Chromium is widely used to make stainless steel, an alloy with iron and other elements. Last year, almost 22 million tonnes of chromium ore were mined all over the world.
Physical properties: Chromium is a silver-gray metal that shines brightly when polished. It is odorless, tasteless and malleable. Chromium is a very hard metal (8.5 on a 10 point scale), with moderate density (7.19 gram/cm3), that melts at 1907C and boils at 2671C. It is a good conductor of heat and electricity.
Chemical properties: Chromium got its name from the Greek word "chroma" which means color. Chromium forms colorful compounds such as Chromium Fluoride (green), Chromium Oxide (deep red) and Silver Chromate (brown). Traces of chromium in gemstones give them dramatic colors. When chromium is exposed to the environment, Chromium Oxide forms a passive layer on the surface, keeping corrosion at bay. This is why chromium is widely used to prevent rusting on steel objects like cars, planes and cutlery. Chromium is also used to give objects a shiny look, like the fenders of a car.
It is often impurities that give some gems their brilliant colors. Chromium impurities make rubies red, and cobalt impurities make sapphires blue.
History: While common metals like iron and copper have been known from pre-historic times, scientists have only known about chromium for two hundred years. When the German prospector Johann Gottlieb Lehmann (1719-1767) first discovered chromium ore (crocoite) in 1761, he thought it was a mixture of selenium and lead, a heavy metal. Chromium was first identified as an individual element by Nicolas-Louis Vauquelin (1763-1829) in 1797. He also found trace samples of chromium in ruby and emerald gemstones, and figured out that the chromium gives the crystals their color.
Production: Chromium ore deposits take two main shapes, depending on how the ore formed by cooling from a hot liquid. The more common shape is a thin layer, called stratiforms, when the molten ore cooled on the surface. The less common form is in chunks, which formed when molten chromium ore cooled underground. South Africa, Kazakhstan, India, Turkey, and Russia are the main producers of chromium today. Chromium is separated from the ore through smelting. During smelting, fuel and ore are put in a large furnace and heated together. The burning coke fuel reacts with the ore, and hot liquid chromium sinks to the bottom. It is then cooled for use by factories and businesses. Pie Chart of Top 5 Chromium Producing Countries...
Uses: Chromium is used to protect surfaces from corrosion. It makes and keeps objects like vehicles, kitchen utensils and electric parts shiny. Chromium is also the element that makes stainless steel "stainless". It does so by coating the steel with a thin shiny layer of chromium that keeps rust out. Chromium is also used for making paints and dyes. The leather tanning industry also uses several chromium salts.
Health: Small amounts of chromium, the variety known as Chromium III, are good for the body. Chromium III is found in black pepper, broccoli, fruit juices and some meats like turkey. It is said to help dieting, reduce cholesterol and change blood sugar into energy for the body. Scientists think that chromium helps the body respond properly to insulin. People who eat too little chromium cannot absorb blood sugar very easily. Most people need 28 nanograms of chromium a day. Another variety of chromium, Chromium VI, is toxic, and sometimes leaks out of factories as industrial waste. It can cause asthma, nosebleeds and nasty rashes on the body. Some old industrial sites have dangerous amounts of chromium in their soil.
Lepora, Nathan. Chromium, 2006: The Elements, Marshall Cavendish, USA.
Chromium, Wikipedia. <http://en.wikipedia.org/wiki/Chromium> accessed on 14-Feb-2009.
Cadmium, Mineral Information Institute. <http://www.mii.org/Minerals/photochrom.html> accessed on 20-March-2009.