Dysprosium

Dysprosium,  ₆₆Dy

General properties
Name, symbol	dysprosium, Dy
Pronunciation	/dɪsˈproʊziəm/ dis-PROH-zee-əm
Appearance	silvery white
Dysprosium in the periodic table
– ↑ Dy ↓ Cf terbium ← dysprosium → holmium
Atomic number (Z)	66
Group, block	group n/a, f-block
Period	period 6
Element category	lanthanide
Standard atomic weight (±) (Ar)	162.500(1)
Electron configuration	[Xe] 4f10 6s2
per shell	2, 8, 18, 28, 8, 2
Physical properties
Phase	solid
Melting point	1680 K ​(1407 °C, ​2565 °F)
Boiling point	2840 K ​(2562 °C, ​4653 °F)
Density near r.t.	8.540 g/cm3
when liquid, at m.p.	8.37 g/cm3
Heat of fusion	11.06 kJ/mol
Heat of vaporization	280 kJ/mol
Molar heat capacity	27.7 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1378 1523 (1704) (1954) (2304) (2831)
Atomic properties
Oxidation states	4, 3, 2, 1 ​(a weakly basic oxide)
Electronegativity	Pauling scale: 1.22
Ionization energies	1st: 573.0 kJ/mol 2nd: 1130 kJ/mol 3rd: 2200 kJ/mol
Atomic radius	empirical: 178 pm
Covalent radius	192±7 pm
Miscellanea
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	2710 m/s (at 20 °C)
Thermal expansion	α, poly: 9.9 µm/(m·K) (r.t.)
Thermal conductivity	10.7 W/(m·K)
Electrical resistivity	α, poly: 926 nΩ·m (r.t.)
Magnetic ordering	paramagnetic at 300 K
Magnetic susceptibility (χmol)	+103,500·10−6 cm3/mol (293.2 K)
Young's modulus	α form: 61.4 GPa
Shear modulus	α form: 24.7 GPa
Bulk modulus	α form: 40.5 GPa
Poisson ratio	α form: 0.247
Vickers hardness	410–550 MPa
Brinell hardness	500–1050 MPa
CAS Number	7429-91-6
History
Discovery	Lecoq de Boisbaudran (1886)
Most stable isotopes of dysprosium
iso NA half-life DM DE (MeV) DP 154Dy syn 3.0×106 y α 2.947 150Gd 156Dy 0.056% is stable with 90 neutrons 158Dy 0.095% is stable with 92 neutrons 160Dy 2.329% is stable with 94 neutrons 161Dy 18.889% is stable with 95 neutrons 162Dy 25.475% is stable with 96 neutrons 163Dy 24.896% is stable with 97 neutrons 164Dy 28.260% is stable with 98 neutrons

Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime. Naturally occurring dysprosium is composed of seven isotopes, the most abundant of which is ¹⁶⁴Dy.

Dysprosium was first identified in 1886 by Paul Émile Lecoq de Boisbaudran, but it was not isolated in pure form until the development of ion exchange techniques in the 1950s. Dysprosium has relatively few applications that cannot be made by other chemical elements. It is used for its high thermal neutron absorption cross-section in making control rods in nuclear reactors, for its high magnetic susceptibility in data storage applications, and as a component of Terfenol-D (a magnetostrictive material). Soluble dysprosium salts are mildly toxic, while the insoluble salts are considered non-toxic.

Characteristics

Physical properties

Dysprosium sample

Dysprosium is a rare earth element that has a metallic, bright silver luster. It is soft enough to be cut with a knife, and can be machined without sparking if overheating is avoided. Dysprosium's physical characteristics can be greatly affected by even small amounts of impurities.

Dysprosium and holmium have the highest magnetic strengths of the elements, especially at low temperatures. Dysprosium has a simple ferromagnetic ordering at temperatures below 85 K (−188.2 °C). Above 85 K (−188.2 °C), it turns into an helical antiferromagnetic state in which all of the atomic moments in a particular basal plane layer are parallel, and oriented at a fixed angle to the moments of adjacent layers. This unusual antiferromagnetism transforms into a disordered (paramagnetic) state at 179 K (−94 °C).

Chemical properties

Dysprosium metal tarnishes slowly in air and burns readily to form dysprosium(III) oxide:

4 Dy + 3 O₂ → 2 Dy₂O₃

Dysprosium is quite electropositive and reacts slowly with cold water (and quite quickly with hot water) to form dysprosium hydroxide:

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

Dysprosium metal vigorously reacts with all the halogens at above 200 °C:

2 Dy (s) + 3 F₂ (g) → 2 DyF₃ (s) [green]

2 Dy (s) + 3 Cl₂ (g) → 2 DyCl₃ (s) [white]

2 Dy (s) + 3 Br₂ (g) → 2 DyBr₃ (s) [white]

2 Dy (s) + 3 I₂ (g) → 2 DyI₃ (s) [green]

Dysprosium dissolves readily in dilute sulfuric acid to form solutions containing the yellow Dy(III) ions, which exist as a [Dy(OH₂)₉]³⁺ complex:

2 Dy (s) + 3 H₂SO₄ (aq) → 2 Dy³⁺ (aq) + 3 SO2−
4 (aq) + 3 H₂ (g)

The resulting compound, dysprosium(III) sulfate, is noticeably paramagnetic.

Compounds

Dysprosium sulfate, Dy₂(SO₄)₃

See also: Dysprosium compounds

Dysprosium halides, such as DyF₃ and DyBr₃, tend to take on a yellow color. Dysprosium oxide, also known as dysprosia, is a white powder that is highly magnetic, more so than iron oxide.

Dysprosium combines with various non-metals at high temperatures to form binary compounds with varying composition and oxidation states +3 and sometimes +2, such as DyN, DyP, DyH₂ and DyH₃; DyS, DyS₂, Dy₂S₃ and Dy₅S₇; DyB₂, DyB₄, DyB₆ and DyB₁₂, as well as Dy₃C and Dy₂C₃.

Dysprosium carbonate, Dy₂(CO₃)₃, and dysprosium sulfate, Dy₂(SO₄)₃, result from similar reactions. Most dysprosium compounds are soluble in water, though dysprosium carbonate tetrahydrate (Dy₂(CO₃)₃·4H₂O) and dysprosium oxalate decahydrate (Dy₂(C₂O₄)₃·10H₂O) are both insoluble in water. Two of the most abundant dysprosium carbonates, tengerite-(Dy) (Dy₂(CO₃)₃·2–3H₂O) and kozoite-(Dy) (DyCO₃(OH)) are known to form via a poorly ordered (amorphous) precursor phase with a formula of Dy₂(CO₃)₃·4H₂O. This amorphous precursor consists of highly hydrated spherical nanoparticles of 10–20 nm diameter that are exceptionally stable under dry treatment at ambient and high temperatures.

Isotopes

Main article: Isotopes of dysprosium

Naturally occurring dysprosium is composed of seven isotopes: ¹⁵⁶Dy, ¹⁵⁸Dy, ¹⁶⁰Dy, ¹⁶¹Dy, ¹⁶²Dy, ¹⁶³Dy, and ¹⁶⁴Dy. These are all considered stable, although ¹⁵⁶Dy decays by alpha decay with a half-life of over 1×10¹⁸ years. Of the naturally occurring isotopes, ¹⁶⁴Dy is the most abundant at 28%, followed by ¹⁶²Dy at 26%. The least abundant is ¹⁵⁶Dy at 0.06%.

Twenty-nine radioisotopes have also been synthesized, ranging in atomic mass from 138 to 173. The most stable of these is ¹⁵⁴Dy, with a half-life of approximately 3×10⁶ years, followed by ¹⁵⁹Dym with a half-life of 144.4 days. The least stable is ¹³⁸Dy, with a half-life of 200 ms. As a general rule, isotopes that are lighter than the stable isotopes tend to decay primarily by β⁺ decay, while those that are heavier tend to decay by β⁻ decay. However, ¹⁵⁴Dy decays primarily by alpha decay, and ¹⁵²Dy and ¹⁵⁹Dy decay primarily by electron capture. Dysprosium also has at least 11 metastable isomers, ranging in atomic mass from 140 to 165. The most stable of these is ^165mDy, which has a half-life of 1.257 minutes. ¹⁴⁹Dy has two metastable isomers, the second of which, ^149m2Dy, has a half-life of 28 ns.

History

In 1878, erbium ores were found to contain the oxides of holmium and thulium. French chemist Paul Émile Lecoq de Boisbaudran, while working with holmium oxide, separated dysprosium oxide from it in Paris in 1886. His procedure for isolating the dysprosium involved dissolving dysprosium oxide in acid, then adding ammonia to precipitate the hydroxide. He was only able to isolate dysprosium from its oxide after more than 30 attempts at his procedure. On succeeding, he named the element dysprosium from the Greek dysprositos (δυσπρόσιτος), meaning "hard to get". The element was not isolated in relatively pure form until after the development of ion exchange techniques by Frank Spedding at Iowa State University in the early 1950s.

Occurrence

Xenotime

While dysprosium is never encountered as a free element, it is found in many minerals, including xenotime, fergusonite, gadolinite, euxenite, polycrase, blomstrandine, monazite and bastnäsite; often with erbium and holmium or other rare earth elements. Currently, most dysprosium is being obtained from the ion-adsorption clay ores of southern China, and future sources will include the Halls Creek region in Western Australia. In the high-yttrium version of these, dysprosium happens to be the most abundant of the heavy lanthanides, comprising up to 7–8% of the concentrate (as compared to about 65% for yttrium). The concentration of Dy in the Earth's crust is about 5.2 mg/kg and in sea water 0.9 ng/L.

Production

Dysprosium is obtained primarily from monazite sand, a mixture of various phosphates. The metal is obtained as a by-product in the commercial extraction of yttrium. In isolating dysprosium, most of the unwanted metals can be removed magnetically or by a flotation process. Dysprosium can then be separated from other rare earth metals by an ion exchange displacement process. The resulting dysprosium ions can then react with either fluorine or chlorine to form dysprosium fluoride, DyF₃, or dysprosium chloride, DyCl₃. These compounds can be reduced using either calcium or lithium metals in the following reactions:

3 Ca + 2 DyF₃ → 2 Dy + 3 CaF₂

3 Li + DyCl₃ → Dy + 3 LiCl

The components are placed in a tantalum crucible and fired in a helium atmosphere. As the reaction progresses, the resulting halide compounds and molten dysprosium separate due to differences in density. When the mixture cools, the dysprosium can be cut away from the impurities.

About 100 tonnes of dysprosium are produced worldwide each year, with 99% of that total produced in China. Dysprosium prices have climbed nearly twentyfold, from $7 per pound in 2003, to $130 a pound in late 2010. The price increased to $1,400/kg in 2011 but fell to $240 in 2015, largely due to illegal production in China which circumvented government restrictions.

According to the United States Department of Energy, the wide range of its current and projected uses, together with the lack of any immediately suitable replacement, makes dysprosium the single most critical element for emerging clean energy technologies - even their most conservative projections predict a shortfall of dysprosium before 2015. As of late 2015, there is a nascent rare earth (including dysprosium) extraction industry in Australia.

Applications

There are not many applications unique to dysprosium. Theodore Gray wrote in his book The Elements: A Visual Exploration of Every Known Atom in the Universe "Look up dysprosium, and you have to go to the fourth page of results before finding anything that isn't a periodic table website's entry for dysprosium, usually an obligatory 'It's an element, so we have to have a page about it' sort of page."

Dysprosium is used, in conjunction with vanadium and other elements, in making laser materials and commercial lighting. Because of dysprosium's high thermal-neutron absorption cross-section, dysprosium-oxide–nickel cermets are used in neutron-absorbing control rods in nuclear reactors. Dysprosium–cadmium chalcogenides are sources of infrared radiation, which is useful for studying chemical reactions. Because dysprosium and its compounds are highly susceptible to magnetization, they are employed in various data-storage applications, such as in hard disks. Dysprosium is increasingly in demand for the permanent magnets used in electric car motors and wind turbine generators.

Neodymium–iron–boron magnets can have up to 6% of the neodymium substituted by dysprosium to raise the coercivity for demanding applications, such as drive motors for electric vehicles and generators for wind turbines. This substitution would require up to 100 grams of dysprosium per electric car produced. Based on Toyota's projected 2 million units per year, the use of dysprosium in applications such as this would quickly exhaust its available supply. The dysprosium substitution may also be useful in other applications because it improves the corrosion resistance of the magnets.

Dysprosium is one of the components of Terfenol-D, along with iron and terbium. Terfenol-D has the highest room-temperature magnetostriction of any known material; which is employed in transducers, wide-band mechanical resonators, and high-precision liquid-fuel injectors.

Dysprosium is used in dosimeters for measuring ionizing radiation. Crystals of calcium sulfate or calcium fluoride are doped with dysprosium. When these crystals are exposed to radiation, the dysprosium atoms become excited and luminescent. The luminescence can be measured to determine the degree of exposure to which the dosimeter has been subjected.

Nanofibers of dysprosium compounds have high strength and a large surface area. Therefore, they can be used to reinforce other materials and act as a catalyst. Fibers of dysprosium oxide fluoride can be produced by heating an aqueous solution of DyBr₃ and NaF to 450 °C at 450 bars for 17 hours. This material is remarkably robust, surviving over 100 hours in various aqueous solutions at temperatures exceeding 400 °C without redissolving or aggregating.

Dysprosium iodide and dysprosium bromide are used in high-intensity metal-halide lamps. These compounds dissociate near the hot center of the lamp, releasing isolated dysprosium atoms. The latter re-emit light in the green and red part of the spectrum, thereby effectively producing bright light.

Several paramagnetic crystal salts of dysprosium (Dysprosium Gallium Garnet, DGG; Dysprosium Aluminum Garnet, DAG; Dysprosium Iron Garnet, DyIG) are used in adiabatic demagnetization refrigerators.

The trivalent dysprosium ion (Dy³⁺) has been studied due its downshifting luminescence properties. Dy-doped yttrium aluminium garnet (YAG:Dy) excited in the ultraviolet region of the electromagnetic spectrum results in the emission of photons of longer wavelength in the visible region. This idea is the basis for a new generation of UV-pumped white light emitting diodes.

Precautions

Like many powders, dysprosium powder may present an explosion hazard when mixed with air and when an ignition source is present. Thin foils of the substance can also be ignited by sparks or by static electricity. Dysprosium fires cannot be put out by water. It can react with water to produce flammable hydrogen gas. Dysprosium chloride fires, however, can be extinguished with water, while dysprosium fluoride and dysprosium oxide are non-flammable. Dysprosium nitrate, Dy(NO₃)₃, is a strong oxidizing agent and will readily ignite on contact with organic substances.

Soluble dysprosium salts, such as dysprosium chloride and dysprosium nitrate, are mildly toxic when ingested. Based on the toxicity of dysprosium chloride to mice, it is estimated that the ingestion of 500 grams or more could be fatal to a human. The insoluble salts, however, are non-toxic.

External links

• WebElements.com – Dysprosium
• It's Elemental – Dysprosium