MICROSTRUCTURAL CHARACTERIZATION OF ALUMINA AND SILICON-CARBIDE SLIP-CAST CAKES

The effect of solids loading, particle-size distribution, and suspensi on viscosity on the resultant microstructure of slip-cast monolithic c eramics prepared from aqueous suspensions of alumina and silicon carbi de was studied, Unimodal alumina suspensions (average particle size = 0.6 mu m) were prepared at 35, 37, and 42 vol%. Silicon cal bide suspe nsions (average particle size = 0.7 mu m) were produced with different quantities of dispersant at 37 vol%. Similarly, aqueous alumina suspe nsions of 42 and 50 vol% were produced with a bimodal particle-size di stribution. The slip-cast microstructures were characterized by mercur y porosimetry and small-angle neutron scattering, which provided pore size (distribution), pore fraction, and pore morphology, Essentially, the combination of these techniques deciphered packing differences obt ained in the cake microstructures, For the alumina cakes produced from the 35, 37, and 42 vol% suspensions, the individual characterization techniques? mercury intrusion, and the neutron scattering measurements showed that the cake microstructures mere similar in pore size and qu antity, However, comparison of the techniques and their assumptions sh owed differences in the pore shape, Mercury porosimetry and neutron sc attering showed bimodal porosity for the cake produced from a mixture of 85% 6-mu m particles and 15% 0.6-mu m particles, Pore volume fracti on and pore size increasers mere correlated with increased viscosity i n the silicon carbide suspensions, In addition, the silicon carbide ca ke microstructures were measured, and homogeneity was evaluated as a f unction of position in the cast.