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ABSTRACT
This work aims at finding the best dispersion in a series of alumina suspensions stabilized with the help of different dosages of an electrosteric dispersant phosphate ester. Time dependent viscosities of these suspensions were measured with the help of a conventional Brookfield viscometer at low shear rate domain of 1–8 sec–1. Sedimentation tests, microscopic observations and gloss value measurement show that some of these suspensions are well-dispersed and some of them are flocculated. Time dependent viscosity measurements for all the well-dispersed suspension and a flocculated suspension were carried out in a conventional Brookfield viscometer. Interestingly, all the well-dispersed suspensions show positive drifts in viscosity with time at a constant shear; however, the magnitude of drifts differed for these suspensions. Rheological measurements show strong evidences of shear induced hydrodynamic migration occurring under the action of the applied shear rates for the well-dispersed suspensions. On the other hand, the flocculated suspensions show just the reverse behavior. Application of short-time shear ramp and long-time shear ramp on the well-dispersed suspensions shows interesting variations. ESA studies conducted for these suspensions showed strong signatures of varying particle sizes for each of these suspensions. The present investigation shows strong indication that the physics behind shear induced diffusion may be utilized to characterize and identify the best dispersion in a series of finely balanced negatively buoyant particulate suspensions by studying the time-dependent viscosities of these suspensions under low shear conditions.
Abbreviations
| = | shear rate | |
| = | shear stress | |
| a | = | particle diameter |
| = | kinematic viscosity of the suspension | |
| = | viscosity of the continuous medium | |
| = | apparent viscosity | |
| = | local viscosity at height | |
| = | radius of the spindle | |
| = | radius of the couette cup | |
| = | rotational speed of the inner cylinder | |
| d | = | |
| E | = | |
| Js | = | sedimentation flux |
| = | shear induced diffusion flux | |
| = | density of particle | |
| = | density of the continuous media | |
| = | gravitational acceleration | |
| = | hindrance factor | |
| = | volume fraction | |
| = | diffusion coefficient perpendicular to the velocity gradient | |
| = | initial height of the well settled layer | |
| = | height in z direction |
Acknowledgments
The corresponding author would like to thank the authorities of Mody University for providing space and other infrastructural support. Sincere thanks also go to Prof. D. Chattopadhayay, Department of the Mechanical Engineering, Mody University for useful discussions and Dr. A. Sen of Central Glass and Ceramic Research Institute, Kolkata for his support in providing the dispersant.
Funding
This work was supported by the Department of Science & Technology, Government of India under the SERC Scheme to the corresponding author vide order no SR/S1/PC-12/2009.