An investigation of the shear thickening and antithixotropic behavior of concentrated coal–water dispersions

Abstract

A study of the flow characteristics of a deflocculated, shear thickening, coal–water suspension indicated a significant antithixotropic behavior. The effect of applied shear rate, particle concentration, and shear zone dimensions were examined using a Couette flow viscometer. The dispersion was composed of refined coal particles with mass median diameter of 2.9 μm suspended in water with sufficient anionic dispersant. The rheological properties of eight dilutions of this suspension, from 47.7 to 54.5 vol %, were studied in detail. Shear stress was observed as a function of shear rate in ramp tests in which γ was increased from 10 to 1000 s−1, and as a function of time at several constant shear rates. All tests were conducted using three rotors to test the effect of annular gap width. The characteristics of the reversible, shear thickening with time phenomenon (antithixotropy) that occurs when sufficient shear rate is applied, is described in terms of three regions. Quantitative relationships that allow the determination of stress as a function of shear rate, particle concentration, and shearing time are developed for one of the rotors. An examination of the anisotropic nature of this phenomenon is also presented.