Search

This dataset contains 3D data acquired with FIB-tomography from porous Zr-oxide. The pore structures of the ceramic materials were investigated in context with optimization of transport properties (aimed for low viscous flow/permeability and high electric conduction via liquid electrolyte in the pores), so that the Zr-oxide is suitable for application as liquid junction (diaphragm) in pH-sensors. Further details on the scientific background are given in Holzer et al., 2016, Materials & Design, 99, 314–327. (http://doi.org/10.1016/j.matdes.2016.03.034). The tomographs represent 9 ceramic materials that were produced with different sintering temperatures (1250, 1300, 1325 and 1350°C) and different sintering times (1, 2 and 3 hours). The study includes quantitative descriptions of relevant microstructure characteristics (porosity, tortuosity, constrictivity, hydraulic radius) and corresponding effective transport prorperties (permeability, conductivity). Each tomograph is presented as stack of 2D-tiff-images in two different versions: as gray-scale images (raw data) and as binarized images (segmented, with solid=black and pores=white). The voxel resolution is 10x10x10 nm for all 18 image stacks.

The demand for targeted radionuclide therapies (TRT) increases worldwide with surging numbers of cancerogenic cases. There is a growing concern that the availability of such medical isotopes may not be sufficient in the long term. In particular, the 177Lu is identified as an important example of a medical isotope to be at risk for future shortages. The challenges of its production routes, as well as the limited accessibility to nuclear research facilities need to be therefore addressed and debated. In this work we discuss the distinctive aspects of forming ceramic targets based on Yb2O3, as this material possesses sufficient chemical and thermal stability under reactor irradiation to obtain the 177Lu radionuclide. The study comprises the Yb2O3 powder to be initially doped with aluminum isopropoxide prior to formation of cylinders with diameter below 1.7 mm. Consequently, the grain-growth and creation of a new phase Yb4Al2O9/ Yb3Al5O12 between formed Al2O3 and Yb2O3 during sintering at 1750 °C in air atmosphere improves the densification and leads to increase of Vicker’s hardness and mechanical stability of such manufactured targets. The stability of Al2O3-doped Yb2O3 targets is tested via impact test through 12 meters long steel tube having two arc points, while the system is pressurized with N2 gas up to 10 bar. Twenty-five specimens are shot through the pipe to simulate the activation route as in the nuclear reactor with 100 % success rate of such an impact test. The post processing of the solid material takes place in autoclaved system at 260 °C, 40 bar and acidic mixture of H2O/HCl/HNO3 until the complete dissolution is achieved, usually no longer than 26 minutes. Thus, allowing the newly created radionuclide to be extracted and further used for medical purposes.

OBJECTIVE: Functionally graded materials find currently an increasing interest, especially in ceramic field, thus broadening the ranges of applications, e.g. for separation membranes, tribological applications, thermal barriers or just esthetic purposes. A general procedure was developed to produce stacks of hundreds of layers with different material properties in such controlled arrangement that smooth macroscopic gradients through the whole block are achieved after firing. As a case study we demonstrate the possibility to create multiple color gradient within ceramic blocks and to machine those to specific shapes. MATERIALS & METHODS: Ceramic powders, cellulose and vinyl acetate‐based aqueous slurries were used to produce flexible green tapes with thickness ranging from 60 to 200 microns. The fabrication of ceramic blocks followed the stacking up of color tapes at room temperature using low‐pressure moldless compaction. Subsequently, the blocks were pre‐sintered, and then CNC machined in various shapes and sintered to full density. Scanning electron microscopy, stereo microscopy and UV‐Vis spectrophotometry were used to analyze the interior microstructure and gradient color zones. RESULTS: Different prefabricated blocks were shaped by CNC milling and subsequently fired. All ceramics specimens, depending on individual material, achieved relative densities around 99 %. The results from CIE Lab color space coordinates that were calculated from spectrophotometer’s reflectance spectra showed high degrees of linearity or reflected the applied material pattern. Results of hardness tests and bending strength were found to be in close match with literature data. There was no significant difference among the perpendicular and parallel layers orientation in stacked blocks. CONCLUSIONS: The developed process allows production of functionally graded ceramic materials. As an example, the study shows smooth transitions between color boundaries within ceramic blocks. It can be co

Mineral-based membranes for high temperature alkaline electrolysis were developed by a phase inversion process with polysulfone as binder. The long-term stability of new mineral fillers: wollastonite, forsterite and barite was assessed by 8000 h-long leaching experiments (5.5 M KOH, 85°C) combined with thermodynamic modelling. Barite has released only 6.22 10-4 M of Ba ions into the electrolyte and was selected as promising filler material, due to its excellent stability. Barite-based membranes, prepared by the phase inversion process, were further studied. The resistivity of these membranes in 5.5 M KOH was investigated as a function of membrane thickness and total porosity, hydrodynamic porosity as well as gas purities determined by conducting electrolysis at ambient conditions. It was found that a dense top layer resulting from the phase inversion process, shows resistivity values up to 451.0 ± 22 Ω cm, which is two orders of magnitude higher than a porous bulk membrane microstructure (3.89 Ω cm). Developed membranes provided hydrogen purity of 99.83 at 200 mA cm-2, which is comparable to previously used chrysotile membranes and higher than commercial state-of-the-art Zirfon 500utp membrane. These cost-effective polysulfone – barite membranes are promising candidates as asbestos replacement for commercial applications.

The ion conductivity of two series of porous ceramic diaphragms impregnated with caustic potash was investigated by electrochemical impedance spectroscopy. To understand the impact of the pore structure on ion conductivity, the three-dimensional (3-D) pore geometry of the diaphragms was characterized with synchrotron x-ray absorption tomography. Ion migration was calculated based on an extended pore structure model, which includes the electrolyte conductivity and geometric pore parameters, for example, tortuosity (τ) and constriction factor (β), but no fitting parameters. The calculated ion conductivities are in agreement with the data obtained from electrochemical measurements on the diaphragms. The geometric tortuosity was found to be nearly independent of porosity. Pore path constrictions diminish with increasing porosity. The lower constrictivity provides more pore space that can effectively be used for mass transport. Direct measurements from tomographs of tortuosity and constrictivity opens new possibilities to study pore structures and transport properties of porous materials.

Porous Diaphragms in pH-Sensors must meet apparently contradicting requirements such has high conductivity vs. low permeability and low outflow rate of the electrolyte vs. high flow velocity. In this study we intend to lay the foundations for knowledge-based materials design, so that the required materials properties can be achieved. This approach is based on a quantitative understanding of the relationships between 3D topological parameters with the corresponding effective transport properties (flow/permeability and conductivity). All transport relevant topological parameters (i.e. tortuosity, constrictivity, porosity and hydraulic radius) are determined by FIBtomography and 3D image analysis. Effective properties (conduction and flow) are determined a) by 3D numerical simulation and b) with experimental characterization. The experimental work includes fabrication and characterization of porous YSZ sintered at 1250, 1300 and 1350 ÅãC. Fundamental relationships are established by comparison of topological data with results from simulation and from experiment. The following design guidelines are then postulated: a) flow properties are adjusted independently from the conduction via manipulation of the hydraulic radius, b) high local flow velocity and at the same time relatively low volume outflow can be achieved by adjusting the constrictivity via manipulation of sintering conditions and with addition of pore former.

Many pH-measurement electrodes rely on porous diaphragms to create a liquid electrolyte junction between reference-electrolyte and the fluid to be measured. In field applications, the diaphragm is required to meet partly contradictory improvement criteria. To minimize measurement errors and to ensure durability of the measurement device, the diaphragm is supposed to maximize electrolyte conductivity and reference-electrolyte outflow velocity, while simultaneously minimizing reference electrolyte flow rate. The task of optimizing the overall performance of this small piece of ceramics has lead to the development of a novel multi-parameter improvement scheme for its (micro-) structural design. The method encompasses the consideration of microscopic material design parameters, such as porosity, pore-tortuosity and constrictivity, macroscopic material parameters such as diaphragm diameter and length, as well as process parameters like internal electrode pressure or the electrolyte viscosity and specific resistivity. Comprising sets of design parameters to dimensionless groups, concrete design guidelines as well as the introduction of a three-dimensional improvement space concept are proposed. The novel design space concept allows the improvement of each possible diaphragm-based measurement set-up, by considering the simultaneous, dimensionless interaction of all relevant design parameters.

Several properties of ceramic foams render them promising substrates for various industrial processes. For automotive applications, the foam properties that need to be further studied include the substrate impact on the exhaust gas flow, in terms of pressure drop and flow uniformity. In this paper, pressure drop measurements are performed with different honeycomb and ceramic foam substrates, and pressure drop correlations are discussed. The flow uniformity upstream and downstream of the substrates is evaluated using particle image velocimetry. The results show that ceramic foam substrates induce higher pressure drop, while increasing the uniformity of the flow. In contrast to honeycomb monoliths, the flow uniformity downstream of ceramic foams does not decrease with increasing flow velocity. The higher flow uniformity of ceramic foams is not only caused by their higher pressure drop, but also by flow homogenization that occurs inside the ceramic foam structure, as a result of the momentum exchange perpendicular to the main flow direction

An impregnated zirconia felt (IZF) diaphragm was developed and investigated to be used as a separator in alkaline electrolysers with focus on the purity of the produced hydrogen and oxygen as well as the voltage-drop over the cell. As a substrate a commercial zirconia felt with a porosity of 94% was used. After the impregnation with inorganic-organic slurry the porosity of the flexible diaphragm was 62%. The impregnated zirconia felt (IZF) diaphragm were characterized in respect to the porosity of the structure and electrochemical resistance and compared to currently in use asbestos-chrysotile and commercially available ceramic matrix composites (CMC). In the electrolysis test cell setup at ambient conditions, the IZF diaphragm showed a lower voltage drop compared to asbestos and the CMC diaphragm, while the hydrogen and oxygen purity is greater than 99.8 %., + ID der Publikation: hslu_101791 + Art des Beitrages: Präsentation Konferenzpapier/Tagungsbeitrag + Sprache: Englisch + Letzte Aktualisierung: 2024-07-30 12:23:43

Production of hydrogen using high pressure alkaline electrolysis is well established and allows obtaining high purity pressurised hydrogen and oxygen gases. The electrolyser's efficiency depends significantly on the ion-conductivity of diaphragms/membranes separating oxygen and hydrogen. Currently used diaphragms are made of asbestos, which are not only prohibited by recent health regulations, but also require high energy consumption. Therefore, we are looking for a new material to substitute asbestos which has an equal or even better performance. High gas purity, i.e., low gas penetration, is achieved through the small size of pores which is smaller than the hydrogen and oxygen bubbles. High ionic conductivity in asbestos is mainly achieved through its excellent wettability, the effects related to the fibrous structure and the specific porosity. The aforementioned properties most probably with the interplay of surface processes influence the ion conductivity. We report our first results of X-ray photoelectron spectroscopic study of pristine and reacted asbestos diaphragms and olivine mineral (Mg2SiO4) in 25% KOH at ambient conditions. The data combined with impedance measurements and tests in the electrolysis cell will allow the evaluation of new possibilities materials for new diaphragms., + ID der Publikation: hslu_101797 + Art des Beitrages: Präsentation Konferenzpapier/Tagungsbeitrag + Sprache: Englisch + Letzte Aktualisierung: 2024-07-30 12:30:09

The ion conductivity of two series of porous ceramic diaphragms impregnated with caustic potash was investigated by electrochemical impedance spectroscopy. To understand the impact of the pore structure on ion conductivity, the three-dimensional (3-D) pore geometry of the diaphragms was characterized with synchrotron x-ray absorption tomography. Ion migration was calculated based on an extended pore structure model, which includes the electrolyte conductivity and geometric pore parameters, for example, tortuosity (τ) and constriction factor (β), but no fitting parameters. The calculated ion conductivities are in agreement with the data obtained from electrochemical measurements on the diaphragms. The geometric tortuosity was found to be nearly independent of porosity. Pore path constrictions diminish with increasing porosity. The lower constrictivity provides more pore space that can effectively be used for mass transport. Direct measurements from tomographs of tortuosity and constrictivity opens new possibilities to study pore structures and transport properties of porous materials.

Several properties of ceramic foams render them promising substrates for various industrial processes. For automotive applications, the foam properties that need to be further studied include the substrate impact on the exhaust gas flow, in terms of pressure drop and flow uniformity. In this paper, pressure drop measurements are performed with different honeycomb and ceramic foam substrates, and pressure drop correlations are discussed. The flow uniformity upstream and downstream of the substrates is evaluated using particle image velocimetry. The results show that ceramic foam substrates induce higher pressure drop, while increasing the uniformity of the flow. In contrast to honeycomb monoliths, the flow uniformity downstream of ceramic foams does not decrease with increasing flow velocity. The higher flow uniformity of ceramic foams is not only caused by their higher pressure drop, but also by flow homogenization that occurs inside the ceramic foam structure, as a result of the momentum exchange perpendicular to the main flow direction