René Winand

Electron conducting organic coating of mild steel by electropolymerization

The aim was to coat mild steel with an electron conducting polymer in order to replace any possible electrochemical corrosion of the metal by another electrochemical reaction occurring on top of the film. In view of potential industrialization, electropolymerization of a water soluble monomer was studied. In most cases, this was achieved by oxidation, and the substrate had to be passivated. Polyaniline, was obtained in nitric acid solution. Films had a good structure but were brittle and powdery on the surface. Except on tin free steel, they were insulating. Polypyrrole was a better candidate. Prepared from a Na2SO4 solution, films were conductive, ensured good corrosion resistance of the substrate but they were brittle and adhesion to the substrate was not high. Furance, thiophene and iron substituted vinylpyridine complex were tried without success. Further, research should consider copolymerization of pyrrole with other monomers.

Electrodeposition of metals and alloys—new results and perspectives

Abstract After a summary of the theory, Winands diagram is introduced. This diagram gives the fields of stability of Fischers main types of electrodeposits as a function of two main parameters: the ratio of the current density to the diffusion limiting current density (mass transfer) and the inhibition. The diagram has been used at Universite Libre de Bruxelles as the basis for the chloride electrodeposition of metals, for high current density plating and electrorefining, and for initiating research concerning organic additives. Important industrial applications have been derived, especially in continuous steel sheet electroplating. The diagram has also been useful for alloys electrodeposition. New research areas include nucleation and initial growth, substrate influenced transition zone, thin film electroplating and electroforming, accurate hydrodynamic characterization of electrolytic cells, organic additives and secondary inhibition studies under plant simulation conditions, metallographic image analysis, micro- and nanoalloys studies, time dependent structures investigation, and deposit to substrate adhesion.

Galvanostatic anodization of titanium: I. Structures and compositions of the anodic films

Abstract The galvanostatic anodization of commercially pure titanium is studied with current densities lower than 500 A m −2 in 1 M sulphuric acid between 25 and 75°C. Two types of electrochemical behaviour are observed: the first type is characterized by a maximum value of the cell voltage and the second one by a continuous increase of the anode to cathode (which is platinum) potential difference. These different behaviours may be related to different structures of the anodic films (as observed by SEM and TEM) and to the compositions of these films (as determined by Auger analysis, RHEED and HEED).

Electrocrystallization - theory and applications

Abstract After a summary of the theory, Winands diagram is introduced. This diagram gives the fields of stability of Fischers main types of electrodeposits as a function ot two main parameters: the ratio of the current density to the diffusion-limiting current density (mass transfer) and the inhibition. The diagram has been used at Universite Libre de Bruxelles as the basis for the chloride electrode-position of metals, for high current density plating and electrorefining, and for initiating research concerning organic additives. Important industrial applications have been derived, especially in continuous steel sheet electroplating. New research areas in nucleation, and in the growth of thin films and foils are discussed.

Galvanostatic anodization of titanium: II. Reactions efficiencies and electrochemical behaviour model

Abstract The efficiencies of the different anodic reactions observed during the galvanostatic anodization of commercially pure titanium in 1 M sulphuric acid between 25 and 75°C have been studied. The two previously observed electrochemical behaviours are characterized by different kinetics for the anodic film growth, the titanium dissolution, the peroxides formation and the oxygen evolution. Finally, a theoretical interpretation of the obtained data is proposed.

Self-colour anodizing of titanium

Abstract Relations between the colours and the electrochemical parameters (current density, quantity of electricity and temperature of the electrolyte) during the anodization of titanium sheets were studied in a 1 M H 2 SO 4 solution. Mathematical theories were developed for the kinetics of growth of the anodic film and for the colours of this film. These theories show that the relation between the growth and the colour of the film is complicated. Nevertheless, it was possible to find experimental conditions that led to uniform and well-defined colours.

Electrocrystallization : fundamental considerations and application to high current density continuous steel sheet plating

In this paper, the main factors influencing the morphology of solid metal obtained at the cathode of an electrolytic cell are discussed. Although the presentation is rather fundamental, important practical conclusions are derived. Specific topics linked to electrogalvanizing are stressed.

Influence of the anodizing procedure on the structure and the properties of titanium oxide films and its effect on copper nucleation

Abstract Thin oxide films are grown electrochemically on commercially pure titanium substrates. Constant potential (potentiostatic), constant current (galvanostatic) and initial constant current followed by constant potential (combined) growth modes are studied. The structure, the composition, the thickness, the electrochemical and the semiconducting properties of the oxide films are considerably influenced by the growth mode even if the final anodizing potential has a constant value.

Auger Electron Spectroscopy Element Profiles and Interface with Substrates of Electroless Deposited Ternary Alloys

Electroless NiMeP alloys (Me = Cu, Sn, Sb) with high phosphorus content (∼11 weight percent) and a low weight percent of the third component (Me) have been plated in acidic baths onto aluminum, iron, and nickel. Scanning Auger electron spectroscopy is applied to study the element profiles and interface with the substrates. Generally the third component follows the profiles of Ni and P, which proves the alloy formation. A surface enrichment in the third element (Me) is observed in all cases. It is very strong when tin is the third component and very weak in the case of antimony, which is more or less uniformly distributed through the thickness. Decrease of surface concentration of phosphorus is noticed when NiSbP is plated. In Cu profiles three different zones exist : a surface enrichment zone, a groove (a zone of reduced concentration), and a plateau (a zone of almost constant concentration). There is no enrichment in the third element at the interface with the substrate for all three alloys and three substrates. At the interface with aluminum prepared for electroless plating with double zincate pretreatment complete dissolution of the zincate layer has been established.

Comparison of wear and corrosion behaviors of Cr and CrN sputtered coatings

Abstract Cr and CrN coatings were prepared by d.c. magnetron sputtering in a pure Ar and a N 2 –Ar atmospheres, respectively. The N 2 –Ar gas composition was chosen in order to allow the production of stoichiometric CrN deposits at the highest possible deposition rate. The columnar growth, low friction coefficient and high hardness of CrN were confirmed for deposits produced at a low temperature. The electrochemical behavior of CrN sputtered deposits in chloride solutions seemed to be similar to the behavior of Cr sputtered deposits. Moreover, it was shown that an anodic polarization treatment of the deposit increases the corrosion resistance of a chromium coating in the presence of chloride ions.