Holmium is achemical element; it hassymbolHo andatomic number 67. It is arare-earth element and the eleventh member of thelanthanide series of elements. It is a relatively soft, silvery, fairlycorrosion-resistant andmalleable metal. Like many other lanthanides, holmium is too reactive to be found in native form, as pure holmium slowly forms a yellowishoxide coating when exposed to air. When isolated, holmium is relatively stable in dry air at room temperature. However, it reacts with water and corrodes readily, and also burns in air when heated.
In nature, holmium occurs together with the other rare-earth metals (likethulium). It is a relatively rare lanthanide, making up 1.4parts per million of theEarth's crust, an abundance similar totungsten. Holmium was discovered through isolation by Swedish chemistPer Theodor Cleve. It was also independently discovered byJacques-Louis Soret andMarc Delafontaine, who together observed itspectroscopically in 1878. Its oxide was first isolated from rare-earth ores by Cleve in 1878. The element's name comes fromHolmia, the Latin name for the city ofStockholm.[8][9][10]
Like many otherlanthanides, holmium is found in the mineralsmonazite andgadolinite and is usually commercially extracted from monazite usingion-exchange techniques. Its compounds in nature and in nearly all of its laboratory chemistry are trivalently oxidized, containing Ho(III)ions. Trivalent holmium ions havefluorescent properties similar to many other rare-earth ions (while yielding their own set of uniqueemission light lines), and thus are used in the same way as some other rare earths in certainlaser and glass-colorant applications.
With a boiling point of 3,000 K (2,727 °C; 4,940 °F), holmium is the sixth mostvolatile lanthanide afterytterbium,europium,samarium,thulium anddysprosium. At standard temperature and pressure, holmium, like many of the second half of the lanthanides, normally assumes ahexagonally close-packed (hcp) structure.[11] Its 67electrons are arranged in the configuration [Xe] 4f11 6s2, so that it has thirteenvalence electrons filling the 4f and 6s subshells.[12]
Holmium, like all of the lanthanides, isparamagnetic at standard temperature and pressure.[13] However, holmium isferromagnetic at temperatures below 19 K (−254.2 °C; −425.5 °F).[14] It has the highestmagnetic moment (10.6 μB) of any naturally occurring element[15] and possesses other unusual magnetic properties. When combined withyttrium, it forms highlymagnetic compounds.[16]
Chemical properties
Holmium metal tarnishes slowly in air, forming a yellowish oxide layer that has an appearance similar to that ofiron rust. It burns readily to formholmium(III) oxide:[17]
4 Ho + 3 O2 → 2 Ho2O3
It is a relatively soft andmalleable element that is fairlycorrosion-resistant and chemically stable in dry air atstandard temperature and pressure. In moist air and at higher temperatures, however, it quicklyoxidizes, forming a yellowish oxide.[18] In pure form, holmium possesses a metallic, bright silvery luster.
Holmium is quite electropositive: on the Paulingelectronegativity scale, it has an electronegativity of 1.23.[19] It is generally trivalent. It reacts slowly with cold water and quickly with hot water to form holmium(III) hydroxide:[20]
2 Ho (s) + 6 H2O (l) → 2 Ho(OH)3 (aq) + 3 H2 (g)
Holmium metal reacts with all the stablehalogens:[21]
Holmium dissolves readily in dilutesulfuric acid to formsolutions containing the yellow Ho(III) ions, which exist as a [Ho(OH2)9]3+ complexes:[21]
2 Ho (s) + 3 H2SO4 (aq) → 2 Ho3+ (aq) + 3SO2− 4 (aq) + 3 H2 (g)
Oxidation states
As with many lanthanides, holmium is usually found in the +3oxidation state, forming compounds such asholmium(III) fluoride (HoF3) andholmium(III) chloride (HoCl3). Holmium in solution is in the form of Ho3+ surrounded by nine molecules of water. Holmium dissolves inacids.[15] However, holmium is also found to exist in +2, +1 and 0 oxidation states.[22][12]
The known isotopes of holmium range from140Ho to175Ho. The primarydecay mode before thestable165Ho, isbeta plus decay todysprosium isotopes, and the primary mode after isbeta minus decay toerbium isotopes. Of the 35synthetic radioactive isotopes among these, the most stable one is holmium-163 (163Ho), with a half-life of 4570 years.[24] The next most stable is holmium-166 (166Ho) having a half-life of 26.812 hours, and others have half-lives under 4 hours.
Themetastable isomer166m1Ho has the unusually long half-life of 1133 years. With a very low excitation energy, it does not decay to the ground state but beta-decays directly, having a particularly rich spectrum ofgamma rays, making this isotope useful as a means forcalibratinggamma ray spectrometers.[25]
Holmium-166 (ground state) has been studied for medical application.[26][27]
Compounds
Oxides and chalcogenides
Ho2O3, left: natural light, right: under acold-cathode fluorescent lamp
Holmium(III) oxide is the only oxide of holmium. It changes its color depending on the lighting conditions. In daylight, it has a yellowish color. Undertrichromatic light, it appears orange red, almost indistinguishable from the appearance of erbium oxide under the same lighting conditions.[28] The color change is related to the sharpemission lines of trivalent holmium ions acting as red phosphors.[29] Holmium(III) oxide appears pink under a cold-cathode fluorescent lamp.
All four trihalides of holmium are known. Holmium(III) fluoride is a yellowish powder that can be produced by reacting holmium(III) oxide andammonium fluoride, then crystallising it from the ammoniumsalt formed in solution.[35] Holmium(III) chloride can be prepared in a similar way, withammonium chloride instead of ammonium fluoride.[36] It has theYCl3 layer structure in the solid state.[37] These compounds, as well as holmium(III) bromide and holmium(III) iodide, can be obtained by the direct reaction of the elements:[21]
The Swedish chemistPer Teodor Cleve also independently discovered the element while he was working onerbia earth (erbium oxide). He was the first to isolate impure oxide of the new element.[9][8][42] Using the method developed by the Swedish chemistCarl 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 substanceholmia (after the Latin name for Cleve's home town, Stockholm) and the green onethulia.Holmia was later found to be theholmium oxide, andthulia wasthulium oxide.[43] The pure oxide was only isolated in 1911 and the metal in 1939 by Heinrich Bommer.[44]: 959 [45]
In the English physicistHenry Moseley's classic paper onatomic numbers, holmium was assigned the value 66. The holmium preparation he had been given to investigate had been impure, dominated by neighboring dysprosium. He would have seenx-ray emission lines for both elements, but assumed that the dominant ones belonged to holmium, instead of the dysprosium impurity.[46]
Like all the otherrare-earth elements, holmium is not naturally found as afree element. It occurs combined with other elements in gadolinite,monazite and other rare-earth minerals. No holmium-dominant mineral has yet been found. The main mining areas are China, United States, Brazil, India, Sri Lanka, and Australia with reserves of holmium estimated as 400,000 tonnes.[43] The annual production of holmium metal is of about 10 tonnes per year.[47]
Holmium makes up 1.3 parts per million of theEarth's crust by mass.[48] Holmium makes up 1 part per million of thesoils, 400 parts perquadrillion of seawater, and almost none ofEarth's atmosphere, which is very rare for a lanthanide.[43] It makes up 500 parts per trillion of the universe by mass.[49]
Holmium is commercially extracted byion exchange from monazite sand (0.05% holmium), but is still difficult to separate from other rare earths. The element has been isolated through thereduction of itsanhydrouschloride orfluoride with metalliccalcium.[30] Its estimated abundance in the Earth's crust is 1.3 mg/kg. Holmium obeys theOddo–Harkins rule: as an odd-numbered element, it is less abundant than both dysprosium and erbium. However, it is the most abundant of the odd-numbered heavylanthanides. Of the lanthanides, onlypromethium,thulium, lutetium and terbium are less abundant on Earth. 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 inxenotime or gadolinite. Yttrium makes up about two-thirds of the total by mass; holmium is around 1.5%.[50] Holmium is relatively inexpensive for a rare-earth metal with the price about 1000 USD/kg.[51]
Applications
A solution of 4% holmium oxide in 10% perchloric acid, permanently fused into a quartzcuvette as an optical calibration standard
Holmium is used to create the strongest artificially generatedmagnetic fields, when placed within high-strength magnets as a magnetic pole piece (also called a magnetic flux concentrator).[56] Holmium is also used in the manufacture of somepermanent magnets.
Holmium can act as a sensitizer in sodium yttrium fluoride which takes advantage of its absorption in theNIR-II window. Holmium allows for lanthanide nanomaterials to have tunable emission and excitation in the NIR-II. Under 1143 nm excitation the interfacial energy transfer to other lanthanides allows a redshift in emission for biological applications.[57] This allows deeper penetration than typically used 980 nm and 808 nm lasers.
Since holmium can absorbnuclear fission-bred neutrons, it is used as aburnable poison to regulate nuclear reactors.[43] It is used as acolorant forcubic zirconia, providing pink coloring,[60] and forglass, providing yellow-orange coloring.[61] In March 2017,IBM announced that they had developed a technique to store onebit of data on a single holmium atom set on a bed ofmagnesium oxide.[62] With sufficient quantum and classical control techniques, holmium may be a good candidate to makequantum computers.[63]
Holmium is used in the medical field, particularly inlaser surgery for procedures such as kidney stone removal and prostate treatment, due to its precision and minimal tissue damage.[64][65] Itsisotope, holmium-166, is applied in targeted cancer therapies, especially for liver cancer,[66] and it also enhancesMRI imaging as a contrast agent.[67]
Biological role and precautions
Holmium plays nobiological role in humans, but its salts are able to stimulatemetabolism.[30] Humans typically consume about a milligram of holmium a year. Plants do not readily take up holmium from the soil. Some vegetables have had their holmium content measured, and it amounted to 100 parts per trillion.[68] Holmium and its soluble salts are slightly toxic if ingested, but insoluble holmium salts arenontoxic. Metallic holmium in dust form presents a fire and explosion hazard.[69][70][71] Large amounts of holmium salts can cause severe damage ifinhaled, consumedorally, orinjected. The biological effects of holmium over a long period of time are not known. Holmium has a low level ofacute toxicity.[72]
^abArblaster, John W. (2018).Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International.ISBN978-1-62708-155-9.
^Yttrium and all lanthanides except Ce, Pm, Tm, and Yb have been observed in the oxidation state 0 in bis(1,3,5-tri-t-butylbenzene) complexes, seeCloke, F. Geoffrey N. (1993). "Zero Oxidation State Compounds of Scandium, Yttrium, and the Lanthanides".Chem. Soc. Rev.22:17–24.doi:10.1039/CS9932200017. andArnold, Polly L.; Petrukhina, Marina A.; Bochenkov, Vladimir E.; Shabatina, Tatyana I.; Zagorskii, Vyacheslav V.; Cloke (2003-12-15). "Arene complexation of Sm, Eu, Tm and Yb atoms: a variable temperature spectroscopic investigation".Journal of Organometallic Chemistry.688 (1–2):49–55.doi:10.1016/j.jorganchem.2003.08.028.
^All thelanthanides, except Pm, in the +2 oxidation state have been observed in organometallic molecular complexes, seeLanthanides Topple Assumptions andMeyer, G. (2014). "All the Lanthanides Do It and Even Uranium Does Oxidation State +2".Angewandte Chemie International Edition.53 (14):3550–51.doi:10.1002/anie.201311325.PMID24616202.. Additionally, all thelanthanides (La–Lu) form dihydrides (LnH2), dicarbides (LnC2), monosulfides (LnS), monoselenides (LnSe), and monotellurides (LnTe), but for most elements these compounds have Ln3+ ions with electrons delocalized into conduction bands, e. g. Ln3+(H−)2(e−).
^Naumann, R. A.; Michel, M. C.; Power, J. L. (September 1960). "Preparation of long-lived holmium-163".Journal of Inorganic and Nuclear Chemistry.15 (1–2):195–196.doi:10.1016/0022-1902(60)80035-8.OSTI4120223.
^Ganjali, Mohammad Reza; Gupta, Vinod Kumar; Faridbod, Farnoush; Norouzi, Parviz (2016-02-25).Lanthanides Series Determination by Various Analytical Methods. p. 27.
^Su, Yiguo; Li, Guangshe; Chen, Xiaobo; Liu, Junjie; Li, Liping (2008). "Hydrothermal Synthesis of GdVO4:Ho3+ Nanorods with a Novel White-light Emission".Chemistry Letters.37 (7):762–763.doi:10.1246/cl.2008.762.
^abcC. R. Hammond (2000).The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC press.ISBN0-8493-0481-4.
^Travis, John C.; Zwinkels, Joanne C.; Mercader, Flora; et al. (2002-06-05). "An International Evaluation of Holmium Oxide Solution Reference Materials for Wavelength Calibration in Molecular Absorption Spectrophotometry".Analytical Chemistry.74 (14):3408–3415.Bibcode:2002AnaCh..74.3408T.doi:10.1021/ac0255680.ISSN0003-2700.PMID12139047.
^Wollin, T. A.; Denstedt, J. D. (Feb 1998). "The holmium laser in urology".Journal of Clinical Laser Medicine & Surgery.16 (1):13–20.doi:10.1089/clm.1998.16.13.PMID9728125.
^Younis, Zaid; Ayyed, Atheer (2024). "Influence of stone location on rate of stone clearance and complication for holmium laser lithotripsy".International Journal of Urology Research.6 (1):84–90.doi:10.33545/26646617.2024.v6.i1b.38.
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