ISSN:
1435-1536
Keywords:
Alcohols
;
card-house
;
clay minerals
;
coagulation
;
edge/face aggregation
;
face/face aggregation
;
montmorillonite
;
salt stability
;
sedimentation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The critical coagulation concentration,c K, of sodium chloride for sodium montmorillonite dispersed in water (solid content 0.025 percent) is 8 mmol/L. It remains virtually constant (7.5–8.5 mmol/L) in water-rich alcohol mixtures (below 50% (v/v) methanol and 40% ethanol and propanol). At higher alcohol contents thec K decreases to 3.6 mmol/L (70 percent methanol), 1.2 mmol/L (70 percent ethanol), and 0.8 mmol/L (60 percent propanol). In the presence of 10−4 M sodium diphosphate thec K in water rises to 195 mmol/L. In contrast to the behavior in the absence of diphosphate, even small amounts of alcohol reduce the critical coagulation concentration. In 70% methanol thec K is 7.5 mmol/L, in 70 percent ethanol 2.5 mmol/L and in 60% propanol 5 mmol/L. The main mechanism is coagulation by contacts between negatively charged edges and faces. At high alcohol contents montmorillonite-alcohol complexes (interlayer solvates) are formed and the colloidal dispersions become unstable even in the absence of salt. Transition from the state with diffuse ionic layers into the quasi-crystalline structure of the interlayer solvates is also evident from the sediment volume which changes with the alcohol content. Maxima are observed which are indicative of band-type structures as intermediate states between the colloidally dispersed particles with repulsive interaction and the discrete particles of the montmorillonite-alcohol complexes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00657786
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