Separation and Purification Technology 74 (2010) 28–37 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Effect of CuO additive on the sintering and performance of niobium-doped strontium cobaltite as oxygen separation membranes Jing Zhao a , Dengjie Chen a , Zongping Shao a,∗ , Shaomin Liu b,∗∗ a State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry & Chemical Engineering, Nanjing University of Technology, No. 5 Xin Mofan Road, Nanjing 210009, PR China b Department of Chemical Engineering, Curtin University of Technology, Perth, WA 6845, Australia article info Article history: Received 12 March 2010 Received in revised form 30 April 2010 Accepted 5 May 2010 Keywords: Perovskite Membrane Sintering aid Copper oxide Oxygen permeation abstract In this work, the effects of CuO addition on sintering behavior, crystal structure and the oxygen perme- ation of SrCo 0.9 Nb 0.1 O 3-ı (SCN) membranes have been investigated. XRD characterization demonstrated that copper could incorporate into the perovskite lattices with certain solubility dependent on tempera- ture. Small amount of CuO (5 wt.%) successfully reduced the sintering temperature of the SCN membrane by 180 ◦ C. A relative density of 95.4% was reached for the membrane with 5 wt.% CuO additive after sintering at 1000 ◦ C. The promoting effect on sintering is likely associated with liquid assisted sinter- ing. The incorporation of copper into the SCN lattice has minimal effect on the membrane sintering but a significant effect on the membrane integrity. As compared to the single-phase SCN membranes, the intro- duction of CuO as a sintering aid does not affect the electronic conductivity of the membrane between 700 and 900 ◦ C, but the oxygen permeability is slightly reduced. Permeation study of the membranes of 0.9 mm thickness demonstrated oxygen fluxes of 1.5, 1.4, 1.3 and 1.2 ml cm -2 min -1 [STP] at 800 ◦ C for the membranes containing 0 (pure SCN), 1, 3 and 5 wt.% CuO, respectively. The results suggest that the introduction of CuO as a sintering aid had a more significant effect on the oxygen surface exchange kinetics than on the oxygen bulk diffusion rate. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Since the pioneering systematic demonstration of high oxy- gen permeation flux through some dense ion-transport ceramic membranes with the perovskite composition of SrCo 1-y Fe y O 3-ı and La 1-x Sr x Co 1-y Fe y O 3-ı by Teraoka et al. in 1980s [1,2], there has been considerable interests from both academic and indus- trial communities in such membranes as an alternative method for oxygen separation from air [3–9]. The enthusiasm for this new tech- nology was triggered by its intrinsic advantages over the traditional industrial scale oxygen production method of cryogenic distilla- tion of air. These advantages include the capability for continuous oxygen production, more size flexibility, and potential reduction in capital cost both for plant construction and oxygen production. The oxygen semipermeability of ion-transport membranes is related to their mixed oxygen-ionic and electronic conductivity at elevated temperatures. When there is an oxygen potential dif- ference between the two membrane surfaces, the oxygen in the ∗ Corresponding author. Tel.: +86 25 83172256. ∗∗ Corresponding author. Tel.: +61 8 92669056. E-mail addresses: shaozp@njut.edu.cn (Z. Shao), Shaomin.Liu@curtin.edu.au, S.liu2@curtin.edu.au (S. Liu). oxygen-rich side atmosphere adsorbs onto the membrane surface, where it dissociates into oxygen ions via a series of complicated surface reactions. The oxygen ions then migrate through the mem- brane bulk to the oxygen-lean side membrane surface with the simultaneous diffusion of electrons in a reverse direction to main- tain local electric neutrality. The oxygen ions then re-combine to form oxygen molecule, which finally releases into the oxygen-lean side atmosphere [10,11]. Macroscopically, it appears as if oxygen molecule can permeate through the membrane. Oxygen-ion con- duction is realized by the diffusion of oxygen ions through oxygen vacancies, while the electron conduction is created via the electron hopping between B-site cations and the oxygen ions via a mecha- nism similar to the Zener double exchange [12,13]. Because of the ion-diffusion mechanism for oxygen permeation, infinite oxygen permeation selectivity is expected if the membrane can be fabri- cated without any penetrating pinholes. Dense ion-transport membranes are typically fabricated by powder synthesis-shape forming-sintering process. Oxide powder is first prepared by a standard ceramic process or a more advanced wet chemical method, and is then formed into flat or tubular shape membranes by extrusion, dry pressing, tape casting or other advanced techniques, these green membranes are finally sintered at elevated temperatures to allow densification [14–16]. In order to achieve a high sintering density, ultrahigh sintering temperatures 1383-5866/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2010.05.004