Praseodymium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol
A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
Pr and the
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
59. It is the third member of the
lanthanide
The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...
series and is considered to be one of the
rare-earth metal
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silve ...
s. It is a soft, silvery, malleable and ductile
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.
Praseodymium always occurs naturally together with the other rare-earth metals. It is the sixth-most abundant rare-earth element and fourth-most abundant lanthanide, making up 9.1
parts per million of the Earth's crust, an abundance similar to that of
boron
Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...
. In 1841, Swedish chemist
Carl Gustav Mosander
Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedes, Swedish chemist. He discovered the rare earth elements lanthanum, erbium and terbium.
Early life and education
Born in Kalmar, Mosander attended school there until he ...
extracted a rare-earth oxide residue he called
didymium
Didymium ( el, , twin) is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially with a gas (propane)-powered forge, where it provides a filter that selectively blocks t ...
from a residue he called "lanthana", in turn separated from
cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...
salts. In 1885, the Austrian chemist
Baron
Baron is a rank of nobility or title of honour, often hereditary, in various European countries, either current or historical. The female equivalent is baroness. Typically, the title denotes an aristocrat who ranks higher than a lord or knig ...
Carl Auer von Welsbach separated didymium into two elements that gave salts of different colours, which he named praseodymium and
neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes i ...
. The name praseodymium comes from the Ancient Greek (), meaning '
leek
The leek is a vegetable, a cultivar of ''Allium ampeloprasum'', the broadleaf wild leek ( syn. ''Allium porrum''). The edible part of the plant is a bundle of leaf sheaths that is sometimes erroneously called a stem or stalk. The genus ''Alli ...
-green', and () 'twin'.
Like most
rare-earth elements, praseodymium most readily forms the +3
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
, which is the only stable state in
aqueous solution
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
, although the +4 oxidation state is known in some solid compounds and, uniquely among the lanthanides, the +5 oxidation state is attainable in
matrix-isolation conditions. The 0, +1, and +2 oxidation states are rarely found. Aqueous praseodymium ions are yellowish-green, and similarly, praseodymium results in various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its ability to filter yellow light from light sources.
Properties
Physical properties
Praseodymium is the third member of the
lanthanide
The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttr ...
series, and a member of the
rare-earth metals
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silve ...
. In the
periodic table
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
, it appears between the lanthanides
cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...
to its left and
neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes i ...
to its right, and above the
actinide
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...
protactinium. It is a
ductile metal with a hardness comparable to that of
silver
Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
.
Its 59 electrons are arranged in the
configuration
Configuration or configurations may refer to:
Computing
* Computer configuration or system configuration
* Configuration file, a software file used to configure the initial settings for a computer program
* Configurator, also known as choice board ...
ef
36s
2; theoretically, all five outer electrons can act as
valence electrons, but the use of all five requires extreme conditions and normally, praseodymium only gives up three or sometimes four electrons in its compounds.
[Greenwood and Earnshaw, pp. 1232–5]
Like most other metals in the lanthanide series, praseodymium usually only uses three electrons as valence electrons, as afterward the remaining 4f electrons are too strongly bound: this is because the 4f orbitals penetrate the most through the inert xenon core of electrons to the nucleus, followed by 5d and 6s, and this increases with higher ionic charge. Praseodymium nevertheless can continue losing a fourth and even occasionally a fifth valence electron because it comes very early in the lanthanide series, where the nuclear charge is still low enough and the 4f subshell energy high enough to allow the removal of further valence electrons.
[Greenwood and Earnshaw, pp. 1235–8] Thus, similarly to the other early trivalent lanthanides, praseodymium has a
double hexagonal close-packed crystal structure at room temperature. At about 560 °C, it transitions to a
face-centered cubic structure, and a
body-centered cubic structure appears shortly before the melting point of 935 °C.
Praseodymium, like all of the lanthanides (except
lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...
,
ytterbium, and
lutetium, which have no unpaired 4f electrons), is
paramagnetic at room temperature. Unlike some other rare-earth metals, which show
antiferromagnetic or
ferromagnetic
Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...
ordering at low temperatures, praseodymium is paramagnetic at all temperatures above 1 K.
Isotopes
Praseodymium has only one stable and naturally occurring isotope,
141Pr. It is thus a
mononuclidic and
monoisotopic element, and its
standard atomic weight
The standard atomic weight of a chemical element (symbol ''A''r°(E) for element "E") is the weighted arithmetic mean of the relative isotopic masses of all isotopes of that element weighted by each isotope's abundance on Earth. For example, is ...
can be determined with high precision as it is a constant of nature. This isotope has 82 neutrons, which is a
magic number that confers additional stability.
This isotope is produced in stars through the
s- and
r-process
In nuclear astrophysics, the rapid neutron-capture process, also known as the ''r''-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", ...
es (slow and rapid neutron capture, respectively).
38 other radioisotopes have been synthesized. All of these isotopes have half-lives under a day (and most under a minute), with the single exception of
143Pr with a half-life of 13.6 days. Both
143Pr and
141Pr occur as
fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...
s of
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
. The primary decay mode of isotopes lighter than
141Pr is
positron emission or
electron capture
Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...
to
isotopes of cerium
Naturally occurring cerium (58Ce) is composed of 4 stable isotopes: 136Ce, 138Ce, 140Ce, and 142Ce, with 140Ce being the most abundant (88.48% natural abundance) and the only one theoretically stable; 136Ce, 138Ce, and 142Ce are predicted to under ...
, while that of heavier isotopes is
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
to
isotopes of neodymium
Naturally occurring neodymium (60Nd) is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and 2 long-lived radioisotopes, 144Nd and 150Nd. In all, 33 radioisotopes of ...
.
Chemical properties
![Praseodymium(III) hydroxide](https://upload.wikimedia.org/wikipedia/commons/1/19/Praseodymium%28III%29_hydroxide.jpg)
Praseodymium metal tarnishes slowly in air, forming a
spalling
Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...
green oxide layer like
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
rust; a centimetre-sized sample of praseodymium metal corrodes completely in about a year. It burns readily at 150 °C to form
praseodymium(III,IV) oxide
Praseodymium(III,IV) oxide is the inorganic compound with the formula that is insoluble in water. It has a cubic fluorite structure. It is the most stable form of praseodymium oxide at ambient temperature and pressure.
Properties and structure ...
, a
nonstoichiometric compound
In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...
approximating to Pr
6O
11:
:12 Pr + 11 O
2 → 2 Pr
6O
11
This may be reduced to
praseodymium(III) oxide
Praseodymium(III) oxide, praseodymium oxide or praseodymia is the chemical compound composed of praseodymium and oxygen with the formula Pr2O3. It forms light green hexagonal crystals. Praseodymium(III) oxide crystallizes in the manganese(III) oxi ...
(Pr
2O
3) with hydrogen gas.
[Greenwood and Earnshaw, pp. 1238–9] Praseodymium(IV) oxide
Praseodymium(IV) oxide is an inorganic compound with chemical formula PrO2.
Production
Praseodymium(IV) oxide can be produced by boiling Pr6O11 in water or acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, col ...
, PrO
2, is the most oxidised product of the combustion of praseodymium and can be obtained by either reaction of praseodymium metal with pure oxygen at 400 °C and 282 bar
or by disproportionation of Pr
6O
11 in boiling acetic acid. The reactivity of praseodymium conforms to
periodic trends, as it is one of the first and thus one of the largest lanthanides.
At 1000 °C, many praseodymium oxides with composition PrO
2−''x'' exist as disordered, nonstoichiometric phases with 0 < ''x'' < 0.25, but at 400–700 °C the oxide defects are instead ordered, creating phases of the general formula Pr
''n''O
2''n''−2 with ''n'' = 4, 7, 9, 10, 11, 12, and ∞. These phases PrO
''y'' are sometimes labelled α and β′ (nonstoichiometric), β (''y'' = 1.833), δ (1.818), ε (1.8), ζ (1.778), ι (1.714), θ, and σ.
[Greenwood and Earnshaw, pp. 643–4]
Praseodymium is an electropositive element and reacts slowly with cold water and quite quickly with hot water to form praseodymium(III) hydroxide:
:2 Pr (s) + 6 H
2O (l) → 2 Pr(OH)
3 (aq) + 3 H
2 (g)
Praseodymium metal reacts with all the stable
halogen
The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
s to form trihalides:
:2 Pr (s) + 3 F
2 (g) → 2 PrF
3 (s)
reen
A rhyne (Somerset), rhine/rhyne (Gloucestershire), or reen ( South Wales) (all pronounced "reen"; from Old English ''ryne'' or Welsh ''rhewyn'' or ''rhewin'' "ditch") is a term used in parts of England and Wales for a drainage ditch, or can ...
:2 Pr (s) + 3 Cl
2 (g) → 2 PrCl
3 (s)
reen
A rhyne (Somerset), rhine/rhyne (Gloucestershire), or reen ( South Wales) (all pronounced "reen"; from Old English ''ryne'' or Welsh ''rhewyn'' or ''rhewin'' "ditch") is a term used in parts of England and Wales for a drainage ditch, or can ...
:2 Pr (s) + 3 Br
2 (g) → 2 PrBr
3 (s)
reen
A rhyne (Somerset), rhine/rhyne (Gloucestershire), or reen ( South Wales) (all pronounced "reen"; from Old English ''ryne'' or Welsh ''rhewyn'' or ''rhewin'' "ditch") is a term used in parts of England and Wales for a drainage ditch, or can ...
:2 Pr (s) + 3 I
2 (g) → 2 PrI
3 (s)
The
tetrafluoride, PrF4, is also known, and is produced by reacting a mixture of
sodium fluoride and
praseodymium(III) fluoride
Praseodymium(III) fluoride is an inorganic compound with the formula PrF3, being the most stable fluoride of praseodymium.
Production
The reaction between praseodymium(III) nitrate and sodium fluoride will produce praseodymium(III) fluoride as a ...
with fluorine gas, producing Na
2PrF
6, following which sodium fluoride is removed from the reaction mixture with liquid
hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock i ...
.
[Greenwood and Earnshaw, p. 1240–2] Additionally, praseodymium forms a bronze
diiodide; like the diiodides of lanthanum, cerium, and
gadolinium, it is a praseodymium(III)
electride
An electride is an ionic compound in which an electron is the anion. Solutions of alkali metals in ammonia are electride salts. In the case of sodium, these blue solutions consist of a(NH3)6sup>+ and solvated electrons:
:Na + 6 NH3 → a(N ...
compound.
Praseodymium dissolves readily in dilute
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
to form solutions containing the
chartreuse
Chartreuse () may refer to:
Food and drink
* Chartreuse (liqueur), a French liqueur
* Chartreuse (dish), a French dish of vegetables or meat tightly wrapped in vegetable leaves and cooked in a mould
Religion
* Carthusians, a Catholic religi ...
Pr
3+ ions, which exist as
2O)9">r(H2O)9sup>3+ complexes:
[Greenwood and Earnshaw, pp. 1242–4]
:2 Pr (s) + 3 H
2SO
4 (aq) → 2 Pr
3+ (aq) + 3 (aq) + 3 H
2 (g)
Dissolving praseodymium(IV) compounds in water does not result in solutions containing the yellow Pr
4+ ions;
because of the high positive
standard reduction potential
Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...
of the Pr
4+/Pr
3+ couple at +3.2 V, these ions are unstable in aqueous solution, oxidising water and being reduced to Pr
3+. The value for the Pr
3+/Pr couple is −2.35 V.
However, in highly basic aqueous media, Pr
4+ ions can be generated by oxidation with
ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
.
Although praseodymium(V) in the bulk state is unknown, the existence of praseodymium in its +5 oxidation state (with the stable electron configuration of the preceding noble gas
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
) under noble-gas matrix isolation conditions was reported in 2016. The species assigned to the +5 state were identified as
2">rO2sup>+, its O
2 and Ar adducts, and PrO
2(η
2-O
2).
Organopraseodymium compounds
Organopraseodymium compounds are very similar to
those of the other lanthanides, as they all share an inability to undergo
π backbonding
In chemistry, π backbonding, also called π backdonation, is when electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a ''π-acceptor ligand''. It is especially common in the organometallic che ...
. They are thus mostly restricted to the mostly ionic
cyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.
[Greenwood and Earnshaw, pp. 1248–9] The coordination chemistry of praseodymium is largely that of the large, electropositive Pr
3+ ion, and is thus largely similar to those of the other early lanthanides La
3+, Ce
3+, and Nd
3+. For instance, like lanthanum, cerium, and neodymium, praseodymium nitrates form both 4:3 and 1:1 complexes with
18-crown-6
18-Crown-6 is an organic compound with the formula 2H4O and the IUPAC name of 1,4,7,10,13,16-hexaoxacyclooctadecane. It is a white, hygroscopic crystalline solid with a low melting point. Like other crown ethers, 18-crown-6 functions as a li ...
, whereas the middle lanthanides from
promethium
Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of onl ...
to
gadolinium can only form the 4:3 complex and the later lanthanides from
terbium to
lutetium cannot successfully coordinate to all the ligands. Such praseodymium complexes have high but uncertain coordination numbers and poorly defined stereochemistry, with exceptions resulting from exceptionally bulky ligands such as the tricoordinate
3">r3 There are also a few mixed oxides and fluorides involving praseodymium(IV), but it does not have an appreciable coordination chemistry in this oxidation state like its neighbour cerium.
[Greenwood and Earnshaw, pp. 1244–8] However, the first example of a molecular complex of praseodymium(IV) has recently been reported.
History
![Auer von Welsbach](https://upload.wikimedia.org/wikipedia/commons/f/f7/Auer_von_Welsbach.jpg)
In 1751, the Swedish mineralogist
Axel Fredrik Cronstedt discovered a heavy mineral from the mine at
Bastnäs
Bastnäs ( sv, Bastnäs or ) is an ore field near Riddarhyttan, Västmanland, Sweden. The mines in Bastnäs were earliest mentioned in 1692. Iron, copper and rare-earth elements were extracted from the mines and 4,500 tons of cerium was produced be ...
, later named
cerite
Cerite is a complex silicate mineral group containing cerium, formula .http://rruff.geo.arizona.edu/doclib/hom/ceritece.pdf Handbook of Mineralogy The cerium and lanthanum content varies with the Ce rich species (cerite-(Ce)) and the La rich speci ...
. Thirty years later, the fifteen-year-old
Wilhelm Hisinger, from the family owning the mine, sent a sample of it to
Carl Scheele
Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish German pharmaceutical chemist.
Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified molybdenum, tungsten, barium, hydroge ...
, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with
Jöns Jacob Berzelius
Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only Jacob Berzelius, 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be on ...
and isolated a new oxide, which they named ''ceria'' after the
dwarf planet Ceres
Ceres most commonly refers to:
* Ceres (dwarf planet), the largest asteroid
* Ceres (mythology), the Roman goddess of agriculture
Ceres may also refer to:
Places
Brazil
* Ceres, Goiás, Brazil
* Ceres Microregion, in north-central Goiás st ...
, which had been discovered two years earlier.
[Emsley, pp. 120–5] Ceria was simultaneously and independently isolated in Germany by
Martin Heinrich Klaproth.
[Greenwood and Earnshaw, p. 1424] Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist
Carl Gustaf Mosander, who lived in the same house as Berzelius; he separated out two other oxides, which he named ''lanthana'' and ''didymia''.
He partially decomposed a sample of
cerium nitrate by roasting it in air and then treating the resulting oxide with dilute
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
. The metals that formed these oxides were thus named ''lanthanum'' and ''
didymium
Didymium ( el, , twin) is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially with a gas (propane)-powered forge, where it provides a filter that selectively blocks t ...
''.
While lanthanum turned out to be a pure element, didymium was not and turned out to be only a mixture of all the stable early lanthanides from praseodymium to
europium
Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanth ...
, as had been suspected by
Marc Delafontaine
Marc Delafontaine (March 31, 1837/1838, Céligny, Switzerland–1911) was a Swiss chemist and spectroscopist who was involved in discovering and investigating some of the rare earth elements.
Career
Delafontaine studied with Jean Charles Galis ...
after spectroscopic analysis, though he lacked the time to pursue its separation into its constituents. The heavy pair of
samarium and europium were only removed in 1879 by
Paul-Émile Lecoq de Boisbaudran and it was not until 1885 that
Carl Auer von Welsbach separated didymium into praseodymium and neodymium.
Von Welsbach confirmed the separation by
spectroscopic analysis, but the products were of relatively low purity. Since neodymium was a larger constituent of didymium than praseodymium, it kept the old name with disambiguation, while praseodymium was distinguished by the leek-green colour of its salts (Greek πρασιος, "leek green").
The composite nature of didymium had previously been suggested in 1882 by
Bohuslav Brauner
Bohuslav Brauner (May 8, 1855 – February 15, 1935) was a Czech chemist from the University of Prague, who investigated the properties of the rare earth elements, especially the determination of their atomic weights. Brauner predicted the e ...
, who did not experimentally pursue its separation.
Occurrence and production
Praseodymium is not particularly rare, despite it being in the rare-earth metals, making up 9.2 mg/kg of the Earth's crust. This value is between those of
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
(9.6 mg/kg) and
samarium (7.05 mg/kg), and makes praseodymium the fourth-most abundant of the lanthanides, behind cerium (66.5 mg/kg), neodymium (41.5 mg/kg), and lanthanum (39 mg/kg); it is less abundant than the
rare-earth elements
yttrium (33 mg/kg) and
scandium
Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the Lanthanides. It was discovered in ...
(22 mg/kg).
[Greenwood and Earnshaw, p. 1229–32] Instead, praseodymium's classification as a rare-earth metal comes from its rarity relative to "common earths" such as lime and magnesia, the few known minerals containing it for which extraction is commercially viable, as well as the length and complexity of extraction.
Although not particularly rare, praseodymium is never found as a dominant rare earth in praseodymium-bearing minerals. It is always preceded by cerium and lanthanum and usually also by neodymium.
![Monazite acid cracking process](https://upload.wikimedia.org/wikipedia/commons/b/b8/Monazite_acid_cracking_process.svg)
The Pr
3+ ion is similar in size to the early lanthanides of the cerium group (those from lanthanum up to
samarium and
europium
Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanth ...
) that immediately follow in the periodic table, and hence it tends to occur along with them in
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phospho ...
,
silicate
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...
and
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
minerals, such as
monazite (M
IIIPO
4) and
bastnäsite (M
IIICO
3F), where M refers to all the rare-earth metals except scandium and the radioactive
promethium
Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of onl ...
(mostly Ce, La, and Y, with somewhat less Nd and Pr).
Bastnäsite is usually lacking in
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
and the heavy lanthanides, and the purification of the light lanthanides from it is less involved. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, evolving carbon dioxide,
hydrogen fluoride
Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock i ...
, and
silicon tetrafluoride. The product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.
The procedure for monazite, which usually contains all the rare earth, as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earth. The acidic filtrates are partially neutralized with
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
to pH 3–4, during which thorium precipitates as hydroxide and is removed. The solution is treated with
ammonium oxalate
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary amm ...
to convert rare earth to their insoluble
oxalates, the oxalates are converted to oxides by annealing, and the oxides are dissolved in nitric acid. This last step excludes one of the main components,
cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...
, whose oxide is insoluble in HNO
3.
[.] Care must be taken when handling some of the residues as they contain
228Ra, the daughter of
232Th, which is a strong gamma emitter.
Praseodymium may then be separated from the other lanthanides via ion-exchange chromatography, or by using a solvent such as
tributyl phosphate where the solubility of Ln
3+ increases as the atomic number increases. If ion-exchange chromatography is used, the mixture of lanthanides is loaded into one column of cation-exchange resin and Cu
2+ or Zn
2+ or Fe
3+ is loaded into the other. An aqueous solution of a complexing agent, known as the eluant (usually triammonium edtate), is passed through the columns, and Ln
3+ is displaced from the first column and redeposited in a compact band at the top of the column before being re-displaced by . The
Gibbs free energy
In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature and pr ...
of formation for Ln(edta·H) complexes increases along with the lanthanides by about one quarter from Ce
3+ to Lu
3+, so that the Ln
3+ cations descend the development column in a band and are fractionated repeatedly, eluting from heaviest to lightest. They are then precipitated as their insoluble oxalates, burned to form the oxides, and then reduced to metals.
Applications
Leo Moser (son of Ludwig Moser, founder of the
Moser Glassworks in what is now
Karlovy Vary
Karlovy Vary (; german: Karlsbad, formerly also spelled ''Carlsbad'' in English) is a spa town, spa city in the Karlovy Vary Region of the Czech Republic. It has about 46,000 inhabitants. It lies on the confluence of the rivers Ohře and Teplá. ...
in the Czech Republic, not to be confused with
the mathematician of the same name) investigated the use of praseodymium in glass coloration in the late 1920s, yielding a yellow-green glass given the name "Prasemit". However, at that time far cheaper colorants could give a similar color, so Prasemit was not popular, few pieces were made, and examples are now extremely rare. Moser also blended praseodymium with neodymium to produce "Heliolite" glass ("Heliolit" in
German
German(s) may refer to:
* Germany (of or related to)
**Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ger ...
), which was more widely accepted. The first enduring commercial use of purified praseodymium, which continues today, is in the form of a yellow-orange "Praseodymium Yellow" stain for ceramics, which is a solid solution in the
zircon
Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...
lattice. This stain has no hint of green in it; by contrast, at sufficiently high loadings, praseodymium glass is distinctly green rather than pure yellow.
Like many other lanthanides, praseodymium's shielded
f-orbital
In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any spe ...
s allow for long
excited state
In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to a ...
lifetimes and high
luminescence
Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light".
It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a cryst ...
yields. Pr
3+ as a
dopant
A dopant, also called a doping agent, is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. When ...
ion therefore sees many applications in
optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
and
photonics. These include
DPSS-lasers, single-mode fiber
optical amplifier
An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback fr ...
s, fiber lasers,
upconverting nanoparticles Upconverting nanoparticles (UCNPs) are nanoscale particles (diameter 1–100 nm) that exhibit photon upconversion. In photon upconversion, two or more incident photons of relatively low energy are absorbed and converted into one emitted photon ...
as well as activators in red, green, blue, and ultraviolet phosphors.
Silicate crystals doped with praseodymium ions have also been used to
slow a light pulse down to a few hundred meters per second.
As the lanthanides are so similar, praseodymium can substitute for most other lanthanides without significant loss of function, and indeed many applications such as
mischmetal and
ferrocerium
Ferrocerium (also known in Europe as Auermetall) is a synthetic pyrophoric alloy of mischmetal (cerium, lanthanum, neodymium, other trace lanthanides and some iron – about 95% lanthanides and 5% iron) hardened by blending in oxides of ...
alloys involve variable mixes of several lanthanides, including small quantities of praseodymium. The following more modern applications involve praseodymium specifically or at least praseodymium in a small subset of the lanthanides:
* In combination with neodymium, another rare-earth element, praseodymium is used to create high-power magnets notable for their strength and durability.
[Rare Earth Elements 101](_blank)
, IAMGOLD Corporation, April 2012, pp. 5, 7. In general, most alloys of the cerium-group rare earths (
lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lantha ...
through
samarium) with 3d
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
s give extremely stable magnets that are often used in small equipment, such as motors, printers, watches, headphones, loudspeakers, and magnetic storage.
*Praseodymium–
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
intermetallic (PrNi
5) has such a strong
magnetocaloric effect
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures, as well as the ranges used in common refrigerators.
A magnetocaloric material warms up when a ma ...
that it has allowed scientists to approach within one thousandth of a degree of
absolute zero
Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibration ...
.
* As an
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
ing agent with
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
to create high-strength metals that are used in
aircraft engine
An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years many ...
s;
yttrium and
neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes i ...
are also viable substitutes.
* Praseodymium is present in the rare-earth mixture whose fluoride forms the core of
carbon arc light
An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc).
The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, ...
s, which are used in the
motion picture industry for
studio
A studio is an artist or worker's workroom. This can be for the purpose of acting, architecture, painting, pottery (ceramics), sculpture, origami, woodworking, scrapbooking, photography, graphic design, filmmaking, animation, industrial design ...
lighting and
projector
A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens, but some newer types ...
lights.
[Emsley, pp. 423–5]
* Praseodymium
compounds give
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
es,
enamels and ceramics a
yellow
Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In the R ...
color.
* Praseodymium is a component of
didymium
Didymium ( el, , twin) is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially with a gas (propane)-powered forge, where it provides a filter that selectively blocks t ...
glass, which is used to make certain types of
welder
In a broad sense, a welder is anyone, amateur or professional, who uses welding equipment, perhaps especially one who uses such equipment fairly often. In a narrower sense, a welder is a tradesperson who specializes in fusing materials together ...
's and
glass blower
Glassblowing is a glassforming technique that involves inflating molten glass into a bubble (or parison) with the aid of a blowpipe (or blow tube). A person who blows glass is called a ''glassblower'', ''glassmith'', or ''gaffer''. A '' lampworke ...
's
goggles.
* Praseodymium oxide in solid solution with
ceria
Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial produ ...
or
ceria-zirconia
Ceria-zirconia is a solid solution of cerium(IV) oxide (CeO2, also known as ceria) and zirconium oxide (ZrO2, also known as zirconia).
Crystal Structure and Stability
The crystal structure adopted by ceria-zirconia depends on the Zr/Ce ratio and ...
has been used as an
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
.
Due to its role in permanent magnets used for wind turbines, it has been argued that praseodymium will be one of the main objects of geopolitical competition in a world running on renewable energy. However, this perspective has been criticized for failing to recognize that most wind turbines do not use permanent magnets and for underestimating the power of economic incentives for expanded production.
Biological role and precautions
The early lanthanides have been found to be essential to some
methanotrophic
Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to s ...
bacteria living in
volcanic mudpots, such as ''
Methylacidiphilum fumariolicum
''Methylacidiphilum fumariolicum '' is an autotrophic bacterium first described in 2007 growing on volcanic pools near Naples, Italy. It grows in mud at temperatures between 50 °C and 60 °C and an acidic pH of 2–5. It is able to oxi ...
'': lanthanum, cerium, praseodymium, and neodymium are about equally effective.
Praseodymium is otherwise not known to have a biological role in any other organisms, but it is not very toxic either. Intravenous injection of rare earths into animals has been known to impair liver function, but the main side effects from inhalation of rare-earth oxides in humans come from radioactive
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high me ...
and
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
impurities.
References
Bibliography
*
*
Further reading
* R. J. Callow, ''The Industrial Chemistry of the Lanthanons, Yttrium, Thorium, and Uranium'', Pergamon Press, 1967.
* Bouhani, H (2020). "Engineering the magnetocaloric properties of PrVO3 epitaxial oxide thin films by strain effects". Applied Physics Letters. 117 (7). arXiv:2008.09193. doi:10.1063/5.0021031.
External links
WebElements.com—Praseodymium
{{Authority control
Chemical elements
Chemical elements with double hexagonal close-packed structure
Lanthanides
Reducing agents