Porosity and cell size control in alumina foam preparation by thermo-foaming of powder dispersions in molten sucrose

• Foaming time, foam setting time and foam volume depend on foaming temperature.
• The foam collapses above a critical foaming temperature.
• Critical foaming temperature decreases with an increase in alumina to sucrose ratio.
• Wide range of porosity and cell size could be achieved.
• Particle agglomeration at higher alumina loading leads to lower compressive strength.

The foaming characteristics of alumina powder dispersions in molten sucrose have been studied as a function of alumina powder to sucrose weight ratio (WA/S) and foaming temperature. The increase in foaming temperature significantly decreases the foaming and foam setting time and increases the foam volume due to an increase in the rate of OH condensation as well as a decrease in the viscosity of the dispersion. Nevertheless, the foam collapses beyond a critical foaming temperature, which depends on the WA/S. The sintering shrinkage depends mainly on the WA/S and marginally on the foaming temperature. The porosity (83.4–94.6 vol.%) and cell size (0.55–1.6 mm) increase with an increase in foaming temperature (120–170 °C) and a decrease in WA/S (0.8–1.6). The drastic decrease in compressive strength and modulus beyond a WA/S of 1.2 is due to the pores generated on the cell walls and struts as a result of particle agglomeration. Gibson and Ashby plots show large deviation with respect to the model constants ‘C’ and ‘n’, especially at higher alumina powder to sucrose weight ratios.