MICROSTRUCTURE AND DENSIFICATION BEHAVIOUR OF SURFACE­ COATED SILICON NITRIDE POWDER

Year 2002, Volume: 6 Issue: 2, 197 - 201, 01.08.2002

Zafer Tatlı

Abstract

For better control of the mechanical
properties of Si3N4 ceramics, it is necessary to
generate homogeneous nıicrostructures, and for this
purpose, chemical heterogeneities must be
minimised, by careful control of powder processing
and the subsequent consolidation steps. Coating of
the starting silicon nitride po"7der is a convenient
'\-vay of incorporating a liquid forming sintering aid
more homogeneously than can be achieved by
current commercial methods such as ball-milling.
Thin layers of oxides, corresponding to additions of
5 w/o MgO have been deposited on the surface of
grains of a commercial silicon nitride powder using
alcoholic solutions containing appropriate amounts
of the metal alkoxide. The resulting powders have
been densified by pressurelesss sintering techniques,
and their sintering characteristics identified in
comparison with equivalent materials produced by
adding the oxide in particulate form. In every case,
a better sintering performance was observed at
lower temperatures for the oxide-coated materials,
with fully dense pressureless-sintered materials
being obtained at temperatures as low as 1525 °C.
Microstructures were observed using a s ... 2400
Hitachi Scanning Electron Microscope (SEM). and
final microstructure was more uniform than that
obtained by conventional method

Keywords

Silicon nitride, MgO, Sintering, Microstructure