The influence of spinel and magnesia powder bed on mechanical properties of alumina sintered under air and nitrogen atmosphere

The aim of the present work was changing the surface properties of alumina ceramic via sintering of samples in spinel MgAl2O4 and magnesia MgO powder bed. During sintering nitrogen and air atmosphere were used; and the reference material was sintered at the same conditions but in an alumina powder bed. All samples were sintered to a density higher than 99.2% of theoretical density of alumina. In order to examine samples SEM, EDX and XRD (X-ray diffraction from 18 to 70 °2Theta) analysis were performed together with B3B flexural strength measurement. Results revealed that by sintering of alumina samples in a spinel powder bed pore-free surfaces were prepared, which had a favourable effect on B3B flexural strength. This was ascribed to the high solubility of Al3+ in spinel at sintering temperatures, which increases the sintering driving force. A further positive effect on B3B flexural strength was observed when samples were sintered in nitrogen instead of air.