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 (phi(m)) attainable was predicted as phi(m) = 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 (D-f) 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. (C) 2002 Elsevier Science B.V. All rights reserved.