Rheological properties of sodium montmorillonite dispersions
1988; Elsevier BV; Volume: 3; Issue: 3 Linguagem: Inglês
10.1016/0169-1317(88)90033-6
ISSN1872-9053
Autores Tópico(s)Electrostatics and Colloid Interactions
ResumoThe rheological behaviour of dispersions of montmorillonite in water is highly pH- and salt-dependent. This is exemplified for 4% (wt/wt) dispersions of montmorillonite from Wyoming and its homoionic sodium form in water, 0.01 M NaCl and 0.1 M NaCl solutions, at different pH and at temperatures from 20°C to 60°C. Generally, the shear stress (for instance, at shear rates of about 100 s−1) decreases sharply in an acidic medium to a minimum around pH 6 (pH 7.5 for the homoionic sodium form) and then increases again very strongly. Thixotropic and antithixotropic behaviour depend on pH, salt concentration and temperature. The presence of Ca2+ ions (molar ratio Na/Ca about 6.5/1) in the “pristine” montmorillonite affects the type of flow very sensitively. Ca2+ ions convert diffuse ionic layers into quasicrystalline structures with a central layer of gegen ions. Attractive potentials are then created in the contact regions between the particles, even in diluted salt solutions. Formation of band-like structures (as in the “Bändermodell” of A. Weiss) is promoted. Further, results are reported on the influence of particle size (fractions < 0.06 μm to 2 μm) on the flow behaviour at different concentrations of homoionic sodium montmorillonites from Amory and Cameron.
Referência(s)