Table 1 - uploaded by Ivan Krastev
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The electrochemical behaviour of ferrocyanide-thiocyanate electrolytes for silver electrodeposition was studied by cyclic voltammetry. The differences in the electrolyte preparation procedure do not affect their electrochemical behaviour at identical silver concentrations. The silver electrodeposition is characterized by two cathodic current maxima...
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Context 1
... salts were dissolved separately and the solutions obtained were mixed in the hot state adding AgNO 3 to the mixture of K 4 Fe CN 6 Á 3H 2 O K 2 CO 3 . During the boiling of the mixture, water was added in portions up to the amounts shown in Table 1. ...
Context 2
... solution was cooled and precipitates were left to settle overnight. They were ®ltered and the solution subjected to volumetric quantitative analysis according to a well known method [18] for the determination of silver concentration in the ®ltrate (Table 1). The solu- tion with its known silver content was used for the preparation of the investigated electrolytes with a predetermined silver ion concentration 18 g dm )3 by adding the respective amounts. ...
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The band gaps and photoelectrochemical properties of electrodeposited CuO films were tuned through annealing as-electrodeposited films in different atmospheres at various temperatures. The direct band gaps of the CuO film descended from 1.80 eV for as-electrodeposited film to 1.76 eV for the film annealed in O2 at 300 °C or 1.64 eV for the film ann...
Citations
... The values for this coefficient larger than 0.5 for Ag deposition were formerly reported in the literature, as by Abbott et al. 11 in DES, but also other authors from aqueous complexing solutions. 31,32 As in the above quoted papers, high a values might be attributable to the existence of both decomplexation of dissolved Ag(I) species to "bare" Ag + , followed by the charge transfer, leading to metal silver. In case the decomplexation is rate-controlling in the overall reduction, high a values could be expected, as for the case of hydrogen oxidation on platinum, whose rate is governed by the adsorption of the molecule prior to very fast charge transfer. ...
In view of selectively recovering precious contents in electronic waste by combined electrochemical leaching and deposition step in the same cell, this study presents electrochemical investigations of the two reactions conducted in green deep eutectic solvents (DESs) for the case of silver. In addition to ethaline 1 : 2 formed from choline chloride and ethylene glycol, propeline 1 : 3 with less nocive propylene glycol was tested. Determination of the density, viscosity and conductivity of the two DES depending on temperature and their water content could lead to ionicity values from 0.70 to 0.90, with a negative effect of these operating parameters. Pure silver can be leached at 1 mA cm⁻² with faradaic yield near 100% from the two DES, provided sufficient temperature and water content below 5 wt%. Electrodeposition was thoroughly examined by cyclic voltammetry and amperometry at transient or steady state at a rotating electrode, leading to Ag(i) diffusivity values in the two DES. Kinetic parameters of the electrodeposition reaction, modelled as irreversible, were also estimated from cyclic voltammograms. Thick silver deposits were produced in 24 h-long tests at 60 °C and 0.25 mA cm⁻² in a dry atmosphere with nearly 100% current efficiency. The deposits were formed by little coalesced regular grains of size 15–20 μm and exhibiting fair adherence.
... Electroplating baths of nitrate [1][2][3][4], uracil [5], thiourea [6], 2-hydroxypyridine [7,8], 5,5-dimethylhydantoin [9,10], ferrocyanide-thiocyanide [11,12], ionic liquids [13][14][15] have been proposed. However, industrial use of these baths is still restricted because their use does not achieve coating of high brightness, compactness, and adhesion; the baths lack stability and the complexing agents are expensive. ...
... This peak is the peak of the reduction of the silver oxide species formed in the anodic direction. A similar behaviour showing this peak was recorded in Krastev's article [12] in which he studied silver electrodeposition from the ferrocyanide-thiocyanate electrolyte by cyclic voltammetry technique. Sodium tetraborate decahydrate (Borax) (line S4-borax added S3) increases the c.d. slightly without changing the reduction potentials as compared to In Figure 4, cathodic peak recorded at -0.1 V was investigated again by changing the vertex voltage during the positive scan. ...
A study of the electrodeposition of silver from 2 different types of electrolytes; (1) neutral pyrophosphatecyanide electrolyte and (2) alkaline high concentrated cyanide electrolyte in the presence of a variety of additives such as 2-mercaptobenzothiazole, potassium selenocyanate, and potassium antimony tartrate was performed. Influence of additives and cyanide concentration on microstructure and kinetics of the cathodic processes were studied. A brightener couple, 2-mercaptobenzothiazole and potassium antimony tartrate, were combined within this investigation and detected to be highly effective for silver electrodeposition. The rapid increase in current density at the same potential interval related to grain refinement effect of potassium antimony tartrate was shown. The cyclic organic compound, 2-mercaptobenzothiazole, polarizes the reduction to high cathodic potential in pyrophosphate electrolyte. However, the sufficient levelling effect required for the mirror-bright appearance seems to be related to the high polarizing effect of the high concentration cyanide content. In the case of pyrophosphate electrolytes, sufficient levelling cannot be achieved, so semigloss coatings are obtained. The low cathodic potential electrodeposition of silver in pyrophosphate electrolyte, which is found to proceed by 3D instantaneous nucleation, is polarized to high cathodic potentials and grows into 3D progressive nucleation and diffusion-controlled growth in high concentration cyanide electrolyte.
... An additional cathodic peak C2 became pronounced around −50 mV during the 2nd scan cycle (Figure 1(b)). This may be due to the incomplete silver dissolution during the first anodic scan, giving rise to the presence of oxidized and nondissolved silver film on the platinum surface from the beginning of the next scan [19]. ...
The electrochemical processes in solutions with a much lower amount of free cyanide (<10 g/L KCN) than the conventional alkaline silver electrolytes were first explored by using cyclic voltammetry. The electrochemical behavior and the effect of KAg(CN)2, KCN, and KNO3 electrolytes and solution pH on the electrodeposition and dissolution processes were investigated. Moreover, suitable working conditions for high speed, low cyanide silver electrodeposition were also proposed. Both silver and cyanide ions concentration had significant effects on the electrode polarization and deposition rate. The onset potential of silver electrodeposition could be shifted to more positive values by using solutions containing higher silver and lower KCN concentration. Higher silver concentration also led to higher deposition rate. Besides maintaining high conductivity of the solution, KNO3 might help reduce the operating current density required for silver electrodeposition at high silver concentration albeit at the expense of slowing down the electrodeposition rate. The silver dissolution consists of a limiting step and the reaction rate depends on the amount of free cyanide ions. The surface and material characteristics of Ag films deposited by low cyanide solution are also compared with those deposited by conventional high cyanide solution.
... It is composed on the basis of potassium dicyanoargentate with an excess of free cyanide ions. A lot of other electrolytes are suggestedonto nitrate, iodide, urea, thiocyanate, sulfamate, thiosulphate, and other bases [6][7][8][9][10][11][12][13][14][15]. A comprehensive review of the electrolytes for silver deposition is presented in the theses of I. Krastev [16,17]. ...
... Literature data about sulfamate, ethylenediaminetetraacetate (EDTA), sulfosalicylate and etc. electrolytes for silver deposition are known [6,[11][12][13][14][15][16][17]. Some data on the most used non-cyanide silver electrolytes are presented in Table 1. ...
Literature data on silver, cobalt and silver-cobalt electrolytes are presented and discussed. The electrodeposition of the silver-cobalt coating is carried out from appropriate cyanide-pyrophosphate electrolytes at 50 °C The studies show possibilities for deposition of compact silver-cobalt coatings with high cobalt content (up to 50%). The deposited coatings could be successfully used for further investigation of their physico-mechanical and electrical properties. © 2011 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria.
Les propriétés des revêtements électrolytiques sont intimement liées à leurs morphologies et structures cristallines, qui sont elles-mêmes fortement dépendantes de la présence d’additifs organiques et des paramètres d’électrodéposition (densité de courant, courant continu vs pulsé). Une alternative intéressante tient dans l’utilisation des ultrasons durant l’électrodéposition, de manière à modifier la microstructure sans utiliser d’additifs, ou au minimum, de réduire leur quantité. La littérature montre que les ultrasons peuvent en effet agir sur l’électrodéposition par la réduction de la taille des grains, de la porosité ou par l’augmentation de la brillance des revêtements.Pour ce travail, les revêtements ont été réalisés à partir d’une solution d’argentage issue de la littérature et d’un électrolyte d’argent-étain spécifiquement formulé pour cette étude et ont été caractérisés par diverses techniques (MEB-EDS, DRX, EBSD). Ces analyses ont été réalisées de façon à évaluer l’effet des ultrasons (20 et 575 kHz) sur leur morphologie, leur structure cristalline et leur composition élémentaire. Pour isoler l’effet des bulles de cavitation de celui propre aux courants de convection, tous les revêtements ont été réalisés exactement au même niveau d’agitation, en absence et en présence d’ultrasons, pour une condition « hydrodynamique équivalente »Lors de l’électrodéposition de l’argent, les ultrasons favorisent une morphologie et une structure cristalline particulière, qui se distingue par une croissance latérale. La mesure de l’uniformité en épaisseur des revêtements réalisés sur des substrats possédant des formes complexes montre que l’utilisation des ultrasons basse fréquence permet également de diminuer la dispersion en épaisseur à une valeur proche de 10%. L’électrodéposition de revêtements d’argent-étain sous ultrasons apporte des modifications considérables en termes d’aspect, d’homogénéité et de composition. Les changements de composition de l’alliage concernent aussi bien le pourcentage élémentaire moyen de chaque métal que la teneur des différentes
The investigation on anode behavior of silver represents an important and integral part of the implementation of membrane technology for obtaining silver concentrates for galvanotechnics. Through recording the galvanodynamic polarization dependencies, evidences are obtained for the kinetics of anode dissolution of silver and the critical densities of passivation in different non-cyanide electrolytes, i.e. pure K4Fe(CN)6, NH4CNS and their mixture, in absence or presence of silver ions in the solution. The maximum admissible anode densities for active dissolution of silver depending on the concentration of the components in the solution, pH, temperature and stirring are determined. It is found that NH4CNS has a depolarizing effect on the process of anode dissolution of silver, which is enhanced with the increase of the concentration of silver. A stronger tendency to passivation of silver is found out in a mixture of K4Fe(CN)6 and NH4CNS and in the presence of silver ions. In such "triple" solution the anode density determined remains 100% almost within the whole area studied and decreases to 95% for densities close to the critical one.
An eco-friendly membrane technology for electrochemical preparation of rodanide silver concentrates for the purposes of electroplating is developed. Theprocesses of mass transfer in three-chamber electrolyzerwith ionite membrane are studied. A detailed balance of the voltage between electrodes in membrane preparation of rodanide silver concentrate in made. It is found that the cathode voltage (Eic,) and the ohmic voltage drop in the catholyte have decisive share in the value of voltage equal to 50% and 37% of the total voltage accordingly. Despite the high current loading of the membrane (P = 8,3 A.dm-2), the ohmic drop of voltage in the membrane (UM) has lower value, which is only 5 % of the value of voltage U that proves the high efficiency and proper selection of the membrane. A quantitative assessment of the anode current efficiency and anode material efficiency is made using the membrane technology developed. Using the chronopotentiometric method, it is found that silver dissolves actively up to anode densities of current equal to 7.5 A dm-2 without passivation and the anode polarization is negligible. The anode efficiency of current is close to 100%.
Cusil (TM) is a eutectic brazing alloy of 72% silver, 28% copper composition; used to join different materials. The large difference between the standard reduction potentials of silver (0.799V) and copper (0.337V) makes their electrochemical codeposition difficult. A complex ion bath containing KAg(CN)(2), CuCN and KCN was used to bring the reduction potentials closer together. The effect of electrolyte concentration on composition and microstructure of electrodeposited Ag-Cu films was investigated at 25 degrees C. A current density of 2 mA/cm(2) was used to codeposit copper and silver based on results of voltammetric studies. It was found that increasing KCN and KAg(CN)(2) and decreasing CuCN concentrations increased Ag contents of deposits. Surface morphology was spherical grained in general. Increasing Ag content of the deposits resulted in finer grained structures, but deposits containing higher Ag concentrations were found to develop dendritic structures especially after the initial deposition of the Ag-Cu alloy coating on the surface.
This paper reports on the reactivity of cyanide ligands released from Ag(I) cyanocomplexes during electrodeposition at very negative potentials. The study is based on in-situ surface-enhanced Raman spectroscopy (SERS) measurements performed during Ag electrodeposition from H2O and D2O based-electrolytes in order to pinpoint isotopic shifts. The investigation is complemented by electrochemical measurements - electrochemical impedance spectrometry (EIS) and cyclic voltammetry (CV) - as well as by SEM micrography. Surface-enhanced Raman spectroscopy spectroscopy disclosed details of the cathodic reactivity of adsorbed cyanide yielding amine that are typical of very negative polarisations and had not been observed in previous studies. The formation of cathodic films resulting from cyanide reactivity and giving rise to cathodic passivation and the cathodic reactivation corresponding to the increase in H. formation rate at the most negative investigated potentials have also been followed by potential-dependent EIS. The dependence of Ag electrodeposit morphology on cathodic potential correlates straightforwardly with the secondary inhibition scenario identified by SERS, CV and EIS.
The electrodeposition of silver at 25 °C from aqueous AgNO3+ citric acid solutions was investigated. This study shows that it is possible to obtain compact, homogeneous and coherent deposits from aqueous AgNO3 solutions containing citric acid (H3Ci). The morphology as well as the roughness of the deposits was independent of the solution composition. On the contrary, deposits obtained from citrate-free solutions were neither homogeneous nor compact. All deposits exhibited a pronounced preferred orientation with a 〈2 1 1〉-texture axis. The XRD diagrams of all deposits presented an additional reflection, which cannot be indexed in terms of an fcc structure. This extra reflection was attributed to the double Bragg reflection from crystallites in twin position. The relevant chemical entity controlling growth inhibition is a neutral associate Ag2HCi formed in the solution between Ag+ and citrate divalent anions HCi2−. Most of the structural features of silver deposits, such as degree of preferred orientation Q2 1 1 or intensity of the observed extra reflection, depend on the concentration of this associate. Consequently, the structural characteristics of deposits can easily be modified by: (a) changing the concentration of AgNO3 and H3Ci and (b) adjusting the pH of the bulk solution by adding HNO3.
