A chemical element, lanthanum, symbol La, the second most abundant element in the rare earth group, is a metal. The naturally occurring element is made up of the isotopes and is one of the radioactive products of the fission of uranium, thorium, or plutonium. Lanthanum is the most basic of the rare earths and can be separated rapidly from other members of the rare earth series by fractional crystallization. Considerable quantities of it are separated commercially, because it is an important ingredient in glass manufacture. Lanthanum imparts a high refractive index to the glass and is used in the manufacture of expensive lenses. The metal is readily attacked in air and is rapidly converted to a white powder.
Lanthanum becomes a superconductor below about -267°C in both the hexagonal and face-centered crystal forms.
Lanthanum Oxide
Lanthanum oxide (La2O3) has a melting point of 2250°C, is soluble in acids, and very slightly soluble in water. This oxide of a rare earth element occurs in monazite and bastnasite. It is marketed as the oxide or as other salts such as the oxalate, nitrate, or hydrate. It quickly absorbs water and CO2 from the atmosphere.
Its chief use is as an ingredient in nonsilica, rare element optical glass with oxides of tungsten, tantalum, and thorium. Lanthanum increases refractive index, decreases dispersion, and is also used in x-ray image intensifying screens that speed up x-ray exposure as much as two to ten times so that diagnostic dosages may be reduced by as much as 80% with fewer retakes. It is also used in barium titanate capacitors.
