a-SiAION ceramics densified with mixed oxide sintering additives

Abstract

Densification and stabilization of ?-sialon ceramics were investigated by using oxides of large cations (Sr2+, La3+, Ce3+, Nd3+) and their equi-molar mixtures with CaO or Yb2O3. All multi-cation and single cation (only Nd3+ and Ce3+) doped samples could be densified to nearly full density even by pressureless sintering. X-ray diffraction of the samples densified with single cations revealed that the oc-sialon structure could accomodate Nd3+ or Ce3+ cations. In Sr- and La- systems, however, S- (-SrO:I.3Al2O3:0.7Si2N2O) and N- (La3Si8O4N) phases were found to be stable rather than a-sialon. In case of multi-cations, a-sialon was observed only as a matrix phase. EDX measurements proved that Ce-, La- and Sr- cations could be accomodated into the a-sialon structure with the presence of calcium or ytterbium. SEM studies revealed that almost glass free grain boundaries could be obtained by careful design of starting compositions