Rheology of concentrated SiC particles in silicon alkoxide sols

Abstract

Silicon carbide (SiC) particles were mixed with silicon alkoxide precursors at the sol level, and their rheological behaviors were examined under various solids concentrations ( ϕ = 0.10–0.22 in volumetric ratios) and shear rates ( γ ˙ = 1 – 1000 s −1). The alkoxide precursors were mixtures of tetraethyl orthosilicate (TEOS, Si(OC 2H 5) 4), ethyl alcohol (C 2H 5OH), H 2O and HCl in a constant [H 2O]/[TEOS] ratio of 11. The powdered mixtures all exhibited a shear-thinning flow behavior over most of the shear-rate range examined. This indicates that the concentrated suspensions were flocculated in character. Relative viscosity of the suspensions increased markedly as ϕ increased, suggesting that the particle interaction becomes more pronounced with the increased ϕ. No evidence was seen found for possible particle–precursor interactions at the sol level that might catalyze gelation of the sols. A theoretical maximum solids concentration ( ϕ m) of the suspensions was determined as ϕ m = 0.26–0.28 over a shear-rate range γ ˙ = 10 – 100 s −1. This reduced ϕ m value partially confirmed the dominance of attractive interparticle van der Waals forces in the particle–precursor mixtures.