The ratio of
current density at a point X on an
interface to the
average current density (
) is called the
relative local current density. The current distribution is described by the function
(or more generally,
where
or
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
where
is the
conductivity of the solution,
the slope of the
overpotential-current curve under the above conditions and
a characteristic length of the system, for instance the radius of a disc electrode.
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
Cite as:
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.
doi:10.1351/goldbook.
