THE FLOW CHARACTERISTICS OF HALLOYSITE SUSPENSIONS

The theology of aqueous suspensions of Na halloysites with different p article shape has been investigated using a Haake rotary viscometer. T hree halloysites from New Zealand were used: Matauri Bay (MB), Te Akat ea (TA) and Opotiki (Op) which are mainly composed of thick long tubul es, short thin laths, and spherules, respectively. Suspensions of the materials subsequently prepared from the MB and TA samples show a pseu doplastic consistency under shear, characterized by a steep initial ri se in sheer stress as shear rate increases, followed by a linear incre ase in stress when a certain shear rate is exceeded. The Op halloysite , on the other hand, shows Newtonian flow behaviour for which shear st ress increases linearly with sheer rate throughout. For MB and TA, the shear stress developed during rotor acceleration is larger than that produced during deceleration, and the corresponding flow curves enclos e a hysteresis loop. As suspension pH increases, the pseudoplastic cha racter decreases as does the amount of hysteresis. Above pH 7.5, flow approaches Newtonian and hysteresis is absent. Plots of Bingham yield value against pH at different ionic strengths (0.003, 0.03 and 0.3 M N aCl) intersect at pH 6.0 for MB and at pH 7.1 for TA. These values are identified with the point of zero charge (PZC) of the particle edge s urface. The flow characteristics of halloysites may be explained in te rms of the influence of particle shape, pH, electrolyte concentrations , and layer composition on particle interactions.