Effect of Heat Treatment on Structure, Morphology and Surface Properties of Halloysite

Halloysite was one of the nanoscale tubular minerals in nature. The objective of the present study was to investigate the effect of heat treatment on structure, morphology and surface properties of tubular halloysite, which were significant in the applications of halloysite as functional materials but had received scant attention in comparison with kaolinite. X-ray diffraction (XRD), thermo gravimetric analysis (TG-DSC), field scanning eletron microscope (FSEM), transmission electron microscope (TEM) and surface area measurement (BET) were adopted to characterize raw and heated minerals. The interior diameter of halloysite tube was about 50 nm, and the length of tube was in the range of 0.5-1.0 μm. A series of substantial changes in crystalline structure and phase state occured in halloysite after heated treatment. The FSEM and TEM images of halloysite showed that the unheated halloysite particles possessed typical cylindrical shapes and contained transparent central areas that run long-itudinally along the cylinder, indicating that the cylinders were hollow and open ended. The morphology of the halloysite had no obvious change before and after heat treatment. Specific surface areas (S_BET) of the raw and heated mineral below 800 °C were similar (in the range of 35-36 m²/g), suggesting that it still maintained tubular structure. (paper)