Technischer Bericht NTB 93-17
Wasserdampfadsorption und spezifische Oberfläche von Tonen
Calculating the specific surface area of calcium clays from their water content with a relative humidity of 75 %, as described by KEELING et al. (1980), only provided good results for clays with predominantly inner crystalline surfaces (smectites). In the case of clays with exclusively external surfaces (illites, kaolinites), the surface areas calculated in this way were more than twice the size of the surface areas determined using nitrogen adsorption (BET).
Calculations of the surface area of calcium clays from water content with a relative humidity of 20 % showed a good correlation with measured nitrogen-BET values for clays which mainly have external surfaces. In the case of clays with predominantly inner crystalline surfaces, only half of the actual surface area was measured.
When determining the specific surface area of clays from water adsorption, it is necessary to know whether predominantly internal surfaces are present or only external surfaces. Independent measurements, for example of the external surface using nitrogen adsorption (BET), are therefore required as an additional source of information.