Subcritical Crack Growth Behavior of A Perovskite‐Type Oxygen Transport Ceramic Membrane

Abstract

We herein report subcritical crack growth (SCG) studies of La 0.2 Sr 0.8 Fe 0.8 Cr 0.2 O 3Àd (LSFCO) perovskite membranes as oxygen transport membranes (OTM). Two sample batches of perovskite were tested to investigate the effect of temperature, specific chemical environments, and loading rate on flexure strengths, using four-point bend tests. The first batch was examined at room temperature in air. The second batch was soaked in an N 2 /air atmosphere at 10001C. Stress rates varied approximately from 0.2 to 90 MPa/s. The strength-probability-time diagram is constructed for design proposes. Flexural strength data indicate that the examined OTM material showed little susceptibility to SCG at room temperature in air. However, the sample is susceptible to SCG in an N 2 /air environment at 10001C. Also, the experiments demonstrate flexuralstrength rate dependency, with strength increasing with the stress rate. The observed phenomena are explained by the decomposition and microstructural transitions in the perovskite.

Subcritical crack growth behavior of a perovskite‐structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxygen transport membrane

“…However, the value of n of BSCF decreases dramatically to 13.83 as temperature rises to 800°C, which is approximately 43% of the value at room temperature. A similar trend has been also found in other perovskite‐structured materials . It indicates that BSCF is much more sensitive to SCG at 800°C.…”

“… Using the SCG parameter n = 24.32 and σ 0 = 77 MPa in Equation , the equivalent stress that would result in the failure of the sample in 1 second is 78.42 MPa. Combination of this stress and 1 − F = 1/e (corresponding to the characteristic strength σ 0 ; e is Euler's constant), where F is failure probability, shows the first data point of the 1 second line on the SPT diagram. Plot the 1 second line with a slope of Weibull modulus 10.2. A series of lines parallel to the 1 second line, with spacing between the lines equaling to (ln 10)/n or 2.3/n. The spacing 2.3/n represents a change in life‐time by a factor of 10 . Each line represents a decade increase in lifetime. …”

“…A similar trend has been also found in other perovskite-structured materials. 35 It indicates that BSCF is much more sensitive to SCG at 800°C. There can be several possible contributions to this phenomenon.…”

Slow Crack Growth and Creep Rupture of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_{3 – <i>δ</i>}

“…The loading rate sensitivity of bending test data can be used to assess the slow crack growth sensitivity of a material. It has been shown that the strength is linked to a particular stress rate σ via [4,5]:…”

“…SCG is generally not well addressed for perovskite type ceramic membrane materials. For the perovskite La 0.2 Sr 0.8 Fe 0.8 Co 0.2 O 3 -δ (LSFC) SCG has been investigated [4]. The SCG is investigated in the present work measuring the stress rate dependence of the fracture strength [5].…”