This title appears in the Scientific Report : 2013 

Innovative Beschichtungs- und Charakterisierungsmethoden für die nasschemische Herstellung von asymmetrischen Gastrennmembranen auf Basis von SiO$_{2}$
Hoffmann, Jan (Corresponding author)
Werkstoffsynthese und Herstellungsverfahren; IEK-1
Jülich Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2013
V, 152 S.
Dissertation, Universität Bochum, 2013
Dissertation / PhD Thesis
Fuel Cells
Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment 195
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Introducing membrane separations in industrial processes has the potential to increase the energy efficiency and reduce the environmental impact of their corresponding processes. One prominent example is the use of membranes for CO$_{2}$ capture in fossil fuel power plants. Ceramic membranes are promising candidates for this application due to their high resistance to significant thermal and mechanical strain. It is well studied and known that SiO$_{2}$-based membranes show the desired gas separation properties for CO$_{2}$. According to the current state of the art, these gas separation properties are based on a molecular sieving process that wasdemonstrated experimentally on a laboratory scale. The lab scale membranes yielded low reproducibility on a small tested area. For potential industrial use, SiO$_{2}$-based membrane production must be readily reproducible and scalable to larger areas. The present work deals with the study of production and characterization methods to increase the reproducibility of graded SiO$_{2}$ membranes. A model system is introduced that utilizes a standardized membrane structure consisting of a $\alpha$-Al$_{2}$O$_{3}$ substrate, a $\gamma$-Al$_{2}$O$_{3}$ interlayer and a SiO$_{2}$-function layer. A characterization routine is developed to evaluate this model system and specific variations of the structure (e.g. the use of alternative substrates). With that routine, it is possible to systematically analyze the individual components of the structure and obtain influencing factors on reproducibility. The characterization of different sets of samples shows that defects in the functional layer contribute largely to reduced reproducibility. A method is developed for the targeted analysis of these defects, which allows for a space-resolved characterization in various optical analysis techniques to be performed. Space-resolved characterization shows that both inhomogeneity in the substrate and contamination with foreign particles causes defects that lower the reproducibility of the resulting SiO$_{2}$ layers. In addition, a novel process for the preparation of SiO$_{2}$ functional layers for gas separation using ink jet printing is introduced. This method is scalable to large areas and offers the advantage of a digital controller. It is shown that by using an appropriate parameter set, SiO$_{2}$-based homogeneous functional layers can be printed on a $\alpha$-Al$_{2}$O$_{3}$ substrate and a $\gamma$-Al$_{2}$O$_{3}$-interlayer. The heat treatment is done by a rapid thermal heating process of the layers, which significantly shortens the duration of the manufacturing process. Characterization of these layers shows that H$_{2}$/CO$_{2}$ selectivity can be clearly achieved up to 50. The results provide a solid starting point for future improvements on the reproducible production of ceramic layers for gas separation. In particular, the method of space-resolved characterization may lead to better evaluation of the factors that influence reproducibility. From an industrial perspective, the developed ink-jet printing model offers the advantages of efficiency, scalability, and reproducible production of SiO$_{2}$ functional layers.