No abstract

The thermal behaviour of astrakanite was investigated by conventional thermal analysis techniques in air and by constant rate thermal analysis (CRTA) under residual water vapour pressure above the sample P H 2 O ¼ 5 hPa. It has been shown that the pathway of the thermal dehydration depends strongly on the nature of atmosphere above the sample. A correlation between structure evolution and thermal behaviour was developed. The apparent activation energies corresponding to the two dehydration steps of Na 2 Mg(SO 4 ) 2 Á4H 2 O were also measured experimentally by means of two CRTA curves and were found equal to 83 ± 7 and 111 ± 8 kJ mol -1 , respectively.