Rheological properties and thixotropy model of concentrated aqueous silicon slurry for gel casting

The effect of poly(acrylic acid) ammonium (PAA-NH4) dispersant on high solids content silicon suspensions was rheologically characterized. The viscosity and fluidity exhibited a strong dependence on the solids concentration, but when subjected to certain amount of dispersant PAA-NH4 adsorption and high speed shear sweep investigations, the suspensions demonstrated shear-thinning and thixotropic behavior as a result of changes to the suspension microstructure. Zeta potential and sedimentation character showed that the dispersant was adsorbed on silicon for efficient stabilization at high solids loadings. A general structural kinetics model was presented to describe the flow behavior of the thixotropic systems. The effect of shear on structure breakdown and build-up, as well as the effect of Brownian motion on build-up were taken into account to the kinetic equation for the structure parameter. Due to the PAA-NH4 absorption modality, thixotropic model characterized the PAA-NH4 concentration-dependent behavior of the suspensions over a wide range of PAA-NH4 concentration.