Alkaline Citrate Bath Research Articles

Electrodeposited Ni-Cu alloy coatings on mild steel for enhanced corrosion properties

Ni rich single-phase Ni-Cu alloy coatings were obtained on mild steel substrates by electrodeposition from stable alkaline citrate baths. Three different baths were prepared with varying Cu2+ concentration. Electrodeposition experiments were performed in the galvanostatic mode at three different current densities of 10, 20 and 30 mA cm−2. The coating compositions calculated from EDAX analysis showed that copper content in the coating increased with an increase in copper content of the bath, but decreased with an increase in current density. It was observed that the morphology of the deposits changed from globular to cauliflower with an increase in current density. Deposits from baths containing lower copper content showed more separated and localised cauliflower structures. The roughness of the deposits was also observed to increase with an increase in current density and to some extent with increase in deposition time. The corrosion potential for all coatings was less negative compared to mild steel, indicating barrier protection properties. Corrosion rate was largely affected by the morphology and roughness of the coatings. At higher current densities and higher deposition time, rougher surfaces and gaps and separations between the cauliflower structures were responsible for higher corrosion rate.

A comparative study on the electrocatalytic activity of electrodeposited Ni-W and Ni-P alloy coatings

Bright Ni-W and Ni-P alloy coatings were synthesized through direct electrolysis from an aqueous alkaline citrate bath. The effect of alloying elements, W and P, on the electrocatalytic activity of Ni was studied, based on their induced codeposition behavior and related to the composition, structure and surface morphology of the developed coatings. The electrocatalytic activity of the alloy coatings towards hydrogen evolution reaction (HER) was studied using electrochemical techniques such as cyclic voltammetry (CV) and chronopotentiometry (CP), in 1.0 M KOH medium. A comparison of the electrocatalytic efficiencies of these Ni-based alloys was made in consideration with its physical and electrochemical characteristics. The obtained results showed that the alloying of Ni with W gives superior properties towards HER, attributed by its better hydrogen adsorption energy than in Ni-P alloy. The surface appearance, chemical composition and phase structure of the coatings were studied using SEM, EDS and XRD analyses, respectively.

Influence of vanillin on the corrosion behavior of Ni-W alloy electrodeposits and its properties

A simple and viable electrodeposition technique has been implemented to fabricate nanocrystalline Ni-W electrodeposits from an alkaline citrate bath with variations of vanillin (additive) concentration. The optimization of additive in the bath was substantiated in terms of its corrosion resistance property (evaluated using Tafel polarization and electrochemical impedance spectroscopy). For alloys deposited in presence of additive (100ppm) in the bath, resulted in low corrosion rate (C.R) and high charge transfer resistance (Rct). The enhanced corrosion resistance property (i.e. low C.R and high Rct) was deduced in terms of its homogenous surface morphology (using scanning electron microscope), reduction in crystalline size (using X-ray diffraction study), diminish in surface roughness value (using atomic force microscopy) as compared with that of electrodeposits obtained in the absence of additive. The inclusion of additive in the electrodeposits during electrodeposition, showed a major impact for its significant corrosion resistance property (C.R.−0.12mm/year and Rct-2177.83Ω·cm2). With an increase in the additive concentration in the bath, the corrosion resistance of the Ni-W coating becomes inferior, due to its porous nature and relative decrease in its capacitive behavior at electrode/electrolyte (corrosive) interface.

Induced codeposition of Ni-W alloy coatings using glycerol as additive and their characterization

As a promising coating material to replace hard chromium coating, the development of nickel–tungsten (Ni-W) alloy coatings of good corrosion protection is of great interest in surface coating technology. Further, the effect of plating variables, including additive on the composition of alloys of induced co-deposition is more vagarious than in other types of alloy deposition. In this regard, an alkaline citrate bath has been formulated for electrodeposition of Ni-W alloy through conventional Hull cell method, using glycerol as additive. Electrodeposition following the induced type of codeposition of Ni–W alloy was carried out onto mild steel (MS) substrate at different current densities (c.d.’s) at room temperature, taking a basic bath. Influence of bath constituents and operating parameters on the appearance, hardness, thickness and composition of the deposits were studied as a measure of their performance against corrosion. Corrosion behaviours of Ni-W coatings, having hard-adherent mirror bright appearance were studied using Tafel’s polarization and electrochemical impedance spectroscopy (EIS) method in 5 wt. % NaCl solution. Experimental results revealed that corrosion protection efficacy of Ni-W coatings increased with deposition c.d., in proportion of its W content. The coating developed at 4.0 A dm-2 was found to exhibit the least corrosion rate (5.3 x 10-2 mm y-1), compared to those at other c.d.’s. The process and product of electrodeposition have been studied using different instrumental methods, such as Cyclic voltammetry (CV), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) study. Experimental observations were analyzed in the light of induced codeposition of Ni-W alloy due to stimulation by Ni+2 ions, and results are discussed.

Characterization and corrosion resistance of electrodeposited Ni–Mo–silicate platelet nanocomposite coatings

Nickel–molybdenum–montmorillonite (Ni–Mo–MMT) nanocomposite coatings were prepared by electrodeposition from an alkaline citrate bath containing different concentrations of exfoliated montmorillonite. X-ray diffraction results revealed that the embedding of silicate platelets modified the texture of the Ni–Mo matrix and increased the grain size. Nanoindentation measurements showed increasing microhardness and Young's modulus for the nanocomposite coatings deposited from 1.0g/L solutions of silicate platelets compared to pure Ni–Mo films. The potentiodynamic polarization and electrochemical impedance measurements showed that the Ni–Mo–MMT nanocomposite layers have higher corrosion resistance in 3.5% NaCl compared to pure Ni–Mo. SEM and AFM micrographs showed a slight increase in the particle size and the surface roughness of the electrodeposited film, respectively as a result of incorporation of MMT particles into the Ni–Mo alloy matrix.

Ni electroplating on AZ91D Mg alloy using alkaline citric acid bath

Abstract Electroplating of Ni on an AZ91D Mg alloy in alkaline citrate baths was studied. It was found that NiSO4 and citric acid form a soluble complex. Ni plating with a smooth surface was obtained from the bath containing 0.55 mol dm −3 of nickel sulfate, 0.28–0.55 mol dm −3 of citric acid, and 0.88 mol dm −3 of aqueous ammonia at pH 10. The cathodic current efficiency decreased with increasing cathodic current density, which is beneficial for obtaining a uniform Ni-plating layer on components with complex shapes. The addition of KCl and saccharin sodium salt to the bath improved anodic dissolution and reduced the stress in the plating layer, respectively. With zinc replacement treatment, an adhesive Ni layer formed on the AZ91D Mg alloy.

Electroless ternary NiCeP coatings: Preparation and characterisation

Electroless ternary NiCeP deposits were prepared from alkaline citrate bath containing nickel sulphate, cerium chloride and sodium hypophosphite. Concentration of rare earth cerium was varied from 1 to 2g/L to obtain ternary deposits containing variable Ce and P contents. The influence of cerium on the deposit properties was analysed. The deposit exhibited a maximum cerium content of 6.2±0.1wt.% when the cerium chloride concentration was 2g/L. The result of the Pd stability test showed that the stability of the bath was reduced due to Ce salt addition. The microhardness measurements made on both as-plated and heat treated samples exhibited a peak hardness of 1006±11VHN for cerium concentration of 1.5g/L. The concept of kinetic strength analysis was proved to be applicable only for binary and not for ternary alloys due to multistep deposition mechanism with different kinetic energies. X-ray diffraction (XRD) patterns of as-plated and heat treated samples revealed peaks corresponding to Ni (111) and nickel phosphide (Ni3P). Higher amount of Ce incorporation in NiP matrix increased the crystallisation temperature of the deposit which could be due to the suppression of nickel crystallisation prior to Ni3P compound formation and thus increasing the activation energy for the formation of stable phases. Surface compositional analysis using X-ray photoelectron spectroscopy (XPS) carried out on as-plated NiCeP-2 deposit showed a prominent peak of P existing in +1 oxidation state as higher alkalinity favoured hypophosphite deposition in the ternary alloy coating. It was observed that the co-deposition of Ce in NiP matrix improved the continuous salt spray exposure for 168h.

Electroless deposition of Co–Mo–P alloys

Influence of the concentration (0–1×10−3M) of Mo(IV) compounds on the electroless deposition of Co–Mo–P alloy from alkaline citrate bath was investigated. The changes of the plating potential, mass of the deposits and hydrogen evolution as well as composition and morphology of the deposits with the concentration of additives were determined. Similar behaviour was observed for all compounds. Increase in the concentration in the bath was accompanied by inhibition of Co–Mo–P deposition and only traces of deposits were obtained at 1×10−3M Mo(VI). Molybdenum content in the deposits was low and oxygen was detected in the layers produced at 5×10−4 and 1×10−3M Mo(VI). Such changes corresponded to a gradual evolution of the morphology of the deposits from needle to fine grained structure, but Na2MoO4 produced deposits of the best quality. Adsorption of ions at the metal/electrolyte interface was proposed as responsible for phenomena observed in the Co–Mo–P system.

Surface morphology and structure of electroless ternary NiWP deposits with various W and P contents

Electroless ternary NiWP deposits were prepared using an alkaline citrate bath. Sodium tungstate concentration in the bath was varied from 5 to 40 g/L to obtain NiWP deposits containing various W and P contents. Deposits were characterized for their structure, composition, morphology and microhardness. A marginal increase in the grain size (from 1.4 to 3.5 nm) was observed with increasing sodium tungstate content in the bath due to the decrease in phosphorus content in the deposit (from 13 to 4 wt.%). Whereas W content in the deposit was increased (0.5–8.2 wt.%) by the addition of 20 g/L of sodium tungstate in the bath beyond that it was decreased to 4 wt.%. Scanning electron microscopy (SEM) images exhibited the nodular morphology of as-deposited coatings. Deposits were heat treated at various temperatures from 200 to 400 °C for 1 h and phases formed were identified by X-ray diffraction (XRD). Microhardness measurements were made for as-deposited and heat treated coatings at various temperatures. The applicability of the concept of kinetic strength analysis was also validated using the microhardness data obtained as a function of heat treatment temperature.

Processing and characterization of CNT/Cu nanocomposites by powder technology

Carbon nanotube/copper (CNT/Cu) nanocomposite powders with different volume fractions of multiwall CNTs (MWNTs) are prepared using e electroless Cu deposition method in alkaline citrate bath. The prepared CNT/Cu nanocomposite powders are investigated with HRSEM. The CNT/Cu nanocomposite powders have morphology of implanted CNTs in the copper particles of about 200 nm in size. An electroless deposited pure Cu powder is also prepared by the same method to compare the properties of pure copper samples and the prepared CNT/Cu nanocomposites. The prepared powders undergo XRD and elemental analysis to evaluate the fabricated CNT/Cu nanocomposites. The XRD patterns and elemental analysis inform that the deposited copper is composed of Cu powder and traces of some elements, e.g., sulfur and oxygen. The CNTs/Cu nanocomposite, as well as the pure copper powders, is sintered by spark plasma at 600 °C and compaction pressure of 20 MPa for one min under 10−3 torr vacuum condition. The microstructure of the sintered nanocomposites is investigated with SEM. The CNTs are homogenously distributed in the copper matrix in the case of CNT/Cu nanocomposites with CNT volume fraction up to 10 vol.% has a porosity of 3%, and the porosity increases by increasing CNT volume fraction due to the agglomeration of the CNTs in the copper matrix. The electrical resistivities of the prepared sintered copper and CNT/Cu nanocomposites are measured with four-probe method. The results show that the highest resistivity is 13.5 µΩ · cm for 40 vol.% CNT/Cu.

Electroless deposited Ni-Re-P, Ni-W-P and Ni-Re-W-P alloys

Coatings of electroless Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys were plated in alkaline citrate baths containing amino alcohols, but not free ammonia ions. The reference Ni–P alloy was used as an intermediate layer in the sandwich: Ni–Me–P/Ni–P/substrate. An extremely homogeneous thickness distribution of all alloy components was found by applying scanning Auger electron spectroscopy (SAES(. The inclusion of refractory metals at the expense of nickel and without substantial change in phosphorus content was established. A non-oxidized state of the codeposited Re and W in Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys was determined by means of X-ray photoelectron spectroscopy examination, as well as by SAES profiles, revealing the absence of oxygen throughout the coatings. All alloy films are amorphous and paramagnetic.

Amorphous Cobalt-Boron Alloy Electrodeposition and Dissolution

SummaryCo-B alloy has been deposited on steel from an alkaline citrate bath. Uniform deposits have been obtained in the current density range of 8–15 Adm −2.Cvclic voltammetric studies on platinum from this bath reveal that the cobalt citrate complexes undergo stepwise electronation with the participation of hydroxyl ions. The borates undergo reduction to boron in the alloy deposition. The hydrogen evolution reaction has been found to be hindered by cobalt and borate ions. Stripping voltammetric curves on the alloy film suggest the dissolution of cobalt from a cobalt rich phase.

Electrode properties of amorphous nickel-iron-molybdenum alloy as a hydrogen electrocatalyst in alkaline solution

Amorphous Ni/Fe/Mo alloys were obtained by electrodeposition from an alkaline citrate bath. The effect of the cathodic current density on the chemical composition, surface morphology of the Ni/Fe/Mo alloys, and the current efficiency of the deposition process was determined. The activity of the Ni/Fe/Mo alloy for the hydrogen evolution reaction (HER) was investigated under various electrolysis conditions in 30 wt.% KOH at 70 °C. The results showed that the Ni 41.49Fe 23.02Mo 35.49 alloy had the best activity for HER and excellent stability under continuous electrolysis. When accompanied by some current interruptions of various durations, the ternary alloy electrode still maintained good activity for HER.

無電解Ｎｉ‐Ｓ‐Ｐ合金めっき皮膜 電極材料の作製

To obtain cathodes for the electrolysis of sodium chloride, by electroless Ni-S-P alloy plating on soft iron plates, deposits containing various levels of sulfur content were prepared using ammoniacal alkaline citrate baths containing sodium hypophophate as the reducing agent and trace additives including sulfur.The following results were obtained:1) Adding 10ppm sodium thiosulfate to the plating bath made it possible to prepare deposits containing up to 5% sulfur.2) In baths not containing sodium citrate, the deposition rate increased, but the sulfur content in the deposits decreased.3) When the thickness of deposits increased, their sulfur content decreased and deposition stopped.

Characterization of nickel-molybdenum and nickel-molybdenum-iron alloy coatings as cathodes for alkaline water electrolysers

Nickel-molybdenum and nickel-molybdenum-iron alloy coatings obtained from alkaline citrate bath on mild steel strips electrolytically have been characterized with a view to employ them as electrocatalytic cathodes to generate hydrogen by alkaline water electrolysis. A detailed investigation on the i- E behaviour, the stability under open circuit conditions, the tolerance to electrochemical corrosion and the long-term stability was carried out. The salient features of the coatings such as the physical characteristics, the chemical compositions, the crystal structure of the phases and the varying effects of a catalytic activation method were analysed with a view to correlate the microstructural characteristics of the coatings with the hydrogen adsorption process. The pathway of hydrogen evolution reaction on these alloy coatings was discussed, keeping in view the very low apparent activation energy values obtained experimentally.

Ｎｉ‐Ｗ合金めっき皮膜の高Ｗ含有率化と皮膜特性

A study was conducted to determine the maximum obtainable tungsten content in the alloy, using ammoniacal alkaline citrate baths of pH7.5-9.0 at 80°C. Sodium citrate and citric acid were considered as the complexing agent. The presence of a large amount of sodium in the bath reduced tungsten content and current efficiency. When a suitable amount of sodium tungstate and nickel sulfate were added to the citric acid baths, alloys up to 51wt%W, corresponding to Ni3W, were obtained. Since alloys exceeding 40wt% W were obtained for the first time, X-ray examination and hardness testing were also conducted. Alloys exceeding 44wt% W (Ni4W stoichiometry) were amorphous, having extremely small atomic size. The Vickers hardness of the 44wt% W alloy was Hv 1350 after heating at 550°C for 1h.

無電解Ｎｉ‐Ｃｕ‐Ｐ合金めっき皮膜の電気抵抗特性

The electric resistance behavior and the structure of electroless nickel-copper-phosphorus alloy films obtained from various kinds of plating baths containing sodium hypophosphite as a reducing agent were investigated by means of an X-ray diffraction method, a film resistance measurement, and a differential scanning carolimetry. It was found that resistivity of films as-plated became constant value more than 1-2μm thickness, and it became smaller when the contained the larger content of copper. For change of resistivity of films by the heat treatment, the ratio of its decrease became larger when the films contained the larger content of phosphorus and its relation corresponded well to the structural variation of films. For the films deposited from caustic alkaline citrate bath, the returning of films became worse, when content of copper incresed. The heat treatment at 300°C 1hr. in vacuum, however, developed its returning. In case of ammonia alkaline citrate bath, the returning of films were better than that deposited from caustic alkaline citrate bath. In all films asplated, the resulting temperature coefficient of resistance (TCR) were lower with decreasing the grain size of film and TCR were larger by the heat treatment.

Electroplating of thin films of Fe-Ni alloys: Some effects of superimposed alternating current on direct current

The effects of superimposing square, sine and triangular alternating currents on a direct current during the electroplating of thin films of Fe-Ni alloys from acidic and alkaline citrate baths under various plating conditions are studied. The composition of the alloys is found to depend on the ratio of alternating to direct current, the a.c. frequency and the waveform. The effect of the alternating current diminished with increase in the frequency and the alternating to direct current ratio. In addition, the effects of pH and temperature on the alloy composition are also reported. The alternating current slightly shifted the cathodic polarization towards the noble direction and decreased the grain size, resulting in smooth and bright deposits. A plausible mechanism for the action of the alternating current is proposed.

亜すず酸ナトリウム添加浴からの無電解ニッケル‐すず‐りん合金めっきについて

A study of electroless nickel-tin-phosphorus alloy plating from ammonia alkaline citrate bath (A-C bath) and from caustic alkaline citrate bath (C-C bath) containing sodium stannite has been made with reference to the effect of the tin content on deposition condition and the corrosion behavior of the alloy. It was found that the deposition rate increased with increasing amount of sodium stannite in A-C bath, but this effect was very small in C-C bath. The tin content in the deposits increased up to 19.2% in A-C bath and 12.4% in C-C bath. In a 0.5M sulfuric acid solution at 30°C, however, the tin cotent in the deposits from A-C bath increased about more than 7% and that from C-C bath increased more than 12%. Severe corrosion of the alloy in the solution is due to the formation of metastable phase Ni3Sn4. The corrosion resistance of the depeposits, containing 2.8% tin and 4.4% phosphorus, from A-C bath, and of the deposits containing 8.4% tin and 8.3% phosphorus, from C-C bath was excellent.

無電解ニッケル‐銅‐りん合金めっきについて

Electroless nickel-copper-phosphorus alloy platings from ammonia alkaline citrate bath (A-C bath) and caustic alkaline citrate bath (C-C bath) containing sodium hypophosphite as a reducing agent were investigated to determine the effect of copper ion concentration on the deposition rate, corrosion resistance and structure of the deposits. The basic bath composition was found to be: nickel sulfate +copper sulfate 0.1M, sodium hypophosphite 0.2M, sodium citrate 0.2M, pH10 (adjusted with NH4OH or NaOH); bath temperature was 80±2°C. The copper content in the nickel-copper deposits were found to be 0% to 44.5% in A-C bath and 0% to 69.0% in C-C bath, respectively, depending on the copper ion ratio in the plating bath. In A-C bath, the deposition rate increased considerably with the copper ion concentration in the bath, but in C-C bath, this effect was very small. The corrosion resistance of the deposits, containing 16.5% copper and 4.7% phosphorus, from A-C bath, and of the deposits containing 8.0% phosphorus, from C-C bath was excellent for a 0.5M sulfuric acid solution at 30°C.