J. Luyten

Preparation of LaSrCoFeO3−x membranes

The last 10 years an alternative production route for oxygen production by using mixed conductors has been investigated. Perovskite mixed electron-oxygen conducting membranes are bulk membranes with a thickness of the order of 1 mm, showing sufficient oxygen fluxes only at temperatures above 800°C. To reach commercially interesting fluxes at lower temperatures, membrane modules with a much higher surface/volume ratio or multilayer membranes with a thin dense skin need to be developed. In our laboratory, dense hollow fibres and porous multilayer substrates were synthesised. The hollow fibres were produced using a polymeric spinning technique based on phase inversion. The multilayer porous substrates were manufactured following conventional ceramic processing routes.

Gelatin gelcasting of ceramic components

Abstract Gelcasting is a new near net shaping technique, which has rapidly evolved from a laboratory invention towards industrial application. In gelcasting, a highly loaded but very fluid slurry consisting of powder, water, disperser and gelformer, is poured into a mould and subsequently gelled. Once gelation has taken place, the part is strong enough to retain its shape and can be demoulded, dried, calcined and sintered. A great advantage of the technique is that very complex shapes can be made with relative ease. In original gelcasting formulations, gelation was obtained through polymerisation of acrylamide monomers, which are classified as neuro-toxic. In this study, however, the feasibility of using a non-toxic gelformer (gelatin) will be reported. Relevant processing parameters such as slurry composition and preparation procedures, de-airing and gelation schedules are reported, along with results of sintering and resulting microstructures.

Proton conductivity in strontium cerates for hydrogen gas sensors in coal gasification systems

Abstract In the framework of the European action on non-nuclear energy (JOULE), an on-line hydrogen Nernst-type gas sensor for coal gasification systems is under development. This electrochemical sensor is based on Yb-doped SrCeO3 as proton conducting solid electrolyte. With regard to the electrical characterization, an in depth impedance analysis was performed in reducing as well as in oxidizing atmospheres and the influence on the bulk ionic conductivity and on the electrodes has been studied. Material compatibility in a simulated coal gasification atmosphere has been investigated. Preliminary results of EMF measurements in an air versus hydrogen concentration cell are presented as well.

Humidity sensitivity of electrochemical hydrogen cells using calcium zirconate ceramics

Abstract The influence of humidity on the conduction of indium doped calcium zirconate is investigated using electrochemical hydrogen concentration cells. The resulting e.m.f. values measured in dry and humidified argon-hydrogen gas mixtures were found to be linear as a function of the logarithm of the hydrogen gradient but with a slope of around 70% of the expected Nernst slope in the dry mixtures. The obtained curves are discussed in terms of mixed hydrogen and oxygen conduction. In addition, electronic conduction at very low oxygen partial pressures was introduced in order to explain all the experimental observations.

Ceramic Foams Coated with Zeolite Crystals

Ceramic foams can be used as filters, dust collectors, light weight components and catalyst carriers. They can be produced by a variety of techniques. The performance of ceramic foams will be strongly improved when their mechanical properties are improved. For this reason, we produced ceramic foams both by a modified reaction bonded (RB) replica technique and by gel casting. With both methods, reticulated foam structures with enhanced mechanical strength were obtained. Zeolites are a special type of materials that are characterized by high catalytic properties. They can be brought on a structured carrier by dip and slurry coating. Nevertheless, in situ coating has as main advantage that the support is used as the base for nucleation. This results in the formation of a chemical bond between the zeolite crystals and the support. The goal of this contribution is twofold: at first we demonstrate how Al2O3 foams with improved mechanical strength can be produced both by the modified RB-alumina replica technique and by gel casting. Secondly, it is shown that these ceramic foams can be coated with (silicalite) zeolite crystals by insitu crystallization from a precursor sol. The two-layer material combinations have been characterized with FESEM, XRD, CT (computer assisted tomography), IA (Image Analysis) and by mechanical tests.

In vitro dissolution behavior of custom made CaP scaffolds for bone tissue engineering

The degradation rate of custom made calcium phosphate scaffolds, designed for bone tissue engineering applications, influences the healing process of critical size bone defects. An optimal degradation rate exists at which the neo-formed bone replaces the CaP (calcium phosphate) scaffold [1]. Consequently investigating the complex degradation behavior (dissolution, reprecipitation, osteoclast activity) of custom made CaP structures gains interest. In this work different in vitro dissolution experiments were performed to study the degradation behavior of 4 by composition different calcium phosphates. Ideally these experiments should have a predictive power regarding the in vivo degradation behavior. In vitro dissolution tests still lack standardization. Therefore this study focuses on the influence of two dissolution constraints: (i) the material’s macrostructure (porous - dense), (ii) the regenerated fluid flow (bath shaking - perfusion). From 4 different CaP compositions porous structures and as a reference dense disks were produced, using the same starting powder and heat treatment. To compare the different dissolution tests, all data was normalized to the CaP surface area. Results show that besides the structural appearances of the CaP structures, also the design of the dissolution test influences the in vitro dissolution behavior. Moreover there is a need to take the morphology of the dissolved material into account. The CaP perfusion tests show dissolution dynamics that resemble the in vivo reality more closely than the shaking bath experiments.

Humidity effects on calcium zirconate ceramics in electrochemical hydrogen cells

In the eighties, Iwahara discovered that doped Sr and Ba cerates show significant proton conduction, at high temperature, and in hydrogen- or water-containing atmosphere [1]. Begin ‘90 it was proved that also doped zirconates (Sr, Ba, Ca) join this family of proton conducting perovskites [2]. Within this group, indium doped CaZrO3 is one of the more interesting materials for applications, being mechanically and chemically particularly stable, and producible in very dense form. Specifically, it was already succesfully incorporated in a hydrogen sensor for liquid aluminium [3]. In principle, this sensor works as a simple electrochemical hydrogen concentration cell described by Nernst. However, as already remarked phenomenologically from the beginning [1], a hydrogen concentration cell using these perovskites shows the theoretically predicted emf, only in the presence of humidity. In this paper we want to go deeper into the reasons for this phenomenon.

Electrochemical sensors for oxygen and lithium detection in Pb17Li

Abstract Over several years, SCK/CEN has acquired experience in developing chemical sensors for liquid metals based on solid electrolytes. In the framework of the European Fusion Program, oxygen and lithium monitoring devices are developed including the required data acquisition system for converting the measured voltages into corresponding element concentrations.

Immobilised Molten Salt Membrane based Magnesium Sensor for Aluminium-Magnesium Melts

Magnesium sensitive probes were constructed and tested in different melts of commercial aluminium-magnesium alloys. The probes were composed of a porous magnesium oxide one closed end tube or thimble to which a magnesium conducting salt is impregnated. The activity of magnesium in the aluminium-magnesium melt was determined with report to a pure magnesium reference contained in the inside of the thimble and sealed from the surrounding atmosphere and melt by zirconia based cement. Measurements were conducted in various commercial aluminium-magnesium alloys under inert atmosphere as well as in air.

Impedance spectroscopy study of superplastic 0.3 mol% CuO modified 3YTZP oxygen sensor material

Abstract Y 2 O 3 stabilized ZrO 2 ceramics are commonly used as oxygen sensor materials, eg in the well known Lambda sensor for automotive application or in high temperature oxygen probes for flue gases. Recently these compounds also become important for their superplastic deformation characteristics. In ceramic sensor fabrication, ceramics are often required in various shapes. The superplastic deformation of 3 mol% Y 2 O 3 stabilized tetragonal zirconia polycrystals (3YTZP) modified with 0.3 mol% CuO and its influence on electrical and structural properties were studied.