Effect of particle size on gelcasting process and green properties in alumina

Alumina (Al2O3) green parts have been gelcast using three kinds of alumina with different particle size (mean particle size: 4.6 μm-AM-21, 0.32 μm-AKP-30, 10 nm-NS-10). The effects of particle size on gelcasting process and green microstructure have been investigated, including process parameters affecting homogeneous green microstructure. The optimum amount of dispersant for each starting material using D-3019 as dispersant was 0.2 wt.% for AM-21, 0.5 wt.% for AKP-30 and 5.0 wt.% for NS-10. The castable solid loading of each starting material, AM-21, AKP-30 and NS-10, was 59, 57 and 15 vol.%, respectively. The contents of monomer added in slips were 3 wt.% for AM-21 and AKP-30, and 6 wt.% for NS-10, respectively, and dimer (cross-linker) of 20% of the monomer concentration was added in all slips. The effect of starting materials, especially particle size, has been analyzed through microstructural analysis and green density. Microstructural analysis revealed that the size and distribution of pores in the green body was radically reduced with decreasing particle size. The green density maximum obtained was ≈59% (AM-21), ≈60% (AKP-30), ≈47% (NS-10) theoretical density (TD), at which the green strength measured was 7.0±0.8 MPa (AM-21), 11.2±0.9 MPa (AKP-30), 7.6±0.6 (NS-10). A deairing step applied before gelcasting enhanced the green strength and modified the microstructure.