Holmium

67 dysprosium ← holmium → erbium - ↑ Ho ↓ Es periodic table
General
Name, Symbol, Number	holmium, Ho, 67
Chemical series	lanthanides
Group, Period, Block	n/a, 6, f
Appearance	silvery white
Atomic mass	164.93032(2) g/mol
Electron configuration	[Xe] 4f11 6s2
Electrons per shell	2, 8, 18, 29, 8, 2
Physical properties
Phase	solid
Density (near r.t.)	8.79 g/cm³
Liquid density at m.p.	8.34 g/cm³
Melting point	1734 K (1461 °C, 2662 °F)
Boiling point	2993 K (2720 °C, 4928 °F)
Heat of fusion	17.0 kJ/mol
Heat of vaporization	265 kJ/mol
Heat capacity	(25 °C) 27.15 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1432 1584 (1775) (2040) (2410) (2964)
Atomic properties
Crystal structure	hexagonal
Oxidation states	3 (basic oxide)
Electronegativity	1.23 (Pauling scale)
Ionization energies (more)	1st: 581.0 kJ/mol
	2nd: 1140 kJ/mol
	3rd: 2204 kJ/mol
Atomic radius	175 pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	(r.t.) (poly) 814 nΩ·m
Thermal conductivity	(300 K) 16.2 W/(m·K)
Thermal expansion	(r.t.) (poly) 11.2 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 2760 m/s
Speed of sound (thin rod)	(r.t.) 64.8 m/s
Shear modulus	26.3 GPa
Bulk modulus	40.2 GPa
Poisson ratio	0.231
Vickers hardness	481 MPa
Brinell hardness	746 MPa
CAS registry number	7440-60-0
Notable isotopes
Main article: [[Isotopes of {{{isotopesof}}}]] iso NA half-life DM DE (MeV) DP 163Ho syn 4570 a ε 0.003 163Dy 164Ho syn 29 min ε 0.987 164Dy 165Ho 100% Ho is stable with 98 neutrons 166Ho syn 26,763 h β- 1.855 166Er 167Ho syn 3,1 h β- 1.007 167Er

Holmium (chemical symbol Ho, atomic number 67) is a relatively soft, silvery-white metallic element that is stable in dry air at room temperature. It is a member of the lanthanide series and is sometimes called a "rare earth metal."

Of all the naturally occurring elements, holmium has the highest magnetic moment. It has therefore been used in high-strength magnets to create the strongest artificially generated magnetic fields. In addition, it is suitable for placement in yttrium-iron-garnet (YIG) and yttrium-lanthanum-fluoride (YLF) solid state lasers found in microwave equipment used for medical and dental procedures. Holmium is also useful in nuclear control rods to absorb neutrons produced by nuclear fission reactions and in a certain type of laser to break up kidney stones. Holmium oxide is used as a yellow glass coloring.

Occurrence and isolation

Like the other rare earth elements, holmium is not found as a free element in nature. It occurs combined with other elements in rare-earth minerals, particularly gadolinite and monazite. Its estimated abundance in the Earth's crust is 1.3 milligrams per kilogram.

Holmium is commercially extracted by ion-exchange from monazite sand (0.05% holmium), but it remains difficult to separate from other rare earth elements. It has been isolated through the reduction of its anhydrous chloride or fluoride with metallic calcium.

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 1878, Per Teodor Cleve independently discovered the element while he was working on erbia earth (erbium oxide).

Using the method developed by Carl Gustaf Mosander, Cleve first removed all of the known contaminants from erbia. The result of that effort was two new materials, one brown and one green. He named the brown substance holmia (after the Latin name for Cleve's home town, Stockholm) and the green one thulia. Holmia was later found to be the holmium oxide and thulia was thulium oxide.

Notable characteristics

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.

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.

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.

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.

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.

See also

• Holmium compounds

References

ISBN links support NWE through referral fees

• Los Alamos National Laboratory – Holmium
• Guide to the Elements – Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
• It's Elemental – Holmium

External links

• WebElements.com – Holmium (also used as a reference)
• American Elements – Holmium (also used as a reference)

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