Thermal Analysis of Lanthanoid Malonate Hydrates in Various Atmospheres

Abstract

The malonate compounds of tervalent lanthanoid ions Ln₂(C₃H₂-O₄)₃·nH₂O(Ln = La — Lu; n = 5 for La, 6 for Ce — Eu and 8 for Gd — Lu) were prepared. The thermogravimetry with a very slow heating rate(2°/h) in water vapor at a reduced pressure (10mm Hg) proved to be very effective to decide the thermal stability of the hydrates and to find their intermediates. The thermal stabilities showed a complicated tendency through the lanthanoid series, but which was fairly interpreted on the basis of the lanthanoid contraction. The TG curves of the anhydrous salts were obtained in static air and in the streams of N₂, O₂ and CO₂. The decomposition intermediates and products which were determined by the thermogravimetry, chemical analysis, evolved gas analysis and infrared and reflectance spectroscopy, varied with the ambient atmospheres. The decomposition processes and mechanisms were proposed.