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Praseodymium
Praseodymium (Pr, atomic number 59) is the third lanthanide — a soft, silvery-yellow, double-HCP metal with a melting point of 931 °C and a 4f³6s² configuration that gives it a large magnetic moment and, uniquely among lanthanides, a stable +4 oxide (Pr₆O₁₁) accessible under ordinary conditions. It is effectively monoisotopic: ¹⁴¹Pr (100%, stable, I = 5/2, NMR-active) is the only naturally occurring isotope. Pr is co-produced with Nd from bastnäsite and monazite, with production dominated by China; it is frequently sold as PrNd mixed metal or oxide when the applications tolerance permits.
Pr is increasingly used in PrNd-Fe-B permanent magnets as a direct substitute for Nd — Pr₂Fe₁₄B has a slightly lower energy product than Nd₂Fe₁₄B but comparable coercivity, and PrNd mixed-metal alloys reduce separation costs while maintaining magnet performance, making Pr an important co-critical material alongside Nd for EV motors and wind turbines. Pr is also used in Pr-Co, Pr-Al, and Pr-Mg alloys for high-temperature aerospace and structural applications, where Pr additions improve creep resistance and high-temperature strength.
Pr₆O₁₁ (praseodymium mixed oxide, yellow) is the principal ceramic pigment for yellow-green colorations in porcelain tiles, sanitaryware, and industrial ceramics — the largest-volume application of Pr by mass — and PrAlO₃-stabilised zirconia is a yellow dental ceramic. Pr³⁺ emission in Pr:YAG and Pr:LiYF₄ lasers spans the visible spectrum (480–720 nm), enabling direct visible laser output without frequency conversion, with applications in flow cytometry, ophthalmology, and laser displays. Pr-doped fibre amplifiers extend EDFA operation to the 1,300 nm O-band for short-reach optical communications.
General Properties
| Property | Value | Notes |
|---|---|---|
| Atomic Number | 59 | 4f³6s²; +3 dominant in solution and in most solid compounds. +4 accessible in the solid state (Pr₆O₁₁, PrO₂) — unique among the light lanthanides apart from Ce. ¹⁴¹Pr (I = 5/2) is NMR-active; the only natural isotope. |
| Atomic Mass | 140.908 u | Monoisotopic: ¹⁴¹Pr (100%, stable). Provides a single clean ICP-MS signal at m/z 141 with no isobaric interference from other stable isotopes, making Pr a reliable REE monitor in geochemical and industrial analysis. |
| Density (20 °C) | 6.773 g/cm³ | Slightly lower than Nd (7.007 g/cm³); Pr₂Fe₁₄B and PrNd-Fe-B alloy densities are comparable to NdFeB (~7.4–7.5 g/cm³). |
| Melting Point | 931 °C (1,204 K) | Slightly lower than La (920 °C) and Nd (1,021 °C). Pr oxidises rapidly in air; all processing requires Ar or vacuum. Produced by Ca-reduction of PrF₃. |
| Boiling Point | 3,130 °C | High boiling point; Pr evaporation must be controlled during PrNd-Fe-B strip-casting and alloy melting. |
| Thermal Conductivity | 13 W/m·K | Low conductivity typical of light lanthanides. Relevant to thermal management of Pr-doped laser crystals (Pr:YAG, Pr:LiYF₄) under CW visible laser operation. |
| Electrical Resistivity | 89 nΩ·m (20 °C) | High resistivity typical of lanthanides; not relevant to most Pr applications. |
| Crystal Structure | α-Pr: double HCP (dHCP), a = 3.673 Å, c = 11.835 Å | dHCP at RT, shared with La and Nd. Transforms to BCC above ~795 °C. |
Mechanical Properties
| Property | Value | Notes |
|---|---|---|
| Tensile Strength | ~240 MPa | Soft and ductile; not used structurally. Relevant to Pr foil and rod fabrication for sputtering targets and PrNd alloy precursor preparation. |
| Young's Modulus | 52 GPa | Low-moderate; closely matched to Nd (51 GPa), consistent with their adjacent positions in the lanthanide series. |
| Hardness | ~35–40 HB (annealed) | Soft; comparable to La and Nd. Pr can be cut with a knife and machined under inert atmosphere. |
| Elongation at Break | ~22% | Good ductility; Pr foil (99.9%+) is used as sputtering target and alloy precursor. |
| Poisson's Ratio | 0.28 | Typical for a light lanthanide. |
Chemical Properties
| Property | Value / Behavior | Notes |
|---|---|---|
| Oxidation States | +3 dominant (PrCl₃, Pr(NO₃)₃); +4 in solid oxides (Pr₆O₁₁, PrO₂) | Pr⁴⁺ is stabilised in the solid state by crystal-field effects but is a very strong oxidant in solution; Pr³⁺ is the only form stable in aqueous chemistry. The mixed-valence Pr₆O₁₁ is the thermodynamically stable air-formed oxide at RT — reduction to Pr₂O₃ occurs above ~400 °C in reducing atmospheres. |
| Corrosion Resistance | Oxidises in air within days; reacts with water and dilute acids; fine powder may ignite | Similar air stability to Nd; should be stored under inert atmosphere or mineral oil. PrNd-Fe-B magnets require the same corrosion protection as NdFeB (Ni or epoxy coatings). |
| Surface Oxide | Pr₆O₁₁ (black, mixed Pr³⁺/Pr⁴⁺) forms in air at RT | Pr₆O₁₁ is the precursor for ceramic pigments, PrNd alloy melting, and Pr:YAG crystal growth. Calcination above 400 °C in reducing atmosphere gives Pr₂O₃ (hexagonal, green); re-oxidation at 400–700 °C in air gives Pr₆O₁₁. |
| Identifier | Value |
|---|---|
| Symbol | Pr |
| Atomic Number | 59 |
| CAS Number | 7440-10-0 |
| UN Number | UN3089 (powder) |
| EINECS Number | 231-120-3 |
| Isotope | Type | Notes |
|---|---|---|
| ¹⁴¹Pr | Stable | 100% natural abundance; I = 5/2, NMR-active. The only naturally occurring Pr isotope — Pr is monoisotopic. ¹⁴¹Pr NMR (I = 5/2; moderate quadrupole moment; shift range ~2,000 ppm) characterises Pr³⁺ coordination in ceramic pigment precursors, PrNd alloy phases, and Pr-doped laser crystals. The single clean ICP-MS signal at m/z 141 makes Pr a reliable REE monitor in geochemical and industrial analysis. σ(thermal) = 11.5 barn — low enough that Pr does not significantly poison reactor environments. |
Scientific & Research Applications
| Use Case | Form Typically Used | Description |
|---|---|---|
| Pr:YAG & Pr:LiYF₄ Visible Lasers | Pr:YAG and Pr:LiYF₄ single crystals (0.1–1 at% Pr, Czochralski or HEM grown); pumped by 444 nm GaN diode laser | Pr³⁺ offers direct visible laser emission on multiple transitions: 480 nm (blue), 523 nm (green), 607 nm (orange), 639 nm (red) — without frequency conversion. Pr:LiYF₄ pumped by 444 nm GaN diodes provides efficient CW visible output useful in flow cytometry, laser displays, ophthalmology, and underwater communications. |
| PrNd-Fe-B Magnet Research | PrNd mixed metal (Pr:Nd ~25:75 to 50:50 by weight); strip-cast PrNdFeB alloy | Pr₂Fe₁₄B has comparable coercivity to Nd₂Fe₁₄B with slightly lower remanence. PrNd mixed-metal alloys are used commercially where full Pr-Nd separation is not cost-effective, and are increasingly specified where Nd supply tightness raises cost concerns. Research also covers Pr additions to SmCo₅ and Sm₂Co₁₇ magnets. |
| Pr-Doped Fibre Amplifiers (1,300 nm) | Pr³⁺-doped fluoride glass fibre (ZBLAN:Pr); 1,017 nm pump | Pr³⁺ in fluoride glass amplifies the 1,300 nm O-band (¹G₄→³H₅ transition), extending optical amplification to short-reach and metro networks where EDFA coverage at 1,550 nm is not available. Research focuses on host glass optimisation to reduce multiphonon quenching and improve gain efficiency. |
| ¹⁴¹Pr NMR Spectroscopy | PrCl₃ or Pr(NO₃)₃ solutions; Pr-doped solid powders | ¹⁴¹Pr NMR characterises Pr³⁺ coordination chemistry in REE separation solvents, ceramic precursor solutions, and Pr-doped optical glass melts. Solid-state ¹⁴¹Pr NMR provides site symmetry information in Pr-containing perovskites and garnets. |
Industrial & Commercial Applications
| Sector | Form / Grade Used | Description |
|---|---|---|
| Ceramic Yellow-Green Pigments | Pr₆O₁₁ (99%+) calcined with ZrSiO₄ at 900–1,100 °C to give Pr:ZrSiO₄ (zircon-encapsulated yellow pigment) | Pr:ZrSiO₄ yellow is the dominant inorganic yellow pigment for porcelain tiles, sanitaryware, and industrial ceramics — it is thermally stable to ~1,300 °C, lead-free, and colour-stable under firing conditions where organic pigments fail. This is the largest-volume Pr application by mass globally. PrAlO₃-stabilised zirconia provides yellow dental ceramic shades. |
| PrNd-Fe-B Permanent Magnets | PrNd mixed metal or PrNd oxide (99%+); sintered PrNd-Fe-B magnets | PrNd-Fe-B magnets are used in EV traction motors, wind turbine generators, and consumer electronics where full Nd/Pr separation is not required. Pr content in commercial NdFeB is typically 20–30% of the rare-earth fraction; as Nd prices rise, higher-Pr formulations become cost-competitive. |
| High-Temperature Alloys | Pr metal (99%+) as Mg-alloy additive; Pr-Al master alloy | Pr additions to Mg alloys (0.5–3 wt%) refine grain size and improve creep resistance at 150–200 °C, relevant to automotive powertrain and aerospace structural castings. Pr-Al alloys improve high-temperature strength and oxidation resistance in Al casting alloys. |
| Glass Colorant & Didymium Filters | Pr₆O₁₁ (0.2–3 wt%) in glass batch; didymium glass (Pr + Nd oxide mixture) | Pr₆O₁₁ imparts a green-yellow tint to glass via Pr³⁺ 4f-4f absorptions. Didymium glass (Pr + Nd oxides combined) is used in glassblower's safety goggles to suppress the intense sodium D-line emission during hot glass work, and in filter glass for spectroscopy. |
| Purity | Applications | Notes |
|---|---|---|
| 99% (2N) | Magnet alloys, glass coloring, and general research. | Standard grade for industrial and laboratory applications. |
| 99.9% (3N) | Lasers, high-performance magnets, and precision optics. | High-purity grade for advanced scientific and technical uses. |
| Synonym / Alternative Name | Context |
|---|---|
| Pr | Chemical symbol; from Greek prasios didymos (green twin), named by Carl Auer von Welsbach in 1885. Used in PrNdFeB magnet alloy specs, Pr:YAG laser datasheets, and ICP-MS REE databases (m/z 141, no isobaric interference). |
| Pr metal | Commercial form designation for ingot, rod, foil, or powder. Used in PrNd alloy strip-casting procurement and sputtering target specifications. |
| Pr element | Scientific designation distinguishing elemental Pr from Pr compounds; used in crystal structure and allotropy literature. |
| Praseodymium metal | Full commercial designation in REACH/RoHS documentation and ASTM REE metal standards. |
| Praseodymium element | Used in academic databases, ¹⁴¹Pr NMR spectroscopy literature, and ceramic pigment chemistry texts. |
| Praseodymium rare earth metal | Trade designation; Pr is co-critical with Nd on EU and US critical materials lists for its role in PrNd-Fe-B magnets for EV and wind turbine applications. |
| Praseodymium rare earth element | Geochemical designation in REE deposit assessments and chondrite-normalised REE pattern databases. Pr/Nd ratio is used to detect Ce anomalies in marine geochemistry (Pr corrects for Ce depletion artefacts). |
| Element 59 | Periodic table designation used in XRF/ICP-MS software, nuclear data libraries, and reactor physics codes (¹⁴¹Pr is a stable fission product end-member from ¹⁴¹Ce→¹⁴¹Pr→stable decay chain). |