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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 per decade).

  • 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.

  • Thermal runaway: 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 temperatures.

  • Thick cells: Conventional cells, such as crystalline silicon cells, which are typically from 4 to 17 mils thick. In contrast, thin-film cells are several microns thick.

  • 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 field.

  • 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 applications.

  • 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.