Aluminum/sodium pliveirahosphate-based closed cell ceramic foams

Hydrous aluminum phosphates containing sodium were obtained by treating aluminum hydroxide with aqueous solutions of sodium orthophosphate or phosphoric acid and sodium hydroxide. The composition of the solids varied according to the initial concentration of reagents, pH of the reaction mixture, number of washings and reaction time. The properties of the solids upon heating are strongly dependent on their chemical compositions as P/Al and Na/Al ratios. Solids with high P/Al and Na/Al ratios are transformed into a closed cell foam in a temperature range 600°C to 1000°C, and solids with lower P/Al and Na/Al do not foam by heating up to 1000°C. The foams and powders were characterized by X-ray diffraction, infrared spectrophotometry, optical and scanning electron microscopy (SEM) and density determinations. The results suggest that the foam skeletal material consists of a glass–ceramic in which AlPO4 crystalline phase is dispersed in a sodium-rich amorphous matrix.