Preparation of ceramic foam spheres by injection molding of emulsions

An emulsion-based injection molding process has been reported for the preparation of ceramic foam spheres from kaolin and alumina. The foam spheres produced from kaolin alone cracked during sintering due to extensive shrinkage and an excessive glass phase. Incorporation of a minimum of 10 wt% alumina in kaolin prevented the cracking of foam spheres during sintering by promoting secondary mullite growth, which decreases both the glass phase concentration and sintering shrinkage. Foam spheres with an interconnected cellular structure having open porosities, average cell sizes and diametrical compressive strengths in the ranges of 76.5 to 82.7 vol.%, 6.8 to 9.2 μm and 1.65 to 0.93 MPa, respectively, were produced from emulsions prepared from hydrogenated vegetable oil and aqueous clay slurries. The interconnected open cell structure and small cell size enabled fast absorption and 100% retention of urea solution for N2O4 scrubber application. The urea solution absorption capacity (71.5 to 80 vol.%) of the foam spheres was much higher than the capacity (45.6 vol.%) of the porous clay ceramic media currently used in N2O4 scrubbers.