Tetragonal-(Zr,Co)O2 solid solution: Combustion synthesis, thermal stability in air and reduction in H2, H2–CH4 and H2–C2H4 atmospheres

The synthesis of Co2+-stabilized zirconia by the nitrate/urea combustion route is investigated. Using seven times the so-called stoichiometric urea proportion allows to obtain for the first time the Zr0.9Co0.1O1.9 solid solution fully stabilized in tetragonal form. The thermal stability in air and the reduction in H2, H2–CH4 and H2–C2H4 atmospheres are studied. The carbon forms obtained upon reduction are investigated. Reduction in H2–CH4 produces many carbon species including short carbon nanofibers, nanoribbons, hollow particles often forming bamboo structures, carbon-encapsulated Co particles and carbon nanotubes. Reduction in H2–C2H4 produces 15–30 nm nanofibers.