Thermal Analysis of Lanthanide Complexes for Nuclear Security

In an effort to meet the growing demand for more rapid separation methods, this work reports the vaporization and thermodynamic characterization of lanthanide complexes as vehicles for the rapid separation of volatile nuclear fission products. Volatile lanthanide β-diketonate complexes can be synthesized and rapidly separated from each other via gas phase chromatographic separations due to differences in adsorption enthalpy. Because adsorption and sublimation thermodynamics are linearly correlated, there is considerable motivation to determine sublimation enthalpies to improve the ability to predict separations effectiveness. A method of thermogravimetric analysis (TGA) was employed in this study on up to four lanthanide β-diketonate complexes to compare volatility and stability across the series and for each chelate. Sublimation enthalpies were determined using the Langmuir method involving isothermal jump heating. Thermogravimetric analysis coupled with a mass spectrometer (TGA-MS) and melting point analysis was used to confirm the occurrence of sublimation as well as confirm the stability of the chelate through the sublimation region. Elemental analysis, mass spectroscopy and infrared spectroscopy were also used to characterize additional ligands in the coordinating sphere and better understand the decomposition ranges of the complexes. Thermal analysis was carried out on lanthanide chlorides and oxychlorides in order to determine the potential for chromatographic separations of these ionic compounds.