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Effect of concentration and pH on the viscous and electrochemical properties of hydrogen bentonites
Published in -
Volume: 47
Issue: 8
Pages: 553 - 577
1. The specific conductivity of dilute suspensions of hydrogen bentonites at first increases linearly with increase of concentration, then rises much more rapidly, being convex to the concentration axis, after which the slope again diminishes. Λ (conductivity per gram of colloid) at first shows a small variation, indicating that it is approximately constant within the limits of experimental error, whereafter it rapidly diminishes and ultimately passes through a minimum. 2. The cataphoretic velocity increases with the concentration and passes through a maximum at approximately the same concentration as that at which Λ passes through a minimum, while yield value first becomes noticeable at approximately this concentration. 3. The pH changes proportionately with -log C. The conductivity per gram of colloid calculated from the hydrogen-ion concentration is appreciably greater than Λ. 4. The extinction coefficient at first diminishes with concentration and then passes alternately through a minimum and a maximum. Similar variations in the extinction coefficient with time have been observed during slow coagulation of hydrogen bentonites. 5. The coefficient of viscosity increases more rapidly with concentration than one would expect from a linear relationship. 6. The apparent specific gravity increases with concentration and reaches a constant value. This constant value of apparent specific gravity agrees fairly well with the specific gravity of dry bentonite (dried at 105°C.) measured in toluene. 7. The results suggest that as concentration rises aggregates are first formed and that at a still higher concentration these aggregates form some sort of structure which possesses yield value. 8. Variations in the yield value, consistency, and thixotropy with pH have been found to be closely related to buffer capacities calculated from titration curves with caustic soda.
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JournalJournal of Physical Chemistry