Influence of Powder Agglomerates on the Structure and Rheological Behavior of Injection‐Molded Zirconia–Wax Suspensions

Surface‐modified zirconia powders with 20% to 100% of the particle surface area covered with stearic acid was blended with 50 vol% of an organic wax vehicle for rheological study. These fractions of surface coverage gave rise to different degrees of powder agglomeration. A further adsorption of the wax on partially modified particle surfaces was examined, which was likely to exhibit different degrees of solid surface‐wax affinity depending upon whether the particle surfaces were “bare” or “premodified.” The rheological behavior of the suspensions revealed that the shear viscosity as well as the yield stress increased appreciably with decreased fractions (or surface coverage) of the pre‐adsorption. The observed suspension rheology due to incomplete surface modification can be accounted for by the formation of agglomerates which suppress suspension flowability to a significant extent. The formation of the agglomerates alters the suspension structure by reduction of the maximum solid concentration (φ max ) that is attainable for a given powder. This change in suspension structure (decrease in φ max ) leads to a restriction of particle mobility, reflected as a linear function of the yield stress of the suspensions.