Key Engineering Materials Vols. 373-374

Abstract: In this work, we encapsulated the titanium oxide particles with a layer of Al2O3 by a sol-gel process and investigated the UV-shielding properties of the obtained Al2O3-TiO2 composites. In this method, Al(NO3)3 aqueous solution mixed with raw titanium oxide powder was hydrolyzed by adding NH3·H2O. The hydrated materials were calcined at 500°C and then the composite of Al2O3-TiO2 was prepared. Different techniques including ICP-AES, XRD, SEM-EDS, and TEM were used to characterize the raw TiO2 and encapsulated TiO2 particles. Chemical analysis showed that TiO2 mass content in the raw titanium oxide particles is 98.25%, and Al2O3 is just 0.75%. After modification, the percentage Al2O3 was increased to 4.48% due to the encapsulation of Al2O3. Trace elements analysis displayed that the concentration of the trace elements were much lower than their original content in the raw titanium oxide, which prove that proved that there was no impurities incorporated into in the sol-gel process. XRD analysis indicated that the modified titanium oxide powders are mainly in phase of rutile, ca. 99.1%, and the profiles exhibit no peaks of crystalline Al2O3 suggesting the layer of Al2O3 exists in amorphous phase. SEM image suggests that the size is in 80~600nm of the raw TiO2 granula and became rougher on the surface, the packing of the agglomerations got looser after modification with Al2O3. HRTEM image shows that the TiO2 particles was evenly coated with a packed layer ~8 nm in thickness. The UV-Vis absorbency experiments showed that the range of wavelength shielded was narrowed from 208-316 nm in the raw titanium oxide to 225-285 nm in the case of the Al2O3-TiO2. The average absorbency of UV was improved from 1.07 to 1.98 at the same content 1.0 μg/mL in the suspended solution. The results reflected that Al2O3 modification process improve the titanium oxide particles UV-shielding properties in selectivity and performance.

Abstract: Based on a high power CO2 laser beam passing by an integral mirror, the bioceramic coatings of gradient composition were designed and fabricated on titanium alloy substrate (Ti-6Al-4V). The relations among laser processing parameters, microstructure and thermal behavior of the gradient bioceramic coatings were investigated. The morphology of the composites was observed by scanning electron microscope (SEM). Phase composition of the coatings was analyzed by X-ray diffraction (XRD). And the thermal behavior of raw powders was evaluated through thermal gravimetry and differential scanning calorimetry (TG-DSC) test. The results demonstrated that the bioceramic coatings were metallurgically bonded to the titanium alloy substrate. The bioceramic coatings contained such bioactive phases as HA and β-TCP, which offered an advantageous condition for osseo-connection. The DSC thermograms showed the endothermic peaks at different temperature, which resulted from the different transitions process, respectively. Furthermore, the DSC results were in accordance with TG data of the powders and showed that with the increasing temperature the weight of sample accordingly decreased.

Abstract: The surface configuration, the size and the shell thickness of the microcapsule were investigated. The average size and shell thickness were 100-200μm and 10nm separately. The mechanism performance of the microcapsule was tested by Nano Indentation Test. The results showed that the shell material—UF behaved as a non-linear viscoelastic material that different from the macroscopical performance. Analyzed and computed the un-load curves by non-linear simulation, the results showed that Educed Modulus of the microcapsule was 8.201GPa, which was a little lower than that of the epoxy resin 9.26GPa. And it also proved that the self-repair microcapsule in the epoxy resin dope would break as the microcrack expanded in the matrix, and let out the repair agent to fill the crack and to recover the matrix.

Abstract: Surface modifications were performed on the tin-doped indium oxide (ITO) substrates for optoelectronic devices, using the different processing techniques. The effects of modification methods on the surface properties of ITO substrates were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ultraviolet-visible (UV-vis) spectrophotometer, standard goniometry and four-probe meter, respectively. The surface free energy as the sum of the dispersion and polar components was evaluated from the measured contact angles using the Owens-Wendt approach. Experimental results demonstrate that except the optical transmittance of the ITO, the surface properties including the stoichiometry, morphology, wettability and sheet resistance of the ITO substrates strongly depend on the modification methods. Compared with the other treatments, the oxygen plasma treatment increases the oxygen concentration and decreases the carbon concentration, reduces the surface roughness and the sheet resistance, and enhances the surface free energy and the polarity, and thereby more effectively improves the surface properties of ITO substrates.

Abstract: Initial attachment and spreading of the inoculated cells determines the long-time viability of cells onto biomedical scaffolds designed for various orthopedic or other clinical applications. The aim of this study was to investigate the influence of biomimetic thin film coating surfaces of bio-derived bone scaffolds with collagen proteins and chitosan on bone marrow mesenchymal stem cells interactions in order to improve cell adhesion, spreading and proliferation. These two merits were used synthetically to generate apatite-based materials that can function as allograft bone grafts in humans. In this study, the thin film coatings were operated by means of soaked, pre-frozen, and freeze-dried step by step. All coatings were characterized using Raman spectra, inverted microscope, atomic force microscopy, and scanning electron microscopy. After that, the bio-derived bone scaffolds with or without thin film coatings were used in bone marrow mesenchymal stem cell culture experiments to study cell adhesion, spreading, viability, proliferation and morphology. Then, the biological morphologies of the fabricated cell-scaffold constructs were detected by scanning electron microscope (SEM). The cell reactions were investigated concerning cell adhesion, migration, spreading, and proliferation under inverted microscope and fluorescence microscopy. The results showed that the bio-derived bone scaffold treated with thin film coatings by using rat-tail type I collagen and chitosan improved the adhesion and spreading of mesenchymal stem cells in comparison to the untreated one. Besides, cell viability and morphology were not affected by the presence of either type of thin film coating. Still, the results assay revealed an increased proliferation of bone marrow mesenchymal stem cells on both types of thin film coatings compared to coating with non-coated controls.

Abstract: WO3 and Ti-doped WO3 electrochromic films were prepared by mid-frequency dual-target magnetron sputtering method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and spectrophotometer were used to characterize the structure, morphology, composition and transmittance properties of the films, respectively. The results show that this method is available to deposit WO3 and Ti-doped WO3 electrochromic films. The as-deposited films prepared at room temperature are amorphous and display good transmittance. The difference value of transmittance between the bleached and coloration states of WO3 film is above 60% at 633nm. Ti-doped WO3 films have smoother surface and smaller grains than undoped ones. Moreover, the crystalline temperature increases after doping titanium, because the titanium atoms influence the lattice distortion of the WO3 films. So it is more convenient for Li+ ions to inject into films and can enhance the response speed and stability of Ti-doped WO3 electrochromic films.

Abstract: Vanadium oxide thin film which has a reversible semiconductor-metal phase transition has been obtained by reactive ion-beam sputtering and subsequent annealing in Ar gas. Micro-analysis shows that this thin film is homogeneous and compact, its spheric grain size is about 50nm and it is composed of VO2 and V2O5. Electrical properties testing indicate that its phase transition temperature is near 60°C, abrupt change of resistivity before and after phase transition is approximate to 3 orders of magnitude, temperature coefficient of resistance (TCR) is about -0.0393K-1 at 25°C and activation energy is about 0.3006eV at the range of low temperature. Using a pulse laser beam with wavelength of 1064nm and pulse width of 10ns, laser damage threshold was obtained to be 20.1mJ/cm2. Damage spot morphology of the film was also researched carefully to discover its laser damage mechanism. All results above prove that this thin film is a perfect thermo-sensitive material that can be used for uncooled infrared detector and laser protection.

Abstract: Owing to the excellent biocompatibility and corrosion-resistance of titanium and bioactivity of hydroxyapatite, the titanium/hydroxyapatite composite material combining their advantages is a highlight with bright prospects in medical clinics. In the present paper, the microarc oxidation (MAO) was performed on commercial pure titanium at first. Furthermore, the hydrothermal treatment (HT)was given with media of deionized water at 200°C for 4h in an autoclave. The surface morphology of the samples was observed by scanning electron microscopy (SEM), and the detailed composition was analyzed with Energy-Dispersive X-Ray Spectroscopy (EDS). The X-ray diffraction analysis (XRD) was employed to characterize the crystal structure of composite. The results indicate that the titania film contains the Ca and P elements on titanium substrate after MAO, which converts into the hydroxyapatite crystals via hydrothermal treatment. The smaller size and amount of hydroxyapatite crystals are found when lower voltage is presented. But there are converse phenomena with higher voltage, especially, the differences can be neglected above 400V. It is shown that the micro-hole and hollow surface of titania film can induce the hydroxyapatite nucleation and growth as two different forming ways. The hydroxyapatite has a preference of forming in hollow surface with lower voltage, however, the presences of the micro-hole and hollow surface of titania film are occurring for higher voltage. The hydroxyapatite forming in micro-hole shows needle-like crystal and high bonding strength with surrounding titania film because of the mechanical restrict force from micro-hole wall. Also it is noted that hydroxyapatite crystals incline to precipitate on the film surface with high Ca and P concentrations after the hydrothermal treatment.

Abstract: Recently, combination of ductile carbonaceous materials with the metallic Sn has received a great deal of interest to be a novel anode material for lithium ion batteries, because of their higher capacity than the conventional graphite anodes and better cycleability than the pure Sn anodes. Electrochemical performance of the Sn/C composite anodes is influenced by the material system, particle size and size distribution of Sn as well as the amount of deposited Sn. This study revealed that a favorable Sn/C composite anode exhibited reduced size and uniformly distributed tin particles. The crystal structure, morphology and elemental distribution were analyzed by XRD patterns, SEM and EPMA, respectively. The carbothermal-reducted Sn/Mesophase graphite powder (MGP) composite anodes exhibited much higher capacity than the bare MGP, and the initial efficiency was also much higher than the metallic tin anode in literatures.

Abstract: TiCl4 treatment was used to chemically agglomerate TiO2 primary nano-particles to form a nanostructured powder in size of submicrometer. Nanocrystalline TiO2 coatings were fabricated by vacuum cold spraying at room temperature using the powder and were employed to assemble dye-sensitized solar cells. TiO2 coating of 10-20μm in thickness was deposited successfully on both F-doped tin oxide (FTO) conducting glass and plastic conducting substrate. The assembled solar cell with an FTO conducting glass yielded a short-circuit current density of 9.7 mA/cm2 and an energy conversion efficiency of 3.3%. Using the plastic substrate, the cell efficiency was 1.9%. These results suggest that TiCl4-treated nanocrystalline TiO2 agglomerates can be used to deposit TiO2 coating by vacuum cold spraying at low temperature for flexible dye-sensitized solar cells.