Rheological Characterization And Application Of Nano-ceria Suspensions

In nanoparticle suspensions, attractive or repulsive forces betweennanoparticles are known to influence strongly the microstructure and give riseto very different rheological behaviors. The rheological properties areimportant for the handling and application of the suspensions and it is aeffective way to predict the dispersion conditions of the suspensions. In thisresearch, the rheology property of ceria slurry CeO₂/water suspensions andCeO₂/base oil suspensions were investigated with the Rheostress.The application of ceria suspension as polishing slurry for chemicalmechanical polishing has received great attention due to its high polishingremoval rate and good surface quality. The dispersion conditions, stability andsurface properties of polishing slurries are important for the storage, transportand application of them while rheological behaviors of the slurries play animportant role in those properties. In this research, the rheology property ofceria slurry was investigated. The effects of pH, particle concentration,temperature and electrolyte concentration were discussed. The results showthat the value of zeta potential has very corresponding relation with rheologyproperty. Lower zeta potential gives rise to a higher apparent viscosity and results in the observed shear thinning property. In the suspension if the particleconcentration is below17.5wt%, ceria slurry exhibits Newtonian behavior andfurther addition of CeO₂, however， higher apparent viscosity andshear-thinning behavior is observed. The influence of temperature on rheologyproperty of ceria slurry appears more complex. If the electrolyte is added intothe slurry, a shift of apparent viscosity to a higher value is observed due to thedecreased zeta potential.The application of inorganic nanoparticles as lubricating additives hasreceived great attention due to its unique anti-wear properties, load-carryingcapacities, friction-reduction behavior and environmental friendly. It isnecessary to study on the rheological properties of nano-particles as additives,because the rheological properties are important for the transport, handlingand application of the suspensions. In this research, the rheological propertiesof ceria suspensions were measured and the effects of particle concentration,temperature and shear time were discussed. The results indicated that shearviscosity increased with the increase of particle concentration. When theweight fraction was below30wt%, the slurries exhibit Newtonian behavior.For higher weight fraction, pronouncedly increasing viscosity and slightlyshear-thinning behavior was observed. Power-law model was used to fit theexperimental data and the solid concentration had an effect on the obtainedparameters. The viscosity and shear thinning behavior decreased astemperature increases. The suspensions with the solid loading higher than 30wt%show the time dependent behavior. The thixotropy decreases with theincrease of temperature and decrease of solid loading. At low temperature,slight temperature increase lead to the sharp thixotropy decrease due to theeffect of Brownian diffusion and convection.Then the CeO₂particles and T321were added into the grease. Tribologicalbehavior were investigated. The results show that the additive can improve theperformance of the grease.