Abstract
Compacted polycrystalline mixtures of zirconia and graphite were made to undergo progressive reaction in a graphite-resistanced high temperature X-ray diffractometer apparatus under nitrogen at atmospheric pressure.
Above a temperature of 1388 K, one could observe a reaction of the transfer of carbon in the gaseous phase (CO-CO2 couple), the increase of this reaction at higher temperatures, and the direct reaction of graphite and nitrogen with zirconia above 1573 K, leading to the formation of zirconium dioxynitride, and then either zirconium mononitride or monocarbonitride, during two distinct stages for 1423 less-than-or-equal-to T (K) less-than-or-equal-to 1883.
An evaluation was made of the composition of these gamma-ZrO(2-x)N(x/2) square x/2 (CaF2-type structure), ZrN and ZrN(1-z)C(z) (NaCl-type structure) cubic phases, considering the variations in their lattice parameters between 293 and 2273 K.
Particular attention is given to gamma-dioxynitride, the linear dilatation of which (alpha-BAR almost-equal-to 13 x 10(-6) K-1) shows a constant composition between 1373 and 2153 K (chi almost-equal-to 0.2). Moreover, this new phase does not quench, the reaction in the solid state below 1373 K leading unavoidably to poorly crystallized monoclinic alpha-ZrO2 and rhombohedral Zr7O11N2 compounds.