High-strength, high-porosity and low-shrinkage Al2O3 ceramics prepared by flexible adjustment of CaCO3 size and content

Abstract

A high-strength, high-porosity and low-shrinkage Al2O3 ceramics was prepared by direct ink writing method (DIW) using CaCO3 as a mineralizer. The effect of CaCO3 size and content on the phase formation, microstructural evolution and properties of porous Al2O3 ceramics sintered at 1400 ℃ were systematically investigated. The results showed that the properties of the porous Al2O3 ceramics were significantly affected by the particle size and content of CaCO3. The fine particle size and increased CaCO3 content could enhance the effective contact area between CaCO3 and Al2O3, facilitating the reaction at high temperatures during the sintering at 1400 ℃. It was found that the favorite sintering condition promoted the formation of calcium hexaluminate (CA6) and calcium dialuminate (CA2). Microstructure analysis revealed that CA6 exhibited a lamellar and tabular morphology, concentrated primarily at the pore boundaries, while some CA6 were adhered on the surface of Al2O3 particles. CA2 were mainly embedded around Al2O3 particles. The increase of CA6 and CA2 contents improved the flexural strength and porosity, and decreased the shrinkage rate. The Al2O3 ceramics with high flexural strength, high porosity and low shrinkage rate were successfully fabricated by adding 20 wt% CaCO3 with the particle size D90 below 7.8 µm. The resulting flexural strength and porosity were 8.9 MPa and 71.9%, respectively, representing an improvement of 21.9% and 19.8% compared to Al2O3 ceramics without CaCO3. Additionally, the shrinkage rate in the X (0.9%), Y (1.1%), and Z (1.5%) directions decreased significantly, and the corresponding reductions were 75.0%, 73.2%, and 74.1%, respectively.