Recent literature on the electrodeposition of metallic coatings containing nanosized particles is surveyed. The nanosized particles, suspended in the electrolyte by agitation and/or use of surfactants, can be codeposited with the metal. The inclusion of nanosized particles can give (i) an increased microhardness and corrosion resistance, (ii) modified growth to form a nanocrystalline metal deposit and (iii) a shift in the reduction potential of a metal ion. Many operating parameters influence the quantity of incorporated particles, including current density, bath agitation (or movement of work piece) and electrolyte composition. High incorporation rates of the dispersed particles have been achieved using (i) a high nanoparticle concentration in the electrolyte solution, (ii) smaller sized nanoparticles; (iii) a low concentration of electroactive species, (iv) ultrasonication during deposition and (v) pulsed current techniques. Compositional gradient coatings are possible having a controlled distribution of particles in the metal deposit and the theoretical models used to describe the phenomenon of particle codeposition within a metal deposit are critically considered.

Electrodeposition of composite coatings containing nanoparticles in a metal deposit

I .. Rates of ionic mass transfer at nickel electrodes rotating about their axes In the center of stationary electrodes were studied using the ferri-ferrocyanide oouple In alkaline solutions. A general mass transfer correlation was found to apply equally well to the dissolution rates of rotating solids and to the rates of ionlo mass transfer at rotating electrodes. This correlation takes into account the physioal properties of the system as well as geometric and hydro dynamic factors. The correlation enables the prediction of limiting currents and concentration polarisation at rotating electrodes under a wide range of conditions. The nature of the polarisation involved in the reduotion of Fe(CNfe~» and the oxidation of Fe(CN#* was also Investigated. The polarisation was found to depend strongly on the presence of "electrode poisons." With freshly prepared solutions, under exclusion of light and with eathodlcally treated nickel electrodes relatively small ehesdcal polarisations were determined. For rotational speeds not exceeding Reynolds number 11,000, the chemical polarisation was found to be negligicle in comparison with the concentration polarisation* Under such conditions the ferro-ferrioyanide oouple can be conveniently used to obtain mass transfer rates for various hydrodynamic conditions, or, conversely, to verify the validity of mass transfer equations by a comparison of experimental .and calculated values of limiting currents and concentration polarisation. The rotating electrode model was found to be most suitable for studying the nature of eleotrolytio polarisation phenomena on aocount of the uniformity of the current distribution as well as of the hydrodynamio diffusion laver at the electrode surfsee.

Mass transfer in electrode processes. 3. ionic mass transfer and concentration polarization at rotating electrodes

Following a brief overview of their history, which dates back to the 1920s with marked developments during the 1960s and 1970s, the principles of composite coatings, achieved by including particles dispersed in a bath into a growing electrodeposited metal layer, are considered. The principles and role of electroplating compared to other techniques for realising such coatings, are considered. A good quality particle dispersion (often aided by a suitable type and concentration of surfactants) appropriate choice of work-piece shape/geometry and controlled agitation in the bath are seen to be prerequisites for achieving uniform coatings having a well-dispersed particle content by electroplating. Examples are provided to illustrate the influence of bath composition and plating conditions on deposit properties. Engineering applications of included particle composite layers are illustrated by examples of hard ceramic, soft ceramic and polymer inclusion composite coatings from the recent literature. Current trends in the development of composite plated coatings are summarised and their diverse applications are seen to include the use of finely structured (especially nanostructured) and functionally active particles together with hybrid and more complex, e.g. hierarchical, structures for applications ranging from tribology to speciality electronics, magnetic and electrochemical energy conversion materials.

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A review of the electrodeposition of metal matrix composite coatings by inclusion of particles in a metal layer: an established and diversifying technology

Electrochemical reduction of halogenated organic compounds is gaining increasing attention as a strategy for the remediation of environmental pollutants. We begin this review by discussing key components (cells, electrodes, solvents, and electrolytes) in the design of a procedure for degrading a targeted pollutant, and we describe and contrast some experimental techniques used to explore and characterize the electrochemical behavior of that pollutant. Then, we describe how to probe various mechanistic features of the pertinent electrochemistry (including stepwise versus concerted carbon–halogen bond cleavage, identification of reaction intermediates, and elucidation of mechanisms). Knowing this information is vital to the successful development of a remediation procedure. Next, we outline techniques, instrumentation, and cell designs involved in scaling up a benchtop experiment to an industrial-scale system. Finally, the last and major part of this review is directed toward surveying electrochemical studi...

Electroreductive Remediation of Halogenated Environmental Pollutants.

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do electrochemistry and photoredox catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) that enable bond formations not constrained by the rules of ionic or 2 electron (e) mechanisms. Instead, they enable 1e mechanisms capable of bypassing electronic or steric limitations and protecting group requirements, thus enabling synthetic chemists to disconnect molecules in new and different ways. However, while providing access to similar intermediates, electrochemistry and photoredox catalysis differ in several physical chemistry principles. Understanding those differences can be key to designing new transformations and forging new bond disconnections. This review aims to highlight these differences and similarities between electrochemistry and photoredox catalysis by comparing their underlying physical chemistry principles and describing their impact on electrochemical and photochemical methods.

Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis.

The application of rotating cylinder electrodes (RCEs) in electrochemistry has been reviewed for the period 1982–1995. Among the applications highlighted are the novel design of cell geometries and reactors for a range of electrochemical processes, voltammetry and analysis, electrodeposition and corrosion. This range amply indicates the widespread acceptance of the RCE for studies in a number of interdisciplinary fields.

J. Gonzalez-Garcia

Papers

The rotating cylinder electrode: its continued development and application