Specific surface area measurements of The Clay Minerals Society source clays were made by the Brunauer, Emmett and Teller (BET) method of adsorption of nitrogen gas. Two replicate measurements of specific surface area were performed for each source clay. All pair values were within 3%, which is very good agreement for this type of measurement.

Abstract~A white calcium bentonite (CAB) from the KiJtahya region, Turkey, contains 35 wt. % opal-CT and 65 wt. % Ca-rich montmorillonite (CAM). Samples were heated at various temperatures between 100-1300~ for 2 h. Thermal gravimetric (TG), derivative thermal gravimetric (DTG), and differential thermal analysis (DTA) curves were determined. Adsorption and desorption of N 2 at liquid N2 temperature for each heat-treated sample was determined. X-ray diffraction (XRD) and cation-exchange capacity (CEC) data were obtaine& The change in the d(001) value and the deformation of the crystal structure of CaM depend on temperature. Deformation is defined here as changes of the clay by dehydration, dehydroxylation, recrystallization, shrinkage, fracture, etc'. The activation energies related to the dehydration and dehydroxylation of CaB calculated from the thermogravimetric data are 33 and 59 kJ mol ~, respectively. The average deformation enthalpies, in the respective temperature intervals between 200-700~ and 700-900~ were estimated to be 25 and 205 kJ moI -I using CEC data and an approach developed in this study. The specific surface area (S) and the specific micropore-mesopore volume (V) calculated from the adsorption and desorption data, respectively, show a "zig zag" variation with increasing temperature to 700~ but decrease rapidly above this temperature. The S and V values were 43 m 2 g ~ and 0.107 cm 3 g ~, respectively, for untreated bentonite. They reach a maximum at 500~ and are 89 m 2 g 1 and 0.149 cm 3 g-~, respectively. The XRD data clearly show that, at 500~ where the irreversible dehydration is completed without any change in the crystal structure, the porosity of CaM reaches its maximum.

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The Hançılı bentonite from Turkey shows significant changes in surface area, micro- and mesoporosity, surface acidity and acid strength with heating from 100 to 900°C for 2 h. The specific surface area (S) and specific micro-mesopore volume (V) of the original and heated samples were evaluated from N2 adsorption and desorption data, respectively, by standard methods. The adsorption of n-butylamine from the solution in cyclohexane on the samples was used to determine the total surface acidity (nm) and the adsorption equilibrium constant (K) was taken as a measure of the acid strength. S, V and nm having initial values of 98 m2g−1, 0.080 cm3g−1 and 4.8 × 10−4 mol g−1, respectively, stayed approximately constant as the temperature increased to 450°C and then decreased almost in parallel with each other, reaching their minimum or zero at 900°C. The total surface acidity, in general, declines with increasing temperature. The most acidic sites, however, increase with heating, and especially at dehydration and dehydroxylation. Acid strength reaches its maximum during the dehydroxylation phase at ∼600°C. It was concluded that the total surface acidity does not necessarily parallel the strength of the most acid sites.

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