Electrochemical formation of cerium-containing oxide coatings on titanium

Possibility and conditions of obtaining cerium-containing oxide coatings on titanium alloys by microarc oxidation in electrolytes with tartrate and citrate cerium complexes were determined. The effect of organic cerium complexes on the kinetic parameters of the microarc oxidation of titanium alloys was studied. Porous oxides coatings containing up to 20% cerium were obtained.     

Electrodeposition of zinc coatings from the solutions of zinc oxide in imidazolium chloride/urea mixtures

To solve the inherent disadvantages in conventional processes for electrodeposition of zinc, it’s necessary to develop more high-efficiency and environmentally friendly electrolytes. In this work, it was found that the dissolution of ZnO was remarkably enhanced in some imidazolium chloride by the addition of urea, and the solubility of ZnO in 1:1 [Amim]Cl/urea mixture was as high as 8.35 wt% at 373.2 K. Electrochemical measurements showed that zinc could be readily electrodeposited from the solutions of ZnO. Bright, dense and well adherent zinc coatings with good purity were obtained from 0.6 M solution of ZnO in 1:1 [Amim]Cl/urea at 323.2 343.2 K. It’s expected that the solutions of ZnO in imidazolium chloride/urea mixtures have the potential to replace the traditional electrolytes, especially toxic zinc chloride-based ones for zinc electroplating, as well as preparation of zinc materials.     

Electrochemical corrosion behavior of nanocrystalline zinc coatings in 3.5% NaCl solutions

The corrosion behavior of electrodeposited nanocrystalline (NC) zinc coatings with an average grain size of 43 nm was investigated in 3.5% NaCl solutions in comparison with conventional polycrystalline (PC) zinc coatings by using electrochemical measurement and surface analysis techniques. Both polarization curve and electrochemical impedance spectroscopy (EIS) results indicate that NC and PC coatings are in active state at the corrosion potentials, and NC coatings have much higher corrosion resistance than PC ones. The corrosion products on both coating surfaces are mainly composed of ZnO and Zn₅(OH)₈Cl₂·H₂O, but the corrosion products can form a relatively more protective layer on NC coating surfaces than on PC coatings. The EIS characteristics and corrosion processes of PC and NC zinc coatings during 330 h of immersion were discussed in detail.     

Nanostructural analysis of mirror-bright zinc coatings

The zinc coatings electrode posited from solution containing dextrin/salicyl aldehyde mixture are examined by the scanning tunneling microscopy (STM). It is shown that mirror brightness of these zinc deposits is associated with flat and mutually parallel hexagonal zinc crystals which are smooth at the atomic level. The mechanism of zinc electrodeposition with these additives is examined by the use of a possibility of STM soft-ware measurements based on root-mean-square roughness analysis of metal surfaces and known as scaling analysis. It is proposed that the zinc growth in the presence of these additives follows the Edwards-Wilkinson model. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 10, pp. 1245–1251. The text was submitted by the authors in English.     

Elecrodeposition of lustrous zinc coatings from sulfate electrolyte

Electrodeposition of lustrous zinc coatings from a sulfate electrolyte containing ZnSO₄, Na₂SO₄, buffer additives, and fixers (products of phenol-formaldehyde condensation) was studied.     

Electrodeposition of lustrous zinc coatings from sulfate electrolyte

The electrodeposition of lustrous zinc coatings from a sulfate electrolyte containing ZnSO₄, Na₂SO₄, buffer additives, and 2-butyne-1,4 diol was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1284–1288.Original Russian Text Copyright © 2004 by Medvedev, Makrushin.     

Colloido-chemical characteristics of zinc oxide in electrolyte solutions

The electrosurface characteristics (total surface charge, electrokinetic potential, and positions of the point of zero charge and isoelectric point) of zinc oxide have been comprehensively studied as depending on pH and background electrolyte (NaCl) concentration. The constants of surface reactions and the adsorption potentials of potential determining of background electrolyte ions have been obtained in terms of the 2pK-model. The aggregation stability of aqueous zinc oxide suspensions has been studied in a wide range of concentrations of 1: 1 and 1: 2 electrolytes, and the threshold of sol coagulation has been found. Within the framework of the DLVO theory, the interaction energy between ZnO particles has been calculated as a function of the interparticle distance. It has been demonstrated that the experimental data can be qualitatively described in terms of the classical DLVO theory, which takes into account only ion-electrostatic and molecular (dispersion) forces of interparticle interaction.     

Potentiodynamic passivation of zinc in aqueous KOH solutions

The potentiodynamic oxidation of an upward-facing, horizontal zinc electrode in unstirred KOH solutions at concentrations in the range 1.0–5.0 M has been studied. Besides electrochemical treatment of the experimental data, the morphological evolution of the electrode surface during the oxidation has been followed by means of a scanning electron microscope. In the initial dissolution region, the Tafel slopes are near 40 mV dec⁻¹(25°C) and the reaction orders with respect to the OH⁻ion about 3, these results being consistent with the mechanisms already proposed by Bockris and by Chang and Prentice. The experimental results suggest that the passivation of zinc takes place by a dissolution-precipitation mechanism. However, the rate determining step for passivation appears to be the resistance of the solution in the pores formed by the precipitation and spreading of a film presumably composed of Zn(OH)₂, which is supposed to be the result of a local supersaturation with Zn(OH)²⁻₄.     

Microstructure and corrosion resistance of electrodeposited zinc alloy coatings

A heat treatment effect on the microstructure and corrosion properties of electrodeposited Zn, Zn-Co, Zn-Fe and Zn-Ni alloy coatings was studied. Surface morphology examinations were carried with AFM, while XRD was used to determine metal lattice parameters, texture and phase composition. Low-temperature annealing (at 225 °C) caused the formation of intermetallic Fe/Zn compounds, a transformation of amorphous oxide inclusions to the crystalline form and a decrease in the Zn lattice parameter for Zn-Co and Zn-Fe alloys. The mentioned structural modifications were not accompanied, however, by corrosion behavior changes of these coatings. On the Zn-Ni alloy, the annealing caused a significant reduction in the diffraction peak width and simultaneous considerable augmentation of the corrosion current. This effect is related to the formation of a less disordered lattice for this alloy.Contribution to the 3rd Baltic Conference on Electrochemistry, GDASK-SOBIESZEWO, 23–26 APRIL 2003.Dedicated to the memory of Harry B. Mark, Jr. (February 28, 1934–March 3rd, 2003)     

Mechanism of chemical deposition of nickel-boron coatings in tartrate-glycine solutions

The effect of glycine additive on the deposition of nickel-boron coatings from tartrate-glycine solutions was studied.     

Migration study of zinc dibutyldithiocarbamate in eye drops solutions

The potential deleterious effects of extractables/leachables in pharmaceutical products and the need to preserve product safety throughout its shelf life have led the three major pharmacopoeias (USP, EP, JP) to require extractable and toxicity testing of container/closure systems. To that, a HPLC/UV method was developed and validated for the detection of zinc dibutyl dithiocarbamate (ZDBC) as potential extractable from pharmaceutical container closure system of eye drops solutions. The method consists of direct extraction of the analyte with chloroform; the lower layer was evaporated to dryness and further reconstituted with acetonitrile. The chromatographic separation was performed on a Nova-Pak C18 column using as mobile phase a mixture of acetonitrile:water. Calibration curves were linear and relative standard deviation was sufficient. Detection limit of ZDBC was found to be 0.015 μg/mL. The HPLC method was further applied in seven currently marketed eye drops solutions, confirming its applicability for monitoring dithiocarbamates migration from container closure systems into the eye drops solutions.     

Mechanism and kinetics of the formation of zinc pack coatings

A zinc deposition method that could be used instead hot-dip galvanizing is pack cementation, where the substrate is heated immersed in a powder mixture containing Zn and a halide activator (NH₄Cl). In the present work the mechanism of this process is examined, along with the effect of temperature and heating time on the coating thickness and structure. For this purpose the coating was deposited and characterized with SEM, while the deposition mechanism was investigated with DSC. From the above examination it was deduced that the deposition of Zn takes place with a multiple-step mechanism, which involves several reactions in the gaseous phase including the formation of volatile zinc halides and finally the diffusion of zinc in the crystal lattice of the ferrous substrate. This procedure is accomplished at about 300°C and leads to the growth of a coating composed by two layers referring to Γ and δ phase of the Fe-Zn system. The coating deposition rate seems to be controlled by the zinc diffusion as its determination at 300 and 350°C showed, where it was deduced that the coating thickness is a linear function of the square root of heating time. However the coating structure is not affected by the heating time and temperature.     

Resistance of zinc thermal sprayed coatings on different corrosive environments

Zinc coatings on ferrous substrates are possible to be applied with thermal spraying. In the present work the corrosion behavior of zinc thermal sprayed coatings deposited on low carbon steel St-37 was examined in a simulated marine atmosphere (salt spray chamber-SSC) and in a dry atmosphere at elevated temperature (400°C). The corrosion progress was examined by means of optical microscopy, scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. From this investigation it was deduced that in the SSC the coating is uniformly corroded, while the main corrosion products are hydrated zinc oxides and chlorides. By contrast at 400°C only a thin, compact and continuous film of ZnO is formed on top of the coating, which remains adherent to the ferrous substrate.     

Codeposition of zinc with nickel from gluconate solutions

Journal of Solid State Electrochemistry - The codeposition of zinc and nickel from slightly acidic chloride, sulfate, and chloride-sulfate solutions containing a gluconate complexing agent was...     

Mixed saturated-unsaturated alkyl-chain assemblies: solid solutions of zinc stearate and zinc oleate

The linear saturated stearic acid and the bent mono-unsaturated oleic acid do not mix and form solid solutions. However, the zinc salts of these acids can. From X-ray diffraction and DSC measurements we show that the layered zinc stearate and zinc oleate salts form a homogeneous solid solution at all composition ratios. The solid solutions exhibit a single melting endotherm, with the melting temperature varying linearly with composition but with the enthalpy change showing a minimum. By monitoring features in the infrared spectra that are characteristic of the global conformation of the hydrocarbon chain, and hence can distinguish between stearate and oleate chains, it is shown that solid solution formation is realized by the introduction of gauche defects in a fraction of the stearate chains that are then no longer linear. This fraction increases with oleate concentration. It has also been possible from the spectroscopic measurements to establish a quantitative relation between molecular conformational order and the thermodynamic enthalpy of melting of the solid solutions.     

Electrochemical reduction of zinc complexes from glycinate solutions

Kinetics of electrochemical reduction of zinc(II) complexes is studied in a wide range of solution pH using the polarization measurements and chronopotentiometry. Adsorption of glycinate ions on zinc electrode and complexing of zinc(II) with glycine are studied using the ¹³C NMR method. Based on the experimental data, the electrochemical behavior of zinc(II)–glycine–water system is considered.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 228–231.Original Russian Text Copyright © 2005 by Berezin, Sagdeev, Gudin, Roev, Mezhevich.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Combined solubility of copper and zinc oxides in ammonia-ammonium solutions

The combined solubility of copper and zinc oxides was studied in ammonia-ammonium chloride solutions with mass fractions of ammonia of 2, 5, 10, 15, 20, and 25% and mass concentrations of ammonium chloride of 43.8, 110, 150, and 180 g/l (based on chloride ion) at 293.15, 303.15, 313.15, and 323.15 K. A eutonic type equilibrium was established in the systems, and the complex ions were mutually salted out.