Category Archives: General

Electrofabrication of Composition Modulated Multilayer Alloy (CMMA) of Co-Ni for Better Corrosion Protection

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Electrofabrication of multilayer Co-Ni alloy coatings were accomplished successfully on mild steel (MS) for better corrosion protection. Multilayer comprised of alternatively formed ‘nano-size’ layers of Co-Ni alloy of different composition have been produced from single electrolyte having Co+2 and Ni+2 ions using modulated (i.e. periodic pulse control) current density. The deposition conditions were optimized for both composition and thickness of individual layers for best performance against corrosion. The process and product of depositions were analyzed using cyclic voltammetry and SEM, PXRD, Hardness Tester, electrochemical AC and DC methods, respectively. The corrosion behavior of multilayer coatings was found to be improved drastically when the thickness of individual layer approached nano regime. The coating having 300 layers, deposited at cyclic cathodic current densities of 2.0 and 4.0 Adm-2 was found to show the least corrosion rate (CR = 0.02 mmpy) compared to monolayer (Co-Ni)4 alloy coating (CR = 2.8 mmpy) deposited from the same bath for same deposition time. Drastic improvement in the corrosion performance of multilayer coatings were explained in the light of changed kinetics of mass transfer at cathode and increased surface area due to layering, respectively.

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Kinetics of Corrosion Inhibition of Aluminum in Alkaline Solutions by Water-Soluble Poly (Vinyl Alcohol) as Synthetic Polymer

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Figure 1.

The influence of water-soluble poly (vinyl alcohol) (PVA) as a synthetic polymer containing secondary alcoholic groups on the rate of dissolution of aluminum (Al) metal in alkaline medium has been investigated using both gasometric and weight-loss techniques. The results showed that addition of poly (vinyl alcohol) to the tested solutions leads to a remarkable decrease in the corrosion rates of Al in alkali. The magnitude of inhibition efficiency was determined and compared to that obtained with other macromolecules containing secondary alcoholic groups. The inhibition action of PVA on Al metal surface was found to obey Freundlich adsorption isotherm. Factors affecting the corrosion process such as the concentration and nature of the inhibitor, concentration of the corrosive medium and the temperature were examined. A tentative inhibition mechanism consistent with the kinetic results obtained is suggested and discussed.

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Pulse plating of nickel-based alloys

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Fig. 1: Cathodic polarisation curves for (a) Ni-Co, (b) Sn-Ni and (c) Ni-W electrolyte systems recorded at a scan rate of 10mVs-1 on a rotating disk electrode at different electrode rotating velocity: 0, 100, 600 and 1000rpm

In the present work, nickel-based alloy coatings (Ni-Co, Sn-Ni and Ni-W) with different microstructures were produced under direct and pulse current conditions. These alloys are of interest as potential replacement for chromium based coatings, especially hard chromium. A replacement for hard chromium coating faces the challenge of providing sufficient hardness values.  For some sliding wear applications, hardness might not be required at the same level as hard chromium, and coating toughness might be more critical.
The effects of the pulse parameters (pulse waveform, pulse frequency and average current density) on the deposit structure and properties of these three systems have been investigated. Pulses have been defined based on the results of electrochemical measurements and numerical process simulation. The surface morphology, microstructure and microhardness of the deposit have been correlated to the pulse parameters applied.
The experimental results showed that applying pulse plating substantially altered the properties of the coatings. The resulting layers exhibited a nano-crystalline microstructure, improved layer compactness and hardness of the nickel-based alloy deposits.

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Application of Gold Electrodes for the Study of Nickel Based Homogeneous Catalysts for Hydrogen Oxidation

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Scheme 1: Schematic presentation of Ni(PCy2Nt-Bu2)22+

Gold and glassy carbon working electrode materials are compared as suitable substrates for the hydrogen oxidation reaction with Ni(PCy2Nt-Bu2)2(BF4)2 used as a catalyst. Voltammetric responses showing electrocatalytic hydrogen oxidation mediated by the homogeneous electrocatalyst Ni(PCy2Nt-Bu2)2(BF4)2 are identical at glassy carbon and gold electrodes, which shows that gold electrode can be used for hydrogen oxidation reaction.

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Choline chloride-Ethylene glycol mixture as electrolyte for nano crystalline Nickel electrodeposits

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Fig. 1a: Comparison of conductivity of Ni(II) chloride dissolved in Ethaline complex

Nickel plating was carried out in stable Nickel ion based deep eutectic solvent (DES). The DES electrolyte stability and possible structure were explained by using Fourier Transform Infrared spectroscopy (FTIR) and Temperature Modulated Differential Scanning Calorimetry (TMDSC) techniques. The conductivity and electrochemical studies for choline based eutectic solvents were analyzed by conductivity cell and electrochemical impedance spectroscopy respectively. Higher current efficiency, thickness and hardness of Nickel were obtained by Pulse current electrodeposition when compared with Direct current electrodeposition. Crystallographic orientation and structural morphology were studied by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) respectively. Coated Nickel plate’s corrosion resistance and porosity properties were checked using potentiodynamic polarization and electrochemical impedance spectroscopy.

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