The effect caused by
dehydration and
rehydration of the synthetic
Na-magadiite was investigated by TGA, XRD, SEM, and (29)Si NMR. Thermal analysis of
Na-magadiite presented two well-defined loss mass stages between 20 and 150 degrees C and another between 270 and 310 degrees C, both related to the removal of interlayer water. The swelling behavior of
Na-magadiite was studied by thermal
dehydration data obtained at 150 and 300 degrees C, and respective
rehydration by water addition. X-ray patterns showed that the
dehydration of
Na-magadiite at 150 and 300 degrees C provoked the basal spacing decrease. The XRD also showed that only the material treated at 150 degrees C returned to the original structure with the
rehydration. (29)Si NMR spectra showed that after
rehydration, the Q(3)/Q(4) relationship presented the same value for
Na-magadiite treated at 150 degrees C. However, this Q(3)/Q(4) value decreased when the treatment was done at 300 degrees C. Kinetic studies of thermal decomposition showed that the
dehydration of
magadiite is based on a phase boundary-controlled reaction, caused by contracting areas. The exfoliation of lamellas with thermal treatment can explain this behavior, as observed in SEM images.