Microstructural Observation of Tubular Halloysite with a High-Resolution Transmission Electron Microscope

Abstract

Halloysite is one of the kaolin minerals with a tubular form. High-resolution transmission electron microscope (HRTEM) images of tubular halloysite could be taken, but this required extreme care because its structure easily changes to an amorphous state by a thermal-electron beam. The selected area diffraction (SAD) pattern showed that the halloysite has a monoclinic structure as a dehydrated form of halloysite (0.7 nm of (001) spacing). Along the c-direction, two types of lattice fringes were observed in the HRTEM images: one is a lattice image with a periodical distance of 0.7 nm spacing, and the other is stripes caused by the domains with 5-10 nm thickness. In addition, a twinned structure was also observed in the halloysite.