Praseodymium
Encyclopedia
Praseodymium is a chemical element
that has the symbol Pr and atomic number
59. Praseodymium is a soft, silvery, malleable and ductile metal
in the lanthanide
group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating.
The element was named for the color of its primary oxide. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare earth oxide residue he called "didymium" from a residue he called "lantana," in turn separted from cerium salts. In 1885, the Austrian chemist baron Carl Auer von Welsbach
separated didymium into two salts of different colors, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasios (πράσιος), meaning green, and didymos (δίδυμος), twin.
Like most rare earth elements, praseodymium most readily forms trivalent Pr(III) ions. These are yellow-green in water solution, and various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its use to filter yellow light from light sources.
in the lanthanide
group. It is somewhat more resistant to corrosion
in air than europium
, lanthanum
, cerium
, or neodymium
, but it does develop a green oxide
coating that spall
s off when exposed to air, exposing more metal to oxidation — a centimeter-sized sample of Pr completely oxidizes within a year. For this reason, praseodymium is usually stored under a light mineral oil
or sealed in glass.
Unlike other rare-earth metals, which show antiferromagnetic or/and ferromagnetic ordering at low temperatures, Pr is paramagnetic at any temperature above 1 K.
to form praseodymium(III,IV) oxide:
Praseodymium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form praseodymium hydroxide:
Praseodymium metal reacts with all the halogens:
Praseodymium dissolves readily in dilute sulfuric acid
to form solutions containing green Pr(III) ions, which exist as a [Pr(OH2)9]3+ complexes:
Other praseodymium compounds include:
, praseodymium-141, which is of use in NMR
and EPR spectroscopy. 38 radioisotopes have been characterized, with the most stable being praseodymium-143 with a half-life
of 13.57 days and praseodymium-142 with a half-life of 19.12 hours. All of the remaining radioactive
isotopes have half-lives that are less than six hours, and the majority of these have half lives that are less than 10 minutes. This element also has 15 nuclear isomer
s, with the longest-lived being praseodymium-138m, praseodymium-134m, and praseodymium-142m . The nuclei of nuclear isomers exist in a delicate equilibrium or metastability
due to at least one nucleon having an excited energy state
.
The isotopes of praseodymium range in mass number
from 121 to 159 . The most common decay mode of 20 isotopes with mass numbers lower than the most abundant stable isotope, praseodymium-141 is beta+ decay
, primarily forming cerium isotopes (58 protons) as decay product
s. The most common decay mode for 18 isotopes with mass numbers higher than praseodymium-141 is beta- decay
, primarily forming neodymium isotopes (60 protons) as decay products.
extracted an oxide he called "lantana" (see lanthana), which was the oxide of the newly discovered element lanthanum
, from a mixture of crude cerium
nitrate. In 1841, Mosander went on to show that "lantana" was the most strongly basic of a mixture of rare earth element oxides and precipitated from acid solution when base was added. The remaining rare earth(s) remained in solution, and Mosander called these remainder salts "didymium
." In 1874, Per Teodor Cleve
concluded that didymium was in fact two elements, and in 1879, Lecoq de Boisbaudran isolated a new earth, samarium
, from "didymium" obtained from the mineral samarskite
. Crude didymium actually contained three elements, and in 1885, the Austria
n chemist
baron Carl Auer von Welsbach
separated didymium into two elements, praseodymium and neodymium
, which gave salt
s of different color
s.
The name praseodymium comes from the Greek
prasios (πράσιος), meaning green, and didymos (δίδυμος), twin. Praseodymium is frequently misspelled as praseodynium.
Leo Moser (son of Ludwig Moser, founder of the Moser Glass
works in what is now Karlovy Vary, Bohemia, in the Czech Republic, not to be confused with Leo Moser
, a mathematician) investigated the use of praseodymium in glass coloration in the late 1920s. The result was a yellow-green glass given the name "Prasemit". However, a similar color could be achieved with colorants costing only a minute fraction of what praseodymium cost in the late 1920s, such that the color 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
), which was more widely accepted. The first enduring commercial use of purified praseodymium, which continues today, is in the form of a yellow-orange stain for ceramics, "Praseodymium Yellow", which is a solid-solution of praseodymium in the zirconium silicate (zircon) 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.
Using classical separation methods, praseodymium was always difficult to purify. Much less abundant than the lanthanum and neodymium from which it was being separated (cerium having long since been removed by redox chemistry
), praseodymium ended up being dispersed among a large number of fractions, and the resulting yields of purified material were low.
Praseodymium has historically been a rare earth whose supply has exceeded demand. This has occasionally led to its being offered more cheaply than the far more abundant neodymium. Unwanted as such, much praseodymium has been marketed as a mixture with lanthanum and cerium, or "LCP" for the first letters of each of the constituents, for use in replacing the traditional lanthanide mixtures that were inexpensively made from monazite
or bastnäsite
. LCP is what remains of such mixtures, after the desirable neodymium, and all the heavier, rarer and more valuable lanthanides have been removed, by solvent extraction. However, as technology progresses, it has been found that praseodymium can be incorporated into neodymium-iron-boron magnets, thereby extending the supply of the much in demand neodymium. So LC is starting to replace LCP as a result.
and bastnäsite
, typically comprising about 5% of the lanthanides contained therein, and can be recovered from these minerals by an ion exchange
process, or by counter-current solvent extraction. Misch metal, used in making cigarette lighters, contains about 5% praseodymium metal.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
that has the symbol Pr and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
59. Praseodymium is a soft, silvery, malleable and ductile metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
in the lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating.
The element was named for the color of its primary oxide. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare earth oxide residue he called "didymium" from a residue he called "lantana," in turn separted from cerium salts. In 1885, the Austrian chemist baron Carl Auer von Welsbach
Carl Auer von Welsbach
Carl Auer Freiherr von Welsbach was an Austrian scientist and inventor who had a talent for not only discovering advances, but turning them into commercially successful products...
separated didymium into two salts of different colors, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasios (πράσιος), meaning green, and didymos (δίδυμος), twin.
Like most rare earth elements, praseodymium most readily forms trivalent Pr(III) ions. These are yellow-green in water solution, and various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its use to filter yellow light from light sources.
Physical properties
Praseodymium is a soft, silvery, malleable and ductile metalMetal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
in the lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
group. It is somewhat more resistant to corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
in air than europium
Europium
Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard silvery metal which readily oxidizes in air and water...
, lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
, cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
, or neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
, but it does develop a green oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
coating that spall
Spall
Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure...
s off when exposed to air, exposing more metal to oxidation — a centimeter-sized sample of Pr completely oxidizes within a year. For this reason, praseodymium is usually stored under a light mineral oil
Mineral oil
A mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....
or sealed in glass.
Unlike other rare-earth metals, which show antiferromagnetic or/and ferromagnetic ordering at low temperatures, Pr is paramagnetic at any temperature above 1 K.
Chemical properties
Praseodymium metal tarnishes slowly in air and burns readily at 150 °CCelsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
to form praseodymium(III,IV) oxide:
- 12 Pr + 11 O2 → 2 Pr6O11
Praseodymium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form praseodymium hydroxide:
- 2 Pr (s) + 6 H2O (l) → 2 Pr(OH)3 (aq) + 3 H2 (g)
Praseodymium metal reacts with all the halogens:
- 2 Pr (s) + 3 F2 (g) → 2 PrF3 (s) [green]
- 2 Pr (s) + 3 Cl2 (g) → 2 PrCl3 (s) [green]
- 2 Pr (s) + 3 Br2 (g) → 2 PrBr3 (s) [green]
- 2 Pr (s) + 3 I2 (g) → 2 PrI3 (s) [green]
Praseodymium dissolves readily in dilute sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
to form solutions containing green Pr(III) ions, which exist as a [Pr(OH2)9]3+ complexes:
- 2 Pr (s) + 3 H2SO4 (aq) → 2 Pr3+(aq) + 3 (aq) + 3 H2 (g)
Compounds
In its compounds, praseodymium occurs in oxidation states +2, +3 and/or +4. Praseodymium(IV) is a strong oxidant, instantly oxidizing water to elemental oxygen (O2), or hydrochloric acid to elemental chlorine. Thus, in aqueous solution, only the +3 oxidation state is encountered. Praseodymium(III) salts are yellow-green and, in solution, present a fairly simple absorption spectrum in the visible region, with a band in the yellow-orange at 589–590 nm (which coincides with the sodium emission doublet), and three bands in the blue/violet region, at 444, 468, and 482 nm, approximately. These positions vary slightly with the counter-ion. Praseodymium oxide, as obtained by the ignition of salts such as the oxalate or carbonate in air, is essentially black in color (with a hint of brown or green) and contains +3 and +4 praseodymium in a somewhat variable ratio, depending upon the conditions of formation. Its formula is conventionally rendered as Pr6O11.Other praseodymium compounds include:
- FluorideFluorideFluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
s: PrF2, PrF3, PrF4 - ChlorideChlorideThe chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
s: PrCl3Praseodymium(III) chloridePraseodymium chloride is the inorganic compound with the formula PrCl3. It is a blue-green solid that rapidly absorbs water on exposure to moist air to form a light green heptahydrate.-Preparation:... - BromideBromideA bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...
s: PrBr3, Pr2Br5 - IodideIodideAn iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...
s: PrI2, PrI3, Pr2I5 - OxideOxideAn oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
s: PrO2, Pr2O3Praseodymium(III) oxidePraseodymium oxide or praseodymium oxide is the chemical compound composed of praseodymium and oxygen with the formula Pr2O3. It forms white hexagonal crystals. Praseodymium oxide crystallizes in the manganese oxide or bixbyite structure....
, Pr6O11 - SulfideSulfideA sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
s: PrS, Pr2S3Praseodymium(III) sulfidePraseodymium sulfide is an inorganic chemical compound.Conditions/substances to avoid are: heat, moisture, acids, flame and thin foils.-References:... - SulfateSulfateIn inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
s: Pr2(SO4)3Praseodymium sulfatePraseodymium sulfate is a Pr compound with formula Pr23. It is an odourless whitish-green crystalline compound. The anhydrous substance readily absorbs water forming pentahydrate and octahydrate.-Properties:... - SelenideSelenideA selenide is a chemical compound in which selenium serves as an anion with oxidation number of −2 , much as sulfur does in a sulfide. The chemistry of the selenides and sulfides are similar....
s: PrSe - TelluridesTelluride (chemistry)The telluride ion is Te2−. It is the final stable member of the series of dianions O2−, S2−, and Se2− ....
: PrTe, Pr2Te3 - NitrideNitrideIn chemistry, a nitride is a compound of nitrogen where nitrogen has a formal oxidation state of −3. Nitrides are a large class of compounds with a wide range of properties and applications....
s: PrN
Isotopes
Naturally occurring praseodymium is composed of one stable isotopeIsotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
, praseodymium-141, which is of use in NMR
NMR
NMR may refer to:Applications of Nuclear Magnetic Resonance:* Nuclear magnetic resonance* NMR spectroscopy* Solid-state nuclear magnetic resonance* Protein nuclear magnetic resonance spectroscopy* Proton NMR* Carbon-13 NMR...
and EPR spectroscopy. 38 radioisotopes have been characterized, with the most stable being praseodymium-143 with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 13.57 days and praseodymium-142 with a half-life of 19.12 hours. All of the remaining radioactive
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
isotopes have half-lives that are less than six hours, and the majority of these have half lives that are less than 10 minutes. This element also has 15 nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
s, with the longest-lived being praseodymium-138m, praseodymium-134m, and praseodymium-142m . The nuclei of nuclear isomers exist in a delicate equilibrium or metastability
Metastability
Metastability describes the extended duration of certain equilibria acquired by complex systems when leaving their most stable state after an external action....
due to at least one nucleon having an excited energy state
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....
.
The isotopes of praseodymium range in mass number
Mass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...
from 121 to 159 . The most common decay mode of 20 isotopes with mass numbers lower than the most abundant stable isotope, praseodymium-141 is beta+ decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
, primarily forming cerium isotopes (58 protons) as decay product
Decay product
In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...
s. The most common decay mode for 18 isotopes with mass numbers higher than praseodymium-141 is beta- decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
, primarily forming neodymium isotopes (60 protons) as decay products.
History
In 1839 MosanderCarl Gustaf Mosander
Carl Gustaf Mosander was a Swedish chemist. He discovered the elements lanthanum, erbium and terbium....
extracted an oxide he called "lantana" (see lanthana), which was the oxide of the newly discovered element lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
, from a mixture of crude cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
nitrate. In 1841, Mosander went on to show that "lantana" was the most strongly basic of a mixture of rare earth element oxides and precipitated from acid solution when base was added. The remaining rare earth(s) remained in solution, and Mosander called these remainder salts "didymium
Didymium
Didymium is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially when a gas powered forge is used, where it provides a filter which selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass,...
." In 1874, Per Teodor Cleve
Per Teodor Cleve
Per Teodor Cleve was a Swedish chemist and geologist.After graduating from the Stockholm Gymnasium in 1858, Cleve matriculated at Uppsala University in May 1858, where he received his PhD in 1863...
concluded that didymium was in fact two elements, and in 1879, Lecoq de Boisbaudran isolated a new earth, samarium
Samarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...
, from "didymium" obtained from the mineral samarskite
Samarskite
Samarskite is a radioactive rare earth mineral series which includessamarskite- with formula: 22O8and samarskite- with formula 22O8 The formula for smarskite- is also given as: O4...
. Crude didymium actually contained three elements, and in 1885, the Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
n chemist
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...
baron Carl Auer von Welsbach
Carl Auer von Welsbach
Carl Auer Freiherr von Welsbach was an Austrian scientist and inventor who had a talent for not only discovering advances, but turning them into commercially successful products...
separated didymium into two elements, praseodymium and neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
, which gave salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s of different color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
s.
The name praseodymium comes from the Greek
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
prasios (πράσιος), meaning green, and didymos (δίδυμος), twin. Praseodymium is frequently misspelled as praseodynium.
Leo Moser (son of Ludwig Moser, founder of the Moser Glass
Moser Glass
Moser a.s. is a luxury, high-quality glass manufacturer based in Karlovy Vary, Czech Republic, previously Karlsbad in Bohemia, Austria-Hungary. The company is known for manufacturing fine stemware, decorative glassware , luxury glass gifts and various art engravings...
works in what is now Karlovy Vary, Bohemia, in the Czech Republic, not to be confused with Leo Moser
Leo Moser
Leo Moser was an Austrian-Canadian mathematician, best known for his polygon notation....
, a mathematician) investigated the use of praseodymium in glass coloration in the late 1920s. The result was a yellow-green glass given the name "Prasemit". However, a similar color could be achieved with colorants costing only a minute fraction of what praseodymium cost in the late 1920s, such that the color 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 language
German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....
), which was more widely accepted. The first enduring commercial use of purified praseodymium, which continues today, is in the form of a yellow-orange stain for ceramics, "Praseodymium Yellow", which is a solid-solution of praseodymium in the zirconium silicate (zircon) 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.
Using classical separation methods, praseodymium was always difficult to purify. Much less abundant than the lanthanum and neodymium from which it was being separated (cerium having long since been removed by redox chemistry
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
), praseodymium ended up being dispersed among a large number of fractions, and the resulting yields of purified material were low.
Praseodymium has historically been a rare earth whose supply has exceeded demand. This has occasionally led to its being offered more cheaply than the far more abundant neodymium. Unwanted as such, much praseodymium has been marketed as a mixture with lanthanum and cerium, or "LCP" for the first letters of each of the constituents, for use in replacing the traditional lanthanide mixtures that were inexpensively made from monazite
Monazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...
or bastnäsite
Bastnasite
The mineral bastnäsite is one of a family of three carbonate-fluoride minerals, which includes bastnäsite- with a formula of CO3F, bastnäsite- with a formula of CO3F, and bastnäsite- with a formula of CO3F. Most bastnäsite is bastnäsite-, and cerium is by far the most common of the rare earths in...
. LCP is what remains of such mixtures, after the desirable neodymium, and all the heavier, rarer and more valuable lanthanides have been removed, by solvent extraction. However, as technology progresses, it has been found that praseodymium can be incorporated into neodymium-iron-boron magnets, thereby extending the supply of the much in demand neodymium. So LC is starting to replace LCP as a result.
Occurrence
Praseodymium is available in small quantities in Earth's crust (9.5 ppm). It is found in the rare earth minerals monaziteMonazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...
and bastnäsite
Bastnasite
The mineral bastnäsite is one of a family of three carbonate-fluoride minerals, which includes bastnäsite- with a formula of CO3F, bastnäsite- with a formula of CO3F, and bastnäsite- with a formula of CO3F. Most bastnäsite is bastnäsite-, and cerium is by far the most common of the rare earths in...
, typically comprising about 5% of the lanthanides contained therein, and can be recovered from these minerals by an ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
process, or by counter-current solvent extraction. Misch metal, used in making cigarette lighters, contains about 5% praseodymium metal.
Applications
Uses of praseodymium:- As an alloyAlloyAn alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
ing agent with magnesiumMagnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
to create high-strength metals that are used in aircraft engineAircraft engineAn aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
s. - Praseodymium forms the core of carbon arc lights which are used in the motion picture industryMovie studioA movie studio is a term used to describe a major entertainment company or production company that has its own privately owned studio facility or facilities that are used to film movies...
for studioStudioA studio is an artist's or worker's workroom, or the catchall term for an artist and his or her employees who work within that studio. This can be for the purpose of architecture, painting, pottery , sculpture, scrapbooking, photography, graphic design, filmmaking, animation, radio or television...
lighting and projectorImage projectorAn image projector is an optical device that projects an image onto a surface, commonly a projection screen.Most projectors creates an image by shining a light through a small transparent image, but some newer types of projectors can project the image directly, by using lasers...
lights. - Praseodymium compoundsChemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
give glassGlassGlass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
es and enamelsVitreous enamelVitreous enamel, also porcelain enamel in U.S. English, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C...
a yellow color. - Praseodymium is used to color cubic zirconiaCubic zirconiaCubic zirconia is the cubic crystalline form of zirconium dioxide . The synthesized material is hard, optically flawless and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate...
yellow-green, to simulate the mineral peridotPeridot-Chemistry:The chemical composition of peridot is 2SiO4, with Mg in greater quantities than Fe.-Etymology:The origin of the name "peridot" is uncertain...
. - Praseodymium is a component of didymiumDidymiumDidymium is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially when a gas powered forge is used, where it provides a filter which selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass,...
glass, which is used to make certain types of welderWeldingWelding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
's and glass blower's gogglesGogglesGoggles or safety glasses are forms of protective eyewear that usually enclose or protect the area surrounding the eye in order to prevent particulates, water or chemicals from striking the eyes. They are used in chemistry laboratories and in woodworking. They are often used in snow sports as well,...
. - Silicate crystals doped with praseodymium ions have been used to slow a light pulseSlow lightSlow light is the propagation of an optical pulse or other modulation of an optical carrier at a very low group velocity. Slow light occurs when a propagating pulse is substantially slowed down by the interaction with the medium in which the propagation take place.Researchers at the Rowland...
down to a few hundred meters per second. - Praseodymium alloyed with nickelNickelNickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
(PrNi5) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zeroAbsolute zeroAbsolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....
. - Doping praseodymium in fluoride glassFluoride glassFluoride glass is a class of non-oxide optical glasses composed of fluorides of various metals. Due to their low viscosity, it is very difficult to completely avoid the occurrence of any crystallization while processing it through the glass transition...
allows it to be used as a single mode fiber optical amplifierOptical amplifierAn 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 from the cavity is suppressed...
. - Praseodymium oxide in solid solution with ceria, or with ceria-zirconia, have been used as oxidation catalysts.
- Modern ferroceriumFerroceriumFerrocerium is a man-made metallic material that has the ability to give off a large number of hot sparks at temperatures at when scraped against a rough surface , such as ridged steel...
firesteelFiresteelA Fire striker is a piece of high-carbon steel used for striking a spark, usually kept in a tinderbox together with flint and tinder.-Usage:...
products, commonly referred to as "flintFlintFlint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey, black, green, white, or brown in colour, and...
", used in lighters, torch strikers, "flint and steel" fire starters, etc., contain around 4% praseodymium.
Precautions
Like all rare earth metals, praseodymium is of low to moderate toxicity. Praseodymium has no known biological role.Books
- R.J. Callow, "The Industrial Chemistry of the Lanthanons, Yttrium, Thorium and Uranium", Pergamon Press, 1967.