Synthesis and properties of high alumina cement-based porous composites in the ZrO2-CaO-Al2O3 system

Abstract

Previous research showed that ZrO2–CaO–Al2O3 (Z-C-A) composites presented high chemical stability, making them suitable as refractory materials. This work obtained porous composites based on CA2–CZ and CA–CA2–CZ phases using commercial high-alumina cement (HAC) and pure ZrO2 powders with CaCO3 and Al(OH)3. The powder mixtures were dry-uniaxially pressed and sintered at 1300 and 1400 °C. The reaction was studied using thermal analysis techniques (TG-DTA). CaAl4O7 (CA2), CaAl2O4 (CA), and CaZrO3 (CZ) were the main phases formed in the ceramics, with c-ZrO2 as a secondary phase. The sintering at 1400 °C promoted the in situ reactions, leading to the formation of the CA2 and CZ phases and producing the reduction of the CA and c-ZrO2 phase content. The high porosity determined in these composites (44–63 %) could be attributed to the thermal decomposition of gibbsite (Al(OH)3) during calcination. In the ceramics with a high content of the CA2 phase (66.7 and 76.7 wt% determined by Rietveld), the thermal expansion coefficient (CTE) reached a minimum value of ∼5.8 × 10−6 °C−1, comparable to that of the mullite. The composite based on CA2-CZ phases (sintered at 1400 °C) presented the highest flexural strength (37 MPa), attributed to its lower porosity and more homogeneous microstructure.