Kinetics of Sn electrodeposition from Sn(II)–citrate solutions

The influence of solution chemistry on the electrodeposition of Sn from Sn(II)–citrate solutions is studied. The distribution of various Sn(II)–citrate complexes and citrate ligands is calculated and the results presented as speciation diagrams. At a SnCl₂·H₂O concentration of 0.22 mol/L and citrate concentration from 0.30 mol/L to 0.66 mol/L, SnH₃L⁺ (where L represents the tetravalent citrate ligand) is the main species at pH below about 1.2 and SnHL⁻ is the main species at pH above about 4. Polarization studies and reduction potential calculations show that the Sn(II)–citrate complexes have similar reduction potentials at a given solution composition and pH. However, the Sn(II)–citrate complexes become more difficult to reduce with higher total citrate concentration and higher solution pH. Nevertheless, SnHL⁻ which forms at higher pH is a favored Sn(II)–citrate complex for Sn electrodeposition due to better plated film morphology, likely as a result of its slower electroplating kinetics. Precipitates are formed from the Sn(II)–citrate solutions after adding hydrochloric acid (to lower the pH). Compositional and structural analyses indicate that the precipitates may have the formula Sn₂L.     

Effect of temperature on Co electrodeposition in the presence of boric acid

The electrodeposition of cobalt from sulphate solutions containing boric acid was investigated using EQCM technique coupled with potentiostatic measurements. The boric acid was added to electrolyte as a buffer to avoid the local pH rise caused by parallel hydrogen evolution reaction (HER). The results showed that the buffer contribution of boric acid is effective in the cobalt electrodeposition at 25 °C; however, cobalt hydroxide is formed simultaneously with cobalt deposition at 48 °C. The M/z values calculated using the Sauerbrey equation and the Faraday Law showed that in the initial stages of deposition at 48 °C, only cobalt deposits were detected, but after 2 s, an important amount of Co(OH)₂ started to be formed.     

Effects of polyethylene glycol and gelatin on the crystal size, morphology, and Sn-sensing ability of bismuth deposits

The influences of citric acid (CA), ethylenediaminetetraacetic acid (EDTA), polyethylene glycol (PEG), and gelatin on the deposition behavior of Bi were systematically investigated through the linear sweep voltammetric (LSV) analysis. Based on the LSV results, deposits plated from a typical solution containing 0.05 M Bi(NO₃)₃·5H₂O and various combinations of complex agents and additives with pH = 3.5 at 1 and 30 mA cm⁻² were characterized by scanning electron microscopic (SEM) and X-ray diffraction (XRD) analyses. The adhesion of deposits and the formation of dendrites were respectively improved and inhibited by the adsorption of PEG onto Bi deposits. With adding the above four compounds, a synergistic effect was shown to reach a nano-sized, sphere-like, porous morphology of a Bi deposit at 30 mA cm⁻². The crystal size and morphology of Bi deposits were found to affect the sensing ability of Sn²⁺ through the square-wave anodic stripping voltammetric (SWASV) analysis.     

金电极线性扫描溶出伏安法测定菠菜中的重金属Pb

采用金电极线性扫描溶出伏安法对菠菜中的重金属Pb进行测定,结果显示对Pb(Ⅱ)测定具有较高准确度,检出限为1.5×10-6g·L-1,回收率在97.4%~102.6%,RSD为2.36%。该法仪器简单、操作简便,测定Pb的灵敏度可达到原子吸收法水平,通过改善工作电极富集能力,进一步提高灵敏度,即可实现多种元素的连续快速测定。     

Electrodeposition of Sn-Bi lead-free solders: Effects of complex agents on the composition, adhesion, and dendrite formation

The influences of complex agents, including citric acid, ethylenediaminetetraacetic acid (EDTA), and polyethylene glycol (PEG) on the electrochemical co-deposition of Sn-Bi alloys were systematically investigated through the linear sweeps voltammetric (LSV) analyses. The onset deposition potential of Bi ions is obviously shifted to a negative value, close to that of Sn ions by the simultaneous addition of the above three compounds into the plating solution. Based on the LSV results, deposits plated from the typical solutions with the Sn⁴⁺/Bi³⁺ ratio of 1, pH of 6.0, and various combinations of complex agents were characterized by scanning electron microscopic (SEM), energy-dispersive spectroscopic (EDS), and X-ray diffraction (XRD) analyses. The 30Sn-70Bi alloy (in wt%) is successfully plated from the typical plating bath containing 0.4 M citric acid, 1.0 M EDTA, and 0.2 M PEG, suggesting the possibility in plating the Sn-Bi alloys with their composition around the eutectic point (42Sn-58Bi). The adhesion of deposits and the formation of dendrites are respectively improved and inhibited by the synergistic effects of these three complex agents. Contrary to this combination, nearly pure Bi deposits are obtained from the typical plating solutions containing complex agents in the other combinations.     

Nucleation of Sn and Sn-Cu alloys on Pt during electrodeposition from Sn-citrate and Sn-Cu-citrate solutions

The initial stages of Sn and Sn-Cu electrodeposition from Sn-citrate and Sn-Cu-citrate solutions on Pt were studied using both current-controlled and potential-controlled electrochemical techniques. For both Sn-citrate and Sn-Cu-citrate solutions, when the current density is controlled to lower than 15 mA/cm², potentials remain almost constant which is appropriate to plate dense and uniform films. When the current density is controlled to between 25 and 35 mA/cm², potentials drop quickly initially, followed by a gradual increase to a constant value. When current density is controlled to higher than 50 mA/cm², potential oscillation happens, and significant hydrogen evolution prevents the formation of dense and continuous Sn and Sn-Cu films. A constant transition time constant indicates a diffusion-controlled process. The diffusion coefficient calculated from the Sand equation is about 3.8 × 10⁻⁶ cm²/s for the Sn-citrate solution and 4.1 × 10⁻⁶ cm²/s for the Sn-Cu-citrate solution. The morphology of both Sn and Sn-Cu deposits plated under different potentials was examined by atomic force microscopy (AFM) and the distribution of each element were analyzed using Auger imaging. Analysis of both the electrochemical results at −0.72, −1.1 and −1.5 V and AFM images for both Sn and Sn-Cu deposits at −1.1 and −1.5 V suggested progressive nucleation controlled by diffusion for both Sn and Sn-Cu electrodeposition. Tin reacted with Pt to form PtSn₄, and co-deposited with Cu to form Cu₆Sn₅ during nucleation, with more Sn forming at higher applied potentials.     

Current efficiency and kinetics of cobalt electrodeposition in acid chloride solutions. Part II: the influence of chloride and sulphate concentrations

The influence of cobalt chloride concentration, total chloride concentration and sulphate in the electrolyte on cobalt deposition were studied. The current efficiency increased and the overpotential for electrodeposition of cobalt decreased with increasing cobalt chloride concentration. Only minor changes were observed with addition of sodium chloride to the cobalt chloride solution. Sulphate electrolyte resulted in lower current efficiency and higher overpotential for electrodeposition when compared to a similar cobalt chloride electrolyte.     

Effect of tartaric acid in the electrodeposition of zinc

The electrodeposition of zinc from sulphate-tartrate baths on a vitreous carbon electrode has been studied. The influence of the tartrate ion on the reduction kinetics of Zn(II) metal ion, and on the mechanism of the electrodeposition process, has been investigated using potentiodynamic and potentiostatic electrochemical techniques and scanning electron microscopy. The voltammetric analysis has shown that the presence of tartrate species in the sulphate bath shifts the reduction potential of Zn(II) to more positive values. A set of equilibria have been proposed to represent the electrochemical process and the influence of pH. From the analysis of the chronoamperometric transients and the SEM images, an instantaneous nucleation with 2D growth at the initial stages has been proposed, and a nucleus density of the order of 10⁹ cm⁻² has been calculated from both techniques. In order to elucidate the correct mechanism of the electrodeposition process the results obtained from chronoamperometric transients must be corroborated by those of direct observation using microscopic techniques.     

CZTSe solar cells prepared by electrodeposition of Cu/Sn/Zn stack layer followed by selenization at low Se pressure

Cu₂ZnSnSe₄ (CZTSe) thin films are prepared by the electrodeposition of stack copper/tin/zinc (Cu/Sn/Zn) precursors, followed by selenization with a tin source at a substrate temperature of 530°C. Three selenization processes were performed herein to study the effects of the source of tin on the quality of CZTSe thin films that are formed at low Se pressure. Much elemental Sn is lost from CZTSe thin films during selenization without a source of tin. The loss of Sn from CZTSe thin films in selenization was suppressed herein using a tin source at 400°C (A2) or 530°C (A3). A copper-poor and zinc-rich CZTSe absorber layer with Cu/Sn, Zn/Sn, Cu/(Zn + Sn), and Zn/(Cu + Zn + Sn) with metallic element ratios of 1.86, 1.24, 0.83, and 0.3, respectively, was obtained in a selenization with a tin source at 530°C. The crystallized CZTSe thin film exhibited an increasingly (112)-preferred orientation at higher tin selenide (SnSe _x ) partial pressure. The lack of any obvious Mo-Se phase-related diffraction peaks in the X-ray diffraction (XRD) diffraction patterns may have arisen from the low Se pressure in the selenization processes. The scanning electron microscope (SEM) images reveal a compact surface morphology and a moderate grain size. CZTSe solar cells with an efficiency of 4.81% were produced by the low-cost fabrication process that is elucidated herein.     

X-射线荧光光谱测定铅基合金中的砷、铜、锑、锡、铋和铅

建立了X-射线荧光光谱测定铅基合金中砷、铜、锑、锡、铋、铅等6种元素的快速分析方法。通过优化测试条件,确定了最佳测试参数,有效地避免了其他元素的干扰。基于干扰元素的强度和浓度,采用经验影响系数法校正绘制标准曲线。结果表明,在一定浓度范围内,砷、铜、锑、锡、铋、铅的标准曲线具有良好的线性关系,其中铋、锑和锡的相关系数均在0.999以上。精密度试验结果表明,测定结果相对标准偏差在0.02%~4.2%。准确度试验结果显示,测定值与参考值基本吻合。     

Cobalt hydroxide film deposited on glassy carbon electrode for electrocatalytic oxidation of hydroquinone

The electrodeposition of cobalt hydroxide film on glassy carbon electrode was prepared by electrochemical method in an alkaline aqueous solution. The electrochemical behavior of hydroquinone on cobalt hydroxide film electrode has been investigated by using cyclic voltammetry and linear sweep voltammetry. The results showed that the film electrode has good electrocatalytic ability for the oxidation of hydroquinone to p-quinone. The recovery of hydroquinone from sample ranged from 94.7% to 102.9% and a rectilinear analytical curve for hydroquinone concentration from 5.0 × 10⁻⁶ to 1.25 × 10⁻⁴ mol/L was obtained. The detection limit was 5.0 × 10⁻⁷ mol/L and the relative standard deviation was 2.63%. Various factors affecting the electrocatalytic activity of cobalt hydroxide film were investigated.     

Morphology and structure of the passive interphase formed during aqueous electrodeposition of polypyrrole coatings on steel

An iron(II) oxalate dihydrate passive interphase was electrodeposited on steel substrate from aqueous oxalate solutions prior to the electrochemical polymerization of pyrrole. The effect of electrochemical process parameters on the morphology and structure of the passive interphase was systematically investigated by scanning electron microscopy(SEM) and X-ray diffractometry (XRD). Our results reveal that the passive interphase is composed of a monolayer of closely packed crystals. The size of the crystals is dependent on the experimental conditions. The iron(II) oxalate dihydrate interphase formed on steel by electrochemical deposition has an orthorhombic structure irrespective of the reaction condition. The unit cell dimensions of the passive interphase formed by electrodeposition are slightly different from those formed by conventional chemical process.     

Electrochemical study on the inhibitory effect of the underpotential deposition of zinc on Zn-Co alloy electrodeposition

Zn-Co alloy electrodeposition from chloride baths containing different Zn²⁺/Co²⁺ ratios was investigated by cyclic voltammetry and anodic linear sweep voltammetry using a Pt electrode. The peaks were attributed by means of EDX analysis, SEM and TEM observations performed on some alloys potentiostatically deposited. In the range of potential where zinc deposits underpotential, cyclic voltammetry showed a complex cathodic peak with one maximum and two shoulders, correlated with the deposition of different cobalt rich alloys. Up to four anodic peaks, two correlated with zinc oxidation from η and γ phases and two correlated with oxidation of solid solutions of zinc in cobalt, were observed. ALSV and TEM indicated that the remarkable increase in Zn content of the alloy, which occurs with a strong inhibition of the process at potentials more negative than that of the cathodic peak and more positive than the bulk deposition potential of zinc, is due to the deposition of γ phase. No inhibition of the alloy deposition process was observed with very low concentrations of zinc (<0.015 M) in the bath containing 0.19 M Co²⁺.     

Current efficiency and kinetics of cobalt electrodeposition in acid chloride solutions. Part I: The influence of current density,pH and temperature

In the electrodeposition of cobalt in chloride electrolytes the evolution of hydrogen is a parasitic reaction. On a rotating platinum disc electrode the current efficiency was calculated as the charge used for anodic dissolution of cobalt at a potential where no other reactions were taking place, divided by the total cathodic charge used for cobalt deposition. The results show that the current efficiency could be measured accurately in this way. In part I the current efficiency and deposition potential are studied as a function of current density and pH. The results show an increase in current efficiency with increasing current density, pH and temperature. The results also indicate a change in the reaction mechanism for electrodeposition when the pH is changed.     

Copper electrodeposition on pyrolytic graphite electrodes: Effect of the copper salt on the electrodeposition process

The electrodeposition of copper on pyrolytic graphite from CuSO₄ or Cu(NO₃)₂ in a 1.8 M H₂SO₄ aqueous solution was investigated. The Cu deposits were formed potentiostatically and characterized by electrochemical methods, scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. It was found that the deposition of copper in the presence of CuSO₄ induced the codeposition of sulfate anions. In addition, electrochemical quartz crystal microbalance revealed that the increase of the Cu mass was higher than expected from Faraday's law with the CuSO₄/H₂SO₄ solution. These results confirmed the specific adsorption of anions during the Cu deposition. On the other hand, the use of Cu(NO₃)₂ resulted in a non-contaminated surface with different surface morphologies. The Cu nuclei size, the population density and the surface coverage were monitored as a function of the deposition potential. From the analysis of the chronoamperometric curves, the nucleation kinetics was studied by using various theoretical models. Independently of the Cu source, the nucleation mechanism follows a three-dimensional (3D) process. Copper nucleates according to an instantaneous mode when the deposition potential is more negative than −300 mV versus Ag/AgCl, while the nucleation was interpreted in terms of a progressive mode at −150 mV. The nuclei population densities were also determined by using two common fitting models for 3D nucleation and growth (Scharifker-Mostany and Mirkin-Nilov-Heerman-Tarallo). Their values are reported here as a function of the deposition potential.     

Effect of pulse plating on composition of Sn–Pb coatings deposited in fluoroborate solutions

Galvanostatic pulsed current (PC) and pulse reverse (PR) plating of Sn–Pb coatings onto copper rotating disks from fluoroborate solutions has been conducted to obtain alloy compositions otherwise not achievable by DC plating. PC plating investigated over a wide range of pulse frequencies (20 Hz–200 kHz) and duty cycles produces coatings with compositions that differ only slightly from those obtained by DC plating at the same current density. On the other hand, the use of PR plating can be dramatic, producing Pb contents both well above and below that achievable by DC plating. Varying the frequency from 20 Hz to 200 kHz with the duty cycle and average current density fixed at 80% and 3.78 A dm^–2 yields compositions between 2.5 and 28 wt.% Pb. The Pb:Sn ratio in the deposit is always lower than that in the plating bath when a PR frequency of 20 Hz is imposed, but generally exceeds it at a frequency of 20 kHz. Alloy composition appears to be closely related to the working electrode potential reached during the anodic pulse. A higher frequency leads to less positive potentials during the anodic pulse and shorter anodic pulse times, which may enhance Sn dissolution and enrich the coating in Pb.     

Nucleation and growth of tin on low carbon steel

The nucleation and growth of tin from stannous sulfate and sulfuric acid with an organic additive of gelatin was studied on low carbon steel. Investigations were conducted by linear sweep voltammetry and current step methods. The agitation effect on the morphology of tin deposits was also studied. From the results, a mechanism of tin deposition on a steel substrate is suggested. Initially, 3D tin crystallites are formed preferentially on step edges, and this is followed by fast covering of neighboring sites with much smaller and densely packed crystallites of about 150-180 nm in size. Without gelatin, the coverage was poor and tri-modal structures were dominating. It is discovered that the synergy between hydrogen co-evolution and gelatin contributes to fast and complete coverage of the steel substrate and the bi-modal grain size distribution is observed. The diffusion coefficient of tin ion was determined according to the Sand equation.     

Zn electrodeposition in the presence of surfactants: Part I. Voltammetric and structural studies

The zinc electrodeposition onto steel substrates in the presence of surfactants with different charged head groups, namely anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (CTAB), and non-ionic octylphenolpoly(ethyleneglycolether)_n, n = 10 (Triton X-100) was studied by cyclic voltammetry. The effect of the switching potential and scanning rate on the deposition process was investigated. The structural characterisation and the chemical composition of the samples prepared potentiostaticaly, in the potential range where the voltammetric cathodic peaks appear, was performed by X-ray powder diffraction (XRD) and by energy-dispersive X-ray analysis (EDS), respectively. The experimental results show that the voltammetric behaviour, namely the deposition potential depends on the presence, nature and concentration of the tested surfactants. Zn deposition occurs at potential values more positive than the estimated equilibrium potential, peak C1, simultaneously with hydrogen formation. This fact is confirmed by XRD measurements. Zn bulk deposits prepared in the absence of surfactants and in the presence of SDS are more crystalline and with a higher grain size than the ones obtained in the presence of CTAB and Triton X-100. These facts may be justified by an increase on the overpotential deposition as the electrochemical study confirms.     

A voltammetric approach to an estimate of metal release from tinplate promoted by ligands present in canned vegetables

A linear sweep voltammetric (LSV) approach is proposed for achieving rapid information on metal release from tinned containers into preserved vegetables. Chopped tomato and pea preserves were chosen as prototypes for acid and nearly neutral canned food, respectively. Metal release in these vegetables tinned into both bare and lacquered containers was compared with that found in synthetic samples containing some organic complexing agents (acetic, ascorbic, citric, malic, oxalic, pyroglutamic acids) present in the vegetables considered, thus showing that some of these components affected markedly the metal release in bare cans. These ligands were concomitantly found to also affect LSV profiles recorded in parallel at Sn and Fe electrodes in synthetic samples, causing the starting potential for their oxidation to be lower, the higher the ligand activity of the species considered. The data indicated that metal release and starting potentials for metal discharge are strictly related, so that LSV is able to provide rapid and useful information on the nature of the protective effect (electrochemical or physical) of tin on the steel underlayer, as well as on the extent of Sn and Fe release.     

EQCM study of the electrodeposition of manganese in the presence of ammonium thiocyanate in chloride-based acidic solutions

The influence of ammonium thiocyanate (NH₄SCN) on the mechanism of manganese electrodeposition from a chloride-based acidic solution was investigated by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The EQCM data were represented as plots dΔm dt⁻¹ versus E, known as massograms. Because massograms are not affected by interference from the hydrogen evolution reaction, they clearly show the manganese reduction and oxidation processes. By comparing the voltammograms with their corresponding massograms, it was possible to differentiate mass changes due to faradaic processes from those due to non-faradaic processes. Morphology, chemical composition and structure of the manganese deposits formed in different potential ranges were analyzed by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD). The results showed that in the absence of NH₄SCN, Mn(OH)_2(s) is formed in the potential range −1.1 to −0.9 V due to the hydrogen evolution reaction in this region. At more cathodic potentials, the deposition of β-manganese and the inclusion of Mn(OH)_2(s) into the deposit occur; both of these species underwent dissolution by non-faradaic processes during the anodic scan. In the presence of NH₄SCN, the formation of α- and γ-manganese was observed. When the potential was ≤−1.8 V and [NH₄SCN] exceeded 0.3 M, the α-manganese phase was favored.