Zinc-nickel alloy coatings are electrodeposited on carbon steel from chloride bath using a technique of chronopotentiometry at different temperatures. The elemental composition and surface morphology analysis of zinc-nickel coated samples are done using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The coated samples are immersed in 3.5 wt.% sodium chloride solution and measurements of corrosion rate are done using linear polarization resistance. Scanning electron microscopy results show that deposition temperature variation has a strong effect which changes the surface morphology and elemental composition of zinc-nickel alloy coatings. The nickel content in the electrodeposited zinc-nickel alloy coatings increases with increasing deposition temperature. Uniformity and compactness of the coatings decrease with an increasing temperature. Cracks intensity increases with increasing deposition temperature which is attributed to internal stress due to factors that might be related to hydrogen evolution reaction. The linear polarization resistance results correlated with the morphology and compositional properties of zinc-nickel alloy coatings deposited at different temperatures, that with an increase deposition temperature, corrosion resistance decreases. Zinc-nickel alloy coatings with high corrosion resistance, compact and uniform morphology with less crack, and nickel content within the range of 12 wt.% to 15 wt.% are achieved with deposited coating at 25 8C.
This paper aims to review the impact of different factors influencing the corrosion resistance of electroless Ni-P based coatings. Emphasis has been given onto the impact of phosphorus content, incorporation of alloying elements, addition of particles and heat treatment which have been discussed in detail and critically reviewed. The effect of corrosive media and coating process parameters on corrosion resistance are studied concisely. Furthermore, the role of the incorporation of various elements and particles’ contents on the corrosion resistance of electroless Ni-P coating are studied systematically. This paper also presents an overview of the latest electrochemical corrosion measuring techniques. The following approaches deserve special attention in the analysis: localized electrochemical impedance spectroscopy (LEIS), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET), scanning droplet cell (SDC), scanning electrochemical microscopy (SECM), scanning Kelvin probe (SKP) and novel contactless technique (NCT).
Abstract. Current density imaging (CDI) is a magnetic resonance (MR) imaging technique that could be used to study current pathways inside the tissue. The current distribution is measured indirectly as phase changes. The inherent noise in the MR imaging technique degrades the accuracy of phase measurements leading to imprecise current variations. The outcome can be affected significantly, especially at a low signal-to-noise ratio (SNR). We have shown the residual noise distribution of the phase to be Gaussian-like and the noise in CDI images approximated as a Gaussian. This finding matches experimental results. We further investigated this finding by performing comparative analysis with denoising techniques, using two CDI datasets with two different currents (20 and 45 mA). We found that the block-matching and three-dimensional (BM3D) technique outperforms other techniques when applied on current density (J). The minimum gain in noise power by BM3D applied to J compared with the next best technique in the analysis was found to be around 2 dB per pixel. We characterize the noise profile in CDI images and provide insights on the performance of different denoising techniques when applied at two different stages of current density reconstruction.
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