Synthesis of a quasi-stable kaolinite and heat capacity of interlayer water

Abstract

The mineral halloysite, in its hydrated and dehydrated forms, has attracted much attention¹ but, in spite of much careful X-ray and electron diffraction work, and electron microscopy, NMR and IR spectroscopic studies, there remain many questions about the crystal structure of the layers, their stacking, as well as the position, motion and bonding of the water molecules (in the hydrated form) to each other and to the surrounding silicate layers. The difficulties associated with studying halloysites are principally due to the great variability observed in natural samples² and, in the hydrated form, the existence of substantial amounts of pore water in addition to interlayer water. We have attempted to simplify the former difficulty by synthesizing a 10-Å hydrate similar to halloysite-10 Å (ref. 3) starting with a well characterized, crystalline kaolinite from Georgia. Here we report the successful synthesis of a 10-Å hydrate which is stable at reduced temperatures and contains no pore water. With this material we have measured C_p for the interlayer water between 110 and 270 K.