Investigation on Densification Mechanism of Calcium Hexaluminate Ceramics Using Digital Image Correlation Method

ABSTRACT The CaAl 2 O 4 –CaAl 4 O 7 (CA–CA 2 ) tailing slag was adopted to replace CaCO 3 , synthesizing calcium hexaluminate (CA 6 ) ceramics through reactive sintering with Al 2 O 3 . Digital image correlation (DIC) technology was employed to monitor volumetric effects in real time, while phases and morphology were combined to elucidate the densification mechanism. The results demonstrate that reducing intermediate reactions while modifying the crystal structure of CA 6 through doping can significantly enhance densification. Thermal expansion, in situ CA, CA 2 , and CA 6 formation sequentially dominated the volumetric expansion. Using CA–CA 2 tailing slag as the calcium source reduced the expansion caused by CA and CA 2 formation. The trace TiO 2 and MgO impurities inherently present in the CA–CA 2 tailing slag dissolved into CA 6 lattice, promoting a morphological transition from plate‐like to equiaxed grains, thereby further enhancing densification. Dense CA 6 ceramics with an apparent porosity of 2.4% and bulk density of 3.39 g·cm −3 were successfully prepared via one‐step sintering at 1700°C and performed good alkali corrosion resistance.