 |
 |
 |
 |
 |
|
|
|
|
|
![[image of flower]](../../ima/flowXS_04.gif)
Batteries |
|
The battery is a device that tranforms chemical power into electrical and power. It is the progenitor of all electrical devices, equipment and machinery, comparable in technological importance to the steam engine. Although many battery applications eventually were replaced by electric motors, the mobility of the battery makes it an important source of electrical power today. Electronic watches, notebook computers, calculators, cell phones, digital cameras, satellites, flashlights, engine igniters, portable radios, televisions, and medical equipment, and many other devices and machines that cannot be connected by wiring to a stationary power source require batteries. Battery research and development has continued from its introduction in 1800 to the present day because of continued demands for more mobile power with longer life and less recharging, weight and cost. A battery is an electrochemical (Galvanic) cell where metals dissolve at different rates in two separate half-cells, each containing an electrolyte, such as sulfuric acid, leaving some electrons in the rest of the metal, which charges it. A salt barrier ("bridge") is placed between the two half-cells to provide electrical contact between them, but without the solutions mixing. This can simply be a strip of filter paper soaked in saturated potassium nitrate solution. The different dissolving rates in the two half-cells cause an unequal number of electrons in the two metals, which results in an electric potential (voltage) between them. If an electrical conductor, such as a wire, connects the two metals, an electric current (electricity) flows. At the same time, ions of the more active metal, which forms the anode, are transferred through the electrolyte to the less active metal, the cathode, and deposited there as a plating, so the anode is consumed (corroded). Some batteries, called primary batteries, are nonrechargeable, e.g., flashlight. In rechargeable batteries (secondary batteries), e.g., automobile, the chemical process can be reversed by a generator, which restores the metals to their original condition. The chemical process in a battery is similar to that in an electrolytic cell, since it is a group of them connected in series or in parallel. Word n.p. Electricity at this time is a scientific curiosity. Static charge is generated by friction and when the amount of charge become large, it arcs across poles as electricity (by definition, moving electric charge) to the amazement of onlookers. A person was often put into the circuit so that the observers could see his hair stand on end. (The person was not killed because the electric current was very small, so its force could not stop a heart.) No useful work is done. This status would change forever by an Italian named Alessandro Volta. In early 1800, Alessandro Volta, an Italian scientist, invents the "voltaic pile", a laboratory version of what would become the battery. Volta first used salt solutions (brine) in bowls that were connected by metal strips. The strips had one end made of copper and the other end made of either tin or zinc. Electricity flows in the strips. He improves this device by making a pile of alternating copper, zinc, and brine-impregnated cardboard disks. A wire is placed between the copper disk at the bottom and the zinc disk at the top. The wire is connected to a switch to open and close both ends of the wire. When the switch is closed, an electric current flowed through the wire. His device is called Volta's pile or a voltaic pile, what would later be called a battery. Asimov 279 This invention stimulates other inventors to improve on his invention and make it do useful work, such as plating metals and running electric lights, electric motors, telegraphs and telephones. Months after Volta's success, William Cruikshank convertes Volta's pile into a workable battery. Singer 177 In 1800, Johann Ritter, a German physicist, passes an electric current through a solution of copper sulfate and copper formed on the the cathode. This begins electroplating, which eventually will develop into an important industry. Asimov 280 Volta's battery was a revolutionary source of energy and power, but it was a laboratory version, and not a practical source of electricity for running machinery. Several other inventors following him tried to improve his battery, but they were all erratic sources of electric current. However, in 1836, the British chemist, John Daniell, produces a battery, eventually called the Daniell cell that uses copper and zinc electrodes to produce a steady current. Asimov 335 These batteries have the serious defect that after the chemicals are used up, the battery must be discarded, thus making them wasteful and costly. In 1859, the French physicist, Gaston Planté, invents a battery that can be recharged. He insulates two sheets of lead with a rubber sheet between them, rolls the plates into a spiral, and places it into a dilute sulfuric acid container. This arrangement produces a battery that can be recharged by passing an electric current through it. This is the first storage battery. Asimov 378 The storage battery invented by Gaston Planté uses a liquid electrolyte, so it is heavy and not easy to move. An improvemement based on the work done between 1867 and 1877 by Georges Leclanché in France results in the dry cell battery, in which the electrolyte is a damp paste, ammonium chloride, with no liquid to leak out. Therefore, this dry cell battery is much more portable than the lead-acid storage battery. In the modern cylindrical flashlight battery, zinc forms the outer casing, which is the cathode, while the anode is composed of a mixture of graphite (carbon) and manganese dioxide depolarizer around a graphite rod to remove the hydrogen that forms. This battery is good only for intermittent work because under constant use the hydrogen forms faster than it can be removed. How 238 |
 |
|
|
|
|
