Bi and Te thin films synthesized by galvanic displacement from acidic nitric baths

Bismuth (Bi) and tellurium (Te) thin films were formed by galvanic displacement of different sacrificial iron group thin films [i.e. nickel (Ni), cobalt (Co) and iron (Fe)] where the formation was systematically investigated by monitoring the change of open circuit potential (OCP), surface morphology and microstructure. The surface morphologies and crystal structures of galvanically displaced Bi or Te thin films strongly depended on the type and thickness of the sacrificial materials. Continuous Bi thin films were successfully deposited with the sacrificial Co. However, dendrites and nanoplatelets were formed from the Ni and Fe thin films. Te thin films were synthesized with all the three sacrificial thin films. Chemical dissolution rate of the sacrificial thin films and mixed potential strongly influenced formation of Bi or Te thin films.     

Electrochemical corrosion properties of metal alloys used in orthopaedic implants

This study concerns an investigation of the corrosion behavior of 316 stainless steel, CoCrMo and Ti6Al4V alloys in simulated body conditions (ringer lactate) at 37 °C by the use of Tafel plots, mixed potential and electrochemical impedance spectroscopy (EIS). Ti6Al4V alloy has the highest corrosion resistance followed by CoCr alloy. Ti6Al4V–CoCrMO was the best couple for galvanic corrosion with the minimum galvanic potential and current values according to mixed potential theory and Tafel method. It was concluded that Ti6Al4V was the most suitable material for implant applications in the human body.     

Bimetallic Pt–Au thin film electrocatalysts with hierarchical structures for the oxidation of formic acid

A series of bimetallic Pt–Au thin films with different Pt/Au ratios were fabricated on glassy carbon (GC) substrates through galvanic replacement reactions between hierarchical Co thin films prepared by cyclic voltammetric deposition and mixed solutions of HAuCl₄ and H₂PtCl₆. The morphologies of the as-prepared Pt–Au thin films resemble those of the sacrificial Co templates, and the Pt/Au ratios in the films are dependent on the HAuCl₄/H₂PtCl₆ molar ratios in the mixed solutions. Because of good stability and excellent synergistic effect of Au and Pt, the bimetallic films with novel structures display unexpected high catalytic activity for the oxidation of formic acid. The as-prepared hierarchical Pt–Au micro/nanostructures are expected to find applications as catalysts in direct formic acid fuel cells (DFAFCs).     

Copper deposition onto silicon by galvanic displacement: Effect of Cu complex formation in NH4F solutions

Copper was deposited onto rotating Si substrates by galvanic displacement in 6.0 M NH₄F to determine the effects of Cu complex formation on deposition rates. Deposition rates decreased with increasing rotation speed, indicating that Cu(I) intermediates, stabilized by NH₃, diffuse away from the Cu surface before they reduce to Cu(0). UV-visible spectra of contacting solutions and direct measurements of mass changes resulting from Cu deposition and Si removal confirmed this proposal. These findings contrast those reported previously for deposition from HF solutions, in which Cu(I) species are unstable and reduce rapidly to Cu(0). These data and mixed-potential theory were used to develop a reaction-transport model that accurately describes the effects of mass transfer and electrochemical reaction rates on Cu deposition dynamics and open-circuit potential (OCP) values. The effects of ascorbic acid and tartrate additives on film properties and formation rates were also examined. Cu reduction kinetics decreased significantly when ascorbic acid (0.01 M) was present. Adhesion of Cu films was improved when ascorbic acid was used, but internal stresses caused films to distort when their thicknesses exceeded 100 nm. Adding potassium sodium tartrate to solutions containing ascorbic acid decreased film stresses and led to robust films with excellent adhesion.     

镀锡钢丝锡层厚度的测定

介绍利用原电池及失重法相结合测定镀锡钢丝的镀层厚度的方法。     

The spatial distribution of Zn during galvanic corrosion of a Zn/steel couple

The spatial distribution of Zn²⁺ during galvanic corrosion of a model Zn/steel couple in 0.01 M NaCl was investigated using a scanning zinc disk electrode. The couple had a coplanar arrangement of a steel substrate with an electroplated zinc layer at the center. During galvanic corrosion, the marked changes in the Zn²⁺ concentration were confined to a thin solution layer ca. 1.0 mm thick above the couple surface. In this thin solution layer above the zinc layer, a higher concentration region of Zn²⁺ in the range of 5-18 mM extended around the zinc layer in the solution during galvanic corrosion. Conversely, above the steel surface distant from the zinc layer, the surface concentration of Zn²⁺ was almost zero during galvanic corrosion. On this surface, the precipitation of zinc corrosion products due to the hydrolysis reaction of Zn²⁺ was observed. The distribution of the Zn²⁺ concentration supported that Zn²⁺ acted as a buffer that suppressed the increased pH due to the cathodic reaction on the steel surface near the zinc layer and almost no corrosion products formed there. The spatial distribution of Zn²⁺ is discussed in relation to the distributions of potential and pH and the surface morphology of the galvanic couple.     

Dissolution of magnetite coupled galvanically with iron in environmentally friendly chelant solutions

The galvanic coupling between magnetite and iron in ethylenediaminedisuccinic acid (EDDS) solutions both with and without added iron(II) ions has been studied using electrochemical methods. The galvanic coupling accelerates the corrosion of iron due to the small shift in its potential in the anodic direction. At the same time, the potential of magnetite is cathodically polarized away from the potential range where the only faradaic process—the reductive dissolution of magnetite—takes place and results in a considerable decrease in its dissolution. Magnetite dissolves faster at the galvanic potential when [EDDS] ? [Fe²⁺] whereas iron is affected to a much lesser extent. The ratio between the rates of dissolution of magnetite at the galvanic potential to that at its steady state potential tends to decrease at higher temperatures and at higher EDDS and Fe²⁺ concentrations. This study shows that temperature plays a decisive role in the dissolution of magnetite coupled to iron. To completely remove it from the iron surface, high temperatures should be used. Corrosion inhibitors have to be considered when high losses of the base metal cannot be tolerated.     

Acidic sulphate leaching of chalcopyrite concentrates in presence of pyrite

Copper concentrates with mineralogy dominated by chalcopyrite have slow leaching kinetics at atmospheric pressure in sulphate media because of the formation of passivation layer on its surface during the leaching. To enhance the leaching rate of the copper concentrate, pyrite was added to act as a catalyst. Pyrite and copper sulphide minerals then form a galvanic cell which increases both the copper leaching rate and yield. Effect of parameters such as solution redox potential, temperature, initial acid concentration, solids content, total initial iron concentration and pyrite to copper sulphide minerals mass ratio were investigated. Mineralogical analyses by XRD were performed on selected leach residues and the feed materials. A copper recovery higher than 80% in 24 h was achieved at a redox potential of 410 mV vs Ag, AgCl, a temperature of 85 °C, 15 g/L of initial acid concentration, a solid content of 7.8% (w/v), a total initial iron concentration 5 g/L and pyrite to copper sulphide minerals mass ratio 2:1. XRD patterns on leach residues showed that candidates for surface passivation, i.e. jarosite and elemental sulphur, were formed at high total initial iron concentrations.     

A corrosion study on W-Cu alloys in sodium chloride solution at different pH

A corrosion study of two types of tungsten-copper(W-Cu)alloys in 3.38 wt.%Na Cl solution with different pH at 25℃were investigated using potentiodynamic polarization and immersion test.It is crucial that the corrosion behavior and preferential attacked phases of the W-Cu alloys were found to alter with p H.The micro-galvanic effect of tungsten phase and copper binder played a significant role.It was also proved that the existence of aggressive chloride ions could accelerate the Cu binder dissolution in acidic and neutral solution,which induced tungsten phase detachment and increased the corrosion rate of the W-Cu alloys.While Cl-would accelerate the Cu binder dissolution of W-Cu alloys at high potential during polarization test in strong alkaline solution.     

A test of "strain toward symmetry" theories.

"2 studies have been reported which offer some support to the 'strain toward symmetry' hypothesis. GSR deflections were found to be associated with disagreement with a positively valent experimenter. 2 topics were used as matters for disagreement, but we were unable to discover significant differences in the deflections associated with the topics used." (PsycINFO Database Record (c) 2010 APA, all rights reserved)