Robocasting of MgO-doped alumina using alginic acid slurries

Abstract

The benefits of MgO doping of alumina for maintaining a homogeneous grain structure have long been established. Therefore in this work a bespoke ink for Robocasting of alumina is developed based on the gelation of alginic acid using magnesium ions, thereby ensuring homogeneous MgO doping of the alumina green body. The shear thinning behavior of alginic acid based solutions was paired with the rheological properties of a partially coagulated colloidal suspension to allow high solid loading inks (up to 50 vol%) with good extrusion behavior. Shear thinning coefficients of n ~ 0.2 were recorded, with yield stresses of 250 Pa and stiffness values in the range 100-1000 kPa. The printed alumina bars reached densities of >98% and unpolished strengths reached up to 326 ± 16 MPa after sintering at 0.4 mol/L magnesium chloride and 45 vol% alumina.