Evaluation of powder loading and flow properties of Al2O3 ceramic injection molding feedstocks treated with stearic acid

Processability of ceramics via injection molding consists in reaching sufficiently high solid loading despite submicrometric size of Al2O3 ceramic particles with a correspondingly high specific surface area. High (critical) solid loading limits injection molding reflected by flow properties of the compounds. This paper is focused on the evaluation of the critical solid loading (CSL) parameter as well as reliable description of the flow properties. As surface active agents are usually incorporated in polymer binders, most often used stearic acid (SA) is combined with three different binders to achieve higher CSL. CSL is determined from evolution of mixing torque based on continuously increasing powder loading from 50 to 60 vol %. Flowability of Al2O3 feedstocks with a fixed powder loading (52 vol %) was analyzed with a capillary rheometer, and viscosity data were predicted by a master curve model representing a fixed functional structure with no adjustable (fitting) parameters. The only variables are shear rate and surface agent (SA) concentration. A deviation from the experimental data does not exceed an experimental error.