Lijing Yang

Corrosion behaviour of die-cast AZ91D magnesium alloys in sodium sulphate solutions with different pH values

The corrosion behaviours of die-cast AZ91D magnesium alloys were investigated in 0.1 mol/L sodium sulphate (Na2SO4) solutions with different pH values. The corrosion rates, morphologies, and compositions of the corrosion products were studied by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffractometry (XRD). The results indicate that the order of corrosion rates in Na2SO4 solutions with various pH values is pH2＞pH4＞pH7＞pH9＞pH12. The corrosion rates in acidic solutions are higher than those in alkaline solutions, and the corrosion products are mainly magnesium hydroxide (Mg(OH)2) and hydrated sulphate pickeringite (MgAl2(SO4)4•22H2O). The results also indicate that the solution pH can influence the corrosion rate and morphology of corrosion products. Chloride ions and sulphate ions have different pitting initiation time.

Phase-transformation-induced hardening in Zn–22Al alloys

A phase-transformation-induced hardening effect is reported in Zn–22Al (Al: 22 wt.%) alloys. The Zn–22Al specimens were held at 300 °C for 10 h and then quenched in water. A hardening effect took place in subsequent artificial aging at 100–200 °C, which was accompanied by a phase decomposition of a soft α 2 phase and a grain coarsening. The phase-transformation-induced hardening affects the hardness more than the grain-coarsening-induced softening, which leads to the age-hardening phenomenon.

Template free growth of robustly stable nanophotonic structures: broadband light superabsorbers

Producing stable ultra-wideband light absorbers by a simple method is challenging for various applications such as solar energy harvesting, thermal regulation and suppression of stray light. Nanostructured refractory materials possess exceptional features enabling them to manipulate incident photons at the subwavelength scale and withstand against severe conditions. Here, we report a sputtering technique-based route to fabricate robustly stable TiAlN black absorbing coatings with a vertically aligned columnar structure, as a unique approach to produce large area metamaterials. The fabrication process is simple, free of any sophisticated patterning approach, substrate-independent, viable and scalable. Robust stability in adverse environments is an exceptional feature of these superabsorbers. Broadband (200–2500 nm) absorption of 89% is achieved from a single TiAlN layer and is increased to 95% after grading with thin anti-reflecting layers. The proposed sputtering based fabrication process would open a new platform to design, prepare and integrate nanophotonic structures, having applications in energy, electronic and optical sectors.

Grain boundary diffusion of magnetron sputter coated heavy rare earth elements in sintered Nd-Fe-B magnet

The diffusion of Tb or Dy heavy rare earth elements (HREEs) coated on sintered Nd-Fe-B magnets by a direct current (DC) magnetron sputtering and its influences on microstructure, magnetic properties and electrochemical properties of the magnets were investigated. The results reveal that the HREE diffuses into the magnet and substitutes some of the Nd to form a (Nd1-x,HREEx)2Fe14B shell. The HREE concentration along the direction perpendicular to the sputtered coating surface shows a dual-trend distribution, which was considered to be induced by a fast diffusion in the grain boundary phase and a slow diffusion in the grain phase. The diffusion of DC magnetron sputtered metallic Tb or Dy shows higher efficiency of HREE consumption and greater gain of the coercivity compared with diffusion sources prepared by some other coating methods or consisted of HREE compounds. The coercivity increases from 14.6 kOe for a 5 mm thick original specimen to 24.0 kOe and 19.5 kOe for the Tb and Dy diffused specimens when the coating thickness on a double surface of the specimen is about 12.0 μm. The HREE-diffused magnets also show better corrosion resistance.The diffusion of Tb or Dy heavy rare earth elements (HREEs) coated on sintered Nd-Fe-B magnets by a direct current (DC) magnetron sputtering and its influences on microstructure, magnetic properties and electrochemical properties of the magnets were investigated. The results reveal that the HREE diffuses into the magnet and substitutes some of the Nd to form a (Nd1-x,HREEx)2Fe14B shell. The HREE concentration along the direction perpendicular to the sputtered coating surface shows a dual-trend distribution, which was considered to be induced by a fast diffusion in the grain boundary phase and a slow diffusion in the grain phase. The diffusion of DC magnetron sputtered metallic Tb or Dy shows higher efficiency of HREE consumption and greater gain of the coercivity compared with diffusion sources prepared by some other coating methods or consisted of HREE compounds. The coercivity increases from 14.6 kOe for a 5 mm thick original specimen to 24.0 kOe and 19.5 kOe for the Tb and Dy diffused specimens when th...

Inhibition Effect of Exopolysaccharide of Vibrio Neocaledonicus sp. on Q235 Carbon Steel inSulphuric Acid Solution

The inhibition effect of exopolysaccharide (EPS) extracted from Vibrio neocaledonicus sp. on carbon steel Q235 has been studied by means of potentiodynamic polarization, electrochemi- cal impedance spectroscopy (EIS) and scanning electronic microscopy (SEM). The results showed that EPS could inhibit effectively the corrosion for Q235 steel in solution of 0.5 mol/L H2SO4 be- cause of that a film of Fe-EPS could formed on carbon steel during the corrosion process. The inhi- bition efficiency reached the maximum when the concentration of EPS was 1.0 g/L. The absorption of EPS on Q235 steel was chemisorption and obeyed the Langmuir adsorption isotherm. The com- position of EPS was identified by using FTIR.

Effect of Vibrio Neocaledonicus sp. on Corrosion Behavior of Copper in Artificial Sea Water

In our previous research, the corrosion inhibitory effect of marine Vibrio neocaledonicus sp. bacterium was introduced for the first time. EIS results showed that the corrosion resistance of carbon steel increased by more than sixty fold in the presence of this bacteria. The aim of this paper is the investigation of bacterial influence on the corrosion process of unalloyed copper. Different electrochemical measures (open circuit potential, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization measurements) and surface analysis techniques (field emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM)) were used. The results showed that: in the presence of bacteria, EOCP (open circuit potential) of copper shifted to negative direction about 500 mV/(vs SCE); while the charge transfer resistance (Rct) and the corrosion current density (I_(corr)) increased and decreased respectively. These results confirmed that the Vibrio neocaledonicus sp. could lessen the corrosion of unalloyed copper. CLSM images showed bacteria could adsorbed on the copper easily, but no obvious biofilm were found on the copper surface. So, it seems the corrosion inhibition of the bacteria is due to bacterial attachment in the first hours of exposure. The mechanism has been discussed in this paper.

Effect of phase transformation on corrosion behaviour of Zn–22Al alloys

Abstract The effect of phase transformation on the corrosion behaviour of Zn–22Al (wt-%) alloys immersed in NaCl solution (3·5 wt-%) at room temperature was investigated. As cast Zn–22Al alloys were isothermally heated at 300 and 250°C (the eutectoid point is 277°C) respectively and then cooled by various rates. Isothermally heated below the eutectoid point, the corrosion resistance of the alloys increased with the decreasing cooling rate. However, when the isothermal heating temperature was above the eutectoid point, the corrosion resistance of Zn–22Al alloys increased with the increasing cooling rate. It can be attributed to the existence of α2 phase, which may lead to smaller potential difference between the microgalvanic cells.