Sulphuric acid electrolytes

Hard anodic films, 50-100/rm thick, for resistance to abrasion and wear under conditions of slow-speed sliding, can be produced in sulphuric acid electrolytes at high current density and low temperature. Current densities range from 250 to 1 000 Am , with or without superposed alternating current in 20-100g/1 sulphuric acid at —4—I- 10°C. Under these conditions, special attention must be paid to the contact points to the article under treatment, in order to avoid local overheating. 

Figure 2.36(a) Schematic representation of the incommensurate close-packed overlayer of Cu on Au formed in the perchlorate electrolyte The open circles are the gold atoms. Only part of the monolayer is shown in order to exhibit the overlayer-underlayer orientation, (b) Schematic representation of the more open lattice formed in the sulphuric acid electrolyte. From Manne... 

As was discussed above, it is essential to determine the effect, if any, that the emersion process has on the double layer. To do this, Wilhelm and colleagues have performed the definitive type of blank experiment. CO was adsorbed onto the Pt working electrode from sulphuric acid electrolyte. After adsorption, the CO-saturated solution was replaced with pure electrolyte. The potential of the electrode was then ramped in order to oxidise off the adsorbate, as C02, and the voltammogram so obtained is shown in Figure 2.118(a). The experiment was then repeated CO was adsorbed as before, but the electrode was emersed and transferred into the UHV chamber, before being re-immersed and the potential ramp applied. The voltammogram so... 

Cyclohexanones are readily reduced to the hydrocarbon in a sulphuric acid electrolyte. Reduction of ketosteroids in dioxan - aqueous sulphuric acid at a lead cathode in a divided cell is a convenient process for converting the carbonyl group to methylene [84,85] and affords as good yields as the alternative non-electrocheniical processes. Menthone is reduced to the hydrocarbon under mild conditions at a mercury cathode when the electrolyte is either magnesium chloride or zinc perchlorate in ethanol [86]. 

Moreover, when lead is used for the electrodes, as it must be with a sulphuric acid electrolyte, considerable overvoltage occurs at the electrodes hence, in spite of increased conductivity the economy in energy is negligibly small. 

Tafel4 has shown the value of a mercury cathode for obtaining a good yield of secondary alcohol in a dilute sulphuric acid electrolyte (40 per cent.). 

Several processes for the extraction of copper by electrometallurgical methods have been devised. The Marchese patent2 aimed at the decomposition of copper matte and deposition of the copper simultaneously in a sulphuric-acid electrolyte with a copper-matte anode and a copper cathode. In Siemens and Halske s patent3 the copper of the ore was oxidized to the cupric state by an acid solution of ferric sulphate, and the copper deposited electrolytically in a second vessel with a diaphragm separating the cathode and the anode. Neither process has been commercially successful. 

The influence of the metal-support interaction on the electrocatalytic activity for methanol oxidation has been evaluated by analyzing the voltammetric behavior of various electrocatalysts differing in terms of surface properties, as expressed by their pHzpc but having similar average particle size (around 3nm). These data were combined with the information gained by cyclic voltammetry (CV) experiments in sulphuric acid electrolyte. In particular, the potential at which the onset of a Pt-OH layer formation on the surface occurs in the anodic sweep and the potential at which... 

Most commercial anodizing of aluminium is performed in sulphuric acid electrolytes to yield oxide films, which, of the order of tens of micrometres thick, provide good corrosion and abrasion resistance, in addition to a useful dye-absorption capability. Other anodizing processes utilize chromic, oxalic, nitric or phosphoric acids, or mixed electrolytes. 

Shukla AK, Ravikumar MK, Arico AS, Candiano G, Antonucci V, Giordano N, et al. Methanol electrooxidation on carbon-supported Pt-WOs- electrodes in sulphuric acid electrolyte. J Appl Electrochem 1995 25 528-32. 

Hogarth MP, Munk J, Shukla AK, Hamnett A. Performance of carbon-cloth bound porous-carbon electrodes containing an clectrodeposited platinum catalyst towards the electrooxidation of methanol in sulphuric acid electrolyte. J Appl Electrochem 1994 24 85-8. 

The majority of aluminium anodizing processes utilize a sulphuric acid electrolyte. However, chromic acid anodizing may be preferred for the following reasons ... 

The process of metals electrodissolution in ionic liquids has been apvplied to develop several electropohshing procedures suitable for stainless steel, when a Type in eutectic has been involved containing ethylene glycol as the hydrogen bond donor (Abbott et al., 2004 Abbott et al., 2006) The anodic dissolution occurs in the same manner as in the case of the aqueous phosphoric and sulphuric acids electrolytes but the current efficiency was significantly improved up to about 90% and the ionic medium is much less toxic and corrosive. 

Sulphuric acid electrolytes are widely used in concentrations between 5% and 25% wt. and temperatures between 15 °C and 38 °C. The films are suitable for hydrothermal sealing (Yaffe 1990 Moutarlier et al., 2005). They are less protective than those formed by CAA. Baths with additions of boric or tartaric acids have been developed as replacements for CAA. 

Surface morphologies of anodic films generated in sulphuric acid electrolyte (a) without pretreatment, and after pretreatments in (b) nickel nitrate, (c) nickel nitrate and neodynium nitrate and (d) nickel nitrate and cerium (III) nitrate. (Reprinted from Li etai, 2010b, Copyright (2010) with permission from Elsevier.)... 

The operation of the lead-acid battery is based on a reversible reaction between the sulphuric acid electrolyte and the active material (Pb02 and Pb) in the plates, thus ... 

Ta ble 1.6 Electromotive force and temperature coefficient of voltage for various concentrations of sulphuric acid electrolyte in the lead-acid battery... 

Figure 1.12 Effect of initial volume of sulphuric acid electrolyte (29% w/w or 35.10g/100 ml) in a lead-acid battery on final end-of-discharge concentration...

The type featuring calcium-lead alloys and immobilized sulphuric acid electrolyte, which reduces but does not completely eliminate gassing, i.e. there is electrolyte volume reduction. Such cells are usually manufactured containing a reserve of electrolyte so that topping up is not required during battery life. 

Controlled-potential techniques have been more commonly used for the separation and purification of indium than for more direct analytical purposes. Plekhanov (115) deposited indium at a cathode potential of —0.5 V (presumably vs. SCE) from dilute hydrochloric acid solution with a 94 per cent current eflSciency Sayun and co-workers (116) prepared purified indium by oxidation of indium amalgam at —0.40 V vs. SCE in a sulphuric acid electrolyte. 

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