Bulk fluidity and apparent wall slip of aqueous kaolin suspensions studied using the cone-cone (KK) sensor: Effect of the sensor surface quality A Physicochemical and engineering aspects

Influence of sensor surface quality on apparent wall slip (AWS) effects in aqueous kaolin suspensions was studied using AWS rotational viscometry with four unconventional cone-cone (KK) sensors of different materials and surface finishing. The fluidity φ[σ] and slip χ[σ] material functions were obtained for three concentrations of kaolin (30, 35, and 40wt.%) applying several gap thicknesses (between 0.6 and 1.6mm). Positive slip coefficients were found in the sensors made from titanium or stainless steel with smooth or sand-blasted surfaces. A negative AWS effect was detected for the sensor made of aluminum alloy with eloxal coated surfaces. This negative AWS effect is interpreted as a consequence of possible formation of a stagnant layer at the walls.