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Lanthanum phosphate
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| Names | |
|---|---|
| Other names
Lanthanum orthophosphate
| |
| Identifiers | |
| |
| ECHA InfoCard | 100.034.003 |
CompTox Dashboard (EPA)
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| Properties | |
| LaPO4 | |
| Molar mass | 233.88 g/mol |
| Appearance | White solid |
| Very slightly soluble in water | |
| Structure | |
| Monoclinic, monazite type (anhydrous) | |
| P21/n, No. 14 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Lanthanum phosphate is an inorganic compound of lanthanum and phosphate with the chemical formula LaPO4. It occurs in an anhydrous monazite-type form and in hydrated rhabdophane-type forms.
Preparation
[edit]Lanthanum phosphate can be prepared by precipitation from aqueous solutions containing La3+ and phosphate ions:
- La3+ + PO43− → LaPO4↓
Hydrated lanthanum phosphate can, for example, be obtained by reaction of soluble lanthanum salts with sodium phosphate. Hydrothermal synthesis has been used to prepare rhabdophane-type LaPO4 nanofibres.[1]
Depending on the synthesis conditions, precipitation can give either hydrated rhabdophane-type LaPO4·nH2O or anhydrous monazite-type LaPO4.[2]
Structure and properties
[edit]Anhydrous lanthanum phosphate adopts the monazite structure. It crystallizes in the monoclinic crystal system in space group P21/n (No. 14). In this structure La3+ is nine-coordinate, while phosphorus occurs in isolated PO4 tetrahedra.[3]
Hydrated lanthanum phosphate forms the rhabdophane structure, with an approximate composition LaPO4·nH2O. Synthetic rhabdophane commonly contains roughly 0.5–1 molecule of water per formula unit.[4]
On heating, hydrated LaPO4 first loses water while retaining the rhabdophane framework. At higher temperatures it irreversibly transforms into the monoclinic monazite phase. The rhabdophane-to-monazite transformation generally occurs between about 500 and 900 °C, depending on preparation conditions.[5] Rhabdophane-type LaPO4 has been reported to remain structurally stable to approximately 650 °C before conversion to monazite.[2]
Lanthanum phosphate is chemically durable and only very slightly soluble in water. Monazite-type LaPO4 also shows high thermal and radiation stability.[3]
Applications
[edit]Lanthanum phosphate has been investigated as a component of high-temperature ceramic composites. Monazite-type LaPO4 forms weak interfaces with materials such as alumina and has therefore been studied as a coating and interphase material in ceramic-matrix composites.[3]
Hydrated rare-earth phosphates, including LaPO4·nH2O, have also been investigated as proton conductors for intermediate-temperature electrochemical applications.[6]
Monazite-type rare-earth phosphates are also studied as durable host materials for immobilization of radioactive elements because of their chemical stability, radiation resistance and ability to accommodate a wide range of cations in the crystal structure.[3]
References
[edit]- ^ Zhang, Youjin; Guan, Hangmin (2005). "The growth of lanthanum phosphate (rhabdophane) nanofibers via the hydrothermal method". Materials Research Bulletin. 40 (9): 1536–1543.
- ^ a b Penot, Claude; Champion, Eric; Goursat, Paul (1999). "Synthesis and characterisation of lanthanum phosphate powders". Phosphorus Research Bulletin. 10: 307–312. doi:10.3363/prb1992.10.0_307.
- ^ a b c d "Synthesis and properties of anhydrous rare-earth phosphates, monazite and xenotime: a review". RSC Advances. 14. 2024. doi:10.1039/D4RA01142B.
- ^ "Thermodynamics and Stability of Rhabdophanes, Hydrated Rare Earth Phosphates REPO4·nH2O". Frontiers in Chemistry. 6 604. 2018. doi:10.3389/fchem.2018.00604. PMC 6304437.
- ^ Jonasson, R. G.; Vance, E. R. (1986). "DTA study of the rhabdophane to monazite transformation in rare earth (La–Dy) phosphates". Thermochimica Acta. 108: 65–72. doi:10.1016/0040-6031(86)85078-X.
- ^ "Thermal Stability and Proton Conductivity of Rare Earth Orthophosphate Hydrates". International Journal of Electrochemical Science. 9 (5): 2285–2300. 2014.