Zirconia‐Based Metastable Solid Solutions through Self‐Propagating High‐Temperature Synthesis: Synthesis, Characterization, and Mechanistic Investigations

Abstract

Cubic Zr 1؊x Me x O y (Me ‫؍‬ Fe, Co, Ni, Cu) metastable solid solutions with metal content significantly higher than equilibrium levels have been synthesized by the self-propagating high-temperature synthesis method based on a thermite reaction between metallic zirconium and the transition-metal oxides CoO, Fe 2 O 3 , CuO, and NiO. Through in situ XRD analysis, it was determined that when heated to 1100°C, the cubic solid solution transformed to the tetragonal phase with the concomitant formation of iron oxide. When cooled to lower temperatures, the tetragonal phase transformed to the monoclinic phase at or below 500°C. Results of auxiliary experiments strongly suggest that the formation of the solid solution takes place behind the combustion front by a reaction between zirconia and the metal.

Reactive Processing in Ceramic‐Based Systems

“…31,32 Some of the materials produced by SHS include single-phase and multi-phase compositions containing oxides, carbides, nitrides, borides, aluminides, or silicides, as well as more complex combinations such as oxynitrides and carbonitrides. [33][34][35][36][37][38][39] SPS is a relatively new technique in which a pulsed electric field is passed through a specimen as it is heated and compressed (hot pressed). 40,41 The enhanced driving force for densification provided by the electric field allows for densification of nano-materials and bio-materials by this method in addition to oxide and nonoxide ceramics.…”

“…The propensity for a material to undergo an SHS‐type reaction depends upon several factors including the amount of heat released by the reaction, the relative density of the initial compact, heat transfer to the surroundings, the rate of heating to the combustion temperature, and the addition of inert diluents to the precursor mixture 31,32 . Some of the materials produced by SHS include single‐phase and multi‐phase compositions containing oxides, carbides, nitrides, borides, aluminides, or silicides, as well as more complex combinations such as oxynitrides and carbonitrides 33–39 . SPS is a relatively new technique in which a pulsed electric field is passed through a specimen as it is heated and compressed (hot pressed) 40,41 .…”