Surface charge density dependency on Al2O3 content in imogolite

An analysis of the available literature data indicates that the cation exchange capacity and surface charge density of imogolite decrease systematically as the mole % of Al₂O₃ (i.e. 100 Al₂O₃/SIO₂ + Al₂O₃) increases. This behavior is analogous to that of synthetic aluminosilicates. In contrast, no relation is apparent between the cation exchange capacity and mole % Al₂O₃ for allophane. This difference is rather striking and although both are amorphic, i.e. show minimal specific X-ray diffraction effects, imogolite is somewhat more crystalline than allophane (Russell et al., 1969)