Preparation of low density carbon foams by foaming molten sucrose using an aluminium nitrate blowing agent

Abstract

Low density carbon foams have been prepared by thermo-foaming of molten sucrose using aluminium nitrate as a blowing agent to produce solid organic foams followed by dehydration and carbonization. Gas bubbles are generated in the molten sucrose due to water vapour produced by the acid catalysed condensation between sucrose hydroxyl groups and NOx gases produced by the thermal decomposition of the aluminium nitrate. Higher melt viscosity achieved by cross-linking of the condensation products of sucrose through co-ordination of the aluminium ions with the hydroxyl groups stabilizes the bubbles against coalescence and rupture. The foam volume, foaming time and setting time depend on the aluminium nitrate concentrations. The carbon obtained by the pyrolysis of the solid organic foams has turbostratic graphite structure. The foams produced have an interconnected near-spherical cellular structure. The carbon foams prepared at aluminium nitrate concentrations in the range of 0.5–4wt.% have a density and average cell size in the ranges of 0.085–0.053g/cc and 1.55–0.83mm, respectively. The alumina (∼0.17–1.34wt.%) produced from the aluminium nitrate is concentrated more on the surface of cell walls, ligaments, and struts.