A comprehensive study of the thermal behavior of rare earth chloride hydrates: resolving contradictions

Rare earth metal chlorides are used as starting materials on electrochemical synthesis of pure metals. These chlorides are hygroscopic and tend to form hydrates. To resolve the uncertainty of the thermal behavior of the hydrates LaCl3 ∙ 7H2O, NdCl3 ∙ 6H2O, SmCl3 ∙ 6H2O, and YbCl3 ∙ 6H2O, a comprehensive study is carried out. Thermogravimetry, differential scanning calorimetry and mass spectrometry were used to reveal the dehydration and hydrolysis processes over the temperature range of 25–700 ºC. Phase compositions of the initial hydrates, intermediate and final products are investigated by the XRD analysis, Raman and IR spectroscopy. Distinctions in the thermal behavior of the studied hydrates were found. The features must be taken into account when obtaining anhydrous rare earth chlorides and in technological processes with its participation.