Junsheng Wu

Phase transition of hollow-porous α-Fe2O3 microsphere based anodes for lithium ion batteries during high rate cycling

In the present paper, hollow-porous α-Fe2O3 microspheres are prepared via cation etching of zinc citrate microspheres and subsequent thermal treatment. The superior performance of the as-obtained α-Fe2O3 microspheres as an anode material for lithium ion batteries is evaluated. After 1000 cycles, the capacity still remains more than 1100 mA h g−1 at a current rate of 1 A g−1. Meanwhile, the crystal size induced phase transition of Fe2O3 microspheres (α → γ → β) is observed during cycling by the measurements of ex situ XRD and TEM, which is responsible for their abnormal performance fluctuation.

Preparation and characterization of bimodal porous alumina–silica and its application to removal of basic nitrogen compounds from light oil

Aluminium nitrate and aluminium isopropoxide were used as aluminium precursors to prepare bimodal porous alumina–silica mixed oxides via the sol–gel method with the addition of nonionic surfactant C16EO10 as the structure-directing agent. The characterization of the mixed oxides was performed using scanning electron microscopy (SEM), nitrogen adsorption/desorption measurements, chemical composition measured by X-ray fluorescence (XRF), and surface acidity was investigated by the Hammett indicator method and Fourier transform infrared spectroscopy (FT-IR) of adsorbed pyridine. It is found that the resultant mixed oxides possess micrometer-range interconnected macropores and nanometer-range mesopores. Studies have shown that relatively large mesopore size materials can be obtained with aluminium nitrate precursor, but relatively high Al content materials can be synthesized using aluminium alkoxide as aluminium precursor. Surface acidity analysis results indicate that the alumina–silica mixed oxides synthesized by present sol-gel method have Lewis acid sites and Bronsted acid sites, and these acid sites exhibit mild strong acidity. Moreover, two different synthesis pathways have little influence on the acidity of alumina–silica prepared by the present method. In addition, the adsorption capacity of such acidic mixed oxides, with bimodal pore structures, for pyridine from diesel oil was studied. The adsorption experiments indicate that these mild strong acidic adsorbents with high surface areas and large macropores are effective in removing basic nitrogen compounds (BNC) such as pyridine from diesel oil, and are easily regenerated by washing with polar solvents.

Preparation and characterization of anticorrosion Ormosil sol–gel coatings for aluminum alloy

AbstractnOrganically modified silicate (Ormosil) coatings have been synthesized through the sol–gel method for corrosion protection of aluminum alloy. Silica-based unmodified coatings were also designed to investigate the effect of tetraethoxysilane (TEOS) content on the properties of the coatings. The surface morphology of the coatings was characterized by scanning electron microscopy. The corrosion resistance was evaluated by immersion test, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. In addition, the surface potential differences of the coated samples were determined by scanning Kelvin probe. The results showed that a better corrosion resistance of unmodified coating was prepared by controlling the TEOS/EtOH/H2O molar ratio of 0.109/1/1.52. Ormosil coatings provided excellent barrier properties and corrosion resistance in comparison with the unmodified sol–gel coatings. The Ormosil coating modified with triethoxyoctylsilane exhibited corrosion resistance properties superior to the other Ormosil coatings after exposure to 3.5xa0wt% NaCl solution for 10xa0days.n

Alkalescent nanotube films on a titanium-based implant: A novel approach to enhance biocompatibility

The interfacial pH value has a marked effect on cell viability because the pro-mineralization activity of osteoblasts increases at alkaline extracellular pH, whereas the pro-resorptive activity of osteoclasts increases under more acidic conditions. To obtain the more favorable alkaline interface, we developed a novel nanotube layer that was incorporated with magnesium oxide on a titanium implant substrate (MgO/NT/Ti) via ethylenediamine tetraacetic acid (EDTA) chelation. This facile immersion-annealing process successfully created a homogeneous magnesium oxide layer with sustained release kinetics and superior hydrophilicity according to the surface characterization and microenvironment measurement. The titania nanotubes on the substrate with an anatase phase exhibited a lower passivation current and a more positive corrosion potential compared with pure titanium, which guaranteed a reasonable corrosion resistance, even when it was wrapped with a magnesium oxide layer. In vitro cell cultures showed that MgO/NT/Ti significantly increased cell proliferation and alkaline phosphatase (ALP) activity. The resulting alkalescent microenvironment created by the MgO layer encouraged the cells to spread into polygonal shapes, accelerated the differentiation stage to osteoblast and induced a higher expression of vinculin. In summary, the incorporated alkalescent microenvironment of MgO/NT/Ti provided a viable approach to stimulate cell proliferation, adhesion, and differentiation and to improve the implant osseointegration.

Evidence of a nanosized copper anodic reaction in an anaerobic sulfide aqueous solution

The present paper reports the use of TEM to investigate the electrochemical behavior of a copper subject to the both free corrosion and polarization in a 0.1 M NaCl + 5 × 10−4 M Na2S aqueous solution at the nano scale. The pure copper is found to be transformed into nano-crystalline Cu2S in the thin region of the copper needle in the solution at open circuit conditions. However, a rough Cu2S layer is formed in the active region of electrochemical polarization, which is then converted to the passive CuS layer with a uniform thickness at higher potentials. Upon the continuous increase of an applied potential, cubic CuS particles with sizes of ∼100 nm are precipitated on the needle surface due to the breakdown of the passive layer. Meanwhile, the growth of a large amount of nanosized CuCl particles is also found, indicating that Cl− ions participate in the electrochemical reaction in the transpassive region. It is worth noting that the present work also provides a simple and cost-effective way for the synthesis of copper sulfides (Cu2S and CuS) through electrochemical processes.

Corrosion of Carbon Steel under Epoxy-varnish Coating Studied by Scanning Kelvin Probe

The corrosion behavior of partly coated carbon steel was investigated by salt spray test and scanning Kelvin probe (SKP) in order to understand the long-term corrosion behavior of coated carbon steel in marine atmosphere environment. The localized corrosion was accurately characterized by SKP in both coated and uncoated regions. The SKP results showed that Volta potential varied with the test time, and the more the corrosion products, the more positive the potential. The borderline between coated and uncoated regions of partly coated steel shifted towards the coated side with the increasing of test time. The coating disbonding rate could be determined according to the shift of potential borderline measured by SKP. The corrosion mechanism of partly coated steel in NaCl salt spray was discussed according to the potential maps and corrosion morphologies.

Galvanic corrosion of magnesium alloy and aluminum alloy by kelvin probe

Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated. The variations of the surface potential were measured using scanning kelvin probe (SKP). The results showed that galvanic effect on the corrosion of AZ91D magnesium alloy is closely related to the potential difference between the anodic and cathodic materials. In the initial period, corrosion only occurred in a narrow area at the coupling interface because of the limited distance galvanic current. Then, the corrosion rate of 2A12 aluminum alloy was accelerated due to its poor stability in strong alkali environment, which was attributed to the strong alkalization caused by the corrosion of AZ91D magnesium alloy. With the increase of the potential of 2A12 aluminum alloy as a result of the continuous covering of corrosion products, the potential difference between the two materials was enlarged, which enhanced the galvanic corrosion.

The influence of Bacillus subtilis on tin-coated copper in an aqueous environment

The influence of Bacillus subtilis (BS) on tin-coated copper in an aqueous environment was investigated by exposing the sample to a culture medium inoculated with BS. Scanning electron microscopy, electrochemical measurements and chemical analyses were performed to study the corrosion mechanism. The experimental results show that BS can adhere and gather on the surface of the sample, resulting in oxygen consumption at the place where the bacteria are densely attached. Increases in the Rct values after the initial immersion showed that corrosion was inhibited, while decreases in the Rct values after the later immersion showed that corrosion was accelerated. Our results suggest that differences in oxygen concentration due to activity of BS are the main reason for corrosion of tin-coated copper.

Microporous corrosion behavior of gold-plated printed circuit boards in an atmospheric environment with high salinity

The microporous corrosion is the main surface failure mechanism of gold-plated components. The microporous corrosion behavior of electroless nickel and immersion gold (ENIG)-plated printed circuit boards (PCBs) in Turpan area which has an atmospheric environment with high salinity was investigated via a field exposure method for 24 months, as well as 3D analysis, FIB technology, composition analysis, and electrochemical impedance spectroscopy and corrosion mechanism model. After 6 months of exposure, the corrosion products filled up the pores and clustered on the surface as mound shape, and a possible corrosion mechanism model was displayed in the study after 24 months of exposure. The results showed that PCB-ENIG mainly suffered microporous corrosion in a high salinity atmospheric environment. The pores on the gold-plated coating were location where corrosion occurred first and the corrosion products were mostly oxides, chlorides, sulfates and carbonates of copper and nickle.