Effect of Nano-Crystalline Boehmite Addition on Sintering and Properties of Alumina Ceramics

In this study, alumina ceramics containing up to 10 wt% of boehmite were sintered at 1550, 1600 and 1650 C-circle for 1 hour. Water absorption, weight loss, porosity and density values were measured after sintering. Boehmite content caused flocculation during mixing in water suspension. Formation of boehmite agglomerates was clearly seen in SEM examination and also it was observed that there were different shrinkages in alumina matrix and in boehmite agglomerates and this caused gaps around agglomerates. Boehmite addition decreased mechanical properties due to the inhomogeneous dispersion of boehmite in alumina mixtures. Large boehmite agglomerates is sintered and shrank differently compared to alumina matrix. These differences caused large grains (agglomerates) of alumina derived from boehmite and also some large crack around these agglomerates. These structural changes resulted in low densities and low flexural strength as the content of boehmite powder increased in the alumina ceramics. This two phased structure in alumina ceramics resulted in large decreases in flexural strength after sintering at 1650 C-circle as 210 and 140 MPa for pure alumina and for 10 wt% boehmite added alumina respectively.