Barium
Scavenging oxygen during the fabrication of vacuum tubes and aiding medical imaging of the digestive tract are two important applications of the element, barium.
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Barium is a soft, silvery metal in the alkaline earth group on the periodic table. Because it is extremely reactive with oxygen, barium is never found in nature as pure metal. Instead, it is found in salts, such as barium sulfate and barium carbonate. Barium’s name came from barys, a Greek word meaning heavy, no surprise given the high density of most of the ores that contain barium.
Barium’s high sensitivity to oxygen might seem like a disadvantage, but scientists have very creatively exploited that property. First, they isolated pure, metallic barium by electrolyzing barium chloride, and then packaged and stored under argon to prevent the barium from reacting with air. One use of pure barium’s affinity with oxygen is in the production of vacuum tubes, such as those originally used in televisions, radios, radar, and telephone networks. Engineers could not remove 100 percent of the air from vacuum tubes by attaching a vacuum pump to the system, but they could add barium, which would react with and remove small amounts of gas from the evacuated space. This technique is still important today for a variety of applications that depend on vacuum tubes, such as high-powered radio transmitters.
Barium salts also extremely toxic if ingested. Thus, it may seem curious that barium plays an important role in medicine. Barium is opaque to X-rays and makes an excellent radiocontrast agent, particularly for imaging a person’s digestive system. The key to success is in selecting the proper barium salt. Barium sulfate is extremely insoluble either in water or in the pH found in the stomach. As a result, a person can drink a solution of barium sulfate, undergo the X-ray tests, and later, the solution will pass from his body without causing any harm.
More information about barium may be found at http://en.wikipedia.org/wiki/Barium