PHYSICAL AND STRENGTH PROPERTIES OF POROUS ALUMINA PRODUCED BY SLURRY BOILING WITH DIFFERENT SOLIDS LOADINGS

The effect of slurry solids loading on the sintered properties of a 94% alumina foam was studied. Slurries with solids content of 30 to 45 wt% were prepared. The porous samples were fabricated using a direct foaming method by boiling the slurries until the alcohol was evaporated. Sintering of the porous alumina was conducted at 1,600 ºC for 2 h. The final properties of porous alumina were investigated. It was found that the samples had similar values of apparent density from 3.55 to 3.57 g/cm³, regardless of solids loading. The apparent densities were similar because the closed pore volumes were also similar. The bulk density (1.73 g/cm³) and the porosity (52%) of samples made from slurries with solids content 30 to 40 wt% were also similar. However, the increase of solids loading to 45 wt% decreased the bulk density to 1.47 g/cm³ and increased the porosity to 59%. This was due to an increase of the open pore volume. The SEM analysis found that the 45 wt% sample had numerous small open pores, not only within the cell structure of the foam, but also in the cell walls. The flexural strengths decreased slightly from 5.5 to 4.7 MPa with increased solids loading. The results showed that the slurry solids loadings offered some control over the foam properties and that the slurry boiling method was capable of producing porous alumina with comparable properties to ceramic foams made by other methods.