Bulk fluidity and apparent wall slip of aqueous kaolin suspensions studied using the cone-cone (KK) sensor: The effect of concentration and temperature

Abstract The material viscometric functions of aqueous kaolin suspensions were measured using rotational viscometry with an unconventional cone-cone (KK) sensor. The fluidity φ [ σ ] and slip χ [ σ ] functions were obtained for various concentrations (30 ÷ 40 wt.%) and temperatures (10 ÷ 40 °C), applying different gap thicknesses (0.6 ÷ 1.6 mm) of a smooth stainless sensor. Both the fluidity and slip functions decrease with increasing kaolin concentration. The fluidity of suspensions decreases also with rising temperature, which is a highly unusual trend. On the contrary, the slip coefficient follows a temperature rise of the fluidity of continuous phase, which supports the hypothesis on existence of a totally depleted slip layer. The relative slip contribution to overall kinematic effect, A , was found to vary over a broad interval. The apparent wall slip dominates at low shear stresses ( A  ≅ 90%), whereas the bulk fluidity prevails at high shear stresses ( A  ≅ 10%).