Electrodeposition and characterization of Zn–Ni alloys as sublayers for epoxy coating deposition

The chemical composition and phase structure of Zn–Ni alloys obtained by electrodeposition under various conditions were investigated. The influence of the deposition solution and deposition current density on the composition, phase structure, current efficiency and corrosion properties of Zn–Ni alloys were examined. It was shown that the chemical composition and phase structure affect the anticorrosive properties of Zn–Ni alloys. A Zn–Ni alloy electrodeposited from a chloride solution at 20 mA cm^–2 exhibited the best corrosion properties, so this alloy was chosen for further examination. Epoxy coatings were formed by cathodic electrodeposition of an epoxy resin on steel and steel modified with a Zn–Ni alloy. From the time dependence of the pore resistance, coating capacitance and relative permittivity of the epoxy coating, the diffusion coefficient of water through the epoxy coating, D(H₂O), and its thermal stability, it was shown that the Zn–Ni sublayer significantly affects the electrochemical and transport properties, as well as the thermal stability of epoxy coatings. On the basis of the experimental results it can be concluded that modification of a steel surface by a Zn–Ni alloy improves the corrosion protection of epoxy coatings.     

Electrodeposition of Co–Ni alloys

Cobalt–nickel alloys were electrodeposited in an acid bath containing various ratios of metallic cations. The effect of the plating variables on the composition and morphology of the deposits obtained on vitreous carbon electrodes was investigated. Different proportions of the two metals can be obtained by using different deposition parameters, but at all Co(ii)/Ni(ii) ratios studied, preferential deposition of cobalt occurs and anomalous codeposition takes place. For a fixed solution composition, the nickel content in the deposit is enhanced by increasing the deposition potential. More homogeneous and fine-grained deposits can be obtained by increasing the cobalt(ii)/nickel(ii) ratio in solution and by ensuring that deposition takes place slowly. Deposits of constant composition throughout the depth of the deposit can be obtained only by stirring the solution during the deposition. In addition, the solution must be stirred in order to minimize the increase in local pH and to prevent hydroxide precipitation. An attempt was made to explain the anomalous codeposition. The results suggest the following sequence of events: first, nickel is deposited; then, cobalt(ii) adsorbs onto the freshly deposited nickel and begins to be deposited. The cobalt(ii) adsorption inhibits subsequent deposition of nickel, although it does not block it completely.     

Electrodeposition and characterization of Au–Cu–Cd alloys

The electrodeposition of Au–Cu–Cd alloys from cyanide baths was investigated under different hydrodynamic conditions. Alloys obtained at different current densities were characterized from the compositional, structural and morphological points of view. Depending on the electrodeposition current density, the deposit structure displays either one or two-phase disordered solid solutions; corresponding changes in mechanical properties were observed. Morphology and roughness show a marked smoothing transition when the current density is increased over the limit for the inception of Cu codeposition. The Cd²⁺ concentration in the bath is a critical factor for control of the electrodeposition process, especially in respect to compositional stability and absence of hydrogen incorporation. Alloy composition was shown to be critically affected by hydrodynamic conditions; strict control of flow conditions is needed in order to obtain alloys of desired and reproducible composition.     

Electrodeposition and properties of cyclically modulated silver–antimony alloys

An investigation was carried out on the influence of electrodeposition conditions on the properties of cyclically modulated Ag–Sb alloys, such as internal stress, microhardness, roughness, electrical contact resistance, wear resistance and plug-in forces. Pulses of different amplitude and duration were used, leading to different composition and thickness of the deposited sublayers, and the resulting changes in the coating properties were demonstrated. The possibility of depositing coatings free of internal stress is shown. The electrical contact resistance does not depend on the multilayer structure of the coating, but on the type and properties of the upper sublayer. The microhardness of the multilayer coatings increases with the increase in their antimony content. It decreases for very short pulses whereby the effect of the higher current density cannot be realized. The wear resistance of the multilayer coatings displays values between those of the respective monolayer coatings deposited under the conditions of separate sublayer deposition. It increases at a very small sublayer thickness, at decreasing contribution of the higher current density and at lower stress values of the multilayer coatings. The roughness of the coatings is not influenced by their multilayer structure, and the plug-in forces increase with the reduction of the sublayer thickness to about 0.03 m.     

Electrodeposition of Zn–Mn alloys in acidic and alkaline baths. Influence of additives on the morphological and structural properties

Electrodeposition of Zn–Mn alloys on steel was achieved using alkaline pyrophosphate-based baths or acidic chloride-based baths. Cyclic voltammetry was used to determine the potential ranges where the various redox processes were taking place. It appeared that the reduction of Mn(II) was generally hidden by the other reduction reactions, especially by the hydrogen evolution reaction. Zn–Mn alloys containing up to 25 at.% Mn in the alkaline bath and 12 at.% in the acidic bath could be obtained at the cost of very low current efficiencies. The characterisation of the deposits obtained either by galvanostatic polarisation or potentiostatic polarisation was performed by Scanning Electron Microscopy and X-Ray Diffraction. Various Zn–Mn phases were obtained, depending on the current densities, the composition of the deposit and that of the electrolytic bath. Two commercial additives usually used for zinc electrodeposition, one in alkaline baths, the other in acidic baths, were tested. Their effects upon the composition, the morphology and the microstructure of the deposit were investigated.     

Electrodeposition of Zn–SiC nanocomposite coatings

Zn–SiC composite coatings were obtained on mild steel substrate by electrodeposition technique with high-current efficiency. A slightly acidic chloride bath, containing SiC nanoparticles and gelatine as additive, was used. The electrodeposition was carried out under galvanostatic control with pulsed direct current; the effect of experimental parameters (temperature, average current density and particles concentration) on composition, morphology and structure of the deposit was studied. Coatings were characterized by means of scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffractometry and Vickers microhardness measurements. Zn–SiC electrodeposits with the best characteristics were obtained by performing electrodepositions at 45 °C, with 20 g L^?1 SiC in the bath and with average current density in the range 100–150 mA cm^?2. Under these experimental conditions, homogeneous and compact coatings, with low-grain size and SiC content ranging from 1.7 to 2.1 wt%, were found to be electrodeposited. Microhardness measurements showed for these deposits an increase of about 50 % with respect to those without nanoparticles obtained in the same experimental conditions.     

Study of the influence of a boric–sorbitol complex on Zn–Mn electrodeposition and on the morphology, chemical composition, and structure of the deposits

Zn–Mn electrodeposition onto Pt from an electrolyte containing boric–sorbitol complex (BSC) or boric acid alone (BA) was studied. The influence of BA or BSC content on the deposition process was investigated by cyclic voltammetry and electrodeposits, produced potentiostatically, were analysed by SEM, EDX, and XRD. The voltammetric studies indicated that an increase in the BSC concentration led to a decrease in the deposition current density. EDX analysis of deposits obtained at −1.60 V showed that increasing the BA or BSC concentration in the bath induced a fall in the Mn content of the electrodeposit and that for BSC this decrease was more significant. SEM images showed that the Zn–Mn electrodeposit obtained in the presence of 0.24 M BSC were smoother than other deposits; hence, BSC acted as a grain refiner at this concentration. XRD analysis of this deposit indicated that it was composed of Zn, Mn, MnZn₁₃, and MnH_0.8.     

Electrodeposition of silver–tin alloys from pyrophosphate-cyanide electrolytes

Using cyclic-voltammetric techniques, a pyrophosphate-cyanide electrolyte for the electrodeposition of compact Ag–Sn alloy coatings is investigated. This electrolyte is suited to further investigations on the alloy composition, structure and properties. The electrodeposition of coatings with up to 40 wt% Sn is possible from the investigated complex electrolytes. The alloy surpasses the saturation limit of the silver lattice with Sn and allows the formation of coatings with phase heterogeneity. At high tin content an ordered spatial distribution of different alloy phases on the cathodic surface can be observed. The pattern formation in this system looks very similar to the phenomena and structures observed during electrodeposition of other silver alloys, such as Ag–Sb, Ag–Bi and Ag–In.     

Electrodeposition of Ni–Co alloys from sulfamate baths

The paper describes the results of electrochemical investigations of Ni–Co deposition from a sulfamate bath in the presence of boric acid and two additives. The individual deposition of nickel was shown to be partly inhibited by the adsorption of sulfamate ions at low polarization; such inhibition was not observed for cobalt. The introduction of saccharin at 100 ppm, with a wetting agent seems to hinder sulfamate adsorption and Ni deposition departs at less cathodic potentials. The presence of cobalt has no effect on nickel deposition, whereas cobalt deposition is hindered by the presence of nickel in the bath. Galvanostatic deposition was carried out at the surface of a RDE and with a rotating cylinder Hull cell. At low current densities deposits with a Co content of approx. 40% were produced, but this content was shown to decrease with the applied current density. Examination of experimental data showed that cobalt deposition is diffusion-controlled and that Co content decreases with the applied current density relative to the limiting current density.     

Electrodeposition of Au–Sn alloys from alkaline baths

A bath for the electrodeposition of white gold alloys of interest for the electroforming of hollow jewellery is proposed. The investigated system is an alkaline KAu(CN)₂ bath for the electrodeposition of Au–Sn alloys. The electrochemical investigations are based on cyclic voltammetry and electrodeposition experiments. Electrodeposited foils were studied from the crystallographic, compositional and morphological points of view. Co-deposition of Au and Sn gives rise to the formation of a series of intermetallic phases, which can be detected by X-ray diffraction and anodic stripping. Deposits are typically polyphasic; the phase composition generally does not correspond to the equilibrium one. Chemical compositions ranging from high-Au to high-Sn can be obtained by galvanostatic deposition at suitable current densities.     

Electrodeposition of zinc–nickel alloys from ammonia-containing baths

This paper describes the use of ammonia-containing baths for Zn–Ni alloy electrodeposition. Buffering properties of the ammonia/ammonium couple limit the local change in pH in the vicinity of the electrode surface caused by simultaneous hydrogen evolution. In addition, it is shown that the divalent zinc and nickel species exist in the form of Zn(NH₃) ₄ ²⁺ and Ni(NH₃) ₆ ²⁺ complexes over a large pH range. The electrochemistry of the deposition at pH 10 was investigated by galvanostatic experiments and cyclic voltammetry, and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys were found to be 40–60% higher from the ammonia-containing bath than from the acidic baths. Reduction of divalent ions and hydrogen evolution were shown to occur at potentials 250mV more cathodic than with baths at pH 5; the deposition mechanism may be affected by complexation of the metal cations by ammonia.     

Electrodeposition and corrosion behavior of Zn–Ni and Zn–Ni–Fe2O3 coatings

A thin film of Zn–Ni–Fe₂O₃ on steel substrates was prepared by electrodeposition technique using Zn–Ni alloy plating solution with nano-sized Fe₂O₃ particles. The cathodic polarization and cyclic voltammetry techniques were used to explain deposition process. The corrosion behavior of deposits was evaluated by polarization and impedance studies. Scanning electron microscope (SEM) images were used to study the surface morphology of coating. The grain size and amount of Fe₂O₃ particles present in composite coating were measured by X-ray diffraction pattern (XRD) and energy dispersive X-ray diffraction spectrometer (EDS), respectively.     

Ignition temperature of coal. 1. Influence of the coal’s composition,structure, and properties

The reactions of coal with the materials used in determining the ignition temperature of unoxidized coal according to Ukrainian State Standard DSTU 7611:2014 are analyzed. First, the ignition temperature of various types of coal from Ukraine, Russia, Canada, Australia, the Czech Republic, Poland, and Indonesia is determined. The influence of the composition, structure, and properties of the coal on its ignition temperature is assessed. The ignition temperature of the unoxidized coal is found to be closely related to the content of organic carbon C^daf and aromatic carbon C_ar, the structural parameter δ characterizing the degree of saturation of the coal’s organic mass, and also the vitrinite reflection coefficient R_o and the yield of volatiles V^daf.     

Synthesis,structure and unprecedented self-assembly strategy of two six-membered Zn–organic macrocycles

Two novel cyclohexane-like metallamacrocycles [ZnCH₃COO(L)]₆·solvent (1) and [Zn(HNO₃)(L)]₆·solvent (2) (HL = 4′-(4-carboxyphenyl)-2,2′:6′,2″-terpyridine) have been synthesized under hydrothermal conditions and characterized by IR spectra, single crystal X-ray diffraction, PXRD analysis, thermogravimetric analysis. The X-ray single crystal diffraction indicates that the self-assembly of the metallamacrocycle generates a fused-ring network that is further assembled into a 3D structure with 1D suprachannels. In particular, a designed self-assembly strategy has been applied to achieving six-membered Zn–organic metallamacrocycles unprecedentedly.     

Normal and anomalous codeposition of Zn–Ni alloys from chloride bath

The codeposition of Zn–Ni alloys from chloride bath has been studied by means of potentiostatic electrodeposition in the potential range –700 to –1100mV vs Ag/AgCl, where both normal and anomalous codeposition occurs. Deposition of alloys of different composition, morphology and structure, depending on the cathodic potential, was found. Analysis of the partial current densities showed that the production of nickel rich alloys in the potential range –700 to –900mV is due to the underpotential reduction of zinc, driven by nickel ion discharge. Morphological and microstructural analyses showed that these alloys have the face-centred-cubic structure of nickel ( phase) and that the addition of zinc in the nickel lattice causes internal stresses in the deposits, which are prevalently amorphous. At potentials more negative than –910mV, corresponding to the equilibrium potential of the zinc rich phase deposition, the rate of deposition of the phase decreases and the further increase in deposit zinc content leads to the formation of the phase, with a decrease in internal stress. In this range of potential, zinc and nickel reduction can occur separately, according to their respective exchange current densities.     

Phase composition,crystal structure and microwave dielectric properties of Mg2−xCuxSiO4 ceramics

In this work, the Mg_2-xCu_xSiO₄(x = 0–0.40) microwave dielectric ceramics were prepared using solid-state reaction method. Compared with the Mg₂SiO₄ sample, the Cu-substituted Mg samples could be sintered at a lower temperature. The Mg_2?xCu_xSiO₄ ceramics exhibit the composite phases of Mg₂SiO₄ and a small quantity of MgSiO₃. The Cu²⁺ ion presented a solid solution with the Mg₂SiO₄ phase and preferentially occupy Mg(1) site. The distortion of MgO₆ octahedron was modified by Cu²⁺ ions, resulting in a positive change in the temperature coefficient of resonance frequency (τ_f) values. Excellent microwave dielectric properties of ε_r = 6.35, high Qf of ～ 188,500 GHz and near zero τ_f = ?2.0 ppm/°C were achieved at x = 0.08 under sintering at 1250 °C for 4 h. Thus, the fabricated ceramics were considered as possible candidates for millimeter-wave device applications.     

Structural,magnetic properties,and electronic structure of Cr1−xMnxO2 solid solution

Bulk Cr_1-xMn_xO₂ samples are prepared by high pressure synthesis technology. The crystal structure, magnetic properties and electronic structure of the samples are investigated by experiments and theoretical calculation. The crystal structure of the samples are indexed to a rutile structure with space group P4₂/mnm. The lattice parameter a of the samples remains basically unchanged in accordance with Vegard's law, but the lattice parameter c decreases due to increasing Mn dopant content (x) as well as strong Metal–Metal bonding along the c-axis. The saturation magnetization of the Cr_1-xMn_xO₂ samples decreases with an increase in x. According to XPS analysis, there is electron transfer between Mn and Cr in Cr_1-xMn_xO₂. Mn exists as Mn²⁺ and Mn³⁺ions, and part of Cr is oxidized to Cr⁶⁺. Based on the XPS analysis, the magnetic moment of Cr_1-xMn_xO₂ is calculated and its value is in accordance with the experimental data.     

Electrodeposition of Cu–Zn alloy coatings from citrate baths containing benzotriazole and cysteine as additives

Alternative electrolytes, such as citrate baths, are now studied, aiming to reduce the toxicity and the cost of the electroplating process while maintaining the decorative qualities and anticorrosive properties of the coatings. For this purpose, brightening and/or leveling compounds are usually added to the base citrate bath. In this work, Cu–Zn alloys were electroplated on mild steel substrates from electrolytes containing sodium citrate and additives (benzotriazole and cysteine) at constant stirring speed. The results showed that coatings produced from baths containing additives were brighter than those obtained from the base citrate bath. Additionally, the presence of benzotriazole directly influenced the coating composition and the properties of the deposited alloy: the amount of zinc in this coating increased excessively, and the coating/substrate corrosion presented a poor anticorrosive performance.     

Electrodeposition of Co–Pd alloys from ammonia solutions and their catalytic activity for hydrogen evolution reaction

Investigations of the influence of electrolysis parameters such as the concentration of metal ammonia complexes, working electrode potential and temperature on the composition, structure and catalytic activity of synthesized alloys for water molecule reduction reaction in 2 M NaOH (T = 25 °C) were conducted. The alloys were deposited under potentiostatic conditions within potential range from ?0.7 to ?1.1 V in electrolytes of pH 9.5, containing ammonia complexes of cobalt(III) and palladium(II), [Co(NH₃)₆]³⁺ and [Pd(NH₃)₄]²⁺, of different concentration ratio. Structural changes in electrodeposited alloys were discussed based on results of X-ray diffraction measurements. An elemental analysis was performed using the energy-dispersive X-ray spectroscopy technique. Finally, based on results of galvanostatic measurements, the Tafel slope within the range of activation control for hydrogen evolution reaction was determined and mechanism of the process was discussed. The alloys presented low Tafel slope value, from 25.4 to 88.7 mV dec^?1. The alloy of the highest activity for hydrogen evolution reaction contained 31.2 at.% of Pd.     

Production of Cr3+ substituted Li–Zn nanocrystalline ferrite by citrate method: Studies on structure,cation occupancy,elastic, optical and magnetic performance

The structural, elastic, optical and magnetic characteristics of Li_0.4Zn_0.2Cr_xFe_2.4-xO₄ (0.0 ≤ x ≤ 0.5; step 0.1) produced using a citrate precursor were studied. X-ray powder diffraction data indicate that all of the generated samples are single-phase spinel structures with no additional phases. The lattice parameter reduces from 8.355 Å to 8.333 Å when the chromium content rises. The crystallite sizes of the compositions were assessed by Scherrer's and Williamson-Hall (W–H) approaches. Infrared (IR) spectroscopy revealed two significant absorption bands generated by vibrations at the tetrahedral and octahedral sites. The elastic moduli (bulk modulus ‘B’, rigidity modulus ‘G’ and Young's modulus ‘E’) as well as the Debye temperature (θ_D) assessed by IR spectroscopy rise as the Cr³⁺ ions concentration increases. Chromium addition inhibits grain growth and enhances the mechanical strength of Li–Zn nanoferrites. Diffuse reflectance spectra (DRS) were utilized to evaluate the optical band gap (E_g) of Li–Zn–Cr nanoferrite, which was found to drop from 1.96 to 1.84 eV. The vibrating sample magnetometer (VSM) was used to perform the magnetic analysis, and various magnetic parameters were derived using the M ? H curves results. Acceptable values of saturation magnetization (78.6–44.05 emu/g) and coercivity (30.87–44.65 G) were found in this system, making these nanoferrites ideal for high-density recording medium and electromagnets applications. Based on the experimental results of lattice parameters, and magnetization, a quite reasonable cation distribution was postulated for all samples. Theoretically predicted lattice parameters and magnetic moments derived from the suggested cation distribution agree with those determined empirically from XRD and VSM results, respectively. The switching field distribution curves were schemed utilizing the first derivative of magnetization data from M ? H loops. The Curie temperature decreases significantly with Cr³⁺ substitution.