Zhongping Yao

Microporous Ni-Doped TiO2 film Photocatalyst by Plasma Electrolytic Oxidation

Ni-doped TiO2 film catalysts were prepared by a plasma electrolytic oxidation (PEO) method and were mainly characterized by means of SEM, EDS, XRD, XPS, and DRS, respectively. The effects of Ni doping on the structure, composition and optical absorption property of the film catalysts were investigated along with their inherent relationships. The results show that the film catalyst is composed of anatase and rutile TiO2 with microporous structure. Doping Ni changes the phase composition and the lattice parameters (interplanar crystal spacing and cell volume) of the films. The optical absorption range of TiO2 film gradually expands and shifts to the red with increasing dosages. Both direct and indirect transition band gaps of the TiO2 films are deduced consequently. Moreover, the photocatalytic activity of the film catalysts for splitting Na2S+Na2SO3 solution into H2 is enhanced by doping with an appropriate amount of Ni. The as-prepared TiO2 film catalyst doping with 10 g/L of Ni(Ac)2 presents the highest photocatalytic reducing activity.

Electric field-induced synthesis of dendritic nanostructured α-Fe for electromagnetic absorption application

In this work, large-scale three-dimensional dendritic α-Fe which possesses two different faces with uniform width of about 3.0 μm and length of about 9.0 μm was directly synthesized using an electric field-induced and electrochemical reduction method in FeSO4 aqueous solution for the first time. This synthesis method shows great advantages including environment-friendliness, extremely low cost and high efficiency. The specific dendritic structure was induced to grow along three of six 〈110〉 crystallographically equivalent directions under a symmetrical electric field. The uniform length of the dendritic α-Fe is subject to Fe2+ concentration gradient. The investigation of the magnetic properties and electromagnetic absorbability indicates that this kind of dendritic α-Fe exhibits both high absorption efficiency with the minimum reflection loss value of −32.3 dB and a broad absorption band up to 12 GHz. The dendritic α-Fe could be an extremely promising electromagnetic absorption material.

Preparation of ceramic conversion layers containing Ca and P on AZ91D Mg alloys by plasma electrolytic oxidation

Abstract Oxide based ceramic conversion layers containing Ca and P were prepared on AZ91D Mg alloy by plasma electrolytic oxidation technique in Na2SiO3 and NaOH systems respectively. The conversion layers prepared in both systems were porous and grey white. The doping of Ca decreased the porosity of the conversion layers in Na2SiO3 system, while increasing the porosity of and the microcracks of the conversion layers in NaOH system. The conversion layer prepared in NaOH system was composed of MgO, and the one prepared in Na2SiO3 system was composed of Mg2SiO4 and MgO; P and Ca only existed in the form of amorphous state in the conversion layer. The doping of Ca decreased the relative content of P while increasing the relative content of Ca in both conversion layers. The ceramic conversion layers in both systems improved the corrosion resistance of the AZ91D Mg alloy in 0·9%NaCl solution by one or two orders of magnitude.

Preparation and structure of microarc oxidation ceramic coatings containing ZrO2 grown on LY12 Al alloy

Abstract Ceramic coatings containing ZrO 2 were prepared in situ on LY12 aluminum alloy by microarc oxidation (MAO) in the mixed solution of zirconate and phosphate solution. The phase composition and morphology of the coatings were studied by XRD and SEM, respectively. The growing mechanism of ceramic coatings was discussed in a preliminary manner. The results show that with an increase in MAO time, the compactness of the coating improved and the thickness increased. From the inner layer to the coating surface, the content of Zr increased, while the content of Al decreased. In addition, the coating was composed of m-ZrO 2 , t-ZrO 2 , and a little amount of γ-Al 2 O 3 . With an increase in reaction time, the relative content of t-ZrO 2 within the coating sharply decreased while the relative content of m-ZrO 2 sharply increased, and then both generally kept at a constant level after 60 min.

Mo-doped titania films: preparation, characterization and application for splitting water

A series of Mo-doped TiO2 films are prepared on quartz substrate by the layer-by-layer assembly method. The films are characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scan electron microscopy (SEM), UV-vis spectrophotometry and fluorescence spectrophotometry. The results show that TiO2 phase transformation from anatase to rutile is promoted with higher dopant concentration. The surface oxygen vacancies (SOVs) of Mo-doped TiO2 films bind photoinduced electrons to further give rise to new photoluminescence (PL) signals, and the intensities of PL signals are in proportion to SOVs content of the films. The photocatalytic activity of TiO2 film is evaluated by measuring H2 evolution from water and the effects of SOVs of Mo-doped TiO2 films on photocatalytic processes are investigated along with their inherent relationships.

Effect of PEO power modes on structure and corrosion resistance of ceramic coatings on AZ91D Mg alloy

Abstract The aim of this work is to investigate the effects of different power modes [constant current (CC), constant voltage (CV) and constant power (CP)] on the structure and corrosion resistance of the plasma electrolytic oxidation ceramic coatings containing Ca and P on AZ91D Mg alloy. The phase composition, morphology and element distribution of the coatings were studied by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The corrosion resistance of the coatings in the simulated body fluid was examined by electrochemical impedance spectroscopy and polarisation curve methods. The results showed that the coatings were of porous structure and mainly composed of MgO. The thickness, surface roughness, the size of the surface micropores and the amount of MgO were all increased with the cell voltage under the same power mode or increased in the sequence CV>CC>CP under the different power modes. The corrosion resistance of coatings was related to the structure characteristics, which were determined by different power modes. Among the different power modes, the corrosion resistance of the coatings is generally increased in the sequence CV>CP>CC, and under the same mode, the proper increase in the cell voltage is liable for improving the corrosion resistance of the coatings.

Solvothermal synthesis of Mn 3 O 4 nanoparticle/graphene sheet composites and their supercapacitive properties

Mn3O4 nanoparticle/graphene sheet (GM) composites were synthesized via a one-pot and low-cost solvothermal process in an ethanol solution. The as-prepared materials were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Results showed that the nanosized Mn3O4 particles had tetragonal hausmannite structure and were successfully loaded on the graphene sheets. Moreover, the electrochemical performances of GM composites produced by different mass percents of Mn2+/graphite oxide (GO) were evaluated by means of cyclic voltammetry and galvanostatic charge-discharge studies. The composite prepared with Mn2+/GO mass percent of 10:90 showed a high specific capacitance of 245 F/g at 5mV/s in the 6M KOH solution and better long-term stability along with 81% of its initial capacitance after 1200 cycles at 0.5 A/g.

Influences of Calcination Ambiences on Phase Composition and High Temperature Oxidation Resistance Property of Ceramic Coatings on Ti–6Al–4V Alloy by Micro-Plasma Oxidation

Compound ceramic coatings with the main crystalline of Al2TiO5 (as-coated samples) were prepared on Ti-6Al-4V alloy by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO2 solution. The coated samples were calcined in Ar and air at 1000oC, respectively. The phase composition, morphology and element content of the coatings were investigated by XRD, SEM and XRF. The samples treated in Ar and the as-coated ones were calcined in air at 1000oC to study the oxidation resistance of the samples. The results showed that Al2TiO5 decomposed and transformed into corundum and rutile TiO2 during the high temperature calcination. Al2TiO5 decomposed very quickly in air and the proportion of Al2O3 to TiO2 was 44:55 after a complete decomposition. On the contrary, Al2TiO5 decomposed very slowly in argon with the final proportion of Al2O3 to TiO2 of 81:18 on the coating surface. The morphology of the ceramic coatings after the calcination was also different. The coatings calcined in argon were fined: the grains and pores were smaller than those of the coatings calcined in air. The weight gains of both coatings changed in the form of parabola law, and the weight gains of the coated samples treated in argon were comparatively lower than that of the as-coated samples. During the high temperature calcination, the samples treated in argon cannot distort easily, compared with the as-coated ones.

Investigation of absorptance and emissivity of thermal control coatings on Mg-Li alloys and OES analysis during PEO process.

Thermal control ceramic coatings on Mg–Li alloys have been successfully prepared in silicate electrolyte system by plasma electrolytic oxidation (PEO) method. The PEO coatings are mainly composed of crystallized Mg2SiO4 and MgO, which have typical porous structure with some bulges on the surface; OES analysis shows that the plasma temperature, which is influenced by the technique parameters, determines the formation of the coatings with different crystalline phases and morphologies, combined with “quick cooling effect” by the electrolyte; and the electron concentration is constant, which is related to the electric spark breakdown, determined by the nature of the coating and the interface of coating/electrolyte. Technique parameters influence the coating thickness, roughness and surface morphology, but do not change the coating composition in the specific PEO regime, and therefore the absorptance (αS) and emissivity (ε) of the coatings can be adjusted by the technique parameters through changing thickness and roughness in a certain degree. The coating prepared at 10 A/dm2, 50 Hz, 30 min and 14 g/L Na2SiO3 has the minimum value of αS (0.35) and the maximum value of ε (0.82), with the balance temperature of 320 K.

Micro-arc formation of ZrO2 ceramic coatings on AZ91D Mg alloy

Abstract The aim of the work has been to prepare ceramic coatings containing the ZrO2 phase on a Mg alloy by micro-arc oxidation technique. The phase composition of the coatings was examined with X-ray diffraction. The surface morphology and the elemental distribution of the coatings were studied with scanning electron microscopy and energy dispersive spectroscopy. The corrosion resistance of the coated samples was examined by the accelerated electrochemical method in 3˙5%NaCl solution. The coating was found to be composed of t-ZrO2 and a little c-ZrO2. There were many residual discharge channels in the coating surface, which made the elemental distribution and surface morphology uneven. The corrosion resistance of the coated samples was much better than that of the AZ91D substrate, from a pitting corrosion resistance and general corrosion resistance stand point.