Inorganic Microporous Membranes for Gas Separation in Fossil Fuel ...

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4 Results and discussion 4.3.1.1 Ketone approach A summary of the stability of the final 8YSZ sols obtained while simultaneously varying the type of carboxylic acid and the solid content is depicted in Table 20. A sol is considered stable when a sol is clear for several months at room temperature. It is clear that the higher the aliphatic chain of the carboxylic acid, the higher the sol stability. In fact, when nanonic acid was used, the obtained sols were stable in the whole range of solid content. Since the carboxylic acid acts as hydrolysis/polymerization catalyst, this behaviour can be explained considering that the lower acid strength of long-chain acid reduces the reaction (growth) rate, decreasing in turn the formation of bigger particles and agglomerates. Bigger particles and agglomerates can destabilize the sol due to sedimentation. These bigger particles are avoided using long-chain acids. Moreover, another effect to be taken into account is when the acid chain length is increased, the 8YSZ nano-particles are somehow better protected or capped, 136 reducing the possibility of agglomeration (Figure 41-A and B). Table 20 Summary of the screened synthesis compositions showing influence of solid content wt% and the type of carboxylic acid on the final sol stability. Shadowed cells represent unstable sols while white ones represent stable clear sols (stable for several months). Fixed molar ratios of the sols include Ac/Zrpropoxide ~1, water/Zr-propoxide ~4 and acid/Ac ~1. § Maximal 8YSZ wt% content was limited by the carboxylic acid solubility, being the maximum values: 20% (acetic), 19% (propionic), 18% (caproic) and 17% (nanonic). Unstable sols start precipitating after a few days or weeks. Solid Content, 8YSZ wt% 2.5 5.0 10 15 Max. § 71 Carboxylic Acid Acetic Propanoic Caproic Nanonic Unstable Sols Stable Sols On the other hand, the sols with a higher solid content show a larger average particle size (Figure 41-C) and are more stabile. The sols have been analysed with the dynamic light scattering technique immediate after the synthesis was finalised. This effect is attributed to the higher concentration of protecting/complexing agents (acetyl acetone and the corresponding carboxylic acid), although the concentration of particles is higher and the collision probability too. 5wt% structure directing agent added to stable sols showed a similar particles size distribution with an average particle diameter of 4.5 nm and a standard deviation (δ) of 1.9 nm (Figure 41-D). Ketone sols with 0, 50, 75, 100 mol %
4 Results and discussion TiO2 in ZrO2 showed similar particle size distributions. The particle size does not seem to be influenced by the type of metal organic precursor. For the whole set of sols, the viscosity was measured in a wide range of shear rates (see Figure 42). The nature of the carboxylic sols, apparently, does not influence the viscosity while the solid content does in an exponential manner. For highly concentrated sols (~ 20 wt% 8YSZ), the viscosity reaches a maximum value of 12.5 mPa•s. Likely, the drying rate is a function of the viscosity which increases when the solid content is decreased. In fact, the difference among the different sols given an acid type is only the amount of 2propanol used as solvent. The drying rate is decreased when the chain length of the carboxylic acid increases. This rheological and drying behaviour has a direct effect on the coating quality obtained, done by manual dipping of glass slips, since apparently the best layers (based on the sol stability and viscosity) are obtained with concentrated sols and those synthesised with caproic or nanonic acid. These pictures are not shown. However, low-concentrated sols are needed to form crack-free layers consisting of small particles. Generally, high concentrated sols results in cracked layers, possible due to too thick coatings. Thus, low-concentration caproic- or nanonic (pelargonic)-catalysed sols are the most promising coating materials. Solid Content YSZ (% YSZ) 20 15 10 5 A NH 2 O OH OH O OH O OH O OH O O OH 0 4 8 12 16 Particle Diameter (nm) C Acetic Acid 72 Carboxylic Acid Aminocaproic Oleic Linoleic Pelargonic Caproic Acetic 8YSZ+F127 8YSZ YSZ 5%wt 0 4 8 12 16 Particle Diameter (nm) 0 4 8 12 Particle diameter (nm) Figure 41 (A) carboxylic chains. Particles size of the sols as function of the carboxylic groups (B), (C) Particle size of the sols as function of the sol content and (D) the influence of the 5wt% structure directing agent on the particle size. D B
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Mitglied der Helmholtz-Gemeinschaft
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Forschungszentrum Jülich GmbH Inst
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List of Abbreviations Ac Acetyl Ace
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Summary CO2 capture and storage mig
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Zusammenfassung Die Abtrennung und
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Content Content CONTENT............
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1 Introduction and aims 1 Introduct
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1 Introduction and aims Candidate m
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2 Theoretical background 2 Theoreti
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2 Theoretical background Despite th
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2 Theoretical background Table 2 Ox
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2 Theoretical background 2.1.2 Micr
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2 Theoretical background Poly-cryst
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2 Theoretical background membranes
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2 Theoretical background Dry or wet
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Page 48 and 49: 3 Experimental 3 Experimental The m
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Page 56 and 57: 3 Experimental 3.4 Characterisation
Page 58 and 59: 3 Experimental Element analysis The
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Page 62 and 63: 4 Results and discussion Abundance
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Page 102 and 103: 4 Results and discussion In pure Ti
Page 104 and 105: 4 Results and discussion In summary
Page 106 and 107: 4 Results and discussion Intensity
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Page 126 and 127: 6 References 22. Shao, Z., Dong, H.
Page 128 and 129: 6 References 65. Van den Berg, A. W
Page 130 and 131: 6 References 108. Wen, T. L., Heber
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Curriculum Vitae - George van der D
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Last but not least, I would like to
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Band | Volume 8 ISBN 978-3-89336-52
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