Отправлено: 15.08.16 06:25. Заголовок: H. VAN OLPHEN SURFACE CONDUCTANCE OF VARIOUS ION FORMS OF BENTONITE

H. VAN OLPHEN Vol. 61
SURFACE CONDUCTANCE OF VARIOUS ION FORMS OF BENTONITE IN
WATER AND THE ELECTRICAL DOUBLE LAYER
BY H. VAN OLPHEN
Publication No. 191, Shell Development Company, Exploration and Production Research Division, Houston, Texas
Received February 66, IS67
From the limited dissociation of the unit layers of bentonite, which remain associated in stacks in dilute suspension despite
the high surface density of charge, it has been concluded that the counterions are held by specific adsorption forces at the
surface, resulting in a condensed electrical double layer. Nevertheless the surface conductance derived from the conduct- ance of bentonite gels on the basis of the concept of a cubic network of clay plates is quite high, and a rather high average mobility has to be assigned to the counterions when they move along the surface, amounting to 0.55 VN~ and 0.19 ucS for so- dium and calcium bentonite, respectively (u = infinite dilution mobility). Although the adsorption force makes it difficult
for ions to move away from the surface, they apparently move comparatively easily along the surface, pomibly by
jumping from one exchange position to the next, in a weak applied electric field. The greater mobility reduction shown by the calcium bentonite is in agreement with the still more condensed character of the double layer containing divalent cat- ions, which is also shown by the higher degree of stacking of unit layers in the calcium bentonite particle, as derived from
viscosity data, and by its lower electrophoretic mobility. Hydrogen bentonite is anomalous in having a low conductance although
its complete dissociation into single unit la ers indicates a well-expanded double layer, However, there is a considerable
replacement of H by A1 in the double layer wzich may constitute a barrier for the movement of the hydrogen ions along the surface. The order of magnitude of the specific surface conductance for the various ion forms is about the same and
amounts to a few times 10-9 ohm-1, The consequences for electric resistivity log interpretation for clay-containing, fluidfilled
porous rocks are briefly discussed.