Controlled rapid charging

Controlled rapid charge timed, voltage-time control, voltage-temperaturecontrol. 

This is understood to imply a charge period of less than 1 h. (When the period is less than 15 min ihe charge is called ultrarapid see below.) Controlled rapid charge implies that there is a system that interrupts the charge before the cells or battery reaches an overcharge state that is mechanically excessive (that is. could oiu t the case). 

Few redox systems exhibit purely reversible control over any reasonable range of a.c. frequencies because the a.c. experiment is faster than the d.c., and effects arising from a slow electron-transfer step show up more dramatically. Therefore, it is more practical to list the characteristics of quasireversible a.c. waves (Table 2). In the present context, use of the term quasireversible is not restricted to couples with values < 10 cm s . Even reasonably rapid charge-transfer processes exhibit slower than reversible behavior at high a.c. frequencies. 

The great advantage of the RDE over other teclmiques, such as cyclic voltannnetry or potential-step, is the possibility of varying the rate of mass transport to the electrode surface over a large range and in a controlled way, without the need for rapid changes in electrode potential, which lead to double-layer charging current contributions. 

A second approach to coulometry is to use a constant current in place of a constant potential (Figure 11.23). Controlled-current coulometry, also known as amperostatic coulometry or coulometric titrimetry, has two advantages over controlled-potential coulometry. First, using a constant current makes for a more rapid analysis since the current does not decrease over time. Thus, a typical analysis time for controlled-current coulometry is less than 10 min, as opposed to approximately 30-60 min for controlled-potential coulometry. Second, with a constant current the total charge is simply the product of current and time (equation 11.24). A method for integrating the current-time curve, therefore, is not necessary. 

Copper and silver combined with refractory metals, such as tungsten, tungsten carbide, and molybdenum, are the principal materials for electrical contacts. A mixture of the powders is pressed and sintered, or a previously pressed and sintered refractory matrix is infiltrated with molten copper or silver in a separate heating operation. The composition is controlled by the porosity of the refractory matrix. Copper—tungsten contacts are used primarily in power-circuit breakers and transformer-tap charges. They are confined to an oil bath because of the rapid oxidation of copper in air. Copper—tungsten carbide compositions are used where greater mechanical wear resistance is necessary. 

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