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The ratio of current density at a point X on an interface to the average current density (Math - ei) is called the relative local current density. The current distribution is described by the function Math - ei (or more generally, Math - ei where Math - text or Math - text are the coordinates of the points of the electrode-solution interface. The primary current distribution is that which establishes itself when the influence of overpotential is negligible. The secondary current distribution is that which establishes itself when the influence of the overpotential cannot be neglected but concentration overpotential is negligible. The secondary distribution is often described in terms of dimensionless numbers of the form
Math - e
where Math - text is the conductivity of the solution, Math - ei the slope of the overpotential-current curve under the above conditions and Math - text a characteristic length of the system, for instance the radius of a disc electrode. Math - text is the Wagner number. It is a quantity which determines the throwing power and characterizes the equalizing influence of overpotential on the current distribution. In electroplating the throwing power is qualitatively defined as 'the ability of a solution to deposit metal uniformly upon a cathode of irregular shape'. The tertiary current distribution is that which establishes itself when the influence of the overpotential (including concentration overpotential) cannot be neglected.
Source:
PAC, 1981, 53, 1827 (Nomenclature for transport phenomena in electrolytic systems) on page 1836
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.
Last update: 2008-10-07; version: 2.0.2.
DOI of this term: https://doi.org/10.1351/goldbook.C01456.
Original PDF version (may be out of date): http://www.iupac.org/goldbook/C01456.pdf.
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