Impact of the sintering parameters on the microstructural and transport properties of 60 wt% Ce0.8Gd0.2O2−δ–40 wt% FeCo2O4 composites

Abstract

The dual-phase composite 60 wt% Ce_0.8Gd_0.2O_2−δ–40 wt% FeCo₂O₄ (60CGO20–FCO) is shown to be an excellent oxygen transport membrane (OTM) with sufficient stability and oxygen permeance. To achieve a mechanically and chemically stable composite material an optimised microstructure should be designed. In general, the modification of the sintering profile is a classical way of achieving microstructure optimization as well as optimization of the functional properties of ceramic materials. Moreover, optimization of the sintering program would be beneficial to minimize the increase in porosity and achieve maximum densification with minimum pore and grain growth during sintering. Thus, the chosen 60CGO20–FCO composite has been subjected to different heat treatments to determine its impact on the main morphology characteristics, such as grain size, pore size, relative density, and porosity. The dwell time was varied between 0 and 100 hours at 1200 °C and seems to have an influence on the fraction of the resulting phases, revealing the formation of a high-temperature CoO phase after 100 hours. In other samples fired for 0–50 hours at 1200 °C fluorite, spinel, and perovskite phases are prevailing. To eliminate the undesired CoO phase the cooling rate has been varied. The results reveal that the 5 hour dwell time at 1200 °C is the most suitable one for the chosen composite material, resulting in a sufficiently dense membrane with well-distributed phases, and can be further utilized for scaling up OTM production.