ABSTRACT
The microbiologically influenced corrosion of 304 stainless steel in the presence of a marine biofilm-forming bacterium Tenacibaculum mesophilum D-6 was systematically investigated by means of electrochemical techniques and surface analyses to reveal the effect of the selective attachment and adsorption of the biofilms on the passivity breakdown of the stainless steel. It was found that the T. mesophilum D-6 was electroactive and could oxidize low valent cations and metal, facilitating the local dissolution of the passive film and the substrate in the film defects, nearly doubling the surface roughness. The biofilms of T. mesophilum D-6 with mucopolysaccharide secreta and chloride ions tended to preferentially adsorb at the defects of the passive film on the steel, yielding non-homogeneous microbial aggregates and local Cl- enrichment there. The adsorption of the bacteria and chloride ions reduced the thickness of passive film by 23.9%, and generate more active sites for pitting corrosion on the passive film and more semiconducting carrier acceptors in the film. The maximum current density of the 304 SS in the presence of T. mesophilum D-6 was over one order of magnitude higher than that in the sterile medium, and the largest pit was deepened 3 times.
Subject(s)
Stainless Steel , Tenacibaculum , Biofilms , Corrosion , Surface PropertiesABSTRACT
Magnesium-air battery has been considered promising for electrochemical energy storage or as a conversion device due to its high theoretical energy density and low cost. However, the experimental energy density is far lower than the theoretical value due to the intense hydrogen evolution of the Mg anode upon discharging. Herein, we have successfully developed a novel Mg64Zn36 (at. %) alloy via single-phase design. The as-prepared Mg64Zn36 anode possesses a high discharge specific capacity of 1302 ± 70 mAh g-1 and extraordinarily high efficiency of 94.8 ± 4.9%, which breaks the records of efficiency among all of the reported Mg anodes. The superior high efficiency is attributed to the anodic hydrogen evolution being inhibited by Zn alloying, which passivates the Mg matrix. The intermediate ion Mg+ produced during discharging is dramatically limited by the integrated passive film and is totally converted into Mg2+ electrochemically through the film. Meanwhile, the uniform discharging products due to the homogeneous microstructure of Mg64Zn36 co-contribute to the high efficiency. The design of the Mg-Zn alloy may open a new avenue for the development of Mg-air batteries.
ABSTRACT
The electrochemical activity of a carbon fiber was characterized at different potentials in 3.5 wt.% NaCl solution, and the fiber cylindrical surface changed by polarization at different potentials was revealed by SEM, AFM, optical microscopy, FTIR spectroscopy, Raman spectroscopy, and XRD. The results showed that the carbon fiber exhibited different electrochemical activities at some polarization potentials; within a 3V potential range the anodic and cathodic polarization current densities stepped up by more than 5 orders of magnitude, and the carbon fiber (CF) surface dramatically changed with time. Strong anodic polarization appeared to facilitate the breakdown of C-C covalent bonds in the carbon fiber and enhance the amorphization of the fiber surface.
ABSTRACT
Hydrogen gas is formed when Mg corrodes in water; however, the manner and extent to which the hydrogen may also enter the Mg metal is poorly understood. Such knowledge is critical as stress corrosion cracking (SCC)/embrittlement phenomena limit many otherwise promising structural and functional uses of Mg. Here, we report via D2O/D isotopic tracer and H2O exposures with characterization by secondary ion mass spectrometry, inelastic neutron scattering vibrational spectrometry, electron microscopy, and atom probe tomography techniques direct evidence that hydrogen rapidly penetrated tens of micrometers into Mg metal after only 4 h of exposure to water at room temperature. Further, technologically important microalloying additions of <1 wt % Zr and Nd used to improve the manufacturability and mechanical properties of Mg significantly increased the extent of hydrogen ingress, whereas Al additions in the 2-3 wt % range did not. Segregation of hydrogen species was observed at regions of high Mg/Zr/Nd nanoprecipitate density and at Mg(Zr) metastable solid solution microstructural features. We also report evidence that this ingressed hydrogen was unexpectedly present in the alloy as nanoconfined, molecular H2. These new insights provide a basis for strategies to design Mg alloys to resist SCC in aqueous environments as well as potentially impact functional uses such as hydrogen storage where increased hydrogen uptake is desired.
ABSTRACT
An in-situ and real-time electrochemical study in a vascular bioreactor was designed to analyze corrosion mechanism of magnesium alloy (MgZnCa) under mimetic hydrodynamic conditions. Effect of hydrodynamics on corrosion kinetics, types, rates and products was analyzed. Flow-induced shear stress (FISS) accelerated mass and electron transfer, leading to an increase in uniform and localized corrosions. FISS increased the thickness of uniform corrosion layer, but filiform corrosion decreased this layer resistance at high FISS conditions. FISS also increased the removal rate of localized corrosion products. Impedance-estimated and linear polarization-measured polarization resistances provided a consistent correlation to corrosion rate calculated by computed tomography.
