alpha-SiAlON ceramics densified with mixed oxide sintering additives

Densification and stabilization of alpha-sialon ceramics were
investigated by using oxides of large cations (Sr2+, La3+, Ce3+, Nd3+)
and their equi-molar mixtures with CaO or Yo(2)O(3). 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 ol-sialon structure could accomodate Nd3+ or Ce3+ cations. In Sr-
and La- systems, however, S- (similar to
SrO:1.3A1(2)O(3):0.7Si(2)N(2)O) and N- (La3Si8O4N11) phases were found
to be stable rather than a-sialon. In case of multi-cations,
alpha-sialon was observed only as a matrix phase. EDX measurements
proved that Ce-, La- and Sr- cations could be accomodated into the
alpha-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.