Cadmium
Cadmium is a metal element that has an atomic number of 48, an atomic weight of 112.41, and is denoted by the atomic symbol Cd. It has a silvery-white luster with a bluish cast. It can be cut with a knife, making it one of the softest of the elements. Chemically, it behaves very much like zinc, the element above it in the periodic table. The element is obtained as a by-product of the preparation of zinc, copper, and lead from their ores.
Cadmium was discovered in 1817 by Dr. Friedrich Stromeyer (or Strohmeyer). Stromeyer was born in Göttingen, Germany, on August 2, 1776. He studied botany, chemistry, medicine, and pharmacy at the University of Göttingen before moving to Paris, France, where he became a pupil of the famous chemist Louis Vauquelin. Stromeyer developed a special interest in mineralogy while studying under Vauquelin.
In 1802, Stromeyer became an instructor at Göttingen and, in 1810, was appointed full professor of chemistry. In addition, he was appointed an inspector general for the state of Hanover. His job was to inspect all the apothecaries (pharmacies) in the state.
On one occasion, Stromeyer found a sample of zinc carbonate mislabeled as zinc oxide. When he analyzed the compound, he found that it did not behave chemically as it should. Pure zinc carbonate, when heated, becomes zinc oxide. Both compounds are white. So one should observe no color change when pure zinc carbonate is heated. Instead, Stromeyer found that his sample of zinc carbonate became first pale yellow, then almost orange as it was heated.
Upon further analysis, Stromeyer was able to show that his sample of zinc carbonate contained an impurity, a compound of a new element that he named cadmium. The name cadmium was derived from the Greek word kadmeia, an old name for zinc carbonate. It reflects the fact that, in nature, cadmium and its compounds are most commonly found in association with zinc compounds.
The most common cadmium-containing mineral is greenockite, cadmium sulfide (CdS). The element's abundance in the earth's crust amounts to no more than about 2 parts in 10 million.
Cadmium is often mixed with other metals to form low-melting point alloys, such as Abel's, Lipowitz's, Newton's, and Wood 's metals. One type of dental amalgam consists of an alloy containing one part cadmium and four parts mercury.
Control rods in nuclear power plants are often made of cadmium. Since the metal absorbs neutrons readily, the rate at which nuclear fission occurs in the reactor core can be controlled by raising and lowering the cadmium control rods.
Cadmium metal is often used to electroplate other metals. The cadmium coating protects against some chemicals and against corrosion, is easy to solder, and provides an attractive finish. Although the cost of cadmium electroplating is high, it may be justified by the special properties offered.
Compounds of cadmium are used in nickel-cadmium batteries (cadmium oxide, CdO), in solar cells (cadmium sulfide, CdS), and in paints (both cadmium oxide and cadmium sulfide).
Cadmium and its compounds are highly toxic. Symptoms of cadmium poisioning include nausea, vomiting, choking, diarrhea, abdominal pain, headache, and respiratory distress. The element is believed to be responsible for a serious outbreak of itai-itai disease in Japan in 1955. The name itai-itai translates as " ouch-ouch," an indication of the pain felt by those who had ingested rice oil contaminated with cadmium. The maximum exposure level for cadmium has been set at 0.05 milligrams per kilogram in food and 0.1 mg per cubic meter of air.
This is the complete article, containing 576 words
(approx. 2 pages at 300 words per page).
