Anodic oxidation of lead in aqueous carbonate solutions. I. Film formation and dissolution at pH = 12

1988 ◽  
Vol 66 (10) ◽  
pp. 2652-2657 ◽  
Author(s):  
D. W. Shoesmith ◽  
M. G. Bailey
Keyword(s):  
Anodic Oxidation ◽  
Electrode Surface ◽  
Film Formation ◽  
Rotating Disk ◽  
Surface Layers ◽  
Compact Layer ◽  
Solid Films ◽  
Carbonate Solutions ◽  
Disk Electrodes ◽  
State Growth

The anodic oxidation of lead has been studied using rotating disk electrodes, under voltammetric and potentiostatic conditions, in aqueous carbonate solutions at pH = 12. The solid films formed on the electrode surface have been identified by X-ray diffractometry. Two distinct surface layers are formed: a compact layer composed of two separate phases, plumbonacrite (Pb10O(OH)6(CO3)6) and hydrocerussite (Pb3(OH)2(CO3)2); and a more dispersed layer of hydrocerussite. The plumbonacrite in the compact layer is formed directly on the electrode surface by a solid-state growth process. The hydrocerussite component of this compact layer appears to form by conversion of the outer layers of plumbonacrite. The dispersed layer is formed by deposition from solution. The extent of deposition is controlled by the rate of transport of soluble Pb2+ species to the bulk of solution.

Anodic oxidation of lead in aqueous carbonate solutions. II. Film formation and dissolution in the pH range 9 to 14

1988 ◽  
Vol 66 (11) ◽  
pp. 2941-2946 ◽  
Author(s):  
D. W. Shoesmith ◽  
M. G. Bailey ◽  
P. Taylor
Keyword(s):  
Anodic Oxidation ◽  
Electrode Surface ◽  
Oxidation Process ◽  
Film Formation ◽  
Electrochemical Techniques ◽  
Rotating Disk ◽  
Base Layer ◽  
Ph Values ◽  
Carbonate Solutions ◽  
Anodic Oxidation Process

The anodic oxidation of lead has been studied in aqueous carbonate solutions at pH values in the range 9 ≤ pH ≤ 14. The solid films formed on the electrode surface have been identified by X-ray diffractometry. The dissolution and film formation processes have been studied by a number of electrochemical techniques at rotating disk electrodes. The anodic oxidation process can be divided into two distinct regions. In the main anodic oxidation process, a variety of surface phases is formed. The nature of the phase formed is pH-dependent. Plumbonacrite (Pb10O(OH)6(CO3)6) formation is observed at all pH values and predominates at pH ≥ 13. At pH < 11, cerussite (PbCO3) is the predominant phase, whereas at intermediate pH values, hydrocerussite (Pb3(OH)2(CO3)2) predominates. The dissolution rate of Pb2+ species from the electrode surface is directly proportional to the solubility of the predominant phase present. At more positive potentials, a reactivation, involving increased dissolution and a further stage of film formation, is observed. Litharge (PbO) is observed to grow underneath the initially formed basic lead carbonates. Dissolution occurs either by the field-assisted dissolution of the base-layer on the electrode or by metal dissolution through faults in the base-layer.

Electrochemical behaviour of silver in aqueous chromate solutions

1998 ◽  
Vol 76 (8) ◽  
pp. 1156-1161 ◽  
Author(s):  
Sayed S Abd El Rehim ◽  
Magdy AM Ibrahim ◽  
Hamdy H Hassan ◽  
Mohammed A Amin
Keyword(s):  
Cyclic Voltammetry ◽  
Electrochemical Behaviour ◽  
Anode Surface ◽  
Cyclic Voltammograms ◽  
Oxidation Peak ◽  
Surface Layers ◽  
Compact Layer ◽  
X Ray ◽  
Solid Films ◽  
Scan Rate

The electrochemical behaviour of silver was studied under cyclic voltammetry and chronoamperometry conditions in aqueous K2CrO4 solutions. The forward cyclic voltammograms exhibited one oxidation peak, A1, due to the formation of Ag2CrO4. The height of the anodic peak, A1, increases with increasing chromate concentration, temperature, and scan rate. The solid films formed on the anode surface have been examined by X-ray diffractometry. The reverse voltammograms exhibited two reduction peaks, C1 and C2, indicating the formation of two distinct surface layers of Ag2CrO4, an inner compact layer reduced in peak C1 and an outer powdery layer reduced in peak C2.Key words: silver electrode, cyclic voltammetry, K2CrO4 solutions.

Kinetics of compact layer formation and growth of 1,10-phenanthroline at the electrode surface

1990 ◽  
Vol 87 ◽  
pp. 1597-1607 ◽  
Author(s):  
L Benedetti ◽  
M Borsari ◽  
C Fontanesi ◽  
G Battistuzzi Gavioli
Keyword(s):  
Electrode Surface ◽  
Layer Formation ◽  
Compact Layer ◽  
Kinetics Of

Mineral interfacial processes in the method of induced polarization

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 1105-1114 ◽  
Author(s):  
James D. Klein ◽  
Tom Biegler ◽  
M.D. Horne
Keyword(s):  
Frequency Domain ◽  
Diffusion Layer ◽  
Electrode Potential ◽  
Rotation Speed ◽  
Low Frequency ◽  
Rotating Disk ◽  
Active Species ◽  
Hydrodynamic Theory ◽  
Electrode Polarization ◽  
Disk Electrodes

A phenomenological laboratory investigation has been conducted of the IP response of pyrite, chalcopyrite, and chalcocite. The technique that was used is standard in electrochemistry and employs rotating disk electrodes. The effect of rotation is to stir the electrolyte and thus to restrict the maximum distance available for diffusion of electroactive aqueous species. For high rotation speed and low excitation frequencies, the mean diffusion length exceeds the thickness of the diffusion layer. The net effect is to reduce the electrode impedance at low frequency. The thickness of the diffusion layer and thus the impedance at low frequency can be controlled by the rotation speed. Measurements using rotating disk electrodes have been conducted in both the time domain and the frequency domain. For both pyrite and chalcopyrite, the results were the same: no dependence on rotation was observed. For frequency domain measurements with chalcocite, a strong dependence on rotation was observed. The interpreted diffusion layer thickness was found to depend on rotation speed to the [Formula: see text] power, in agreement with results predicted by hydrodynamic theory. The results of this study imply that there are two physical processes responsible for electrode polarization in the IP method. For chalcocite and perhaps other related copper sulfide minerals, the probable mechanism is diffusion of copper ions in the groundwater. In case, the phenomenon is correctly described by the Warburg impedance. Chalcocite’s distinctive response is thought to be related to its forming a reversible oxidation‐reduction couple with cupric ions in solution. No other common sulfide mineral forms a reversible couple with its cations in solution. For the other minerals of this study, the lack of dependence on rotation implies that diffusion of active species in the electrolyte is not the controlling process. Possible alternate mechanisms include surface controlled processes such as surface diffusion or adsorption phenomena. Ancillary data obtained during this study indicate the interface impedance of chalcopyrite is proportional to the electrode potential which in turn can be controlled by rotation speed, electrolyte composition, or application of an external dc current or voltage. This implies that the surface concentration of active species is dependent on electrode potential.

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