Ceramic foam substrates for automotive catalyst applications: fluid mechanic analysis

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 directio

Multi-parameter improvement method for (micro-) structural properties of high performance ceramics

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

Three-dimensional pore structure and ion conductivity of porous ceramic diaphragms

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

Multi-layer molded part

patent submitter:VITA Zahnfabrik H. Rauter GmbH & Co. K

Mehrschichtiger Formkörper

patent submitter:VITA-Zahnfabrik H. Rauter GmbH & Co K

Development of Yb2O3-based ceramics for indirect production of 177Lu used in targeted radionuclide therapies

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

Multi-color gradient ceramics produced by aqueous tape casting

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 concluded that process does not negatively affect the mechanical properties and density of ceramic bodies. Furthermore, it provides a more flexible way of creating gradient zone through the ceramics. This makes it a very attractive method, especially for dental applications, but also for other esthetic demands e.g. jewelry and watch industry

Ceramic foam substrates for automotive catalyst applications: Fluid mechanic analysis

ISSN:0723-4864ISSN:1432-111

FIB-tomography data of porous Zr-oxide fabricated with varying sintering conditions

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