MilliporeSigma
  • The role of amorphous precursors in the crystallization of La and Nd carbonates.

The role of amorphous precursors in the crystallization of La and Nd carbonates.

Nanoscale (2015-07-02)
Beatriz Vallina, Juan Diego Rodriguez-Blanco, Andrew P Brown, Jesus A Blanco, Liane G Benning
ABSTRACT

Crystalline La and Nd carbonates can be formed from poorly-ordered nanoparticulate precursors, termed amorphous lanthanum carbonate (ALC) and amorphous neodymium carbonate (ANC). When reacted in air or in aqueous solutions these precursors show highly variable lifetimes and crystallization pathways. We have characterized these precursors and the crystallization pathways and products with solid-state, spectroscopic and microscopic techniques to explain the differences in crystallization mechanisms between the La and Nd systems. ALC and ANC consist of highly hydrated, 10-20 nm spherical nanoparticles with a general formula of REE2(CO3)3·5H2O (REE = La, Nd). The stabilities differ by ∼2 orders of magnitude, with ANC being far more stable than ALC. This difference is due to the Nd(3+) ion having a far higher hydration energy compared to the La(3+) ion. This, together with temperature and reaction times, leads to clear differences not only in the kinetics and mechanisms of crystallization of the amorphous precursor La- and Nd-carbonate phases but also in the resulting crystallite sizes and morphologies of the end products. All crystalline La and Nd carbonates developed spherulitic morphologies when crystallization occurred from hydrous phases in solution at temperatures above 60 °C (La system) and 95 °C (Nd system). We suggest that spherulitic growth occurs due to a rapid breakdown of the amorphous precursors and a concurrent rapid increase in supersaturation levels in the aqueous solution. The kinetic data show that the crystallization pathway for both La and Nd carbonate systems is dependent on the reaction temperature and the ionic potential of the REE(3+) ion.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Neodymium, powder, −40 mesh, ≥99% trace rare earth metals basis
Neodymium, rod, 50mm, diameter 12.5mm, cast, 99%
Neodymium, rod, 100mm, diameter 12.5mm, cast, 99%
Neodymium, rod, 100mm, diameter 6.35mm, cast, 99%
Neodymium, rod, 50mm, diameter 6.35mm, cast, 99%
Sigma-Aldrich
Lanthanum, powder, −40 mesh, under oil, 99.9% trace rare earth metals basis
Sigma-Aldrich
Lanthanum, pieces
Lanthanum, rod, 50mm, diameter 6.35mm, cast, 99%
Lanthanum, foil, not light tested, 100x100mm, thickness 0.025mm, as rolled, 99%
Lanthanum, foil, not light tested, 50x50mm, thickness 0.025mm, as rolled, 99%
Lanthanum, foil, not light tested, 25x25mm, thickness 0.025mm, as rolled, 99%
Lanthanum, foil, 25x25mm, thickness 0.125mm, as rolled, 99%
Lanthanum, foil, 25x25mm, thickness 0.1mm, as rolled, 99%
Lanthanum, foil, 100x100mm, thickness 0.125mm, as rolled, 99%
Lanthanum, foil, 100x100mm, thickness 0.1mm, as rolled, 99%
Lanthanum, rod, 100mm, diameter 6.35mm, cast, 99%
Lanthanum, foil, 50x50mm, thickness 0.1mm, as rolled, 99%
Sigma-Aldrich
Sodium carbonate, BioXtra, ≥99.0%
Sigma-Aldrich
Sodium carbonate-12C, 99.9 atom % 12C
Sigma-Aldrich
Sodium carbonate, BioUltra, anhydrous, ≥99.5% (calc. on dry substance, T)
Sigma-Aldrich
Sodium carbonate, anhydrous, powder, 99.999% trace metals basis