Katsuya Nakaishi

The viscosity of a dilute suspension of sodium montmorillonite in an alkaline state

Abstract The viscosity of a suspension of sodium montmorillonite (at pH 10) was measured using a capillary viscometer as a function of electrolyte (NaCl) concentration. The concentration of clay was made sufficiently low so that the effective volume fraction could be analysed on the basis of viscosity equations. The solvent condition was maintained in an alkaline condition such that the electrostatic attraction between the edge and the face of the clay could be ignored. The results are summarized as follows. (i) In contrast to the dispersed suspension, the effect of hydrodynamic interactions in the flocculated suspension was significant even when the volume fraction of the clay was below 10 −4 . (ii) The value of the effective volume fraction Φ e of suspended flocs correlated in the order of magnitude with the volume of flocs measured in the sediment volume. (iii) There are two distinct regimes in the flocculated region. That is, in the range 6.0 × 10 −2 to 1.0 × 10 −1 M NaCl concentration, Φ e is nearly constant, while above 1.0 × 10 −1 M, Φ e increases gradually. This increment can be interpreted as an increase in the attractive force between clay sheets which is consistent with the results of the force-distance profile for mica sheets reported by Israelachivili and Adams (J. Chem. Soc. Faraday Trans. I 74 (1978) 975).

Flow characteristic of dilute Na montmorillonite suspension

Abstract The objective of this paper was to study the flow properties of dilute Na montmorillonite suspensions. Until now, a very dilute Na montmorillonite suspension has been treated as a Newtonian fluid. However, this paper shows a different behavior. Consistency curves of dilute suspensions, measured over different measuring times, may exhibit a different behavior from that of a perfect Newtonian fluid with a concentration of 33–36 kg/m 3 . The simple viscoelastic model a Maxwell model proposed by the authors in a previous paper analyzes this behavior. The theoretical analysis predicted that the consistency curve measured in au extremely short measuring time shows negative shear-rate thixotropy, and the loop disappears as time increases. The experimental results confirmed the validity of the analysis. The consistency curves of a dilute clay suspension over extensive measuring times allow estimation of the relaxation time and the shear modulus of the suspension as well as the coefficient of viscosity.

Settling velocity of a sodium montmorillonite floc under high ionic strength

Abstract The settling velocity of a single floc of sodium montmorillonite coagulated under a condition of high ionic strength was analyzed as a function of floc diameter to determine the fractal dimension of the floc. The obtained values of the fractal dimension were found to be approximately 2.0 irrespective of ionic strength and pH values. This result clearly demonstrated that the difference of the viscosity of coagulated montmorillonite suspension against ionic strength earlier reported is not affected by the difference of the fractal structure of a floc but by that of the attractive force between individual clay particles in a floc.

Rheological study on thixotropic flow: effect of time scale on flow types measurement

Abstract The object of this study is to clarify the dependence of the flow type of a clay suspension (shear-rate thixotropy or negative shear-rate thixotropy) on the time scale of measurement. First, we propose a dynamic analysis of thixotropic flow by introducing a parameter expressing the degree of softening into the Maxwell model. Then, using the above analysis, we show theoretically the dependence of the type of flow on the time scale of measurement. When a clay-water system develops structure, we measure several consistency curves for the sample by changing the time scale of measurement from shorter to longer times compared to the relaxation time T M . We are thus able to find curves that demonstrate different mechanical characteristics i.e., curves showing negative shear-rate thixotropy over shorter measurement times and curves showing shear-rate thixotropy over longer measurement times. Furthermore, we are able to predict that the measurement time that indicates changes in flow types decreases as the structure of the clay-water system develops. Finally, we performed consistency experiments for Na-montmorillonite suspensions at mass concentrations 57 kg/m 3 and 60 kg/m 3 to investigate the validity of the analysis; the experimental results did indeed confirm the validity of the analysis (i.e., it was proved that thixotropic properties of a clay dispersion system depend on the length of the measurement time T ). Further, an increase in the mass content greatly affects the thixotropic properties.