Chemical stability in H2S and creep characterization of the mixed protonic conductor Nd5.5WO11.25-d

[EN] The integration of hydrogen permeable membranes in catalytic membrane reactors for thermodynamically limited reactions such as steam methane reforming can improve the per-pass yield and simultaneously produce a high-purity H-2 stream. Mixed protonic electronic materials based membranes are potential candidates for these applications due to their elevated temperature operation, good stability and potentially low cost. However, a specific mechanical behavior and stability under harsh atmospheres is needed to guarantee sufficient lifetime in real-world processes. This work presents the mechanical characterization and a study of the chemical stability under H2S containing atmospheres for the compound Nd5.5WO11.(25-8) Mechanical characterization was performed by micro indentation and creep measurements in air. Chemical stability was evaluated by XRD and SEM and the effect of the H2S on the transport properties was evaluated by impedance spectroscopy. Under H2S atmospheres, the total conductivity increases at 600 degrees C and 700 degrees C. The conductivity increase is attributed to the incorporation of S2- ions in oxide-ion sublattice. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.This work was financially supported by the Spanish Government (ENE2014-57651-R and SEV-2012-0267 grants). Authors would like to thank to U. Gerhards, M. Fabuel, T. Osipova and Dr. Wesel for WDS and SEM analysis.Escolástico Rozalén, S.; Stournari, V.; Malzbender, J.; Haas-Santo, K.; Dittmeyer, R.; Serra Alfaro, JM. (2018). Chemical stability in H2S and creep characterization of the mixed protonic conductor Nd5.5WO11.25-d. International Journal of Hydrogen Energy. 43(17):8342-8354. https://doi.org/10.1016/j.ijhydene.2018.03.060S83428354431

High-temperature compressive creep behaviour of perovskite-type oxides SrTi1-xFexO3-δ

Compressive creep tests have been performed on mixed ionic-electronic conducting perovskite-type oxides SrTi1-xFexO3- (STF, x = 0.3, 0.5 and 0.7). Observed activation energies and stress exponents, at 800–1000 ◦C and in the stress range 10 100 MPa, indicate that the steady-state creep rate of STF under these conditions is predominantly limited by cation lattice diffusion (Nabarro-Herring creep). The effective stress exponents reflect a contribution of dislocation creep to the mechanism of creep in STF30 (x = 0.3). The observed creep rates are compared with those exhibited by related perovskite-type oxides, and are discussed in view of the possible application of STF as oxygen transport membrane (OTM)

Creep behavior of perovskite-type oxides Ba0.5Sr0.5(Co0.8Fe0.2)1−xZrxO3−δ

Compressive creep tests have been performed on perovskite-type oxides Ba0.5Sr0.5(Co0.8Fe0.2)1–xZrxO3−δ (BSCF-Z100·x), where x = 0.01, 0.03, 0.05 and 0.1, for the use as oxygen transport membrane, in air at 800–950 °C and at nominal stresses of 30 MPa and 63 MPa. X-ray diffraction and microstructural observations support a solid solubility limit of ZrO2 between 0.03 < x < 0.05. Evidence is found for the formation of (Ba,Sr)ZrO3 secondary phases in grain boundaries at compositions beyond this limit. Zr substitution of (Co,Fe) in BSCF is found to suppress grain growth significantly, which is attributed to a solute and/or particle drag (Zener pinning) mechanism. Observed activation energies and stress exponents point to diffusional creep as the predominant mechanism for creep in BSCF-Z100·x ceramics, at T ≥ 850 °C. This is further supported by the fact that the grain-size-normalized steady-state creep rate varies little for the different BSCF-Z100·x compositions. It was confirmed that Zr substitution does not significantly affect the thermal hysteresis of the creep behavior as observed for pure BSCF