Experiments on aqueous suspensions of Fe2O3 particles indicated that the viscosity increased with temperature rather than decreased as is usual and, in terms of the Arrhenius law, the activation energy appeared to be negative. Results were interpreted in terms of an activation energy in which the activation entropy becomes important. The energy required for flow is partially used to break up the colloidal structure of the suspensions and as the structure becomes more stable at higher temperatures, the viscosity increases. Results can be interpreted in terms of a kinetic equation having positive valued activation enthalpies together with negative valued activation entropies. (C) 2016 Elsevier B.V. All rights reserved.