Al-Pillared saponites. Part 2.—NMR studies
A saponite from Ballarat was intercalated with Al polycations by four different procedures involving different sources of polycations, and stabilised by calcination (pillared). 29Si and 27Al solid-state MNR of both the intercalated and the pillared samples have been measured and are discussed. 29Si NMR leads us to propose a pillaring mechanism, involving H+ attack of the clay tetrahedral sheet followed by AlO4 tetrahedra inversion, similar to that previously proposed for beidellites. 27Al NMR reveals that the pillars are not fundamentally modified upon calcination at 500 °C although they undergo reversible dehydration reactions; at 750 °C and above, a strong pillar reorganisation occurs prior to collapse of the global structure.