MgAl₂O₄ Foams Obtained by Combustion Synthesis

Abstract

This work aims to study magnesium aluminate (MgAl2O4) ceramic foams obtained by combustion synthesis in solution without the need of surfactants to stabilize bubbles. The ceramic suspension containing acetone (75 wt%), calcined powder (25 wt%) and a mixture of glycerine (80 % blonde glycerine and 20 % crude glycerine) in the fraction of 100 % with respect to solids was prepared in an alumina ball mill, for 60 min. Subsequently, the suspension was heated at 40 °C, for 30 min, until it became rigid. In order to promote foaming, the suspension was heated to 70 °C and then the following substances were added to it: 2.5 wt% distilled water, 25 wt% Al(NO3)3.9H2O), 12.5 wt% (Mg(NO3)2.6H2O) and 0.625 wt% of a glycerine mixture (80 % blonde glycerine and 20% crude glycerine). After additions the suspension was stirred for 5 min at 950 rpm in a mixer. The resulting foams were dried at 40 °C, for 24 h, in a muffle and fired in two steps, i.e., heating at 0.5 °C/min up to 600 °C/120 min and at 5 °C/min up to 1600 °C/120 min.The obtained materials were characterized by SEM, TEM and from tomographic images. The results showed that the obtained magnesium aluminate foams have a high porosity (97 %), a high connectivity and pore sizes (diameters) between 30 and 1200 µm.