Effect of polymeric dispersant on rheological behavior of nickel–terpineol suspensions

The rheological behavior of submicrometer nickel powders dispersed in terpineol solvent was investigated in terms of dispersant type, dispersant concentration (0.5–10% of the powder weight) and solids loading (3–10 vol.%) over a shear-rate range 1–1000 s−1. Seven commercially available polymeric dispersants of varying natures were used in the study; among which, the polymeric surfactants featured with nonionic functional groups provided the best dispersion effectiveness. The suspension viscosity reached a minimum as the dispersant concentration exceeding 2 wt.% of the solids to a viscosity level about 60% of the suspension containing no dispersant. The suspensions all appeared pseudoplastic over the shear-rate range investigated, revealing the mixtures were flocculated in structure. The maximum solids concentration (φm) attainable was predicted as φm=0.113±0.014 in the given suspension system. The rheological measurement further revealed that the particulate network formed in the flocculated slurry was most likely of a fractal nature; to which, an attractive van der Waals force dominated the interparticle potentials. An estimated fractal dimension (Df) of 2.13 was determined experimentally, suggesting a reaction-limited cluster–cluster aggregation may be in operative or the aggregates may have undergone substantial flow-induced rearrangement upon shearing.