Binary organic-inorganic gels, in which a carbonaceous gel obtained fr
om a coal tar pitch and a zirconia gel are combined, were prepared as
precursors for carbothermal reduction with and without simultaneous ni
tridation to form Zr(C,O,N) solid solutions. Zirconium(IV) propoxide a
s the starting material for zirconia was hydrolyzed in the presence of
acetylacetone in order to avoid undesirable precipitation. After pyro
lysis at 800 degrees C, a precursor consisting of reactive carbon and
nanometer-sized ZrO2 was obtained. Its behavior on heat treatment was
investigated by TG, X-ray analysis, and nitrogen adsorption. Microporo
sity was generated by crystallization of the zirconia constituent in t
he temperature range 800-1100 degrees C. The carbothermal conversion i
nto Zr (C,O,N) begins under nitrogen at about 1100 degrees C and under
argon at about 1200 degrees C; mesoporosity is additionally formed in
both cases. The final products at 1500 or 1600 degrees C-solid soluti
ons of cubic Zr(C,O) or Zr(C,O,N)-are assemblages of fine crystallites
with grain sizes of 1 mu m and less. The formation of these sub-micro
meter crystallites may be explained by the high homogeneity and reacti
vity of the gel-derived carbon reactant. Nitrogen adsorption is shown
to be a useful technique to follow the reduction reactions in gel prec
ursors.