Thermal analyses of mono- and divalent montmorillonite cationic derivatives

Abstract DTA and TG analyses were carried out for mono- and divalent cationic derivatives of Jelsovy-Potok montmorillonite. A certain relation between the charge density and the highest dehydration DTA peak was established for both series, since the two variables are a function of the magnitude of binding the hydrated water molecules. According to the charge density levels the cationic derivatives can be classified into three categories: (i) the single peak group falls in the range of charge density lower than 1 C m −2 ; (ii) the double peak group falls between 1 and about 2 C m −2 ; and (iii) for the higher charge densities three peaks are observed. The Ba derivative presents the only exception in this series. As the charge density increases, not only the number of dehydration peaks increases, but also the isolation between them becomes better, i.e., the overlapping of these peaks decreases in the order Ca > Li > Mg. The slopes of the TG curves in the temperature range 200–500°C increase with increase in charge density on the cationic derivative. This indicates that the rate of dehydration differs by changing the exchangeable cation of the surface, whereas the rate of dehydroxylation for all derivatives is the same since they all have the same origin.