Rheology and microstructure of concentrated zirconia-alumina suspensions for gelcasting composites
The relations among colloidal stability, suspension rheology, and solids loading are elucidated for zirconia-alumina mixtures containing 20 volt ZrO{sub 2}, based on solids. The lower colloidal stability of ZrO{sub 2} limits the rheological properties of this system. If the zeta potential of ZrO{sub 2} is less than 49 mV, high degrees of pseudoplasticity, high yield stress, high viscosity, and long relaxation times characterize the binary suspensions. These effects occur, despite the fact that ZrO{sub 2} is the minor ceramic constituent. If the zeta potential of ZrO{sub 2} is maintained above 49 mV, suspensions with high solids loading (55 vol%) can be prepared which behave as Newtonian fluids over the 0-to-200 s-1 shear rate range and as an elastic solid at higher rates. As the solids loading of a highly stable binary suspension is increased, the rheological properties change. They evolve from those of a near Newtonian-like fluid with nearly independent particles (40 vol%) to those of a pseudoplastic fluid with a weakly interacting particle network (50 vol%) to those of an elastic-like solid composed of crowded, strongly repulsive particles (55 vol%). Low-shear conditions for suspension-transport and mold-filling operations that ensure a homogeneous arrangement of ZrO{sub 2} and Al{sub 2}O{sub 3} particles in a gelcast ceramic seem promising.
- Research Organization:
- Oak Ridge National Lab., TN (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 10162846
- Report Number(s):
- CONF-921101--133; ON: DE93015339
- Country of Publication:
- United States
- Language:
- English
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