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History

Holmium (Holmia, Latin name for Stockholm) was discovered by Marc Delafontaine and Jacques-Louis Soret in 1878 who noticed the aberrant spectrographic absorption bands of the then-unknown element (they called it "Element X").  Later in 1879, Per Teodor Cleve, a Swedish chemist, independently discovered the element while he was working on erbia earth (erbium oxide).

Using the method developed by Carl Gustaf Mosander to discover lanthanum, erbium and terbium, Cleve looked for impurities in the oxides of other rare earth element.    He started with erbia, the oxide of erbium (Er₂O₃), and removed all of the known contaminants.  The result of that effort was two new materials, one brown and one green.   He named the brown substance holmia (after the Latinized name for Cleve's home town, Stockholm) and the green one thulia.  Holmia is the oxide of the element holmium and thulia is the oxide of the element thulium.  Holmium's absorption spectrum was observed earlier that year by J. L. Soret and M. Delafontaine, Swiss chemists.

Characteristics

Like most of the rare-earth metals, holmium is a relatively soft and malleable element that is fairly corrosion-resistant and stable in dry air at standard temperature and pressure.  In moist air and at higher temperatures, however, it quickly oxidizes; forming a yellowish oxide.  In pure form, holmium possesses a metallic, bright silvery luster.

Like most of the other rare-earth metals, it is silvery and soft, and can be pounded or rolled into very thin sheets. At normal temperatures it is fairly inert but will oxidize at high temperatures and humidities.

Holmium is generally obtained from monazite sand, where it is present to the extent of about 0.05%. Most holmium use is confined to research.

A trivalent metallic rare earth element, holmium has the highest magnetic moment (10.6µB) of any naturally-occurring element and possesses other unusual magnetic properties.  When combined with yttrium, it forms highly magnetic compounds.

Occurrence

Like all other rare earths, holmium is not naturally found as a free element. It does occur combined with other elements in the minerals gadolinite, monazite, and in other rare-earth minerals.  It is commercially extracted via ion-exchange from monazite sand (0.05% holmium) but is still difficult to separate from other rare earths. The element has been isolated through the reduction of its anhydrous chloride or fluoride with metallic calcium.  Its estimated abundance in the Earth's crust is 1.3 milligrams per kilogram.

Applications

Because of its magnetic properties, holmium has been used to create the strongest artificially-generated magnetic fields when placed within high-strength magnets as a magnetic pole piece (also called a magnetic flux concentrator).  Since it can absorb nuclear fission -bred neutrons, the element is also used in nuclear control rods.   Other commercial applications of the element include;

• its very high magnetic moment is suitable for use in yttrium-iron-garnet (YIG) and yttrium-lanthanum-fluoride (YLF) solid state lasers found in microwave equipment (which are in turn found in a variety of medical and dental settings).

• Holmium oxide is used as a yellow glass coloring.
• Holmium is used in a laser to break up kidney stones while being minimally invasive.

Few other uses have been identified for this element.

Compounds

Holmium forms no commercially important compounds. Some of holmium's compounds include: holmium oxide (Ho₂O₃), holmium fluoride (HoF₃) and holmium iodide (HoI₃).

Isotopes

Natural holmium contains one stable isotope, holmium-165.  Some synthetic radioactive isotopes are known, the most stable one is holmium 163, with a half life of 4570 years.  All other radioisotopes have half lives not greater than 1.117 days, and most have half lives under 3 hours.

Precautions

The element, as with other rare earths, appears to have a low acute toxic rating.   Holmium plays no biological role in humans but may be able to stimulate metabolism.