SAED and HRTEM Investigation of Palygorskite

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Abstract
The microstructure of palygorskite from Longwang Mountain of Xuyu County, Jiangsu Province, was studied by energy dispersive X‐ray analysis (EDX), selected‐area electron diffraction (SAED) and high‐resolution transmission electron microscopy (HRTEM). The average composition of the palygorskite studied is (Si7.38Al0.62) (Al0.96Fe3+0.62Mg2.86□0.56)Ca0.03K0.06O20(OH)2(OH2)4, which is rich in Mg. Several SAED patterns from a single crystal of palygorskite were obtained with different zone axes. The polymorphs (monoclinic and orthorhombic) are unequivocally distinguished by distant interplanar angles, even though they possess similar sets of d‐values. High‐resolution images of three principal zones ([010], [100] and [110]) were obtained. The lattice fringes on HRTEM images along [010] have spacings of 0.319 nm. These fringes are interpreted as periodic alterations of two tetrahedral (T) sheets and one octahedral (O) sheet (‐TT‐O‐TT‐O‐). We have directly observed trioctahedral and dioctahedral individual palygorskite particles along [100]. They are all presented as dark lines along [001], but the width of dark lines corresponding to trioctahedral crystals (0.913 nm) is twice that of the dioctahedral ones (0.456 nm). This is because the trans‐sites are occupied by cations in trioctahedral palygorskite. The width of dark lines along [110] is 1.024 nm, a bit thinner than the theoretical spacing (1.044 nm). This is because water molecules quickly leave the structure upon the irradiation by the electron beam.

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