Evaluation of corrosion resistance of electrodeposited nanocrystalline Ni–Fe alloy coatings

Nickel–iron alloys with a compositional range of 24–80?wt-% iron were electrodeposited on a copper substrate from a sulphate-based bath and using a stirring rate of 100?rev?min^?1. The effect of applied current density and Ni²⁺/Fe²⁺ metal ion ratio of plating bath on the properties of alloy coatings was examined. Crystal structure and grain size of Ni–Fe alloy coatings were investigated using X-ray diffraction technique. Field emission scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyse the surface morphology and chemical composition of coatings. Microhardness test was applied to evaluate the hardness of the coatings. Finally, the electrochemical behaviour of the Ni–Fe alloy coatings was studied by a polarisation test in 10?wt-% H₂SO₄ solution. Results revealed that current density and plating bath composition had a strong effect on the characteristics of coatings. As the iron content of alloys produced increased, their corrosion resistance improved with the best corrosion resistivity being achieved at a metal ion ratio of 0.5 and applied current density of 2.5?A?dm^?2.     

Catalytic effect of visible light and Cd2+ on chalcopyrite bioleaching

The effects of visible light and Cd²⁺ ion on chalcopyrite bioleaching in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans) were studied by scanning electron microscopy (SEM), synchrotron radiation X-ray diffraction (SR-XRD), and X-ray photoelectron spectroscopy (XPS). The results of bioleaching after 28 days showed that the copper dissolution increased by 4.96% with only visible light, the presence of Cd²⁺ alone exerted slight inhibition effect on chalcopyrite dissolution and the concentration of dissolved copper increased by 14.70% with visible light and 50 mg/L Cd²⁺. The results of chemical leaching showed that visible light can promote the circulation of iron. SEM results showed that Cd²⁺ promoted the attachment of A. ferrooxidans on chalcopyrite surface under visible light. SR-XRD and XPS results indicated that visible light and Cd²⁺ promoted chalcopyrite dissolution, but did not inhibit the formation of passivation. Finally, a model of synergistic catalysis mechanism of visible light and Cd²⁺ on chalcopyrite bioleaching was proposed.     

Study on a Medium Speed and Long Life-span Electroless Nickel Plating Process

A study has been made of the mechanism of hypophosphite-reduced acidic electroless nickel (EN) plating. The influences of temperature, pH value, reagents of pH, complex reagents and stabilizer etc. have been studied. Lactic acid and malic acid are selected as complexing reagents. KIO₃, HAc and ammonia are selected as stabilizer, buffer and pH regulator respectively. A new medium speed, long life-span and useful EN plating process has been developed.     

Investigation of corrosion resistance of electrodeposited Ni–W/SiC composite coatings

In this research, Ni–W/SiC composite coatings were electrodeposited from a plating bath containing suspension of SiC particles. The influences of SiC particle concentration in the plating bath on the composition of composite coatings were investigated. The surface morphology and composition of the composite coatings were characterised by scanning electron microscopy, energy dispersive X-ray measurements and X-ray diffraction analysis. The corrosion characteristics of Ni–W/SiC composite coatings were investigated by mass loss and electrochemical measurements, including open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarisation in a 3·5 wt-%NaCl solution. The results showed that the addition of SiC particle to the deposition bath of Ni–W significantly increased the corrosion resistance. The significant improvement in corrosion resistance observed for Ni–W/SiC composite coatings (17100 Ω cm²) compared to Ni–W (5619 Ω cm²) could have resulted from the microstructural differences.     

Electrochemical studies of Zn-Ni alloy coatings from non-cyanide alkaline bath containing tartrate as complexing agent

The Zn-Ni alloys have been electro-deposited from a non-cyanide alkaline bath containing tartrate as a complexing agent for Ni²⁺ ions. A water soluble polymer is used as a brightener. It was prepared by the reaction of epiclorohydrin with hexamethylenetetramine and mercaptobenzimidazol. Its effect on co-deposition process was examined. It was found that adding brightener in plating bath has a great effect on the cyclic voltammogram and galvanostatic measurements during the electrodeposition. Under the examined conditions, the electrodeposition of the alloys was of anomalous type. X-ray diffraction measurements revealed that the alloys consisted δ-phase (Ni₃Zn₂₂). The composition and morphology of the deposits were also studied by using scanning electron microscopy (SEM) and energy dispersive analysis X-ray (EDAX), respectively. The effect of optimum plating bath conditions on the corrosion resistance is studied by Tafel polarization.     

Effect of rare earth (Ce, La) compounds in the electroless bath on the plating rate, bath stability and microstructure of the nickel-phosphorus deposits

Effects of added rare earth elements (RE) in the acidic hypophosphite plating bath on the plating rate, bath stability and microstructure of the electroless nickel-phosphorus (EN) deposits were studied. The surface appearance and microstructure were examined under a reflection optical microscope and a scanning electron microscope equipped with an in-situ energy dispersive X-ray spectroscopy, which can evaluate the elemental analysis of deposits. It was demonstrated that the rare earth elements can decrease grain size and refine microstructure.The deposition rate of the Ni-P deposits was estimated by gravimetric, polarization and quartz crystal microbalance (QCM) methods. Results revealed that up to an optimum concentration of rare earth elements, the deposition rate increases. The stability test method was used to determine the stabilization effect of RE on the stability of the bath. It was found that the addition of RE significantly improved the Pd stability of the EN bath.     

Synthesis and characterization of chemically deposited nickel substituted CdSe thin film

The technologically important Cd_0.5Ni_0.5Se thin film has been developed by solution growth technique on non-conducting glass substrate in tartarate bath containing Cd⁺², Ni⁺² ions and sodium selenosulphate in an aqueous alkaline medium at room temperature. Various preparative conditions of the thin films are outlined. The films were characterized by X-ray diffraction, scanning electron microscope, optical absorption and electrical measurements. The X-ray diffraction study indicates that the film is polycrystalline in nature with hexagonal phase. Scanning electron micrograph shows that the film is homogeneous with well-defined grains. The films have high optical absorption coefficient. Thermoelectric power measurement shows p-type conduction mechanism.     

Electrodeposition of high performance multilayer coatings of Zn–Co using triangular current pulses

Abstract

Compositionally modulated alloy (CMA) coatings of Zn–Co were electrodeposited on to mild steel from an acid chloride bath containing thiamine hydrochloride, as an additive. Electroplating was carried out galvanostatically from a single bath containing Zn²⁺ and Co²⁺ ions. Gradual change in composition in each layer was effected by triangular current pulses, cycling between two cathode current densities. Compositionally modulated alloy coatings were developed under different conditions of cyclic cathode current density and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarisation and electrochemical impedance spectroscopy. The formation of multilayer and corrosion mechanism was analysed using scanning electron microscopy. The corrosion resistances of CMA and monolithic alloy coatings were compared with that of the base metal. Compositionally modulated alloy coating at optimal configuration, represented as (Zn–Co)_{2·0/4·0/300}, was found to exhibit ～80 times better corrosion resistance compared with monolithic (Zn–Co)_3·0 alloy, deposited for the same length of time from the same bath. Improved corrosion resistance was attributed to the formation of n-type semiconductor film at the interface, supported by Mott–Schottky plots. Decrease in corrosion resistance at high degree of layering was found, and is due to lower relaxation time for redistribution of solutes in the diffusion double layer, during plating.     

Adsorption of Cd2+ in aqueous solutions using KMnO4-modified activated carbon derived from Astragalus residue

Activated carbon obtained from Astragalus residue was chemically activated by KOH and modified with KMnO₄. The samples were characterized by N₂ adsorption, Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy, and Boehm titration. Accordingly, the original and modified carbon materials were used for the removal of Cd²⁺ from aqueous solution by batch adsorption experiments. Results showed that the contents of oxygen-containing functional groups increased, and MnO₂ was nearly uniformly deposited on the surface of activated carbon after modification by KMnO₄. The adsorption kinetics was described by pseudo-second order model. Langmuir model fitted the adsorption-isotherm experimental data of Cd²⁺ better than the Freundlich model. The maximum adsorption capacities of the activated carbon before and after modification for Cd²⁺ were 116.96 and 217.00 mg/g, respectively. KMnO₄ considerably changed the physicochemical properties and surface texture of activated carbon and enhanced the adsorption capacity of activated carbon for Cd²⁺.     

Influence of process parameters for coating of nickel–phosphorous on carbon fibers

The nickel–phosphorous (Ni–P) coating on carbon fiber was studied, using sodium hypophosphite as a reducing agent in alkaline medium. The effects of process parameters such as time, stabilizer concentrations, pH of the plating bath and plating bath's temperature on the electroless Ni–P coating efficiency were investigated. Structural study using X-ray diffraction (XRD) indicates that nickel deposition rate increases with increasing coating time and temperature. The nickel (Ni) recovery efficiency decreases with an increase of stabilizer concentration. From scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), it has been confirmed that the coating thickness and nickel content increase with an increase of coating time and temperature. The bath temperature of 25 °C, pH of 9, and stabilizer concentration of 25 g/L is good to get a good and uniform coating of Ni on carbon fiber. Thermal stability was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). From TGA study it is evident that the nickel coating increases thermal stability of the nickel-coated carbon fiber. I–V (current vs voltage) measurement shows Ni-coated fiber is more conducting in nature.