.

Liu Z.,University of Queensland | Liu Z.,Northeastern University China | Liu Z.,State Key Laboratory of Porous Metal Materials | Horikawa T.,University of Queensland | And 3 more authors.
Journal of Colloid and Interface Science | Year: 2012

Using Grand Canonical Monte Carlo simulation, we have studied the effects of confinement on argon and methanol adsorption in graphitic cylindrical and slit pores. Linear chain, zigzag and incomplete helical packing are observed for argon adsorption in cylindrical pores. However, for methanol adsorption different features appear because the electrostatic interactions favour configurations that maximize the hydrogen bonding among methanol molecules. We have found zigzag chains with hydrogen-bonded structures for methanol adsorption in cylindrical and slit pores. To investigate how dense the adsorbed phase is and how many molecules could be packed per unit physical volume of the solid, we consider two different definitions of pore density; one based on the physical volume and the other on the accessible volume. That based on accessible volume gives a measure of the fluid density, while that based on the physical volume gives a measure of how much adsorbate can be stored per unit volume of the adsorbent. It is found that the adsorbate is denser in cylindrical pores, but that slit pores can pack more molecules per unit solid volume. We also discuss the effects on the isosteric heat of argon and methanol of pore size, pore geometry and loading. © 2011 Elsevier Inc..

Liu Z.,Northeastern University China | Liu Z.,University of Queensland | Do D.D.,University of Queensland | Nicholson D.,University of Queensland | Xi Z.,State Key Laboratory of Porous Metal Materials
Adsorption Science and Technology | Year: 2010

This paper describes an investigation of argon adsorption into carbon nanotubes at temperatures below the triple point, using a grand canonical Monte Carlo simulation to study the effects of confinement and surface strength on the 2D transition. In large pores, it was found that 2D transitions can occur in more than one layer, but are absent in higher layers for small pores. The 2D critical temperature of the first layer for a small pore (R = 1.2 nm) was found to be ca. 66 K (MWCNT) and 65 K (SWCNT), compared to 55-59 K observed experimentally for a flat graphite surface. This is because of the overlapping effects due to the surface curvature or the confinement in a carbon nanotube. Assuming a weaker carbon surface by reducing the graphene surface strength by 40% for SWCNT, the 2D critical temperature was only modestly reduced to 63 K. This suggests that the experimental data at 59 K might be attributed to other factors, other than confinement effects. An imperfect surface is suggested and, employing 5% defects on this surface, the 2D critical temperature has been determined as 58 K which is in better agreement with the experimental value of 59 K.

Liu Z.,University of Queensland | Liu Z.,State Key Laboratory of Porous Metal Materials | Liu Z.,Northeastern University China | Do D.D.,University of Queensland | Nicholson D.,University of Queensland
Molecular Simulation | Year: 2012

We present a thermodynamic analysis of the mid-density scheme that was introduced recently as a simple alternative to more complex methods (such as the gauge cell and the thermodynamic integration procedures) for determining the equilibrium phase transition in pores. A construction of configurations having densities falling between those of the low- and high-density states inside the hysteresis loop is carried out with a canonical Monte Carlo simulation (NVT, where the number of particles N, the system volume V and the temperature T in the system are constant), and it is found that this nucleation state has two coexisting phases of alternating liquid bridges and gas cavities. This state is maintained at a threshold chemical potential, μ eq (obtained with the Widom insertion method), which is the coexistence chemical potential. When this nucleation state is in contact with an infinite reservoir (grand canonical ensemble) of chemical potential less than μ eq, the system will evolve to a low-density state. On the other hand, when it is exposed to a chemical potential greater than μ eq, the system will evolve to a high-density state. We test this method with a number of examples of cylindrical pores, and investigate the effects of the pore size, the simulation box length for the case of infinite pores, the pore length for the case of finite pores and the temperature. When the pore is finite in length, the coexistence is no longer a first-order transition, like the one observed in an infinitely long pore, but instead shows a second-order transition with a continuous, but sharp change from a low-density state to a high-density state. © 2012 Copyright Taylor and Francis Group, LLC.

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