Influence of bound water layer on the viscosity of oxide nanopowder suspensions

Nanopowder suspensions exhibit much higher viscosities compared to micron size powders. The current viscosity models greatly underestimate the viscosity of nanopowder suspensions and hence are inaccurate. Recently, it was shown that a bound water layer around the particles is partially responsible for the high viscosities of alumina nanopowder suspensions. In the present study, the existence and effect of the bound water layer on suspension viscosity has been validated for other oxide systems such as zirconia, yttria stabilized zirconia and titania. The water melting events were studied by low-temperature differential scanning calorimetry (LT-DSC) to investigate the nature of the bound water and how it varied by different oxide systems. Onset of the bound water for these oxides varied from −1 to −7 °C. The variation in melting behavior of bound water was related to the presence of charged species in solution and gel-like hydroxide formation. The bound water content was estimated and incorporated into a modified Krieger–Dougherty (K–D) equation. The modified equation was employed to interpret the experimental data. Intrinsic viscosity values were estimated as 11.6, 6.6, 5.1 and 3.1 at a shear rate of 50 s−1 for alumina, titania, zirconia and YSZ, respectively. Increasing shear rate predicted lower intrinsic viscosity values. Modified K–D equation could predict the suspension viscosity much better than the other available models in literature while distinguishing the differences between oxide systems.