Constant rate thermal analysis of cobaltoblödite and cupper–kröhnkite at low water vapor pressure 5 hPa

Thermal decomposition mechanisms for cobaltoblödite Na 2 Co(SO 4 ) 2 ·4H 2 O and cupper–kröhnkite Na 2 Cu(SO 4 ) 2 ·2H 2 O have been developed using constant rate thermal analysis technique under controlled residual water vapor pressure above the sample P_H_2O = 5 hPa . The apparent activation energy of each dehydration process was measured by means of two CRTA curves without any presumption to the kinetic low. Correlation between structure and thermal behavior was highlighted. It has shown that dehydration of cobaltoblödite mineral occurs in two steps with formation of Na 2 Co(SO 4 ) 2 ·1.5H 2 O and Na 2 Co(SO 4 ) 2 as intermediate and final phases, respectively. The activation energies of both dehydration steps are 167 kJ mol −1 and 107 kJ mol −1 , respectively. For cupper–kröhnkite mineral, its dehydration occurs in one step leading to Na 2 Cu(SO 4 ) 2 . The corresponding activation energy was found equal to 71 kJ mol −1 .