D. R. Gabe

Electrodeposited zinc alloy coatings

Abstract This review examines the range of zinc alloy electrodeposited coatings that are available as finishes for continuous steel strip and also possible replacements for electroplated cadmium. Each system is described in terms of available electrolytes, physical properties and corrosion resistance. It is apparent that zinc-nickel, zinc-iron and zinc-cobalt are the most widely utilized, although zinc-manganese, which appears to have excellent corrosion resistance, is in all probability unavailable commercially. Zinc-tin is also discussed, being recognized as another possible replacement for cadmium.

The rotating cylinder electrode

Printed in Great Britain. Constant Surface and bulk concentrations Diffusion coefficient Characteristic dimension Faradaic equivalence Shear force Friction factor (Diffusion) current (Limiting) current density Mass flux (see Equation 24) Constant Length of cylinder Gap between cylinder and cell bottom Segment length Index, integer Radii of inner and outer cylinders Radial distance RDE roughness factor (see Equation 4)

The role of hydrogen in metal electrodeposition processes

The incidence of codeposition of hydrogen during electrodeposition, described as a cathodic inefficiency in plating processes, is reviewed and the effects of hydrogen on the deposits produced discussed. Characteristic electrode features leading to hydrogen evolution and hydrogen absorption are discussed and the causes of hydrogen embrittlement, which may be regarded as essentially electrochemical in origin, are defined.

The rotating cylinder electrode: a review of development

Recent developments in the theory and applications of rotating cylinder electrodes are reviewed. Particular attention is paid to the mass transfer behaviour and the development of turbulent flow patterns, and its exploitation in electrochemical reactors for a variety of applications including metal deposition from waste and effluent liquors.

The rotating cylinder electrode: its continued development and application

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.

Residual stresses in electrodeposits of nickel and nickel–iron alloys

Abstract The mechanical properties of micro-hardness and internal stress, obtained using the EFCO stressometer and X-ray diffraction, have been measured as a function of bath composition, ‘on/off’ cycles, current density, types of plating and solution pH.The electrodeposition of nickel and nickel–iron alloy on copper and mild-steel substrates from Watts and Ni/Fe baths have been investigated, using both direct current and pulsed-current electrolysis, with various ratios of ‘on’-time to ‘off’-time. Distinct differences between direct and pulsed processes revealed themselves in the surface characteristics, micro-hardness data, CCE data, internal stress measurements, pH data, various current density and finally composition of the deposits. The implications of using pulse plating to control the quality of electrodeposits have been considered.

The development of passivation coatings by cathodic reduction in sodium molybdate solutions

Abstract The incidence of marked arrests (inflections) on cathodic polarization curves for substrate metals of zinc, tinplate and platinum in sodium molybdate-based solutions has been examined. On tinplate, a reaction mechanism based upon mechanical degradation of the film, as opposed to a direct reduction process, has been proposed, correlating electrochemical and ESCA-type data.

Some passivation studies on tin electrodes in alkaline solutions

Abstract In attempts to learn more about the nature of protective films on tinplate some studies were carried out on pure tin electrodes in alkaline solutions above pH9. Potentiostatic anodic polarization methods were used with the intention of determining the mechanism of the passivation processes. It was found that the formation of tin oxide films was essentially a two-stage process, the second stage involving the formation of stannic hydroxide (Sn(OH) 4 ). Examination of films produced at certain overpotentials indicated that this probably took place by the oxidation of stannous oxide or a hydrated form of stannous oxide.

Porosity of Electrodeposited Coatings: Its Cause, Nature, Effect and Management

219 1. Classification 219 2. The Physical Attributes of Pores 221 3. Factors Influencing Porosity in Electrodeposited Coatings 223 3.1 The Effect of Surface Preparation 223 3.2 The Effect of an Undercoat 225 3.3 The Effect of Coating Thickness 227 3.4 Plating Bath Effects 230 3.5 The Effect of Porosity on a Coatings Performance ... 234 4. Methods for Detecting Porosity 237 5. Pore Detection Tests 238 5.1 Chemical Pore Detection Tests 238 5.2 Ferricyanide Type Tests 239 5.3 Hot Water Test 239 5.4 Gaseous Pore Detection Reagents 242 5.5 Other Chemical Pore Detection Tests .·, 243 5.6 Electrochemical Pore Detection Methods 245 5.7 Anodic Methods of Pore Detection 245 5.8 Cathodic Methods of Pore Detection 248 6. Physical Methods for Studying Porosity 248 6.1 Studies of Porosity Using Microscopy 249 6.2 Other Physical Methods for Studying Porosity 250

The production of compositionally modulated alloys by simulated high speed electrodeposition from a single solution

Simulation of high speed electrodeposition, using a rotating cylinder electrode, has been carried out in order to obtain an operating window for applied current density and cathode electrode movement as a means of agitation. The electrolyte used was based on an acid sulphate, zinc-nickel alloy. Electroplating was carried out at room temperature in the range of current density from 0.5–130 A dm−2 and at cathode speeds of 0–1500 rpm on 99.5% purity iron tube. By assessing the deposit characteristics in terms of appearance, composition, crystal structure and corrosion resistance and correlating these results, it is possible to predict the conditions for production of compositionally modulated alloys from the simple zinc-nickel non-complexing electrolyte system.