Continuous electrodeposition

Lingane and Jones devised an electrogravimetric procedure for the successive determinations of copper, bismuth, lead, and tin in the presence of various other metals. After each deposition the pH and electrode potential are adjusted, and the cathode is replaced in the solution for continued electrodeposition. 

Nano-particulate tungsten oxide films were also synthesized by pulsed electrodeposition in libraries. Particle sizes between 45 330 nm were achieved by varying pulse duration from 5 ms to 500 ms. Films prepared by continuous electrodeposition had an average particle size of approximately 375 nm. As the pulse time decreased, particle size decreased as well. For a 5 msec pulsed deposition, the average particle size was approximately 45 nm. We checked the particle size with respect to deposition time (30 sec to 30 min, that is 3,000 to 180,000 pulses) and found that particle size was independent of total number of pulses the total number of pulses seemed to affect only film thickness and not the final particle size. 

Saba, J. et al.. Continuous electrodeposition of polypyrrole on carbon nanotube-car-bon fiber hybrids as a protective treatment against nanotube dispersion. Carbon. 2012. 

Fountoulakis, S. G., Continuous Electrodeposited Coatings for Steel Strip, ASM Handbook, VoL 5, Surface Engineering, ASM International, Metals Park, OH, 1994, pp. 349-359. 

Anodic deposition is controlled by either fluid shear (cross-flow filtration) (48), similar to gel-polarization control, or by continual anode replacement (electrodeposited paints) (46). High fluid shear rates can cause deviations from theory when E > (49). The EUF efficiency drops rapidly... 

At the start the cathode is invariably a metal different from that to be deposited. Frequently, the aim is to coat a base metal with a more noble one, but it may not be possible to do this in one step. When a metal is immersed in a plating bath it will corrode unless its potential is sufficiently low to suppress its ionisation. Fortunately, a low rate of corrosion is tolerable for a brief initial period. There are cases where even when a cathode is being plated at a high cathodic (nett) current density, the substrate continues to corrode rapidly because the potential (determined by the metal deposited) is too high. No satisfactory coating forms if the substrate dissolves at a high rate concurrently with electrodeposition. This problem can be overcome by one or more of the following procedures ... 

Pseudomorphism received methodical study from about 1905. A micro-section taken across the interface between a substrate and an electrodeposit shows the grain boundaries of the former continue across the interface into the deposit (Fig. 12.5). As grain boundaries are internal faces of metal crystals, when they continue into the deposit the latter is displaying the form of the substrate. Hothersall s 1935 paper contains numerous excellent illustrations with substrates and deposits chosen from six different metals, crystallising in different lattice systems and with different equilibrium spacing. Grain boundary continuation and hence pseudomorphism is evident despite the differences. 

Fig. 12.5 Pseudomorphism grain boundaries in the substrate (5) are continued in the electrodeposit (D)...

Fig. 12.6 (a) Co-ordination across a substrate S-electrodeposit D interface on the atomic scale produces epitaxy, (b) a non-epitaxial deposit has no co-ordination and (c) epitaxy would be expected to produce grain boundary continuation at the interface, though in fact grain boundaries often continue to thicknesses far greater than those at which epitaxy disappears... 

Continuous plating of wire and strip is, unlike the preceding techniques, a prefabrication process. The production of tinplate is the largest scale continuous operation, but any electrodeposit may be applied this way. Subsequent fabrication processes arc likely to damage the coating, so that pre-coating is best reserved for ductile coatings which are anodic to the substrate in service, as is the case for tin. 

In his classic treatise, Brenner reported that over 500 alloy electrodeposition systems had then been studied in depth —that number has now been substantially increased — yet barely 10 to 20 have any real degree of industrial exploitation. The list continues to grow and the present type of work on alloys can be divided into three classes ... 

Electrodeposition of metals can be performed under different electrochemical modes. In the work mentioned in Ref. [18], it was performed in potentiostatic mode. The potential value for formation of platinum nanoparticles is —25 mV vs. SCE the deposition is performed from 2.5 mM solution of H2[PtCl6] in 50 mM KCl. The size of nanoparticles formed depends on the reduction charge. Continuous monitoring of the charge in potentiostatic mode is provided by different potentiostats, for example, by Autolab-PG-stat (EcoChemie, The Netherlands). Conditions for deposition of other metals should be selected according to their electrochemical properties. 

In order to provide for purification of the electrolyte, diaphragm cells are used to form separate anode and cathode compartments, and the anodes are encased in loose-fitting, open-weave bags to facilitate the removal of slime with the anodes. The anolyte is continuously taken out, purified and fed into the cathode compartments where nickel electrodeposits on the cathodes. A small hydrostatic head of purified electrolyte in the cathode compartment is maintained in order to prevent the diffusion of anolyte with its impurities into the cathode compartments. 

This technique is applied to mixtures of metal ions in an acidic solution for the purpose of electroseparation only the metal ions with a standard reduction potential above that of hydrogen are reduced to the free metal with deposition on the cathode, and the end of the reduction appears from the continued evolution of hydrogen as long as the solution remains acidic. Considering the choice of the cathode material and the nature of its surface, it must be realized that the method is disturbed if a hydrogen overpotential occurs in that event no hydrogen is evolved and as a consequence metal ions with a standard reduction potential below that of hydrogen will still be reduced a classic example is the electrodeposition of Zn at an Hg electrode in an acidic solution. 

Simultaneous and continuous measurements of extracellular pH, potassium K+, and lactate in an ischemic heart were carried out to study lactic acid production, intracellular acidification, and cellular K+ loss and their quantitative relationships [6, 7], The pH sensor was fabricated on a flexible kapton substrate and the pH sensitive iridium oxide layer was electrodeposited on a planar platinum electrode. Antimony-based pH electrodes have also been used for the measurement of myocardial pH in addition to their application in esophageal acid reflux detection. 

The limits of detection for metals in seawater using in situ graphite tube electrodeposition will be governed by the deposition time. Unlike laboratory analyses, there will be no depletion of metals from the solution when lengthy deposition times are used, since fresh sample is being continuously pumped through the electrode. It should therefore be possible to detect the extremely... 

Electrodeposition was used to prepare a biaxially textured Gd2Zr207 (GZO) buffer layer on Ni-W substrates.129 Buffer layers provide chemically inert, continuous, and smooth bases for the growth of the superconductor oxide films. They also prevent both the diffusion of metal to the high-temperature superconductor (HTS) layer and the oxidation of the metal substrate when superconductor oxide films are processed at high temperature (-800 °C) in an oxygen atmosphere (100ppm or more). 

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