Mechanical Properties of Wet‐Coagulated Alumina Bodies Prepared by Direct Coagulation Casting Using a MgO Coagulating Agent

Abstract

High strength and Young's modulus of wet‐coagulated bodies is key to the success of a direct coagulation casting (DCC) process. The yield strength and Young's modulus of wet‐coagulated alumina bodies prepared at various concentrations of ammonium poly(acrylate) dispersant and MgO coagulating agent has been evaluated. The yield strength and Young's modulus of the wet‐coagulated bodies, prepared at a MgO concentration equivalent to react with the dispersant, increased with an increase in the dispersant concentration due to the binding of alumina particles by the Mg‐poly(acrylate) formed by the reaction between the dispersant and MgO. Addition of MgO higher than the equivalent amount to react with the dispersant increased the yield strength, Young's modulus, and brittleness of the wet‐coagulated bodies. This is due to a combination of an increase in the cohesive force between particles and a decrease in homogeneity of the particle network in the wet‐coagulated body induced by heterocoagulation of alumina and MgO particles having opposite surface charges. The high yield strength (up to 472 kPa) and Young's modulus (up to 110 MPa) achieved would facilitate easy and successful removal of the wet‐coagulated bodies even from intricate shape molds.

Colloidal processing: enabling complex shaped ceramics with unique multiscale structures

“…Uniaxial and diametral compression tests are frequently used to evaluate the mechanical properties of both wet and dry particulate materials, the latter being a unique test that allows for an indirect tensile test of brittle solids due to the biaxial stress state. These methods were being increasingly utilized to study the tensile or compressive strength, fracture behavior, and deformation behavior of wet or dry particulate materials under particular conditions. Moreover, as applications demand finer control of microstructures and porosity structures, determining mechanical and thermomechanical properties along with elastic constants for colloidal materials produced via the methods listed in this review are becoming increasingly important …”

Magnesia induced coagulation of aqueous PZT powder suspensions for direct coagulation casting

“…This bridging of PZT particles by Mg 2+ ions through the ammonium poly(acrylate) adsorbed on the particles resulted in rapid viscosity increase and gelation of the suspension. Further, the wet-coagulated body prepared from 50 vol.% PZT suspension at dispersant concentration of 0.43 wt% and at MgO concentration of 0.097 wt% showed very high compressive strength (175 kPa) compared to the strength of wet-coagulated bodies (3.7 kPa) prepared from 50 vol.% alumina slurry at the same dispersant and MgO concentrations [21]. The higher strength of wet-coagulated bodies also suggests the cross-linking of PZT particles by Mg 2+ ions through the ammonium poly(acrylate) adsorbed on the particle surface.…”

“…Recently we have reported a novel coagulation method for direct coagulation casting of alumina suspensions prepared using ammonium poly(acrylate) dispersant using MgO as coagulating agent [19][20][21][22][23]. In this, Mg 2+ generated from the sparingly soluble MgO reacts with the un-adsorbed ammonium poly(acrylate) in the dispersion medium and form precipitate of Mg-poly(acrylate).…”

Direct Coagulation Casting of Alumina Suspension by High Valence Counter Ions Using Ca(IO3)2 as Coagulating Agent

“…reported a novel near‐net‐shape direct coagulation casting method using ammonium poly(‐acrylate) as dispersant, and the generation of Mg 2+ ions from sparingly soluble MgO. The Mg 2+ ion reacts with the un‐adsorbed ammonium poly(acrylate) in the dispersion medium to form precipitate of Mg‐poly(acrylate), and it induces the desorption of dispersant from the alumina particle surfaces, which leads to insufficient dispersant surface coverage and the coagulation of suspension . We also developed a new direct coagulation method by high valence counter ions (DCC‐HVCI) using calcium iodate as coagulating agent…”