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Due to their potential for long durability, ceramic membranes are currently being investigated for various hydrogen-related applications [1]. One of the challenges in developing novel membranes is controlling the porous structures to achieve high hydrogen permeation without compromising their structural stability. During sintering, a technique in which solid ceramic powders are heated to high temperatures, the loose packing of the powder, which determines the pore network, solidifies [2]. Sintering is a process driven by surface minimization, which causes a diffusion-enhanced compaction of the particles. It is hence difficult to predict the final pore structure from the initial configuration of the loose powder.
Sintered ceramic membranes have been analysed before with conventional microscopy techniques (i.e. optimal microscopy, electron microscopy). However, the evolution of the surface and respective surface energies during sintering has never been quantified. These properties are needed to model the particle shrinkage behaviour for high-accuracy predictions of performance. In this study, we combined inverse gas chromatography (iGC) and atomic force microscopy (AFM) to qualitatively and quantitatively determine surface energies, surface areas, and nano-scale topographies in ceramic membranes. Inverse gas chromatography is used to calculate surface areas and surface energies from retention curves of fluid probes injected into the porous ceramic membranes [3]. Atomic force microscopy assesses the interaction between a nano-tip and the surface, mapping surface topography and measuring surface stiffness [4].
Results suggest that the surface area of the particles decreases with increasing sintering temperature. Simultaneously, surface energy distributions vary, indicating a change in the crystalline assembly at the surface. Together, iGC and AFM enable to relate sintering temperature, heating rate, and dwelling time to the properties of the internal surface, which is of particular interest for increasingly complex chemical compositions of ceramic membranes considered for hydrogen applications, such as aluminium oxide, zirconium oxide, or lanthanum tungstate. In the future, this methodology could be applied to a wider range of sintering conditions and to novel chemical compositions proposed in industry. The final goal is to unravel the physics of surface evolution during sintering, to predict membrane performance from the initial powder composition.
[1] J. Kniep, M. Anderson, and Y. S. Lin, “Autothermal Reforming of Methane in a Proton-Conducting Ceramic Membrane Reactor,” Ind Eng Chem Res, vol. 50, no. 22, pp. 12426–12432, Nov. 2011, doi: 10.1021/ie2010466.
[2] W. Deibert, M. E. Ivanova, W. A. Meulenberg, R. Vaßen, and O. Guillon, “Preparation and sintering behaviour of La5.4WO12−δ asymmetric membranes with optimised microstructure for hydrogen separation,” J Memb Sci, vol. 492, pp. 439–451, 2015, doi: https://doi.org/10.1016/j.memsci.2015.05.065.
[3] F. Thielmann, “Introduction into the characterisation of porous materials by inverse gas chromatography,” J Chromatogr A, vol. 1037, no. 1, pp. 115–123, 2004, doi: https://doi.org/10.1016/j.chroma.2004.03.060.
[4] F. J. Giessibl, “Advances in atomic force microscopy,” Rev Mod Phys, vol. 75, no. 3, pp. 949–983, 2003, doi: 10.1103/RevModPhys.75.949.
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