Papers by Author: Xin De Bai

Abstract: To improve its visible light response capability, a new narrow bandgap zinc ferrite semiconductor was in-situ introduced into the matrix of titanium dioxide nano film. ZnFe2O4 doped TiO2 composite films have been successfully formed on glass and stainless steel substrates from aqueous solution through equilibrium reaction between iron (III)-titanium (IV)-fluoric complex and boric acid, followed by in-situ hydrothermal conversion and crystallization in the Zn2+-contained basic environment. The obtained films were densely packed and had no visible cracks; clear photovoltaic responses were observed in the anodic direction, and they were much larger in the presence of ferrite dopant. It is suggested that the shift of the corrosion potential was ascribed to photo-induced charge separation between the conduction band of ZnFe2O4 and its counterpart TiO2 nano-particles.

Abstract: TiO2 is one kind of semiconductor-based photocatalyst. TiO2 shows relatively high reactivity and chemical stability under ultraviolet (UV) light. However TiO2 is a poor absorber of photons in visible light. In order to improve the absorption efficiency, the coatings of TiO2/WO3, WO3 and TiO2 on ITO were prepared by liquid phase deposition (LPD) and dip coating method, their microstructure, surface properties, photoelectrochemical properties are investigated in this paper. XRD results showed that the phases on the composite coatings are mainly anatase, rutile and WO3 respectively, the SEM results showed that the coatings of TiO2 and TiO2/WO3 are distributed evenly on the materials surface. The electrochemical experiment results showed that open circuit potential of TiO2 and TiO2/WO3 with presence of the UV light illumination were about -343 mV and –650 mV respectively, comparatively the rest potential of 304 stainless steel is about 48 mV, which means that the TiO2 or TiO2/WO3 coatings can protect 304 stainless steel from corrosion, and TiO2/WO3 coatings retained for a while anticorrosion even absence of UV light.

Abstract: Anodic aluminum oxide (AAO) is commonly used as a starting template for fabrication of several kinds of functional nanoscale devices due to its homogeneous nanohole structure with high aspect ratio. In this paper, high density and uniform titanium dioxide nanotube array films were prepared via liquid phase deposition method by immersing the AAO templates in an aqueous ammonium hexafluorotitanate solution. The phase and microstructure of the nanotube array films were characterized by X-ray diffraction and field-emission scanning electron microscopy. It was found that the mean inner diameters of nanotube are 40-100 nm, mainly depended on different templates and post treatment condition; the phase of as-deposited TiO2 array film was amorphous, while it became anatase at above 400°C.

Abstract: Ag doped TiO2 whiskers were synthesized by calcining metatitanic acid with potassium car= bonate to form tetratitanate whisker precursor, following by proton-exchanged and immobilized with Ag+. The post treatment conditions for whiskers synthesis were investigated and the phase composition, morphology and photocatalytic performance were characterized. The results showed that the TiO2 whiskers had an aspect ratio more than 15 and the absorption edge of Ag doped titania whiskers were red shifted to 50 nm. The result of methylene blue degradation revealed that the photocatalytic performance of Ag doped TiO2 whisker has been greatly improved.

Abstract: TiO2 is one kind of semiconductor-based photocatalyst. TiO2 shows relatively high reactivity and chemical stability under ultraviolet (UV) light. However TiO2 is poor absorber of photons in the solar spectrum. In order to improve the absorption efficiency, the coatings of TiO2/ZnFe2O4, ZnFe2O4and TiO2 on ITO were prepared by dip coating method, their microstructure, surface properties, photocurrent and photo absorption are investigated in this paper. XRD results show that the phases on the composite coatings are mainly TiO2 and ZnFe2O4 and the main phase on ZnFe2O4 and TiO2 coatings is ZnFe2O4 and TiO2 respectively, the SEM results show that the coatings of TiO2 and TiO2/ZnFe2O4 are distributed evenly on the materials surface and the AFM results show that the grain size is about 20nm. The experimental results also show that the absorption wavelength of composite coatings of TiO2/ZnFe2O4 is 454nm, which is larger than that of TiO2 coatings (370nm). Under the irradiation of Xe lamp light, a photocurrent of 27µA/cm2 on the materials surface could be obtained.

Abstract: Thin wall tubular Lithium aluminate ceramics have special application background. The microwave synthesis of LiAlO2 ultrafine powder, shape forming and microwave sintering of lithium aluminate pipes with 1mm in thickness were conducted in this paper. The results showed: (1) A controllable ratio of alpha to gamma phase LiAlO2 with average particle size of 0.3 µm can be synthesized via microwave radiation at temperature of 650-800°C within an hour; (2) Cold press and cold isostatic press are feasible methods to form LiAlO2 thin-wall tube and their mechanical properties are superior to those molded via hot pressure casting. (3) Lithium aluminate ceramic was successfully fabricated via microwave sintering, a uniform crystal size within 2-4µm, a typical bimodal pore size distribution and a average compressive strength more than 600MPa were obtained at 1300°C for 30min.

Abstract: Antibacterial titanate nanotubes were synthesized by alkali digesting of metatitanic acid via hydrothermal route, following by cation-exchanged and immobilized with Ag+, Zn2+ and Cu2+. The conditions for nanotube synthesis and ion exchange were investigated; the microstructures of as-synthesized nanotubes were characterized by XRD, SEM, XPS and DTA/TG. The antibacterial performance of cation-doped titanate nanotubes was tested and evaluated by Escherichia Coli. and staphylococcus aureus.

Abstract: A series of ammonium titanium phosphate nanocrystals were prepared by hydrothermal synthesis method, and characterized by XRD, IR, XPS, SEM and DTA/TG. The results showed that themicrostructures of the materials could be rod- or sphere-like nanocrystals with aqueous pH values changing from 0 to 5, and could be flake like nanocrystals when a certainty of oxalic acid was added to the hydrothermal systems. The hydrothermal duration and temperature were not the main factors influencing the morphology of the products, but longer time and higher temperature would make the material more highly crystalline. The hydrothermal synthesizing mechanism on different experimental conditions was also discussed.

Abstract: The molybdenum powder doped with rare earth oxide was processed by powder metallurgy method and a new style thin film cathode material was firstly processed by Spark Plasma Sintering (SPS) method in this paper. The secondary emission property of such kind of cathode materials were studied, the maxim secondary emission coefficient after the material was activated at 1600°C reached to 3.84 about double that of traditional cathode materials application in magneto. The microstructure, element analysis and phase constitution of materials before and after the secondary emission property was measured were studied through SEM, EDAX and XRD. The results show that a rare earth layer about 5um thickness was created after the material was activated at 1600°C. The material grain size is about 1 um or even smaller and the distribution of elements in such materials is even.