Effects of additives on zinc electrodeposition from alkaline zincate solution

The effects of additives on the surface and cross-sectional morphologies of zinc deposits on iron substrate from alkaline zincate solution were characterized by scanning electron microscope (SEM). The cathodic reaction mechanisms under various concentrations of additives were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. It is found that with increasing the additive A content in the bath solution, the nucleation overpotential (NOP) value is obviously increased and the inhibition effect is strengthened. This may be mainly due to the adsorption of additive A on the cathodic electrode surface, which can cover the active sites and block the discharge reduction. The results of EIS analysis indicate that the rate-determining step of zinc electrodeposition process is changed from mixed control step into electrochemical reduction step in the presence of additive A. However, any quantity of additive B has little effect on the NOP value and the inhibition effect is not obvious. Furthermore, addition of additive A and additive B at the same time displays the strongest inhibition effect and shows a strong synergism because of their co-adsorption on the cathodic electrode surface.     

Electrochemical deposition of nanocrystalline zinc on steel substrate from acid zincate bath

Nanocrystalline zinc coatings were deposited from acid zincate bath containing newly synthesized condensation product. The effect of bath constituents, pH, temperature and current density on the deposit nature were investigated through Hull cell experiments. Current efficiency, throwing power, cathodic polarization and corrosion behavior in 3.5 wt.% NaCl were studied under optimum concentration of additives. Salt spray test and electrochemical measurements showed that nanocrystalline zinc coatings have better corrosion resistance than the zinc coatings deposited from a simple acid zincate bath without additive. The surface morphology and thickness (cross section) of the zinc deposits were studied by scanning electron microscopy (SEM). The preferred orientation and average grain size of the zinc electrodeposit were obtained by X-ray diffraction analysis. The particle size was also characterized by TEM analysis. Energy X-ray diffraction (EDX) and FT-IR spectral analysis were carried out to determine the inclusion of addition agent in the deposit. The experimental results indicated that the addition of condensation product of thiamine hydrochloride (THC) and furfural (FFL) leads to a more uniform nanocrystalline deposition with the grain sizes varying from 20-22 nm.     

改进碱性锌酸盐镀锌添加剂

研究了以氧化锌为主盐、氢氧化钠为络合剂的镀锌工艺添加剂的改进，在改进过程中，对两种添加剂的性能指标进行了测试和对比。选出了最优配比。     

Nature of the potential of nonpolarized zinc electrode in zincate solutions

The effect of components of alkaline zincate solution and surface compounds, which form on metal zinc in the alkaline solutions, on the nature of nonpolarized electrode potential (E) is studied. It is proposed to determine the nature of E by taking into account more rigorously the activities of all solution components. It is found that in the zincate solutions, the potential of nonpolarized metal zinc is the potential of Zn/Zn(OH)₂, OH⁻ electrode of the second kind. Original Russian Text ? V. Rezaite, L. Deresh, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 4, pp. 368–372.     

Effects of magnetic fields on crystal growth

Abstract

The effects of a constant uniform magnetic field on thermoelectric currents during dendritic solidification were investigated using a two-dimensional enthalpy based numerical model. Using an approximation for three-dimensional unconstricted growth, the resulting Lorentz forces generate a circulating flow influencing the solidification pattern. Under the presence of a strong magnetic field secondary growth on the clockwise side of the primary arm of the dendrite was encouraged, whereas the anticlockwise side is suppressed due to a reduction in local free energy. The preferred direction of growth rotated in the clockwise sense under an anticlockwise flow. The tip velocity is significantly increased compared with growth in stagnant flow. This is due to a small recirculation at the tip of the dendrite; bringing in colder liquid and lowering the concentration of solute.     

Enhancing the adhesion of copper electroplates to steel substrates. Cyanide-free alkaline baths

Adhesion of copper electroplates from pyro- and polyphosphate, ammoniate, and polyamine electrolytes to samples of steelCt3 and 10kii was investigated. Conditions for the formation of deposits with high adhesion were determined.     

Inhibition of zinc dissolution in borate-sulfate electrolytes by benzoimidazoles

The effects of the concentrations of sodium sulfate, benzoimidazole, and its derivatives on active and passive zinc dissolution and local depassivation were studied. The correlations between the effect of substituted benzoimidazoles and the basicity, polarizability, and hydrophobicity were determined. Original Russian Text ? V.V. Ekilik, V.V. Chernyavina, G.N. Ekilik, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 3, pp. 262–267.     

Influence of organic additives on the behaviour of zinc electroplating from alkaline cyanide-free electrolyte

Two similar polymeric organic compounds from the polyquaternium family were studied as levelling additives in an alkaline cyanide-free zinc plating electrolyte. One additive (LA) has amide bonds between its monomers and the other (LU) has urea unions in its chemical structure. Copper cementation on zinc and gas evolution during aging of the zinc coatings were used to evaluate the effect of the chemical structure of the organic additives on the characteristic deleterious aging process of the coatings when electrodeposited with LA. Scanning electron microscopy and X-ray diffraction were used to follow surface morphology and crystallographic modifications of the coatings during aging. Faster copper cementation kinetics, zinc whiskers growth, blistering of the coating and N₂, CH₄, CO₂ and H₂ evolution were observed during accelerated aging of the coatings when LA was used. The coatings produced with LU did not show any aging effect. These studies show the strong influence that subtle changes in the chemical structure of the organic additive may have on the performance of zinc coating during storage.     

Corrosion behavior of phosphorus containing zinc alloy deposits obtained from alkaline electrolyte

Zinc‐alloy depositions are now largely used thanks to their good corrosion behaviour (as compared to zinc depositions). Phosphorus was introduced in the metallic matrix in order to increase the corrosion resistance of Zn‐Ni platings. Strongly alkaline electrolytes were used (pH=12‐12.5), in order to obtain Zn‐Ni‐ P deposits. The characteristics of these depositions (chemical composition, structure) were studied in correlation with their performances of corrosion resistance. The qualitative analysis carried out by X‐ray diffraction revealed that as part of Zn‐Ni alloy, P reduces the grain size, also bringing about a tendency towards an amorphous crystal lattice.     

锌浸渣还原焙烧-磁选回收铁

在查明锌浸渣工艺矿物学的基础上,采用还原焙烧将铁酸锌分解为氧化锌和磁性氧化铁,再通过磁选的方法回收铁,达到锌、铁分离的目的。实验考查了焙烧温度、焙烧时间、还原剂用量对铁酸锌分解率、铁回收率和铁品位的影响。结果表明:在焙烧温度为950℃、焙烧时间为1 h及还原剂添加量为10%和5%的条件下,铁酸锌分解率达到72.05%,铁回收率可达到91.79%,精矿中铁的品位为50%左右。焙烧及磁选过程中颗粒的团聚包裹是铁精矿品位不高的主要原因。     

Influence of magnetostatic fields of a ferromagnetic substrate on the electrodeposition of nickel dendrites

The influence of the magnetic state of a ferromagnetic wire substrate on the morphology of deposited nickel obtained by electrolysis has been studied. It has been demonstrated using statistical analysis that in the course of nickel electrodeposition without external magnetic field the dimensional characteristics of the arising dendritic structures are affected significantly by the residual magnetization of the substrate. When in the course of Ni electrodeposition even a weak dc magnetic field is applied perpendicularly to the wire axis, nearly identical structures are formed; that is, the system “forgets” its previous magnetic state. The magnetic properties of the substrate were visualized using powder patterns.     

Visualization of nonuniform magnetic fields by gadolinium-cobalt amorphous films

Configurations of magnetic domain structure of gadolinium-cobalt amorphous films with a perpendicular anisotropy under the effect of spatially nonuniform magnetic stray fields produced by various miniature sources have been studied. The domain structure of the amorphous films has been shown to qualitatively and quantitatively reflect the symmetry and magnitude of the normal component of the nonuniform magnetic fields and, similar to iron garnets, can be used for topographying stray fields. New features of the domain structure have been found during the visualization of small-scale sources of stray fields, on the one hand, and fields characterized by a small gradient, on the other hand.     

Inhibition of the anodic dissolution of iron in alkaline solution by metal complex ions

The possible inhibiting effects of GaO₃^3?, GeO₃^2?, CrO₃^2?, and MoO₄^2? ions on anodic and cathodic reactions on iron in 5 M KOH were studied. It was shown that a concentration of these ions of 10^?3 M inhibits the anodic iron dissolution reaction 2–3 times, while no effect on the hydrogen evolution reaction was observed. The effect was explained by the underpotential deposition of adatoms of the metal complexing ions on the iron electrode.     

Change of the equilibrium state of ferromagnetic MnBi by high magnetic fields

Differential thermal analysis was carried out for ferromagnetic material MnBi in the temperature range 300-773 K in magnetic fields up to 45 T to investigate the effect of high magnetic fields on its decomposition process and corresponding phase diagram. The decomposition temperature T_t (MnBi → Mn_1.08Bi + liquid Bi) increases from 632 K (at a zero field) to 714 K by applying a magnetic field of 45 T. Furthermore, the magnetocaloric effect of MnBi is observed in 11.5-45 T in the vicinity of 689 K, showing that a field-induced composition process occurs. The obtained results show that the equilibrium state of MnBi can be controlled by a high magnetic field.     

The passivation of zinc in slightly alkaline solutions

The inhibition of zinc corrosion by Na₂HPO₄ in a slightly alkaline electrolyte has been investigated by a.c. impedance measurements. A corrosion process controlled by the diffusion of ions through a passivating layer has been determined. The corrosion resistance has been observed to be increased by the healing of the passivating layer which always follows a short-time breakdown of the layer, due to an anodic potential jump.     

Mn-Zn soft magnetic ferrite nanoparticles synthesized from spent alkaline Zn-Mn batteries

Using spent alkaline Zn-Mn batteries as raw material, Mn-Zn soft magnetic ferrite nanoparticles are prepared by multi-step processes including acid leaching, chemical treatment of battery iron shells and citrate-nitrate precursor auto-combustion. Acid leaching and chemical treatment mechanisms are investigated. Dried gels thermal decomposition process, auto-combustion, phase composition, morphological and magnetic properties of as-prepared Mn-Zn ferrite nanoparticles are characterized by thermogravimetric and differential thermal analysis, X-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer. Synthesized Mn-Zn ferrite nanoparticles (Mn_0.5Zn_0.5Fe₂O₄) have pure ferrite phase, larger saturation magnetization (M_s = 60.62 emu g⁻¹) and lower coercivity (H_c = 30 Oe) compared with the same composition ferrites prepared by other techniques due to better crystallinity. Mn-Zn ferrite nanoparticles synthesis method presents a viable alternative for alkaline Zn-Mn batteries recycling.     

用碱性Na_2EDTA溶液从次氧化锌烟灰中选择性回收铅(英文)

采用碱性Na2EDTA溶液从次氧化锌烟灰中回收铅。探讨温度、浸出时间、Na2EDTA浓度和起始NaOH浓度对铅、锌浸出率的影响。得到最优实验条件如下:液固比5:1 mL/g、搅拌速度650 r/min、Na2EDTA浓度0.12mol/L、NaOH初始浓度0.5 mol/L、温度70°C、浸出时间120 min。在最优实验条件下,铅、锌、氟和氯的平均浸出率分别为89.92%、0.94%、62.84%和90.02%。浸出液用于电沉积铅粉。在温度为60°C、电流密度为200A/m2、H3PO4浓度为1.5 g/L、铅离子浓度不低于5 g/L时,电沉积铅粉平均电流效率大约为93%,阴极铅纯度高于98%。电沉积1 kg铅粉大约消耗0.218 kg Na2EDTA和0.958 kW·h电能。     

Corrosion behaviour of zinc–nickel alloy coatings electrodeposited in additive free chloride baths

Abstract

Corrosion behaviour of nanocrystalline Zn–Ni alloy coatings (with 3 to 18 at-%Ni) electrodeposited on steel substrate from additive free chloride baths by DC plating has been investigated by measurement of open circuit potential with time and neutral salt spray test. The alloy coatings containing up to 16 at-%Ni exhibited an increase in resistance to the appearance of white and red rust with increasing Ni content. The resistance to the appearance of white rust and ability to protect the underlying steel substrate decreased with further increasing Ni content. This has been considered to be due to reduced passivating ability of the alloy coating with a significant rise in the grain size above 50 nm.