Enhancement of the compressive strength of highly porous Al2O3 foam through crack healing and improvement of the surface condition by dip-coating

Highly porous ceramic foams with open or closed cells have a wide variety of industrial applications, such as high-temperature filtration, absorption, catalyst support, lightweight materials, and high-temperature structural components. The mechanical strength of these highly porous ceramics decreases when the porosity in the foam reaches 90%. This work investigated the preparation of a highly porous Al2O3 substrate with a porosity of approximately 90% using a direct foaming technique, and coatings were deposited onto the substrate using Al2O3 slips prepared with powders of different particle sizes via a dip-coating process. Upon coating the surfaces of the foam, the surface condition was improved, and cracks were healed, producing a versatile material with good compressive strength. The interface between the Al2O3 coatings with different particle sizes and the substrate was analysed by observing the microstructure of the specimens, and their compressive strengths were compared with the compressive strength of an uncoated specimen after sintering at 1600 °C and 1700 °C for 1 h.