m: The letter "m" when used as a prefix
before a unit symbol indicates a multiplier of 10-3. Symbol of "milli".
E.g., mV = 10-3 volt, one millivolt, one thousandth of a volt.
M: The letter "M" when used as a prefix
before a unit symbol indicates a multiplier of 106. Abbreviation
of "meg" or "mega". E.g., MΩ = 106 ohm, one megohm, one million ohms.
(The symbol is the letter "M" followed by the "Greek capital omega" letter,
some browsers unfortunately do not support this.)
letter "μ" when used as a prefix
before a unit symbol indicates a multiplier of 10-6. Abbreviation
of "micro". E.g., μV = 10-6 volt, one microvolt, one millionth of
mA: Symbol and abbreviation of milliampere
(= 10-3 ampere, one thousandth of an ampere).
μA: Symbol and abbreviation of microampere
(= 10-6 ampere, one millionth of an ampere).
phenomena occurring under the influence of magnetic field.
Maintenance: The procedures
which are required in order to keep a battery in proper operating conditions.
They may include trickle-charging to compensate for self-discharge, addition
of water to the electrolyte, etc.
Maintenance-free battery: A rechargeable
battery which does not require periodic "topping up" (addition of water) to
maintain electrolyte volume. See also sealed battery.
Mass transport: The phenomenon of movement
(transportation) of mass (e.g., chemical compounds, ions) from one part of the
system to another. Most of the time this occurs through diffusion and convection.
Under special circumstances it can also occur through electromigration since
the movement of the electrically charged ions also carries mass with them (e.g.,
ionic current through an ion-exchange membrane. The mass transport and the charge
transport are typically "decoupled" in electrochemistry; that is, the reacting
species and the charge carrying species are not necessarily identical. E.g.,
one would intuitively assume that during electroplating of copper from a solution
of copper sulfate all the mass and charge required for the electrode reaction
at the cathode would be carried by the copper cations in the solution. That
is not the case at all. In the presence of a large excess of supporting electrolyte,
all the current is carried by electromigration of the ions of the supporting
electrolyte (both in the bulk solution and in the diffusion layer) while all
the mass is carried by the copper ions by convection in the bulk solution and
by diffusion in the diffusion layer. In the absence of any supporting electrolyte,
all the mass is still carried by the copper ions, while the current is divided
between the copper cations and the sulfate anions according to the ratio of
their transport numbers (both in the bulk electrolyte and in the diffusion layer).
The situation is maybe more self-explanatory in the case of an electrically
neutral molecule reactant that cannot carry any current.
Mass-transport overpotential (polarization):
See concentration overpotential.
Measuring electrode: See working electrode.
Mediated reaction: See indirect electrolysis.
Mediator: See indirect electrolysis.
Meg or mega: When used as a prefix before
a unit name it indicates a multiplier of 106. E.g., megohm = 106
ohm, one million ohms. Symbol: "M".
Megohm: 106 ohm, symbol:
"MΩ" (one million ohms). (The symbol is the letter "M" followed by the "Greek
capital omega" letter, some browsers unfortunately do not support this.)
Membrane: See separator.
Membrane electrode: An ion-selective
electrode assembly terminating in an ion permeable (e.g., ion-exchange) membrane
sensing element. The membrane separates the internal filling solution (that
contains a fixed concentration of the ion to be detected) and the test solution.
The potential across the membrane depends on the concentration ratio of the
ion in the two solutions. The assembly also contains an internal reference electrode
immersed in the filling solution, serving as an electrical contact with a stable
potential. The potential of this assembly is then measured against an external
reference electrode immersed in the test solution. See also Donnan potential.
Membrane potential: See Donnan potential.
Metal deposition/dissolution: A class
of electrode reactions involving oxidation/reduction of a solid metal and its
dissolved ion, e.g., if a copper metal rod is immersed in a copper sulfate solution,
the copper cations can be cathodically reduced to copper metal, or the copper
metal can be anodically oxidized to copper ions. Compare with a redox reaction
where both the oxidized and the reduced species are in solution. The terms "electrodeposition"
and "electrodissolution" are often used to describe these reactions. These reactions
are used in many technologies, such as electroplating, electrowinning, and electrorefining.
And also in electrogravimetry.
Metal displacement reaction: See cementation.
Metal plating: See electroplating.
Metal refining: See electrorefining.
mho: Alternative name of siemens.
micro: When used as a prefix before
a unit name it indicates a multiplier of 10-6. E.g., microvolt =
10-6 volt, one millionth of a volt. Symbol: "µ".
microampere: 10-6 ampere,
symbol: "μA" (one millionth of an ampere).
microelectrode: A small electrode, with
dimensions not larger than a few millimeters, and typically with dimensions
of a small fraction of a millimeter.
microvolt: 10-6 volt, symbol:
"μV" (one millionth of a volt).
Migration: See electromigration.
milli: When used as a prefix before
a unit name it indicates a multiplier of 10-3. E.g., millivolt =
10-3 volt, one thousandth of a volt. Symbol: "m".
milliampere: 10-3 ampere,
symbol: "mA" (one thousandth of an ampere).
millivolt: 10-3 volt, symbol:
"mV" (one thousandth of a volt).
Mixed potential: The electrode potential
when two electrode reactions occur on the same electrode surface. The mixed
potential has a value in between the equilibrium potentials of the two electrode
reactions. The mixed potential is a steady-state phenomena, with the corrosion
potential being a good example.
MΩ: Symbol and abbreviation of megohm
(= 106 ohm, one million ohms). (The symbol is the letter "M" followed by the
"Greek capital omega" letter, some browsers unfortunately do not support this.)
Mobility, ionic: See ionic mobility.
mol: The measurement unit and symbol
mole: See gram-mole.
Molar concentration: See concentration.
Molarity: See concentration.
Molecular weight: The weight of a molecule
of a compound that may be calculated as the sum of the atomic weights of its
Molecule: The smallest physical unit
of a substance that retains all the physical and chemical properties of that
substance. It may consist of a single atom or of a group of atoms bonded together
Molten-carbonate fuel cell: A fuel cell
that employs a molten, ionically conductive salt (carbonate) as electrolyte.
Due to the high melting point of these salts, these fuel cells must operate
at high temperatures.
Multimeter: Instrument that can be used
for the measurement of more than one parameter. Typically, it can be used to
measure current, potential, and resistance.
mV: Symbol and abbreviation of millivolt
(= 10-3 volt, one thousandth of a volt).
μV: Symbol and abbreviation of microvolt
(= 10-6 volt, one millionth of a volt).