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Inorganic membrane supports, for hydrogen separation, must provide adequate surface morphology for the deposition of thin film membranes while offering acceptable permeability and mechanical strength. Supports prepared from stabilized suspensions of Sumitomo AKP30 and AKP15 powder were shown to exhibit ideal surface morphology (average roughness ∼ 30 nm ) and excellent mechanical strength ( > 200 MPa ) , but inadequate permeability, ∼ 1 × 10 - 6 mol / m 2 s Pa for H 2 at STP. The colloidal stabilization, subsequent vacuum filtration and sintering of coarse ∼ 3 μ m O α - Al 2 O 3 particles are shown to increase pore size from ∼ 70 nm (AKP30) to ∼ 700 nm (AA3) and consequently improve permeability by ∼ 10 × . The cost price of these supports can be decreased and sufficient flexural strength achieved with a low temperature phosphate bonding technique. Through the precise control of the colloidal chemistry and consolidation process, the near surface morphology of the supports can be intrinsically graded with ∼ 0.5 μ m particles gradually coarsening to ∼ 3 μ m . Supports generated in this manner then exhibit a smooth surface morphology comparable to AKP15 supports (average roughness ∼ 100 nm ) and mechanical strengths of ∼ 100 MPa .

The micro-structural integrity of meso-porous inorganic membranes is of critical importance in their prolonged application. Inspection by transmission electron microscopy of state-of-the-art γ-alumina membrane cross-sections, made by focused ion beam milling, reveals structural defects which adversely affect performance, reproducibility, and lifetime. It is shown that the use of macro-porous supports with a smooth, defect-free deposition surface for membrane dip coating, in combination with purified precursor sols and clean processing, leads to major improvements in micro-structural homogeneity and properties of the membranes. Large particle contaminants/agglomerates can be effectively removed from precursor sols by high-speed centrifugation or ultrasound-assisted screening. While centrifugation is the most practical method for routine use, filter screening provides a more complete removal of agglomerates and larger particles (>80 nm O). Application of the purified membrane precursor sols results in membranes in which connected pore defects (pinholes) are no longer detectable for a membrane thickness of >500 nm thick. The almost complete absence of connected pinholes, obtained with improved membrane processing, is demonstrated by near-100% retention of CaCl 2 in aqueous solution by nano-filtration. The γ-alumina processing experience, collected in our group in the years 2002–2006, is accumulated in a 34-step processing protocol for γ-alumina membranes with a >500 nm single layer thickness.

Permeation porometry, aka “permporometry” is used as a tool to investigate the connected pore size distribution of asymmetric meso-porous membranes. The method is based on the selective filling of specific sized pores with a condensable vapor, and the analysis of a permeating non-condensable gaseous probe through the remaining open pores. The technique is frequently proposed as a convenient means of detecting pinholes in supported membranes. However, artifacts are found to arise in the desorption isotherm due to a combination of chemical diffusion of the probe gas through the pore-blocking liquid, cyclohexane, and the desorption of cyclohexane from the support. These artifacts can be misinterpreted as pinholes and/or overwhelm the contributions of real pinholes. γ-Alumina membranes of various thickness, supported on smooth homogeneous α-Al2O3 compacts, are used to demonstrate the occurrence of these artifacts. Non-condensable probe gasses O2 and Ne are used to identify the crucial difference between the Knudsen and chemical diffusion of the probe through either pinholes or a condensate filled membrane. In addition it is shown how analysis of chemical diffusion permeance through the membrane can be used to obtain the membrane's tortuosity for chemical diffusion.

A new solvothermal technique for synthesizing nanostructured microspheres of nickel oxide (NiO), zinc oxide (ZnO) and tricobalt tetraoxide (Co3O4) using nitrate precursors, urea and sodium dodecyl sulfate as a surfactant is described. The microspheres were shown to exhibit a morphology resembling a collection of platelets with nanoscale thickness. The surface area of the microspheres ranges from 62.8(± 0.3) to 192.9(± 1.3) m2/g, which appears to correspond to the density of platelet packing in the microsphere. The interior structure of the microspheres was investigated with a dual beam focused ion beam-scanning electron microscope and shown not to develop a hollow center.

Continuous, thin, oriented zeolite A membranes are produced by a two-step synthesis on macroporous α-Al 2 O 3 supports. In the first step, zeolite A nano-cubes with ∼350-nm edges are prepared as a native impurity phase in zeolite Y synthesis dispersions, the support surface is pre-modified with a cationic polymer having a selective affinity for zeolite A. The thus-treated support is contacted with a colloidally stable dispersion of zeolite A and Y mixture in water, which results in selective, dense-packed deposition of the zeolite A cubes with one face aligned to the average support surface. In a second step of hydrothermal epitaxial growth, the seed layer grows epitaxially into a continuous, meso-defect free, ∼1 μm thick zeolite A layer, already after 1 h of treatment. This microstructure of the membrane compares very favorably to what is commonly obtained. The pH value of the zeolite mixture suspension is found to have a major influence on seed layer morphology, and thereby, on the quality and orientation of zeolite A membrane after short synthesis times. The final zeolite A membrane thickness and morphology is controlled by varying secondary growth synthesis time. The approach presented is thought to be of generic use for the preparation of oriented zeolite membranes.

Inorganic membranes consist of a stand-alone or supported material with special transport properties, able to operate at elevated temperatures and pressures. Inorganic membranes are classified according to the presence and size of connected porosity. Dense membranes have 100% selectivity for H 2 and O 2 , and acceptable flux at high temperature. Micro-porous membranes have 2 nm ∅ pores and combine high but 100 % H 2 selectivity with higher fluxes at lower temperatures. Meso-porous membranes have 2–50 nm ∅ pores, a good thermo-chemical stability, very high fluxes over a wide temperature range, and moderate Knudsen selectivity for separation of light molecules ( H 2 ) from heavier ones ( CO 2 ) . Meso-porous membranes are also considered for pressure-driven water purification. Large scale introduction of inorganic membranes has been hindered by lack of structural definition, reproducibility, and accurate design parameters. The present paper shows how these problems can be addressed by synthesis and characterization of smooth, strong and surface-defect free supporting structures.

The microstructure of state-of-the-art chemical solution deposited indium tin oxide thin films typically consists of small randomly oriented grains, high porosity and poor homogeneity. The present study demonstrates how the thin film microstructure can be improved significantly by tailoring the precursor solutions and deposition conditions to be kinetically and thermodynamically favorable for generation of homogeneous textured thin films. This is explained by the occurrence of a single heterogeneous nucleation mechanism. The as-deposited thin films, crystallized at 800 °C, have a high apparent density, based on a refractive index of ∼ 1.98 determined by single wavelength ellipsometry at 633 nm. The microstructure of the films consists of columnar grains with preferred orientation as determined by X-ray diffraction and transmission electron microscopy. The resistivity, measured by the four point probe method, is ∼ 2 × 10 − 3 Ω cm prior to post-deposition treatments.

Strong and permeable macro-porous α-Al2O3 membrane supports are made by colloidal filtration of 20 vol% dispersions of α-Al2O3 with an average particle size of 600 nm. Intact compacts with very good surface quality were obtained at an optimum pH of 9.5 and dosage of 0.2 wt% ammonium aurintricarboxylate (Aluminon), based on dry alumina. The colloidal stability of the aluminon-stabilized slurries is confirmed by ξ potential measurements. Slight sintering of dense-packed α-Al2O3 compacts was found to result in >67% packing density and a bimodal pore-size distribution as derived from shrinkage behavior and gas adsorption studies. Non-stationary single gas permeation measurements showed improved gas permeability, compared with α-Al2O3 compacts prepared using powder with a smaller particle size (300 nm). The strength of the disk-shaped alumina compacts within the porosity range of 30%–20% increased from 100 to 300 MPa with a standard deviation of 20 and 50 MPa, respectively.

High-temperature gas sensors based on semiconducting metal oxides show potential for optimization of combustion processes, resulting in efficient energy use and minimization of emissions. Such metal oxides can function as gas sensors because of the reaction of the sensing gas (e.g., CO) with ionosorbed oxygen species on the oxide surface with the resulting increase in conductivity. A limitation of metal oxide sensors is their difficulty of distinguishing between different gases. Designing selectivity into sensors necessitates a better understanding of the chemistry of gas-solid interactions at high temperatures. In this paper, we have used in situ infrared spectroscopy to monitor the dehydration of a hydrated anatase surface up to 600 degrees C and also to examine the hydration/dehydration of anatase held at 400 degrees C. When the O-H stretching region (3000-3800 cm(-1)) was primarily focused on, it was found that water loss from the titania surface proceeded at lower temperatures (200 degrees C) through desorption, whereas at higher temperatures, water dissociation to terminal (approximately 3710 cm(-1)) and bridged (approximately 3660 cm(-1)) hydroxyl groups was noted. With a further increase in temperature to 600 degrees C, the bridged hydroxyl groups disappeared faster than the terminal ones. The electrical resistance of anatase at 600 degrees C was measured in the presence of moist gas streams and resulted in an increase in conductivity in the presence of water. In situ vibrational spectroscopy indicated a temporal correlation between the appearance of the bridging hydroxyl group and the change in electrical resistance. Several possible mechanisms are discussed. The chemical reaction of water with anatase at high temperatures necessitates that water be removed from the gas stream to avoid interference. A strategy involving the use of a hydrophobic microporous filter that can reject water and let gases such as CO pass unimpeded is examined. Successful use of such a concept has been demonstrated with a silicalite filter using moist CO gas streams.

Nanostructured ceramic thin films and membranes are used for protective or functional purposes and prepared on dense or porous substrate materials. Wet chemical methods enable cheap, low-temperature, mass-scale manufacturing routes. They produce fine-grained porous and dense micro-structures that cannot be realized otherwise. In wet-chemical processing, clean nanoparticle dispersions are deposited on the substrate at, primarily, ambient conditions. The deposition is followed by a (rapid) thermal processing treatment to remove liquids and organic additives, to convert precursors to the target composition, and to establish the final porous and dense micro-structure. In the synthesis of precursor dispersions it is very important to obtain nanoparticles with a near-isometric shape and a fairly narrow particle size distribution, without the formation of secondary (agglomerate) structures. In particular the latter requires careful control of solution and interfacial chemistry to achieve proper colloidal stability, during and after the synthesis process. Characterization of coating integrity, defect morphology and defect population is done by decoration methods, microscopy, ellipsometry and statistical methods that employ membrane transport properties.