Oxidation kinetics and mechanism of a zirconia based composite dispersed with 304L particles

• The oxidation kinetics of 304L particles dispersed into a zirconia matrix at 800 °C showed a short initial acceleration followed by a much slower period.
• Inward growth of Cr2O3 nodules was observed first along zirconia/metal interfaces whereas an iron-rich (Fe, Cr) mixed oxide scale developed outwards around the metal particles.
• The jumps method was used to prove that the oxidation kinetics in the second period of time was controlled by a rate-determining step and enhanced by an increase in the oxygen partial pressure.
• Mechanisms decomposed into elementary steps were proposed to describe the inward and outward growths. The oxidation kinetics in the second period of time, related to the outward growth of the Fe–Cr mixed oxide layer, was found to be controlled by cations vacancy diffusion and to obey a Po23/16 law.

The oxidation at 800 °C of 304L particles dispersed in a zirconia ceramic showed behaviour different from that usually observed for 304L. SEM observations revealed inward growth of Cr2O3 nodules and outward growth of an iron-rich (Fe, Cr) mixed oxide scale. The method of jumps indicated first that a rate-determining step was controlling the kinetics, then that oxidation was favoured by an increase of the oxygen partial pressure. Growth mechanisms of both types of oxides were proposed; the Fe–Cr mixed oxide growth accounted for the major part of the mass gain and was controlled by the diffusion of metal vacancies obeying a PO23/16 law.