Preparation of alumina microcrystalline ceramics by nano-Al₂O₃ spheres and mass transfer kinetics research

Abstract

The spherical and dense alumina nanoparticles were used to prepare alumina microcrystalline ceramics. The effect of granulation and sintering parameters on the microstructure and mechanical properties of the ceramics was studied. The results show that fine green body can be obtained with the addition of 0.8% (mass fraction) PVA, and the density of green body can also be improved. With the increase of sintering temperature from 1400℃ to 1550℃, the density is increased from 74.1% to 97.5%, while the grain size of the ceramics is only increased gradually from 0.6 μm to 1.4 μm owing to the stable spherical shape and the uniformly packed pores. With the increase of holding time from 30 min to 120 min at 1550℃, the porosity is decreased from 4.8% to 0.4%, and the grain size is then increased from 1.2 μm to 2.7 μm. Besides, the sintering activation energy of the employed spheres is 788 kJ/mol, which proves that the particles are inactive during earlier and medium stage of sintering, and the spheres are benefit to obtain microcrystalline ceramics. The ceramic sintered at 1550℃ for 90 min has a density of 98.9%, an average grain size of 1.6 μm, a hardness of 26.4 GPa and a bending strength of 574 MPa.

Keywords

• alumina ceramics
• microcrystalline structure
• spherical particle
• mass transfer