Modified low molecular weight polyacrylic acid as a dispersant for spontaneous coagulation casting of alumina ceramics

Slurries with high solid loading and low apparent viscosity are critical for spontaneous coagulation casting (SCC) and other in situ slurry solidification techniques. This work evaluated polyacrylic acid (PA) with a low molecular weight modified as a superior dispersant (M–PA) to increase the versatility and applicability of SCC, which traditionally employs Isobam 600AF as a dispersant in combination with Isobam 104. Varying the ratio of M–PA to Isobam 104 increased the solid loading of the alumina slurry—formulated with a commercial powder (D₅₀ = 0.45 μm)—from 56 to 58 vol%. The relative density of the alumina green body increased from 62.0% to 67.0%. The ceramics derived from a 56 vol% solid loading slurry, when sintered at 1550 °C, exhibited a relative density of 98.7%, a Vickers hardness of 17.3 GPa, and a flexural strength of 583 MPa, surpassing those of ceramics prepared with other dispersants. The ceramics derived from a 58 vol% solid loading slurry, when sintered at 1500 °C, exhibited a relative density of 98.9% and a Vickers hardness of 17.8 GPa. These findings demonstrate the potential of M–PA to broaden the applicability of SCC and suggest that the strategy of using a low–molecular–weight dispersant may enable the fabrication of high–density green bodies through SCC, resulting in high mechanical properties of ceramics under low sintering temperatures.