New EGA findings revealed that the small endothermal event preceding that of the main decomposition of commercial NaHCO3 involves the simultaneous evolution of water and CO2. At very high sensitivity, EGA experiments evidenced that the above (limited) evolution of gases also took place from the
recrystallized material for which thermal methods gave no indication of endotherms.
Careful reexamination of previous DSC results indicated that for one kind of recrystallized material a very small endotherm
had been neglected. Renewed experiments revealed that this endotherm can be enhanced if the samples are prepared by crushing
and sieving in a wet atmosphere. Parallel FT-IR experiments on commercial and recrystallized materials demonstrated the presence
of carbonate in samples that had previously been taken just beyond the first small endotherm; this confirmed the EGA results.
SEM experiments showed that surface texture changes take place when samples are heated to temperatures just above that of
the preliminary endotherm. On the basis of these new findings, the interpretation previously given to the small endotherm
is revised and detailed knowledge is gained on the mechanism of decomposition of NaHCO3.