Thermal stability and decomposition behaviors of some hydrous transition metal chlorides

In this work, the thermal stability of CuCl 2 , CoCl 2 , MnCl 2 , and their corresponding hydrates was studied by combining with calorimetry and lattice energy calculation. The dissolution enthalpies of both anhydrates and hydrates in water with different molalities at 298.15 K were measured to calculate the standard molar enthalpies of formation. The hydration enthalpies and the lattice energies were calculated to disclose the stabilities of the compounds, indicating that the MnCl 2 ·4H 2 O has the highest stability among the three hydrates. Meanwhile, the detailed thermal decomposition behaviors were evaluated with differential scanning calorimetry and thermogravimetric analysis. For CuCl 2 ·2H 2 O, the crystal water is lost by one step directly with the temperature ranges from 350 to 410 K. The decomposition process contains four steps for CoCl 2 ·6H 2 O and obtains its monohydrate in the temperature range from 320 to 479 K. For MnCl 2 ·4H 2 O, two thermal decomposition steps occur from 325 to 500 K, while two consecutive peaks with no clear boundary indicate that the complex reactions appear.