Thursday, January 17, 2008

Primary Batteries

Primary batteries are made today in hundreds of shapes and sizes and utilize several chemical reactions. Their development and production, however, has been a slow process. Alessandro Volta made the first battery, used flashlights, cameras and radios, was derived directly from battery developed by the French chemist George Leclanche in 1860s.

The battery in its original form had a zinc rod amalgamated with mercury as anode, a conducting mix of manganese dioxide (MnO2) and Carbon in porous pot as cathode, a central carbon rod or plate as current collector, and a saturated solution of ammonium chloride (NH4Cl) as electrolyte. The cell was assembled in a glass jar and produced about 1.5 volts. In spite of its lack of portability, it was widely used in telephones and doorbells until well into the 20th century and was an excellent example of a technical advance that became an immediate commercial success.

The modern dry cell replaced the liquid replace the liquid electrolyte with a paste consisting of a mixture of zinc chloride (ZnCl2) and NH4Cl. A zinc anode was fashioned as a cylindrical cell container, and the cathode remained MnO2 and Carbon.

In alkaline dry cell, the electrolyte is potassium hydroxide (KOH). A more recent innovation, this type of battery supplies larger currents and is used in radios, tape recorder, shavers, and hearing aids. Even higher currents are obtained when mercuric oxide (HgO) replaces the MnO2 as cathode.

Storage Battery
For many years in standard secondary (storage) system has been the lead-acid battery. Nickel-cadmium batteries have also become common. In recent years other type have been developed that are applicable to specialized demands.

The lead-acid battery was invented in 1860 by Gaston Plante. The electrolyte is sulfuric acid (H2SO4), the electrode are lead and lead dioxide (PbO2). Three or six cells are placed within a plastic or rubber container, the form seen in automobiles. Recently, small D-size batteries of this type have been introduced.

In more recent years the power demands of product such as portable recorders, calculators and implanted biochemical devices fostered a search for batteries with higher energy-to-weight ratios, more consistent voltage outputs, and longer lifetimes. Now in common use for such purposes are secondary nickel-cadmium batteries, in which cadmium serves as the negative electrode, nickel oxide (Ni2O3) as positive electrode, and KOH as the electrolyte.

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