Crystal phases in the system MgCl2–OC(NH2)2–H2O: thermal stability and decomposition

Abstract Crystal phases in the system MgCl 2 –OC(NH 2 ) 2 –H 2 O have been studied and discussed. The conditions for obtaining MgCl 2 ·OC(NH 2 ) 2 ·4H 2 O, MgCl 2 ·4OC(NH 2 ) 2 ·2H 2 O, MgCl 2 ·6OC(NH 2 ) 2 and MgCl 2 ·10OC(NH 2 ) 2 have been specified. The crystal structures of MgCl 2 ·OC(NH 2 ) 2 ·4H 2 O and MgCl 2 ·6OC(NH 2 ) 2 have been solved for the first time. The thermal behavior of the four studied phases has been investigated in the temperature range from room temperature to 600 °C applying simultaneous thermal and mass-spectroscopy analyses. In-situ time-resolved powder diffraction analysis in the temperature range from 25 to 230 °C has been used in order to clarify the structural transformations upon heating. Research has revealed that the most stable compound upon heating is MgCl 2 ·6OC(NH 2 ) 2 . For all the studied samples, the decomposition of the urea component has been observed to start closely after the melting. The decomposition processes are more complex for the H 2 O-containing phases, where the water molecules releasing occurs in stages. Magnesium analog of bis-biuret-zinc-chloride have been detected among the intermediate phases obtained during the decomposition of the studied compounds.