Thermal analysis of tributylammonium montmorillonite and laponite

Montmorillonite and Laponite loaded with different amounts of tributylammonium cations (TBAH⁺), up to 40 and 30 mmol, respectively, per 100 g clay, were studied by thermo-XRD-analysis. TBAH-smectites heated at 300 and 420°C exhibited basal spacings of 1.30 and 1.24 nm, attributed to smectite tactoids with low- and high-temperature-stable monolayer charcoals, respectively in the interlayers. DTA-EGA and TG of the TBAH-smectites showed four stages of mass loss labeled A, B, C and D. Stage A below 250°C, accompanied by an endothermic DTA peak, resulted from the dehydration of the clay. Mass loss stages B, C and D, at 250-380, 380-605°C and above 605°C, respectively, accompanied by exothermic DTA peaks, were due to three oxidation steps of the organic matter. In mass loss stage B (first oxidation step) mainly organic hydrogen was oxidized to H2O whereas carbon and nitrogen formed low- and high-temperature-stable charcoals. In stages C and D (second and third oxidation steps) low- and high-temperature- stable charcoals were oxidized, respectively. Dehydroxylation of the smectites occurred together with the second and third oxidation steps. Thermal mass loss at each step was calculated from the TG curves showing that in montmorillonite the percentage of high-temperature-stable charcoal from total charcoal decreased with higher TBAH⁺ loadings of the clay whereas in Laponite this percentage increased with higher loadings of the clay.