Wiki Article
Lanthanum hydroxycarbonate
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| Names | |
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| Other names
Lanthanum carbonate hydroxide
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| Identifiers | |
| ChemSpider | |
PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| LaOHCO3 | |
| Molar mass | 215.92 g/mol |
| Appearance | White crystalline solid |
| Density | 4.48 g/cm3 |
| Melting point | 310 °C (decomposes) |
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 hydroxycarbonate, also known as lanthanum carbonate hydroxide, is an inorganic compound of lanthanum with the chemical formula LaOHCO3. It occurs in several crystalline forms and can be converted thermally into lanthanum oxycarbonate and ultimately lanthanum oxide.
Preparation
[edit]Lanthanum hydroxycarbonate can be prepared from aqueous solutions of a lanthanum salt in the presence of carbonate or carbon dioxide. One route uses lanthanum nitrate, ammonia and carbon dioxide.
A simplified sequence is:
- La(NO3)3 + 3 NH4OH → La(OH)3 + 3 NH4NO3
- CO2 + H2O ⇌ H2CO3
- La(OH)3 + H2CO3 → LaOHCO3 + 2 H2O
Hydrothermal methods can be used to control both the morphology and crystal structure of the product. Orthorhombic LaOHCO3 has been obtained at about 160 °C, whereas synthesis at about 180 °C gives the hexagonal phase.[1]
PVP-assisted hydrothermal synthesis has also been used to produce hierarchical LaOHCO3 microspheres composed of plates and nanorods.[2]
Structure and properties
[edit]Lanthanum hydroxycarbonate is known in both orthorhombic and hexagonal forms.[1] The orthorhombic phase has been reported in space group Pmcn.[3]
The phase obtained depends on synthesis conditions. In hydrothermal synthesis on glass substrates, the lower-temperature orthorhombic material formed discrete flaky rhombic crystals, whereas the higher-temperature hexagonal phase formed compact rhomboidal crystals.[1]
The hexagonal form has been reported to exhibit significant second-harmonic generation, making it of interest as a nonlinear optical material.[1]
Hydrated lanthanum hydroxycarbonate phases are also known; these lose their water of crystallization on heating.[3]
Nanostructured LaOHCO3 also exhibits photoluminescence. Hierarchical material prepared by PVP-assisted hydrothermal synthesis showed emission near 420 nm, with intensity dependent on particle morphology and size.[2]
Thermal decomposition
[edit]Lanthanum hydroxycarbonate decomposes in stages on heating. The first stage produces lanthanum oxycarbonate, La2O2CO3, with loss of water and carbon dioxide:
- 2 LaOHCO3 → La2O2CO3 + H2O + CO2
Further heating decomposes the oxycarbonate to lanthanum oxide:
- La2O2CO3 → La2O3 + CO2
The exact decomposition temperatures depend on preparation conditions, particle morphology and experimental atmosphere. Studies have reported onset of conversion to the oxycarbonate from approximately 310–430 °C and conversion of the oxycarbonate to La2O3 at higher temperatures.[3][2]
References
[edit]- ^ a b c d Han, Zhaohui; Yang, Qing; Lu, G. Q. (2004). "Crystalline lanthanum hydroxycarbonates with controlled phases and varied morphologies prepared on non-crystalline substrates". Journal of Solid State Chemistry. 177 (10): 3709–3714. doi:10.1016/j.jssc.2004.06.044.
- ^ a b c Wang, Gang; Wang, Hui; Bai, Jintao; Ren, Zhaoyu; Bai, Jinbo (2013). "PVP-assisted assembly of lanthanum carbonate hydroxide with hierarchical architectures and their luminescence properties". Chemical Engineering Journal. 214: 386–393. doi:10.1016/j.cej.2012.10.033.
- ^ a b c Bakiz, Bahcine; Guinneton, Frédéric; Arab, Madjid (2010). "Elaboration, characterization of LaOHCO3, La2O2CO3 and La2O3 phases and their gas-solid interactions with CH4 and CO gases". M. J. Condensed Matter. 12 (1).