holmium

67 dysprosium ← holmium → erbium - ↑ Ho ↓ Es Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	holmium, Ho, 67
Element category	lanthanides
Group, Period, Block	n/a, 6, f
Appearance	silvery white
Standard atomic weight	164.93032(2)  g·mol−1
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·cm−3
Liquid density at m.p.	8.34  g·cm−3
Melting point	1734 K (1461 °C, 2662 °F)
Boiling point	2993 K (2720 °C, 4928 °F)
Heat of fusion	17.0  kJ·mol−1
Heat of vaporization	265  kJ·mol−1
Specific heat capacity	(25 °C) 27.15  J·mol−1·K−1
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−1
	2nd:  1140  kJ·mol−1
	3rd:  2204  kJ·mol−1
Atomic radius	176  pm
Covalent radius	192±7  pm
Miscellaneous
Magnetic ordering	paramagnetic
Electrical resistivity	(r.t.) (poly) 814 nΩ·m
Thermal conductivity	(300 K) 16.2  W·m−1·K−1
Thermal expansion	(r.t.) (poly) 11.2 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 2760 m/s
Young's modulus	64.8  GPa
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
Most-stable isotopes
Main article: Isotopes of holmium iso NA half-life DM DE (MeV) DP 163Ho syn 4570 yr ε 0.003 163Dy 164Ho syn 29 min ε 0.987 164Dy 165Ho 100% 165Ho is stable with 98 neutrons 166Ho syn 26.763 h β− 1.855 166Er 167Ho syn 3.1 h β− 1.007 167Er
References

Holmium (pronounced /ˈhoʊlmiəm/) is a chemical element with the symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a relatively soft and malleable silvery-white metallic element, which is stable in dry air at room temperature. A rare earth metal, it is found in the minerals monazite and gadolinite. Holmium has the highest magnetic strength of any element and therefore is used for the polepieces of the strongest static magnets. Because holmium can absorb nuclear fission-bred neutrons, it is also used in nuclear control rods.

Characteristics

Physical

Ho₂O₃, left: natural light, right: fluorescent lamp light

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.

Holmium oxide has some fairly dramatic color changes depending on the lighting conditions. In daylight, it is a tannish yellow color. Under trichromatic light, it is a fiery orange red, almost indistinguishable from the way erbium oxide looks under this same lighting. This is related to the sharp emission bands of the phosphors.^[1]

A trivalent metallic rare earth element, holmium has the highest magnetic moment (10.6 µ_B) of any naturally-occurring element and possesses other unusual magnetic properties. When combined with yttrium, it forms highly magnetic compounds.^[2]

Chemical

Holmium metal tarnishes slowly in air and burns readily to form holmium(III) oxide:

4 Ho + 3 O₂ → 2 Ho₂O₃

Holmium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form holmium hydroxide:

2 Ho(s) + 6 H₂O(g) → 2 Ho(OH)₃(aq) + 3H₂(g)

Holmium metal reacts with all the halogens:

2 Ho(s) + 3 F₂(g) → 2 HoF₃(s) [pink]

2 Ho(s) + 3 Cl₂(g) → 2 HoCl₃(s) [yellow]

2 Ho(s) + 3 Br₂(g) → 2 HoBr₃(s) [yellow]

2 Ho(s) + 3 I₂(g) → 2 HoI₃(s) [yellow]

Holmium dissolves readily in dilute sulphuric acid to form solutions containing the yellow Ho(III) ions, which exist as a [Ho(OH₂)₉]³⁺ complexes:^[3]

2 Ho(s) + 3 H₂SO₄(aq) → 2 Ho³⁺(aq) + 3 SO₄^2-(aq) + 3 H₂(g)

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 ground-state half lives not greater than 1.117 days, and most have half lives under 3 hours. However, the metastable ^166m1Ho has a half life of around 1200 years because of its high spin. This fact, combined with a high excitation energy resulting in a particularly rich spectrum of decay gamma rays produced when the metastable state de-excites, makes this isotope useful in nuclear physics experiments as a means for calibrating energy responses and intrinsic efficiencies of gamma ray spectrometers.

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").^[4][5] Later in 1878, Per Teodor Cleve independently discovered the element while he was working on erbia earth (erbium oxide).^[6][7]

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.^[8]

Occurrence and production

Gadolinite

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. The main mining areas are China, United States, Brazil, India, Sri Lanka and Australia with reserves of holmium estimated as 400,000 tonnes.^[8]

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.^[9] Its estimated abundance in the Earth's crust is 1.3 mg/kg. Holmium obeys the Oddo-Harkins rule: as an odd-numbered element, it is less abundant than its immediate even numbered neighbors, dysprosium and erbium. However, it is the most abundant of the odd-numbered heavy lanthanides. The principal current source are some of the ion-adsorption clays of southern China. Some of these have a rare-earth composition similar to that found in xenotime or gadolinite. Yttrium makes up about two-thirds of the total by weight; holmium is around 1.5%. The original ores themselves are very lean, maybe only 0.1% total lanthanide, but are easily extracted.^[10] Holmium is relatively inexpensive for a rare-earth metal with the price about US$ 1000 per kg.^[11]

Applications

Holmium has the highest magnetic strength of any element and therefore is 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, it is also used in nuclear control rods.^[8]

Holmium is used 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 lasers emit at 2.08 microns and therefore are safe to eyes. They are used in medical, dental and fiber-optical applications.^[2]

Holmium is one of the colorants used for cubic zirconia and glass, providing yellow or red coloring.^[12] Holmium-containing glass has sharp asorption peaks in the spectral range 200-900 nm. It is therefore used as a calibration standard for UV/visible spectrophotometers^[13] and is available commercially.^[14]

The radioactive but long-lived Ho-166m1 (see "Isotopes" below) is used in calibration of gamma ray spectrometers.^[15]

Precautions

The element, as with other rare earths, appears to have a low degree of acute toxicity. Holmium plays no biological role in humans but may be able to stimulate metabolism.^[9]

See also

• Holmium compounds

References

• Guide to the Elements – Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1

External links

Wikimedia Commons has media related to: Holmium

Look up holmium in Wiktionary, the free dictionary.

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