A review on the corrosion resistance of electroless Ni-P based composite coatings and electrochemical corrosion testing methods

This paper aims to review the impact of different factors influencing the corrosion resistance of electroless Ni-P based coatings. Emphasis has been given onto the impact of phosphorus content, incorporation of alloying elements, addition of particles and heat treatment which have been discussed in detail and critically reviewed. The effect of corrosive media and coating process parameters on corrosion resistance are studied concisely. Furthermore, the role of the incorporation of various elements and particles’ contents on the corrosion resistance of electroless Ni-P coating are studied systematically. This paper also presents an overview of the latest electrochemical corrosion measuring techniques. The following approaches deserve special attention in the analysis: localized electrochemical impedance spectroscopy (LEIS), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET), scanning droplet cell (SDC), scanning electrochemical microscopy (SECM), scanning Kelvin probe (SKP) and novel contactless technique (NCT).

The Corrosion and Wear Behaviors of a Medium-Carbon Bainitic Steel Treated by Boro-Austempering Process

The effects of boro-austempering treatment on growth kinetics of borided layers, microstructure, and properties in a medium-carbon bainitic steel were investigated. The microstructure, distribution in coatings, corrosion, and wear properties of boro-austempered steels were characterized by a microscope, field-emission electron probe micro analyzer, scanning vibrating electrode technique system and wear resistance machine. The results show that the corrosion resistance of steels in different corrosive mediums was significantly enhanced by boro-austempering treatment. In addition, the wear performance of borided layers was improved by more than two times compared to bainitic substrates, proving a better wear property of samples treated through the boro-austempering route. The solubility of carbon and silicon in borides is very little. In addition, the dual-phase coating of FeB and Fe2B was observed, and the internal stress induced during the growth of Fe2B and FeB was almost eliminated. The preferential crystallographic growth directions of Fe2B and FeB are [001] and [010], respectively, which belongs to the (100) plane. Finally, the kinetics equation d2 = 0.125·t of the borided layers at 1223 K was established.

Insitu SVET studies on the current density distribution on dissolving of Mg, MgZn2, Mg2Si and Al4Cu2Mg8Si7 surfaces in NaCl solutions

Purpose This paper aims to acquire the current density distribution on dissolving of Mg, MgZn2 (η -phase), Mg2Si (ß-phase) and Al4Cu2Mg8Si7 (Q-phase) surface in NaCl solutions. Design/methodology/approach MgZn2 (η -phase), Mg2Si (ß-phase) and Al4Cu2Mg8Si7 (Q-phase) are important intermetallic compounds found in aluminum alloys. Insitu scanning vibrating electrode technique (SVET) was used to acquire the current density distribution on dissolving of Mg, MgZn2 (η -phase), Mg2Si (ß-phase) and Al4Cu2Mg8Si7 (Q-phase) surface in NaCl solutions scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) was used to characterize the corroded surface. Findings SVET maps reveal that these compounds display characteristic dissolution features. Mg and MgZn2 displayed localized anodic and cathodic sites while that of Al4Cu2Mg8Si7 > Mg2Si displayed a diffused distribution of anodic and cathodic sites. The magnitude of the integrated anodic current densities on the compounds was noted to decrease with the progress of time, and the order of the magnitude of the current density with respect to the compounds is Mg > Mg2Si > Al4Cu2Mg8Si7 > MgZn2. SEM/EDX reveal that the highest mass loss recorded after the SVET test was manifested by Mg2Si followed by MgZn2 then Al4Cu2Mg8Si7. Originality/value Auxiliary information on the current density distribution on the corroding sample surface at the microscopic scale has been provided by SVET thereby taking care of certain limitations of traditional corrosion monitoring techniques such as gravimetric, hydrogen evolution and electrochemical measurements.

ELECTROCHEMISTRY OF IMMOBILIZED MICROPARTICLES AND MICRODROPLETE: ACCESS TO FUNDAMENTAL DATA OF SOLID MATERIALS AND IONS

The idea to study the electrochemistry of immobilized microparticles has been published by this author for the first time in 1989. In the last 32 years, this approach has been shown to be very successful not only for analytical characterization of solid materials, but also applicable to extract thermodynamic and kinetic data, and even to determine the age of metal specimen. In 2000, it has been shown that the electrochemistry of immobilized microdroplets gives an elegant access to determine the Gibbs free energies of ion transfer between immiscible solvents. These measurements are performed with a standard 3-electrode potentiostate and can be used also for solvents, which cannot be used in experiments with the classical 4-electrode technique. The electrochemistry of microparticles and microdroplets share several common features with respect to the electrode mechanisms: in both cases three-phase electrodes are realized and ion and electron transfer proceed simultaneously. This talk reviews the activities of the speaker and his cooperation partners during the last 3 decades paying special attention to those results, which are of general interest.

Vacuolar H+-ATPase and Na+/K+-ATPase energize Na+ uptake mechanisms in the nuchal organ of the hyperregulating freshwater crustacean Daphnia magna.

The nuchal organ of the embryos and neonates of the cladoceran, Daphnia magna, has been shown to be a site of Na+ influx and H+, NH4+ and Cl− efflux. This study combines the scanning-ion selective electrode technique with application of inhibitors of specific transporters to assess the mechanisms of Na+ transport across the nuchal organ. Na+ influx across the nuchal organ was inhibited both by inhibitors of the Na+/K+-ATPase (ouabain, bufalin) and by inhibitors of the vacuolar H+-ATPase (bafilomycin, N-ethylmaleimde, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, KM91104, S-nitrosoglutathione). Na+ influx was unaffected by the epithelial Na+ channel blocker benzamil, but was sensitive to ethylisopropyl amiloride and elevated external ammonium concentrations, consistent with roles for Na+/H+ and Na+/NH4+ exchangers in the apical membrane but not Na+ channels. Transport across the basolateral membrane into the hemolymph is proposed to involve the Na+/K+-ATPase and a thiazide-sensitive Na+:Cl− cotransporter. Keywords: Daphnia magna, Na+/K+-ATPase, V-ATPase, Iionoregulation, Nnuchal organ

Corrosion Studies using the Scanning Vibrating Electrode Technique (SVET) - A Brief Review

Background: The Scanning Vibrating Electrode Technique is an important technique in the field of corrosion. The technique has helped researchers to understand corrosion mechanisms in real time, due to the availability of commercial systems, which are user friendly, having a high degree of sensitivity and reliability. The technique provides quantitative and qualitative measurements by utilising a vibrating probe at a fixed height over the sample. Objective: The paper provides a basic understanding of the technique, including a brief history, development, method of measurement and then highlighting some applications of the technique. Conclusion: The paper shows the usefulness of the technique and its’ importance in corrosion research.

EFFECTS OF TEMPERATURE ON MILD STEEL GRADIENT-DISTRIBUTED WBE IMMERSED IN 3.5 wt.% NaCl SOLUTION

To study the corrosion behavior of carbon steel in seawater at different temperatures, a novel electrochemical method called gradient-distributed wire beam electrode technique with high temporal and spatial resolution has been employed. This new wire beam electrode was prepared by three kinds of carbon steel with different carbon contents so that it can evaluate three materials simultaneously in the same corrosion medium (3.5[Formula: see text]wt.% NaCl solution) and improve the accuracy of tests results. After the gradient-distributed wire beam electrode soaked in 3.5[Formula: see text]wt.% NaCl solution for 8[Formula: see text]h, compared with measured at room temperature, the corrosion rate was accelerated greatly and polarity reversal of potential-current was also observed.