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Electrochemistry Dictionary - T
Tafel slope: the slope of the straight
line portion of a polarization curve, usually occurring at more than 50 mV from
the open-circuit potential, when presented in a semi-logarithmic plot in terms
of volts per logarithmic cycle of current density (commonly referred to as volts
Tafel line: See Tafel equation.
Tafel plot: See Tafel equation.
Tafel slope: See Tafel equation.
Taper charging: A charging regime delivering
moderately high rate of current when the battery is at a low state of charge
and tapering the charging current to lower rates as the battery is charged.
Terminal: The external electrical connection
posts of an electrochemical cell to which a power source or a load can be connected.
For example, in case of a battery, to which either a load (e.g., motor, light
bulb) can be connected to use the electrical energy of the battery, or to which
a charger can be connected to charge the battery. Every battery has only two
terminals (positive and negative) independent whether the battery contains one
or more cells internally. This term is also used for cell stacks and for electrolytic
cells. A terminal can also be called a "pole."
Tertiary current distribution: A current
distribution that is controlled by the resistivity of the solution (see primary
current distribution), the activation overpotential (see secondary current distribution),
and the concentration overpotential. The concentration changes occurring at
the working electrode surface affect the rate of the electrode reaction and
can therefore be considered as an additional surface resistivity.
Thermal battery: A type
of reserve cell which is activated by raising the temperature.
Thermal management: The
means whereby a battery system is maintained within a specified temperature
range while undergoing charge or discharge.
A process in which a cell undergoes an uncontrolled rise in temperature
due to the passage of increasing current (on, say, short-circuit discharge or
constant voltage charging) as the temperature rises.
Thermocell (thermogalvanic cell): A
galvanic cell consisting of two identical half cells that are kept at different
Conventional cells, such as crystalline silicon cells, which are
typically from 4 to 17 mils thick. In contrast, thin-film cells are several
Thin-film cells: Photovoltaic cells made
from a number of layers of photo-sensitive materials. These layers are typically
applied using a chemical vapor deposition process in the presence of an electric
Third kind electrode: See electrode
of the third kind.
Three-electrode cell: An electrochemical
cell containing a working electrode, a counter electrode, and a reference electrode.
A current may flow between the working and counter electrodes, while the potential
of the working electrode is measured against the reference electrode. This setup
can be used in basic research to investigate the kinetics and mechanism of the
electrode reaction occurring on the working electrode surface, or in electroanalytical
Throwing power: A qualitative term used
in electroplating to describe the ability of the system to produce a uniformly
thick deposit on the substrate surface. That is, the "throwing power" is considered
"good" when the current distribution is uniform even on an irregularly shaped
substrate. The throwing power is a function of both the geometrical arrangement
in the electroplating cell and the composition of the plating solution.
Totally-polarized electrode: Alternative
expression for ideal polarized electrode.
Transference number: See transport number.
Transition time: Characteristic time
in a chronopotentiometric experiment indicating the exhaustion of a reactant
concentration at the electrode surface. The potential of the electrode changes
sharply upon reaching the transition time.
Transport number: The fraction of the
total current carried in a solution by a given ion. Ions may carry drastically
different portions of the total current if their mobilities are different. E.g.,
in a solution of sodium chloride, less than half of the current is carried by
the positively charged sodium cations and more than half is carried by the negatively
charged chloride anions because the chloride ions are able to move faster (they
have a larger ionic mobility). The transport numbers of the anion and the cation
adds up to unity. As a matter of fact, the case when the ions move equally and
the transport number of both ions is equal to 0.5 is a rarity. The Hittorf method
is an experimental technique for the determination of the transport numbers.
Also called "transference number." For the simplest case of a solution of a
single salt of univalent ions, the transport numbers are defined as the mobility
of the ion divided by the sum of mobilities of the two ions. If there are more
than one solutes present (e.g., an acidified sodium chloride solution or a mixture
of sodium chloride and potassium bromide), every ion will have its own transport
number with the sum of them being unity. In these cases, the concentrations
of the ions must also be taken into account in the calculation of the transport
numbers, and in the case of polyvalent ions, the charges of the ions must also
be accounted for.
Trickle charging: A method of maintaining
a rechargeable battery in a fully charged condition by continuous, long-term,
slow-rate charging, at a level sufficient to balance self-discharge and occasional
discharge. Also called "boost charging." See also float charging.
True current density: See current density.
True electrode area: The surface area
of an electrode taking into consideration the surface roughness. For a perfectly
smooth electrode, it is equal to the geometric electrode area, but it is larger
than that for most electrodes. The ratio of the two defines the roughness factor.
Tuberculation: Development or formation
of small mounds of corrosion products on the inside of steel or iron pipes.
These tubercles roughen the inside of the pipe, increasing its resistance to
water flow and the possibility of erosion corrosion.
Two-electrode cell: A classical electrochemical
cell containing two electrodes.