Obtention and characterisation of cobalt+copper electrodeposits from a citrate bath

The electrodeposition of cobalt+copper alloy on vitreous carbon, copper and nickel electrodes in a citrate bath at pH ca. 5 has been studied for two [Co(II)]/[Cu(II)] ratios in solution. Voltammetric and stripping results on vitreous carbon show that co-deposition of the two metals takes place under these conditions. Electrodeposition leads to the formation of a solid solution of cobalt in copper, detected by only one oxidation peak that shifts from the copper to the cobalt position as the applied current density–applied potential is made more negative. Structural XRD analysis and compositional analyses, confirm the formation of a cobalt–copper solid solution of face-centred-cubic (fcc) structure. Diffractograms show peaks that appear at diffraction angles between the lines corresponding to copper and fcc cobalt. The value of the fcc lattice constant a of the alloy decreases linearly with the increase in the cobalt percentage in the deposits, following Vegard's law. Deposits obtained at the same charge and current density from the same bath on different substrates have similar morphology: nodular-grained deposits at low deposition current densities–applied potentials, which evolve gradually to more fine-grained and structured deposits as the cobalt percentage in the deposits is increased.     

阳极氧化制备的钛表面不同微观形貌膜层耐腐蚀性研究

目的 探讨阳极氧化制备的钛表面不同微观表面形貌在人工模拟体液中的耐腐蚀性。方法 通过阳极氧化法处理纯钛样品（PT）,制备亚微米多孔（S）、微米多孔（M）、微米-亚微米复合多孔（MS）3种不同微观表面形貌氧化钛膜层的样品。采用扫描电子显微镜（SEM）观察样品表面形貌特征,X射线衍射仪分析表面晶型组成,表面粗糙度仪测试表面粗糙度,并对膜层横断面样品行SEM扫描观察膜层横断面结构和测量膜层厚度。采用电化学综合测试系统测试样品在人工模拟体液中的自腐蚀电位（Ecorr）、自腐蚀电流密度（Icorr）和极化电阻（Rp）,获得Tafel曲线。结果 阳极氧化对钛样品表面改性获得了微米多孔、亚微米多孔、微米-亚微米多孔3种不同的微观表面形貌。S样品氧化膜中的阻挡层厚度最大。阳极氧化处理后的样品比未处理的纯钛样品的耐腐蚀性增加;阳极氧化处理样品中,耐腐蚀性能由强到弱依次为S样品、M样品、MS样品,S样品的Ecorr最大,Icorr最小,Rp最大,耐腐蚀性能最优。结论 阳极氧化处理可以提高纯钛在人工模拟体液中的耐腐蚀性,亚微米多孔表面钛样品的耐腐蚀性能最优。     

Optical characterization of bismuth reversible electrodeposition

Reversible electrodeposition of metallic bismuth onto transparent conducting substrates was studied with interest in the electrochromic phenomena produced by plating and stripping a thin metallic film. Different bismuth films were prepared potentiostatically by applying potential steps of different amplitude (whilst maintaining the electric charge at a constant value), and the change in transmittance was followed in situ simultaneously during the electrodeposition process. A large change of transmittance was observed for constant charge films prepared at different deposition potentials. As the absorbance is related to the deposition charge (amount of metallic bismuth electrodeposited), changes in optical properties of equivalent films must be related to large changes in film morphology; this was corroborated by scanning electron microscopy. The effect of copper additives was also analyzed: this produced changes in film morphology, leading to bidimensional deposition being predominant over the tridimensional process.     

Synthesis of iron–palladium binary alloy nanotubes by template-assisted electrodeposition from metal-complex solution

The ordered arrays of Fe–Pd binary alloy nanotubes were synthesized from the mixed metal-complex solution by a simple electrodeposition method with the assistance of nanoporous anodic alumina (AAO). The electrodeposition potentials of Fe²⁺ and Pd²⁺ can be controlled by complexing agents, which has allowed for the fabrication of the Fe–Pd nanotubes by the AAO-template-assisted electrodeposition. Furthermore, the adjustment of the cathodic current density has caused the variation of the inner diameters and Fe–Pd composition ratios of the alloy nanotubes. Although the as-prepared Fe–Pd nanotubes are comprised of f.c.c. crystal structures, the metastable phase structure has been converted to L1₂ supper-lattice structure by annealing. The results of this work have shown a potential applicability of AAO-template-assisted electrodeposition to the preparation of other new binary alloy nanotubes by selecting adequate complexing agents.     

Electrochemical and X-ray absorption spectroscopy studies of copper coatings on a hydrogen storage alloy

Electroless copper deposits were made on the surface of LaNi_4.7Sn_0.3 particles with the aim of studying the influence on the charge/discharge performance of this metal hydride alloy. Cu layers were produced using formaldehyde and hydrogen as reducing agents and the near-range order and composition investigated as a function of deposition method by X-ray absorption spectroscopy. The electroless layer deposited using formaldehyde was shown to be mainly in the metallic state (Cu⁰). The copper layer prepared using hydrogen resulted in a mixed phase formed by metallic and oxidized copper species. Results also indicated that the copper layer protects the Ni atoms against corrosion, but this does not help in capacity retention during the charge/discharge cycling of the alloy. The electrode coated with the hydrogen reduced copper layer had lower discharge overpotentials relative to the uncoated electrode, implying an increase in the exchange current density for the process.     

Mechanistic studies of electrodeposition for bioceramic coatings of calcium phosphates by an in situ pH-microsensor technique

A pH-microsensor technique was developed to measure in-situ the pH value at the titanium alloy ∣ solution interface for the first time during the electrodeposition process of calcium phosphate coatings. Electrochemically prepared iridium oxide was used as a pH sensitive material, which is of a good response behavior in the measured solutions. The pH response slope was ?70.2 mV/pH at 60°C. The results indicated that the interfacial pH increased with the applied current density, first jumped to a maximum, then slowly decreased at the controlled current density during the electrodeposition process. Incorporating the results of composition and structure of electrodeposition coatings characterized by X-ray diffraction (XRD) patterns and Raman spectra, the measurement of the interfacial pH was informative for further understanding of the electrodeposition mechanism of calcium phosphates. The interfacial pH may determine the precipitation reaction and the electrodeposition products at the titanium surface.     

Kinetics and growth modes of quasi-2d silver branched electrodeposits produced in the presence of a supporting electrolyte

Quasi-2d silver electrodeposits were grown electrochemically at constant potential from aqueous Ag⁺ ion-containing solutions in the presence of a supporting electrolyte, at room temperature, using a three-electrode quasi-2d circular electrochemical cell. Open branching and dense radial branching patterns were distinguished on the centimetre scale, and growth mode transitions could be observed during the process. Branching patterns exhibited a mass fractal behaviour with a mass fractal dimension increasing from that expected for a DLA-like pattern to that of a dense branching pattern as either the cathodic overpotential (η_c) or the Ag⁺ ion concentration in the solution (c) was increased. The electrodeposition current increased with time exhibiting different regimes depending on whether an open branching or a dense radial branching growth mode prevailed. When the electrodeposition time exceeded a certain critical value, the radial growth rate of electrodeposits (v_r) approached a v_rαη_cc relationship. The experimental morphologies and growth kinetics were reproduced by Monte Carlo simulations of a growth model in which depositing particles follow a biased random walk.     

Calculations of the exchange current density for hydrogen electrode reactions: A short review and a new equation

After reviewing relevant equations for the calculation of exchange current density, a new equation is derived for hydrogen electrode reactions to correct for the influences of the hydrogen concentration change in the vicinity to the electrode surface. This equation is able to describe the polarization curve shape in the small polarization region as well as to calculate the exchange current (density). The abilities of this equation are demonstrated by the data obtained with a Pt rotating disk electrode in 0.1 mol l⁻¹ KOH solution. The exchange current density at 298 K under 1 atmosphere hydrogen pressure is found to be 0.103 mA cm⁻² with an apparent activation energy of 33.5 kJ mol⁻¹. At a constant temperature, the exchange current is found to be proportional to the square root of the hydrogen partial pressure in the solution.     

In situ electrochemical scanning tunneling microscopy of Co(0001) single crystal electrodes in acidic solution

The surface of a Co(0001) single crystal electrode was examined by in situ electrochemical scanning tunneling microscopy (STM) in 0.05 M Na₂SO₄ at pH 3 under potential control. Cyclic voltammetry indicated that the anodic dissolution of Co proceeds without passivation, and the anodic current was almost proportional to applied potential. The Co(0001)-(1 × 1) structure was observed on atomically flat terraces in the potential range between the hydrogen evolution and the onset of the anodic dissolution. At the foot of the rising anodic current-potential curve, a hexagonal surface lattice with (5 × 5) symmetry corresponding closely to that of CoO(111) or Co(OH)₂(0001) was also observed. In the early stages of anodic dissolution, the process proceeded in the layer-by-layer mode, forming atomically flat terraces extending over large areas. By reapplying a negative potential after the anodic dissolution, well-defined terrace-step structures were restored, suggesting that the electrodeposition also took place preferentially at step edges.     

Evaluation of a reactor model and cathode materials for batch electrolysis of l-cystine hydrochloride

A batch reactor model was used to predict the reactant concentration decay during constant current density (2000 A m^?2) electrolysis of l-cystine hydrochloride to l-cysteine hydrochloride at a variety of cathode materials in 2 M HCl at 298 K. A divided parallel plate reactor of 1 dm² projected cathode area was operated in the batch recycle mode with a catholyte volume of 2 dm³. The effect of the average linear flow velocity of the catholyte (0.033–0.123 m s^?1) was studied and it was found that the system could be modelled as a batch reactor. At high reactant levels (i.e. at short times) the rate of reduction was under charge transfer control and at low reactant levels (i.e. at longer times) pure mass transport control ensued. The ability of the model to describe the experimental data was dependent on the hydrogen overpotential at the cathode material. A good fit was obtained at high hydrogen overpotential cathodes (such as mercury-plated copper and lead) but the fit was poorer at materials having a lower hydrogen overpotential (which include titanium, carbon, tin, stainless steel, copper, nickel and molybdenum).     

Nicotinic acid as brightener agent in copper electrodeposition

Copper electrodeposition on platinum electrodes from slightly acidic solutions of copper sulphate containing nicotinic acid (NA) is studied. The electrochemical results indicate that NA produces an inhibition of the copper deposition, probably related to the additive adsorption. Also, complex species formation between NA and cuprous ions occur at the interface. Nicotinic acid acts as a very effective brightener producing highly uniform and smooth surfaces of copper deposits. Surface morphology, brightness and adherence depend on the potential at which the deposition is performed.     

Tin–zinc electrodeposition from sulphate–tartrate baths

The electrodeposition of tin–zinc alloys with 20–30% Zn by weight from sulphate–tartrate baths at pH 4 and 5 and different c_L/(c_Sn + c_Zn) ratios was studied. The anodic stripping analysis of the deposits was correlated with their morphology, composition and phase structure both on vitreous carbon and on copper electrodes. The use of tartrate anion as a complexing agent allows deposits to be obtained with a uniform composition and morphology under stirred conditions during the electrodeposition process. The deposited tin–zinc alloy is a mixture of Zn and βSn phases, with a Zn content of around 20% by weight.     

Initial stages of the electrocrystallization of copper from non-cyanide alkaline bath containing glycine

An electrochemical study on the initial stages of copper electrodeposition onto nickel substrate from non-cyanide alkaline bath containing glycine as complexing agent is presented in this work. The studied parameters were copper concentration, glycine concentration, and deposition potential. Upon scanning in the negative direction, one cathodic peak was observed, which is associated to copper electrodeposition from CuL₂ complex at pH 10.0 (where L⁻ is the anion form of glycine). Analysis of the chronoamperograms indicates time-dependent nucleation mechanisms. A progressive nucleation mechanism without overlap of diffusion zones, which involved an electron transfer reaction (at short times) and a progressive nucleation mechanism with overlap of diffusion zones (at long times). Non-linear fitting methods were applied to obtain the growth and nucleation kinetic parameters from theoretical equations proposed to describe this system.     

Electrochemical properties of corroded amalgams

Three types of amalgam, one conventional, ANA 68, and two with high copper content, Dispersalloy (dispersed type) and ANA 2000 (single composition type), were investigated. The amalgams were immersed for periods of 7 wk at a time, up to 35 wk, in 23 ml (37 degrees C) of 0.9% NaCl aqueous solutions and in 0.9% NaCl solution buffered with NaH2PO4 (8.8 mM) and Na2HPO4 (1.2 mM). The amalgam specimens were embedded in epoxy resin. The surface area of amalgam exposed to the solutions was 0.2 cm2 for each specimen. Every 7 wk the corrosion potential was measured, the amalgam specimens lightly brushed with a soft toothbrush, and the solutions renewed. After 14-21 wk and 35 wk the currents during anodic polarization sweeps over the amalgams were recorded. The corrosion potential for the high-Cu amalgams was somewhat more positive (noble) in the phosphate buffered solution than in the non-buffered solution during the 35 wk of corrosion. The phosphate buffer reduced the reactivity of the amalgams during anodic polarization. Corrosion made the amalgams more passive during the anodic polarization. However, all the elements leached from the amalgams into the solutions throughout the entire experiment.     

Electrochemical processing of Cu and Ni nanowire arrays

Cu and Ni nanowire arrays were fabricated by potentiostatic electrodeposition into track-etched polycarbonate (PC) membranes. The diameters of nano-sized cylindrical pores in PC membranes varied from 15 to 200 nm. The transient current variation was divided into four stages during the growth of Cu and Ni nanowires. The nanowires were observed with FE-SEM and TEM. The aspect ratio of nanowire reached from 50 to 400. The diameters of nanowires were not perfectly uniform along the length. A knurled type of morphology was observed on the surface of nanowire with 15 nm diameter. Such a morphological variation was not governed by the overpotential, but attributed to the original shape of nanopore wall in PC membranes track-etched with heavy ions.     

Creep and rupture of dental amalgam under bending stress

The bending creep of six different dental amalgams was continuously measured up to 30 days under different static loads. All six amalgams induced creep rupture within 30 days under 9 kgf of static load and some of them did under the lower static load. The high copper amalgams resisted for a longer period of time compared to the low copper amalgams. The admixed high copper amalgam had the highest creep value at rupture under the same load, which indicates that this amalgam is more flexible under continuous loading than the other amalgams. The rupture time was approximately proportional to the reciprocal of the creep rates and the rupture time drastically increased as the creep rate decreased. This result basically explains and supports the previously reported correlation between the compressive creep during a specific period of time and the marginal fracture of amalgam restorations.     

EQCM study of electrochemical modification of Bi2S3 films in the Zn-containing electrolyte

The electrochemical behavior of Bi₂S₃ as-deposited on Au using the successive ionic layer adsorption and reaction method has been investigated in the Zn²⁺-free background and Zn²⁺-containing electrolytes at different pH by electrochemical quartz crystal microbalance coupled with cyclic voltammetry and X-ray photoelectron spectroscopy. It has been shown that when the Bi₂S₃ film is reduced in the Zn²⁺-containing electrolyte Zn²⁺ ions are involved in electrochemical bismuth sulfide reduction and are partially reduced together with the bismuth sulfide film. The bismuth sulfide film initiates the adsorbed Zn²⁺ ions reduction prior to the traditional overpotential deposition of it. Reduction of Zn²⁺ ions prior to the overpotential deposition of Zn depends on solution pH: at pH 5 it occurs at more negative potential values and the observed mass changes due to Zn electrodeposition are greater than at solution pH 3. After bismuth sulfide film reduction in the Zn²⁺-containing electrolyte, Zn was detected as ZnO and metallic Zn at pH 5, while at pH 3 only ZnO was detected.     

Electrochemical reactions with adsorption of the reactants and electrosorption. Simple analytical solutions for a Henry isotherm

A theoretical treatment of an electrochemical reaction O + ne^? R with adsorption of the reactants is presented when the adsorption, at equilibrium, obeys a Henry isotherm. A simple analytical solution, valid for any degree of adsorption of O and or R, is established for a polarographic wave. In LSV, for slow sweep rates and weak adsorption, both the cathodic and anodic peaks have a ‘diffusional’ character; for high sweep rates and strong adsorption, they are both of a ‘surface’ nature. In the intermediate case, one peak has a ‘diffusional’ character (deposition process), while the other is of a ‘surface’ nature (redissolution process). Expressions of the peak potentials are given in all cases, for reversible or irreversible reactions. Study of their variations with log v allows some or all of the diverse constants (surface and heterogeneous rate constants, adsorption coefficients, transfer coefficients, etc.) to be determined. The case of normal pulse polarography is discussed briefly. Electrosorption is formally equivalent, as far as the diffusional problem is concerned, to the case where only one entity is adsorbed. Similarities and differences between the two cases are analyzed.     

Evaluation of the long-term corrosion behavior of dental amalgams: influence of palladium addition and particle morphology.

OBJECTIVES: The purpose of this investigation was to evaluate the long-term corrosion behavior of experimental amalgams as a function of particle morphology and palladium content. METHODS: Samples of four experimental high copper amalgams were prepared according to ADA specifications. Two of them had the same chemical composition but one had lathe cut particles (LCP) and the other had spherical particles (SP). The two others had spherical powders with an addition of 0.5 wt% of palladium (SP 0.5) and 1 wt% of palladium(SP 1) for the other. Corrosion resistance was evaluated by electrochemical techniques in Ringer's solution in a thermostated cell at 37 degrees C for samples aged 5, 8, 12, 16 months and 10 years. Potentiokinetic curves were drawn and the potential and the current density corresponding to the first anodic peak were registered. RESULTS: For all the amalgam samples the corrosion behavior improves over the 10-year period. SP samples exhibit a better behavior than LCP. Palladium addition improves corrosion behavior as compared to samples without palladium. No real difference is found regarding the amount of palladium between 0.5 and 1%. The potentials progress from a range between 0 and 20 mV/SCE to a range of 60-80 after 10 years. The stabilization of the potential begins after only 16 months. Except for the LCP, all the values converge to the same level of 80 mV/SCE. SIGNIFICANCE: The addition of no more than 0.5 wt% Palladium in a high copper amalgam powder improves the corrosion behavior of the amalgam up to a period of 10 years. The potential of the first anodic peak increases for each amalgam, probably in relation to the evolution of the structure of the material. Clinically, it is of interest to consider the good electrochemical behavior of older restorations when contemplating the repair or replacement of such fillings. At the same time, galvanic current can occur when a new amalgam restoration is placed in contact with an old one even if the same amalgam is used. In this situation, the new filling will be anodic and its degradation will be accelerated.The evaluation of the corrosion behavior of dental amalgams has to take into account the age of the samples.     

Characterization of anodic tin passive films formed in citrate buffer solutions

Voltammetry, chronoamperometry and SEM were employed to derive mechanistic information about the electroreduction processes that take place after cathodic polarization of a previously oxidized tin surface. This information proved useful to gain a deeper insight into the complex passivation process as well as into the passive layer changes generated by the anodizing procedure. Tin electrodes were anodized in citric–citrate buffers with pH 5. Three cathodic contributions were detected in the voltammetric response and they were correlated with three maxima present in the electroreduction current transients. Two electroreduction processes correspond to the electroreduction of tin surface species with different oxidation state and generated during the anodic potential sweep within the secondary passivity range. From these two processes only the electroreduction of the Sn(IV)-containing anodic film is dependent on anodizing time and hydrodynamic conditions of the electrolyte. Synchronized with the latter reaction occurs the electrodeposition of tin metal from a Sn(IV)-complex in solution.