1 Mechanical properties of La2NiO4+δ membranes for gas separation Xinzhi Chen, Mari-Ann Einarsrud and Tor Grande Department of Materials Science and Engineering Norwegian University of Science and Technology (NTNU) 2 Outline • Introduction • Material • Water based tape casting • Mechanical properties • Summary 3 Introduction / oxygen production Cryogenic Distillation: Proven Oxygen Supply Technology o Mature, reliable technology o Energy consumption intensive o complicated process Pressure swing adsoption: Convinient Oxygen Supply Technology o Mature, flexible technology o Low oxygen purity 4 Introduction / MIEC membranes Gas sensor Cathode for SOFC Oxygen separation membrane Mixed ion and electron conducting (MIEC) materials Combined reactor for syngas production or natural gas conversion 5 Introduction / requirements Requirements for high temperature ceramic oxygen permeation membranes Permeability Chemical stability Mechanical strength MIEC membranes Production cost Thermal stability 6 Introduction / model Decreasing the thickness of dense membrane Increasing the flux Appropriate porous support Providing main mechanical strength O2 Modified surface Dense memb. O2- O2 Porous support e SAME candidate materials as the dense memb. or NOT 7 Material / La2NiO4+σ Candidate material for dense thin membrane Vladislav V. Kharton, et.al. Chem. Mater. 2007, 19, 2027-2033 La Chemical expansion of La2NiO4+σ is almost independent of oxygen content variation due to anisotropic crystal structure Ni O Additionally Sufficient permeation flux High catalytic activity Ideal structure of La2NiO4+σ Anisotropic diffusion 8 Material / La2NiO4+σ Synthesized by spray pyrolysis La2NiO4+σ as-synthesized powder Agglomerate size: 8 ~ 20 um 10 20 30 40 2-Theta 50 60 70 80 9 Water based tape casting / La NiO 2 4+σ membranes 10 Mechanical properties / fracture strength Ball on ring test of La2NiO4+σ membranes 2 Weibull distribution 1 ln(ln(1/(1-F))) 0 -1 -2 -3 -4 4.55 4.60 4.65 ln 4.70 4.75 4.80 Fracture surface Average biaxial fracture strength: 109 MPa Weibull modulus : 17 Relative density: 96 % Fracture strength value (porosity ~ 52 %) in literature is less than 25 MPa at R.T B.X.Huang, et.al, Thermo-mechanical properties of La2NiO4. J.Mater Sci (2011) 46:4937 - 4941 Transgranular fracture mode is expected 11 Mechanical properties / hardness Indentation hardness of La2NiO4+σ pellet 950 Load: 1.96 N 900 700 650 600 Hardness 800 750 2 4 6 8 10 Load (N) 12 14 16 18 20  700 0.98 60 0.97 600  Relative density 500 50 40 400 30 300 0.96 0.95 0.94 0.93  Grain size 100 0 0.99 70 200 Indentation size effect can be found 1.00 80 1300 1350 20 0.92 10 1400 1450 o Sintering temperature ( C) 1500 0 0.91 0.90 Relative density 800 Grain size (um) 850 Indentation hardness (GPa) Indentation hardness (GPa) 900 12 Mechanical properties / fracture toughness Indentation fracture toughness of La2NiO4+σ pellet 0.14 0.12 Load: 1.96 N 80 0.99 70 0.08 0.98 0.06 Relative density 0.04 50  0.02 40 0.00 -0.02 30 0.97 0.96 0.95 Relative density 60 Grain size (um) 1/2 Fracture toughness (Mpa m ) Fracture toughness  0.10 Grain size -0.04  -0.06 20 0.94 10 -0.08 -0.10 1.00 90 0.93 1300 1350 1400 1450 1500 0 o Sintering temperature ( C) The fracture toughness value is much lower than the typical value of ordinary polycrystalline ceramics (2-6 MPa m1/2 ) Optical microscopy image of indent 13 Mechanical properties / discussion 950  0.10 Load: 1.96 N 900 Indentation size: ~15 um 1/2 Fracture toughness (MPa m ) Fracture toughness 0.05  0.00 800 Hardness 750 -0.05 Hardness (GPa) 850 Load 700 -0.10 0 5 10 15 20 25 Grain size (um) Grain boundary effect would be less and less when the grain size is larger than indentation size 650 30 Indentor Specimen 14 Summary ► Developed a successful method for La2NiO4+σ water based tape casting, membranes with a density of above 96 % of the theoritical density were prepared by this method. ► La2NiO4+σ has very good chemical stability, but a poor mechanical properties, fracture strength: ~109 MPa; hardness: ~780 GPa; fracture toughness: ~0.1 MPa m1/2 ► Asymmetric membranes with La2NiO4+σ as support are expected to have poor mechanical performance in long term operation condition, therefore alternative materials as the porous support are necessary. 15 Acknowledgement This work has been carried out with support from the BIGCCS Centre, performed under the Norwegian research program Centres for Environment-friendly Energy Research (FEM). The authors acknowledge the following partners for their contributions: 15