Enhancement and mechanism of vermiculite thermal expansion modified by sodium ions

Abstract

Aimed at improving vermiculite's thermal expansibility, a novel method of Na⁺ modification has been proposed. The modification effects were characterized via X-ray fluorescence spectroscopy, X-ray diffraction, and thermogravimetric-differential thermal analysis. The result indicated that sodium ions entered vermiculite interlayers through the exchange of interlamellar calcium ions. The effects of the heating time on the expansion ratio of Raw-V and Na-V samples were investigated at the temperature range of 400–700 °C. The result indicated that the maximum increment in the expansion ratio could reach up to 26.5% after Na⁺ modification. The influencing mechanism of Na⁺ modification on the thermal expansibility of vermiculite was explored via molecular dynamics simulation and the binding energy and dehydration enthalpy change calculation. The simulation and calculation results showed a good agreement with the expansion experiment result. This study provides a novel method for the preparation of high-performance expanded vermiculite.