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Abstract

Adsorption-desorption calorimetry (ADCAL) was used to determine surface areas of 10 mineral powders, including 4 clay minerals, and carbon black. The method involved flowing a carrier liquid (pure heptane) through a small amount (< 0.4 g) of sample in the sorption cell of a commercial microcalorimeter. When thermal equilibrium was established, pure heptane was replaced by a heptane solution containing n-butanol (n-BuOH) as an adsorbate. The maximum integral enthalpy of adsorption of n-BuOH on the surface was assumed to be proportional to the surface area of the sample. The empirical proportionality constant was determined using a reference sample (SiO2 or kaolinite (KGa-l)) of known BET surface area.

Well-characterized powders of TiO2 (anatase) and very poorly crystalline SiO2, ZnO, and carbon black of known BET specific surface areas ranging from 24.3 to 0.64 m2/g were used as standards to determine the internal consistency of the method. A precision of ±4% was obtained; the specific surface areas determined by ADCAL were within ± 5% of the BET values. The method was applied to three nonex-panding clay minerals (a well crystallized (KGa-l) and a poorly crystallized (KGa-2) kaolinite and pal-ygorskite (PF1–1)), one expanding clay mineral (Wyoming montmorillonite (SWy-1)), and two minerals with low specific surface areas ( < 0.5 m2/g), olivine and microcline. Except for the expanding clay and the very low surface area microcline, the specific surface areas determined by ADCAL were within ± 4% of the BET values. The advantages of this method are that it is fast ( < 2 hr/sample), only a small amount of sample is required ( < 0.4 g), and it can be conducted at room temperature.

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