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Cr, A. Jonathan Buhalis
CHROMIUM
by Jonathan Buhalis

History

"Chrome" as a reflective finish is probably more familiar than the actual metal it comes from. In the late 18th century, that metal was an unknown component of brightly colored minerals from the Ural mountains that were used as pigments in paint. French chemist Louis Nicolas Vauquelin spent two years analyzing these minerals, culminating in 1797 in the discovery of a new metal. Vauquelin also detected his new metal in beryl, that is, emeralds, and also in rubies.

emerald gemstone, A. Jonathan BuhalisRubies, emeralds, and paint pigments – the new metal was named from the Greek chroma meaning "color". Indeed, chromium makes many brightly colored compounds that for decades were its primary use. Such compounds are used to color paint, enamel, and glass.

Chromium as a pigment is actually a minority use in modern times. Chromium plating on steel was developed as electroplating became commonplace in the 19th century. Also in that century, the ability of chromium alloy was recognized to protect steel from corrosion. Stainless steel that includes around 18% chromium was developed in the early 20th century.

Mining and Production

Chromium occurs in a few minerals, but the only one commercially mined is chromite, an oxide of iron and chromium. South Africa is the biggest producer, followed by Kazakhstan and India.

Chromium is produced from its ore by smelting with coal and an active metal such as aluminum that will strip away the oxygen. Since most chromium (95%) is used in alloying with steel, it is normally traded and shipped in the form of ferrochromium (an excessively rich alloy) rather than the pure metal.

Properties and Uses

Chromium as a metal is lustrous and hard, but almost never used in its pure form. By far the biggest use for chromium is in stainless steel, so called because it "stains less". This is the preferred alloy of steel when looks and durability are more important than extreme levels of hardness or toughness.

Chrome finish is a thin layer of chromium deposited on (usually) steel to form an attractive shiny surface that also hinders corrosion. The chromium (immediately converted to chromium oxide) layer is actually thin enough to be transparent; the shine is the underlying steel.

Comparatively small amounts of chromium are still used in pigments for paint and dye.
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Content by Jonathan Buhalis
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