Determination of thermodynamic stability of neodymium chloride hydrates (NdCl3·xH2O) by dynamic transpiration method

Abstract

Synthesis of rare earth chlorides in the anhydrous form is crucial for the production of rare earth metals in the electrolysis process. Knowledge of thermal stability of rare earth chloride hydrates is therefore of great interest which may help in deciding the experimental condition for its production. In this study, dehydration scheme of NdCl3·6H2O(s) was investigated by thermal analysis techniques. Thermal decomposition of NdCl3·6H2O(s) to NdCl3(s) is found to proceed through the formation of NdCl3·3H2O(s), NdCl3·2H2O(s) and NdCl3·H2O(s) in the temperature range 330–450 K. Thermodynamic stability of the NdCl3·6H2O(s) and its intermediate products has been determined by measuring the vapor pressure of water over the compounds employing dynamic transpiration technique. The standard molar Gibbs energy of formation of NdCl3·6H2O(s) and its intermediate hydrates have been derived from the measured vapor pressure data.