Surface potential sweep

Hamilton IC, Woods R (1981) An investigation of surface oxidation of pyrite and pyrrhotite by linear potential sweep voltammetry. J Electroanal Chem 118 327-343... 

For the Pt6oRu4o alloy, however, the intensity of the Ru3binding energy of the Pt4/7/2 CL were unchanged after the potential sweeps. Therefore, it can be concluded that the surface composition of the PtgoRu4o alloy was maintained without any Ru dissolution in 0.05 M H2SO4 solution during the potential sweeps up to 0.80 V. 

Samjeske G, Miki A, Osawa M. 2007. Electrocatalytic oxidation of formaldehyde on platinum under galvanostatic and potential sweep conditions studied by time-resolved surface-enhanced infrared spectroscopy. J Phys Chem 111 15074-15083. 

In an ideal case the electroactive mediator is attached in a monolayer coverage to a flat surface. The immobilized redox couple shows a significantly different electrochemical behaviour in comparison with that transported to the electrode by diffusion from the electrolyte. For instance, the reversible charge transfer reaction of an immobilized mediator is characterized by a symmetrical cyclic voltammogram ( pc - Epa = 0 jpa = —jpc= /p ) depicted in Fig. 5.31. The peak current density, p, is directly proportional to the potential sweep rate, v ... 

The RHSE has the same limitation as the rotating disk that it cannot be used to study very fast electrochemical reactions. Since the evaluation of kinetic data with a RHSE requires a potential sweep to gradually change the reaction rate from the state of charge-transfer control to the state of mass transport control, the reaction rate constant thus determined can never exceed the rate of mass transfer to the electrode surface. An upper limit can be estimated by using Eq. (44). If one uses a typical Schmidt number of Sc 1000, a diffusivity D 10 5 cm/s, a nominal hemisphere radius a 0.3 cm, and a practically achievable rotational speed of 10000 rpm (Re 104), the mass transfer coefficient in laminar flow may be estimated to be ... 

Figure 3.19 Relation between A and the degree of surface oxidation 0olj)Jt i—Qo/Qu) in anodic-going and cathodic-going potential sweeps at 50mVs l. From Angerstein-Kozlowska...

The Ag electrodes were subjected to potential sweep ORCs at 10 mV s"1 in either 0.1 M KC1 or 0.1 M KBr from an initial potential of -0.30 V to more positive potentials. After ca. 30 mC cm-2 of anodic charge was passed, the direction of potential sweep was reversed to reduce the Ag halide surface to Ag metal. The roughened electrode was then removed under potential control at -0.30 V and immersed in the Pb2+-containing test solution for SERS studies. 

The most well known work that Conway and his colleagues completed in Ottawa was on the analysis of potential sweep curves. I had been critical of the application of potential sweep theory to reactions which involved intermediates on the electrode surface and, working particularly early with Gilaedi and then with Halina Kozlowska, and to some extent with Paul Stonehart, Conway developed an analysis of the effect of intermediate radicals on the shape and properties of potential sweep showing how interesting electrode kinetic parameters could be thereby obtained. 

Fig. 6-96. Change in differential capacity of an interfadal double layer leading or not leading to interfadal lattice transformation in anodic and cathodic potential sweeps for a gold electrode surface (100) in perchloric add solution Ey = critical potential beyond which the interfadal lattice transforms from (5 x 20) to (1 x 1) E = critical potential below which the interfadal lattice transforms from (1 x 1) to (5 x 20) Ejm = potential of zero charge VacE = volt referred to the saturated calomel electrode. [From Kolb-Schneider, 1985.]...

Since the 1960s , various electrochemical methods such as linear potential sweep voltammetry, cyclic voltammetry etc. and various surface analysis apparatuses such as infrared spectra, X-ray photoelecfron spectroscopy etc. have been developed to investigate the electrochemical reaction mechanism involved in the flotation of sulphide minerals (Fuerstenau et al., 1968 Woods, 1976 Ahmed, 1978 Stm, 1990 Feng, 1989 Buckley, 1995 Arce and Gonzalez, 2002 Bulut and Atak, 2002 Costa et al., 2002). 

Abstract This chapter first explains the natural flotability of some minerals in the aspect of the crystal structure and demonstates the collectorless flotaiton of some minerals and its dependence on the h and pH of pulp. And then the surface oxidation is analysed eletrochemically and the relations of E to the composition of the solutions are calculated in accordance with Nemst Equation. The E h-pH diagrams of several minerals are obtained. Thereafter, electrochemical determination such as linear potential sweep voltammetry (LPSV) and cyclic voltammetry (CV) and surface analysis of surface oxidation applied to the sulphide minerals are introduced. And recent researches have proved that elemental sulfur is the main hydrophobic entity which causes the collectorless flotability and also revealed the relation of the amount of sulfur formed on the mineral surfaces to the recoveries of minerals, which is always that the higher the concentration of surface sulphur, the quicker the collectorless flotation rate and thus the higher the recovery. 

Many investigators have used different techniques to study the electrochemical behavior of different sulphide mineral electrodes in solutions of different compositions. Linear potential sweep voltammetry (LPSV), and cyclic voltammetry (CV) have been perhaps, used most extensively and applied successfully to the investigation of reactions of sulphide minerals with aqueous systems. These techniques have provided valuable information on the extent of oxidation as a function of potential for various solution conditions and have allowed the identity of the surface products to be deduced. 

There is significant agreement between the lower potential boundary of the flotation region and the potential at which the anodic ciurent begins in a potential sweep. The amoimt of extracted sulphur on the sulphide minerals can be correlated with their collectorless flotation behaviors. The higher the concentration of surface sulphur, the faster the collectorless flotation rate and thus the higher the recovery. 

Buckley, A. N., Hamilton, I. C., Woods, R., 1985. Investigation of the surface oxidation of sulphide minerals by linear potential sweep and X-ray photoelectron. In K. S. E. Forssberg(ed.), Flotation of Sulphide Minerals, Elsevier. Amsterdam, 6 41 - 60 Buckley, A. N. and Woods, R., 1990. X-ray photoelectron spectroscopic and electrochemical studies of the interaction of xanthate with galena in relation to the mechanism. Int. J. Miner. Process, 28 301 - 311... 

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