Failure Mechanisms of Ba0.5Sr0.5Co0.8Fe0.2O3−δ Membranes after Pilot Module Operation

Membranes, vol. 12, pp. 1093

Abstract

The step from the testing of oxygen transport membranes on a lab scale to long-term operation on a large scale is a challenge. In a previous study, membrane failure was observed at defined positions of one end of the cooled tubular Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes after an emergency shutdown. To understand the failure mechanisms, strength degradation and transient stress distribution were investigated by brittle-ring tests and finite element simulations, respectively. A 15% decrease in the characteristic strength of 162 MPa was proven after aging at 850 °C and was attributed to grain coarsening. The reduction in characteristic strength after thermal shock ranged from 5 to 90% depending on the cooling rates, and from 5 to 40% after the first and 20th soft thermal cycling. Simulations indicated the chemical strains induced by a 10-bar feed air and 50 mbar permeate pressure, which caused tensile stresses of up to 70 MPa at the outer surface. These stresses relaxed to 43 MPa by creep within a 1000 h operation. A remaining local stress maximum seemed to be responsible for the fracture. It evolved near the experimentally observed fracture position during a 1000 h permeation and exceeded the temperature and time-dependent strength. The maximum stress was formed by a chemical strain at temperatures above 500 °C but effective creep relaxation needed temperatures above 750 °C.

Authors 5

1. Simone Herzog corresponding Aachen Institute for Materials Applications in Mechanical Engineering

   RWTH Aachen University

   Affiliation as printed

   Institute for Materials Applications in Mechanical Engineering (IWM), RWTH Aachen University, Augustinerbach 4, 52062 Aachen, Germany

2. Chao Liu Aachen Institute for Materials Applications in Mechanical Engineering

   RWTH Aachen University

   Affiliation as printed

   Institute for Materials Applications in Mechanical Engineering (IWM), RWTH Aachen University, Augustinerbach 4, 52062 Aachen, Germany

3. Nicolas Nauels Aachen Aachener Verfahrenstechnik (AVT)

   RWTH Aachen University

   Affiliation as printed

   Aachener Verfahrenstechnik (AVT), Mechanical Process Engineering, RWTH Aachen University, Forckenbeckstraße 51, 52074 Aachen, Germany

4. Anke Kaletsch Aachen Institute for Materials Applications in Mechanical Engineering

   RWTH Aachen University

   Affiliation as printed

   Institute for Materials Applications in Mechanical Engineering (IWM), RWTH Aachen University, Augustinerbach 4, 52062 Aachen, Germany

5. Christoph Broeckmann Aachen Institute for Materials Applications in Mechanical Engineering

   RWTH Aachen University

   Affiliation as printed

   Institute for Materials Applications in Mechanical Engineering (IWM), RWTH Aachen University, Augustinerbach 4, 52062 Aachen, Germany