A Comparative Study on the Corrosion Behaviour of Hard Anodic Coatings on AA 6061 Obtained Using DC and Pulsed DC Power Sources

The corrosion behaviour of the hard anodic coatings prepared by three different methods viz., conventional hard anodizing （C-HA）, pulse hard anodizing （P-HA） and low voltage room temperature pulse hard anodizing （LVP- HA） on AA 6061 was compared using electrochemical impedance spectroscopy （EIS） and linear polarisation. Scanning electron microscope （SEM） was used to study the surface morphology before and after corrosion. EIS data revealed that no significant difference in corrosion resistance was observed among three types. Rp, Icorr and Ecorr were found to be highly stable over the exposure period up to 72 h which confirms the excellent corrosion resistance. The studies indicate that the corrosion resistance of LVP-HA and P-HA, which are processed at lower voltage and at relatively higher temperatures, are comparable to that of C-HA which is processed at sub-zero temperatures and high operating voltages. The corrosion resistance of all coatings was found to be improved after hydrothermal sealing.     

Influence of strain Bacillus cereus bacterium on corrosion behaviour of carbon steel in natural sea water

This paper examines the corrosion behaviours of carbon steel immersed in sterile natural sea water with and without strain Bacillus cereus. Electrochemical studies, including Tafel plots and electrochemical impedance spectroscopy (EIS) were performed to evaluate the variation of the corrosion behaviour of carbon steel in medium containing B. cereus as compared to the sterile control samples. The results of Tafel plot measurements showed significant reduction in the corrosion rate in the presence of bacterial biofilm produced by strain B. cereus. The EIS data showed that the charge transfer resistance is greater in a medium containing B. cereus and increases with immersion time.     

Corrosion of heat treated magnesium alloy ZE41

This paper investigates the effect of heat treatment upon the corrosion morphology and mechanism of ZE41 alloy. The results of optical and scanning electron microscopy (SEM) together with potentiodynamic polarisation reveal the importance of the microstructure in the initiation and propagation of corrosion in an aqueous environment. The corrosion of the heat-treated alloy is significantly altered due to changes in the microstructure, specifically the Zr-rich regions and the grain boundary T-phase.     

Effect of antimony, bismuth and calcium addition on corrosion and electrochemical behaviour of AZ91 magnesium alloy

This study investigated the effect of antimony, bismuth and calcium addition on the corrosion and electrochemical behaviour of AZ91 magnesium alloy in 3.5% NaCl solution. Techniques including constant immersion, electrochemical potentiodynamic polarisation, scanning electron microscopy (SEM), energy dispersed spectroscopy (EDS) and X-ray diffraction (XRD) were used to characterise electrochemical and corrosion properties and surface topography. It was found that corrosion attack occurred preferentially on Mg₃Bi₂ and Mg₃Sb₂ particles while Mg₁₇Al₈Ca_0.5 and Mg₂Ca phases showed no detrimental effect on corrosion. Combined addition of small amounts of bismuth and antimony to the AZ91 alloy resulted in significant increase in corrosion rate.     

Application of PEO75PPO30PEO75 stabilised polymeric micelles for improved corrosion resistance of composite zinc coatings

The influence of stabilised polymeric micelles (SPM) on the structure, corrosion properties and durability of electrodeposited composite zinc coatings is presented and discussed. The core-shell-type SPM used are based on poly-propylene oxide (core) and poly-ethylene oxide (shell). The deposition and dissolution processes of zinc in the presence or absence of SPM have been investigated by the cyclic polarisation method. The corrosion behaviour and protective ability of the composite coatings have been evaluated in a model corrosion medium of 3% NaCl solution by means of polarisation resistance measurements. The changes in the zinc matrix as a result of the embedded SPM were investigated by an X-ray diffraction method.     

Effect of carbon nanotubes on corrosion of Mg-CNT composites

Carbon nanotubes (CNTs) may be added to Mg matrix to produce composites of better mechanical properties, but their effect on the corrosion behaviour is not well understood. The corrosion resistance of pure Mg and its composites reinforced with 0.3 and 1.3 wt.% CNTs was studied in 3.5 wt.% NaCl solution using immersion testing and electrochemical measurements. It was found that the corrosion rate was increased considerably by the presence of CNTs because of microgalvanic action between the cathodic CNTs and the anodic Mg matrix.     

Validation of a fuel cell compression spring equivalent model using polarisation data

Fuel cell stack compression is a vital part of the manufacturing process, however limited research exists in predicting the optimal compression force to maximise fuel cell performance. This paper validates a spring equivalent model proposed in a previous publication which, when coupled with literature derived gas diffusion layer (GDL) optimal compression data, can predict the compression force required based on gas diffusion layer and gasket properties. The error between the model and the optimal performance of the stack is a maximum of 6.4%. This is a positive indication as to the model's validity. In addition, the compression homogeneity applied by the compression system to the flow field plate is measured to confirm the GDL is experiencing the predicted compression force. The impact of this research is a reduction in development time and cost as less empirical testing will be required to identify optimal fuel cell stack compression.     

低偏振灵敏度行波半导体光放大器的实验研究

本文报导了一种具有低偏振灵敏度的行波半导体光放大器。通过有效地设计放大器的端面增透膜系，使得端面残余反射率低于１０－４，从而获得低于２ｄＢ的偏振灵敏度。     

Low apparent valence of Mg during corrosion

Our recent data on Mg corrosion has been reanalysed because of the recent criticism that our previous data analysis was inadequate. Re-analysis leads to similar conclusions as previously. The apparent valence of Mg during corrosion was in each case less than 2.0, and in many cases less than 1.0. Moreover, these values were probably over-estimates. The low values were consistent with the evolving hydrogen gas acting as an insulator, so that the corrosion of parts of the specimen could occur isolated from the electrochemical measurement system.