Abstract
The flow characteristics for 2.5%dispersions of smectites were investigated by a continuous and variable rpm viscometer of concentric-cylinder type. The smectite samples used were a purified bentonite product Kunipia-F, a synthesized hectorite-like clay product Laponite RD and a fluorhectorite-like clay specimen FH-03 hydrothermally synthesized at 150°C in 2 h. The flow curve for the Kunipia-F dispersion was essentially the same as those for colloidal coagulated sols, and could be accounted for by two parameters, plastic viscosity and yield value. On the other hand, shear rate and shear stress flow curves for 2.5% dispersions of RD and FH-03 showed mountain-shaped parts caused by their gel formation. Peak positions of the mountain-shaped parts were time-dependent. After a short set time, a first peak appeared at 40 s-1, then an additional peak followed at 119 s-1 as the set time became longer, and ultimately the first peak tended to disappear. This may indicate that both RD and FH-03 gels were formed in two stages. The differences of flow characteristics between RD and FH-03 dispersions are summarized as follows;
(1) The mountain-shaped parts in the flow curves for FH-03 dispersions appeared faster than that for RD dispersion, implying that FH-03 dispersion formed gel structure more quickly compared with RD dispersion, (2) The hysterisis loop area in the flow curve for FH-03 dispersion was larger than that for RD dispersion, indicating that FH-03 dispersion has higher thixotropic nature than RD dispersion, (3) The hysterisis loop was divided into two areas, one responsible for the gel structure and the other for the coagulated sol structure. The former was dominant in FH-03 dispersion and so was the latter in RD dispersion.
