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ANODE/CATHODE
Anode: In an electrochemical cell, the electrode at which oxidation occurs; the positive electrode in an electrolytic cell and the
negative electrode in a voltaic cell.
Cathode: In an electrochemical cell, the electrode where reduction is occurring; the negative electrode in an electrolytic cell and
the positive electrode in a voltaic cell.
CORROSION POTENTIAL
The electrode potential at which anodic and cathodic rates of reaction are equal.
Symbolized Ecorr. Ecorr
is formally a mixed potential and refers to an electrode where metal oxidation is the
anodic reaction.
ELECTRICAL DOUBLE LAYER
Layer which forms at solid/liquid interfaces as a result of a net charge on the solid
surface (usually negative) causing a localized layer of neutralizing counterions (usually
positive) from the solution phase to form near the solid surface.
MICROBIALLY
INFLUENCED CORROSION (MIC) The microbially assisted establishment of an
electrochemical cell, or direct microbial stimulation of the anodic or cathodic reactions.
(Note: Though MIC is sometimes called Microbially Induced Corrosion, the use of the
word influenced is preferred by microbiologists.)
NOBLE A metal or alloy which in
nature occurs commonly in the free state. Also refers to the electrochemical state of
metals whose corrosion products are formed with a low negative or a positive free energy.
OVERPOTENTIAL (AKA overvoltage) The deviation of an electrode potential from
its equilibrium value required to produce a net flow of current across an
electrode/solution interface.
ACTIVATION OVERPOTENTIAL The electric potential difference over and above the
equilibrium value required to produce a net flow of current across an electrode/solution
interface.
CONCENTRATION OVERPOTENTIAL An electric potential difference caused by
differences in electroactive species concentration between bulk solution and the electrode
surface. Occurs when electrochemical reaction is sufficiently rapid to lower surface
concentration of electroactive species below that of bulk solution. Negligibly small when
reaction rate constant is much smaller than the mass transfer coefficient.
VALENCE VS. CHARGE OF
ION The valence is the number of loosely bound electrons a neutral atom
can give up or accept in forming a bond; it is a theoretical number. In ionic bonding the
electrons are completely transferred, and bonding is electrostatic. In purely covalent
bonding electron pairs are equally shared and only partially transferred. All degrees of
electron transfer are possible, resulting in differing extents of covalent and ionic
bonding. The charge of a species is the total number of protons minus the total
number of electrons multiplied by the charge of an electron. This again has only a rough
theoretical significance, since the charge on a species can be diffusely spread over a
large number of solvent molecules in solution (solvation shell).
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