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After appropriately preparing the surface of AISI316 steel, the Ni–Co–P coating layer was deposited on the substrate using the electroless method using baths with different mole ratios of CoSO4/NiSO[Formula: see text]. Coating rate, weight percentage of the alloy elements, corrosion rate and coating layer hardness were studied in the achieved coating layers. The coating rate of the Ni–Co–P coating layer is a function of the mole ratio of CoSO4/CoSO[Formula: see text], sodium hypophosphite concentration, bath temperature, bath pH and plating time. The electroless deposits studied in this paper are in crystal form. The XRD pattern of the Ni–Co–P deposits shows the peaks related to Ni-fcc and tetragonal Ni[Formula: see text]P5. X-ray diffraction pattern confirms the formation of the Ni3P phase during annealing for 1[Formula: see text]h at 400∘C.

Purpose The composition and corrosion behaviors of recycled and virgin Pb anode were investigated in industrial zinc electrowinning solution with different methods. The purpose of this study is the illustration of good anticorrosion activity of virgin Pb anodes compared to recycled one in industrial operation, while the compositions of both of them are the same which obtained from quantmetry method. Design/methodology/approach Its corrosion properties and electrocatalytic activity toward oxygen evolution reaction were appraised using potentiodynamic polarization, electrochemical impedance spectroscopy, galvanostatic polarization and ionic equilibrium methods. In addition, composition of anodes investigated with X-ray photoelectron spectroscopy (XPS) method. The surface composition of samples was studied via X-ray diffractogram (XRD). Findings The results indicate that the anodes display different anodic behaviors during the galvanostatic polarization. Virgin Pb anode shows a “potential reduction” about 320 mV lower than recycled Pb anode after 6 h of polarization; also, the stable potential after 72 h for virgin Pb anode is 100 mV lower than recycled Pb anode. Also, The XPS results show a trace amount of Cl in recycled anodes which cause the more corrosion activity. XRD results indicate that virgin Pb anodes have been covered by more oxides than recycled anodes after 72 h of electrowinning. Originality/value The treatment of corrosion behavior by virginity has not been detected by any researchers yet. Therefore, it is imperative to study the corrosion behavior and exact composition analysis of virgin and recycled Pb anodes to comprehension of them. This paper fulfills this need.

It is an important challenge to reduce the carbon content in nanostructured bainitic steels for commercialization purposes while still being able to gain the desired microstructural characteristics in nanoscale and not to deteriorate the strength–ductility combinations. That is the point at which an appropriate heat treatment procedure design would be an important parameter. This article aims to investigate how to obtain nanostructured bainite in steel with 0.26 wt% carbon content by applying multi-step austempering procedures. One-, two- and three-step austempering processes have been implemented, and proper heat treatment temperatures and approaches were selected based on dilatometry tests. Results indicated that it has become possible to achieve bainitic ferrites and austenite films with overall thicknesses of 164, 145 and 132 nm and 134, 105 and 90 nm at the end of one-, two- and three-step austempering heat treatments, respectively. Meanwhile, microstructural characteristics resulted in enhanced mechanical properties with ultimate tensile strength (UTS) of 1435, 1455 and 1428 MPa in combination with elongation levels of 15.4, 13.6 and 11.4% after implementing those heat treatments. Finally, it has been shown that applying the multi-step austempering heat treatments resulted in enhanced yield strength and impact toughness values due to the microstructural characteristics and proper heat treatment procedure design.

The Zn-Ni-Mn/Zn Ni multi-layer coatings were electrodeposited under switching potential regime from an alkaline solution. In order to deposit Zn Ni layers, more positive potential −1560 mV was used as first electrodeposition potential in each cycle. More negative potentials −1860 mV and −1980 mV was used as the second potential in the various potential regime. The pulse-electrodeposited samples showed a smoother surface compared to coatings electrodeposited at a constant potential. Also, potentiodynamic polarization and electrochemical impedance spectroscopy were used to study the corrosion resistance of these coatings. All coatings electrodeposited at constant potential showed passivation behavior, while such behavior was only seen in pulse-electrodeposited samples from bathes with Mn2+ concentration higher than 1.17 μM. Samples electrodeposited using −1860 mV as the second potential for 30 s in each cycle had more positive corrosion potential and lower corrosion current density compared to samples deposited at a constant potential, while samples electrodeposited under potential regimes with more negative second potential had more negative corrosion potential and higher corrosion current density. The electrochemical impedance curves showed that the coatings electrodeposited at constant potential had higher polarization resistance and the passive layer formed at their surface was more compact than the pulse-electrodeposited ones.

The selective precipitation of zinc from zinc–nickel sulfate solution with the Zn/Ni molar ratio of 20:1 was studied. Dropwise addition of 0.5 mol/L NaOH solution into the zinc–nickel sulfate solution containing 0, 0.01, 0.02, 0.03 and 0.04 mol/L ethylene diamine tetraacetate (EDTA) as a chelating agent was done. The equilibrium analysis of precipitation pathway was performed using Visual MINTEQ program. The equilibrium analysis showed that the presence of small amounts of EDTA can prevent nickel precipitation in alkaline conditions without any negative effect on zinc precipitation. On this basis, more than 90% of zinc could be precipitated as a product with about 50% Zn and only 0.11% Ni at pH=9.0 merely as a result of the presence of 0.03 mol/L EDTA in the solution. The stirring time of 120 min after precipitation was found to be essential for more complete separation. The X-ray diffraction studies on the precipitate revealed that the precipitated phase was Zn4(OH)6SO4.4H2O.

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 corr...

The potentiostatic electrodeposition of Zn−Ni−Mn was carried out in an alkaline solution with the addition of Mn salt. The effects of electrolyte Mn2+ concentration and deposition potential on the surface morphology, phase structure and corrosion behavior of coatings were studied. The results of corrosion polarization showed that the presence of higher Mn content in Zn−Ni−Mn coatings could lead to the formation of a good passive layer with a 7-fold increase in Rp of coating and a significant decrease in the corrosion current density compared to those of Zn−Ni coating. The XRD and the XPS analyses from the surface of Zn−Ni−Mn after corrosion test showed that the passive layer was composed of zinc hydroxide chloride, zinc oxide, zinc hydroxide carbonate, and manganese oxides.

As a unique type of nickel films, black nickel coatings possess remarkable optical and electrical properties but limited applications owing to their poor structure and corrosion resistance. In this study, black nickel coatings were electrodeposited on St37 steel and optimized utilizing nickel Watts bath modified with potassium nitrate. By investigating the coating structure and current efficiency (CE), optimum bath was determined as 190 g/L NiSO4, 25 g/L NiCl2, 30 g/L H3BO3, and 25 g/L KNO3 which resulted in CE of 79% and a compact structure. Next, cyclic voltammetry and chronoamperometric tests revealed that the dominant deposition mechanism was instantaneous nucleation. Besides studying the changes in CE and cathodic polarization, the improvement of properties with addition of imidazole was investigated by studying the surface morphology, phase structure, light absorption, and corrosion behavior using SEM, XRD, differential reflectance spectroscopy (DRS), potentiodynamic polarization, and electrochemical impedance spectroscopy tests, respectively. Adding imidazole to the deposition bath reduced the grain size and crack width from micro-scale to nano-scale, without affecting its nucleation mechanism or light absorption property. Also, imidazole enhanced the corrosion resistance of the black nickel coatings by 62% reduction of corrosion current density and increasing its polarization resistance by 58%.

This paper introduces and discusses some potential effects of dilution in aqueous precipitation processes. The response of a sulfate solution comprising of 0.3 mol L−1 Zn and 0.015 mol L−1 Ni diluted with NaOH solution has been simulated. Considerable changes in separation pH, separation potential and precipitating minerals, have appeared after dilution. An increase in separation pH from 6.86 to 7.45 due to 100 times dilution has been predicted. It has also been revealed that the selectively precipitable zinc decreases from 89.4 to 85.7 % as a result of dilution. The products of zinc precipitation from undiluted and 100 times diluted solutions should be ZnO and Zn4(OH)6SO4, respectively, according to equilibrium analysis. Despite the acceptable agreement of experimental results, the full agreement has been restricted in some cases by kinetic difficulty of ZnO precipitation and local high pH zone effect that has led to nickel co-precipitation.

The aim of this study is to investigate the effect of phosphate solution with Ca 2+ additives on weight, surface morphology and electrochemical behavior of phosphated Zn–Ni film. In order to characterize structure and morphology of surface, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied, respectively. Results showed that the main composition in produced coatings was hopeite Zn 3 (PO 4 ) 2 ·4H 2 O, which has high corrosion resistance. On one hand, in the presence of Ca 2+ cations in solution, the weight of phosphate coating decreased, but on the other hand surface uniformity and corrosion resistance of the coating increased.

In the current research, the effect of low-temperature calcination on the crystal structure, morphology and corrosion properties of sol-gel derived dip-coated amorphous Al2O3 on plain carbon steel with a nickel electrodeposited intermediate layer was investigated. Alumina sol suspension was prepared via Yoldas method and modified by the addition of polyvinyl alcohol (PVA). The coatings were calcinated at 300 °C and 500 °C, and the stability of sol suspensions was evaluated by zeta potential analysis. Phase transformation temperature and thermal properties of alumina sol were investigated using DSC analysis. The morphology and composition of coatings before and after potentiostatic test was studied using FESEM and EDS. XRD analysis were conducted to characterize the crystal structure and phase of synthesized alumina. FTIR spectroscopy were used to characterize obtained composites. Finally, the corrosion behavior of coatings was analyzed using OCP, potentiostatic polarization, and EIS. The results revealed that the calcined coating at 300 °C has a corrosion current density of 0.15 μA.cm−2, which is 15 times better compared to bare substrate (icorr = 2.3 μA.cm−2), and also 50 times better than the calcined coating at 500 °C (icorr = 7.8 μA.cm−2). This phenomena attributed to carbonaceous residues from PVA in the alumina coating calcined at 300 °C and its crack-free surface; thus, showed better corrosion resistance than those calcinated at 500 °C.

The aim of this study is to investigate the effect of nitrate and nitrite on the weight, morphology and electrochemical properties of phosphated Zn-%12Ni electrodeposite coatings. In order to investigate the phase structure and surface morphology of samples, X-ray diffraction and scanning electron microscopy were employed. Also, to measure the corrosion resistance behavior of the coats, Potentiostat/Galvanostat test was used. The results showed that nitrite accelerator reduces coating weight and surface porosity simultaneously obtaining by phosphate solution. Furthermore, coatings being obtained by the nitrite accelerator had a higher corrosion resistance than that of the nitrate accelerator.

The present investigation involves the separation of zinc and nickel from a sulfate solution using the acidic leaching of zinc plant residue after cadmium removal step as precursor (42.88 wt% Zn, 8.50 wt% Cd and 2.33 wt% Ni). Separation of nickel from the solution was done by pouring it into a strong alkaline sodium hydroxide solution due to precipitation of nickel hydroxide and conversion of zinc to the soluble $${\text{Zn}}({\text{OH}})_{4}^{2 - }$$ complex. Higher degrees of separation were reached by pouring more diluted solutions into the stronger alkaline media. To clear pursue of the process, design of experimental methodology was applied for experiments. Scrutinizing different washing steps on nickel-rich precipitates shows that the washing process decreases zinc content and thereby increases overall selectivity coefficient. Outcomes show that, at the optimized condition, Ni/Zn weight ratio in the solid product becomes about 104 times higher than the initial ratio in the initial feed solution and a nickel concentrate with 29.98 wt% Ni and 5.99 wt% Zn is achieved. At the same time, the chemical analysis of filtrate shows only 4.4 mg·L−1 Ni in the alkaline zinc solution, which means that over 99 % nickel is recovered. The study on changes of zinc concentration with time shows that the process could be completed only after few minutes.

The aim of this study is to investigate the effect of nitrate and nitrite on the weight, morphology and electrochemical properties of phosphated Zn-%12Ni electrodeposit coatings. In order to investigate phase structure and surface morphology of samples, X-ray diffraction and scanning electron microscopy were employed. In order to measure corrosion resistance behavior of the coats, Potentiostat/Galvanostat test was used. The results showed that nitrite accelerator reduces coating weight and surface porosity simultaneously obtaining by phosphating solution. Furthermore, coatings which were obtained by the nitrite accelerator had a higher corrosion resistance than that of the nitrate accelerator.

The inhibiting behavior of bis-(2-benzothiazolyl)-disulfide on mild steel corrosion was evaluated in 1 M HCl solution. Weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques were used in this study. In EIS technique, by performing Kramers–Kronig transformations, the experimental results validated, before fitting any theoretical model on them. The obtained results showed that the inhibition efficiency (%IE) increases by increasing the concentration of bis-(2-benzothiazolyl)-disulfide up to 2.02 × 10−4 M (%IE ∼ 62–68). Between the results obtained from various used techniques, a good agreement was found. Polarization curves indicate that the inhibition of the inhibitor is a mixed anodic–cathodic nature and Langmuir isotherm is found as an accurate isotherm describing the adsorption behavior. It also found that its inhibition mechanism of bis-(2-benzothiazolyl)-disulfide is at the interval of physical adsorption and chemical binding. The inhibition efficiency of the inhibitor decreased by rising of temperature in the range of 25–55 °C and these results, verified adsorption behavior of the inhibitor.

The inhibiting behavior of Nile Blue and Indigo Carmine organic dyes on mild steel corrosion was evaluated in 1 M HCl solution, separately, by weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy techniques. Results show that the inhibition efficiency (%IE) increases with the increasing concentration of Indigo Carmine up to 9.65 × 10−05 M (%IE ~ 98) and Nile Blue up to 1.08 × 10−04 (%IE ~ 75–80). Good agreement was found between the results obtained from the different techniques used. Polarization curves indicate that the inhibition of the both inhibitors is of a mixed anodic–cathodic nature, and Langmuir isotherm is found to be an accurate isotherm describing the adsorption behavior. The inhibition mechanism of the inhibitors involves chemisorption interaction between the inhibitor and the mild steel. The inhibition efficiency for both inhibitors decreased by the rising temperature in the range of 25–55 °C, and these results verified the chemisorption behavior of both the inhibitors.

Fe–Si alloys are of significant commercial and academic interests, due to the large diversity of their physical properties. In practice, alloy powders are unsuitable because of their hardness, poor compactibility and resulting excessive tool wear. Therefore the powder mixture route is suitable as alloying technique. The properties of the Fe–Si sintered materials depend strongly on the influence of the element Si and content of it, which influence mainly the compactibility and the sintering behaviour as well as sintering parameters such as the optimum temperature. In this study, Cr–Mo prealloyed steel powders with different Si contents were prepared by powder mixture route. Mixed powders compacted under pressing pressure of 600 MPa, and then sintered at 1120 and 1250 °C. It was found out that in Si alloyed Cr–Mo steels sintered at higher temperatures such as 1250 °C, an intermediate liquid phase appeared and caused extreme shrinkage and distortion, but strongly accelerated sintering and had a beneficial effect also on homogenization.

The inhibiting behavior of 6-aminohexanoic acid (C 6 H 13 N0 2 ) on mild steel corrosion in 1 M HCI as corroding solution at 25 °C was evaluated by weight loss, polarization, and electrochemical impedance spectroscopy (EIS) methods. The weight loss, polarization, and EIS measurements were relatively in good agreement together. Results obtained by the three methods showed that the inhibition efficiency (%IE) increases with increasing the concentration of 6-aminohexanoic acid up to 6.86 × 10 -05 M (about %IE = 80). It was also found that the adsorptive behavior of the investigated inhibitor on the steel surface followed Langmuir-type isotherm, the 6-aminohexanoic acid acted as a mixed type inhibitor and its inhibition mechanism obeys from the chemisorption interaction between 6-aminohexanoic acid and the mild steel.