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For camera lenses.
(Greek lanthanein, to lie hidden) Mosander in 1839 extracted a new earth lanthana, from
impure cerium nitrate and recognized the new element.
Lanthanum was isolated in relatively pure form in 1923. Iron exchange and solvent
extraction techniques have led to much easier isolation of the so-called
Lanthanum is found in rare-earth minerals such as cerite, monazite, allanite, and
bastnasite. Monazite and bastnasite are principal ores in which lanthanum occurs in
percentages up to 25 percent and 38 percent respectively. Misch metal, used in making
lighter flints, contains about 25 percent lanthanum.
The availability of lanthanum and other rare earths has improved greatly in recent
years. The metal can be produced by reducing the anhydrous fluoride with calcium .
Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife.
It is one of the most reactive of the rare-earth metals. It oxidizes rapidly when exposed
to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly.
The metal reacts directly with elemental carbon,
and with halogens.
At 310C, lanthanum changes from a hexagonal to a face-centered cubic structure, and at
865C it again transforms into a body-centered cubic structure.
Natural lanthanum is a mixture of two stable isotopes, 138La and 139La. Twenty three
other radioactive isotopes are recognized.
Rare-earth compounds containing lanthanum are extensively used in carbon lighting
applications, especially by the motion picture industry for studio lighting and
projection. This application consumes about 25 percent of the rare-earth compounds
produced. La2O3 improves the alkali resistance of glass, and is used in making special
optical glasses. Small amounts of lanthanum, as an additive, can be used to produce
nodular cast iron.
There is current interest in hydrogen sponge alloys containing lanthanum. These alloys
take up to 400 times their own volume of hydrogen gas, and the process is reversible.
Every time they take up the gas, heat energy is released; therefore these alloys have
possibilities in an energy conservation system.
Lanthanum and its compounds have a low to moderate acute toxicity rating; therefore,
care should be taken in handling them.
The metal costs about $5/g.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.