Title: SiC-Based Multilayer for Applications in Extreme Environment - H2 Generation Plants
Authors: VEGA BOLIVAR Claudia
Publication Year: 2011
JRC N°: JRC66426
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC66426
Type: PhD Theses
Abstract: The purpose of this research is to develop SiC-based multilayers, for applications in extreme environment such as H2 generation plants. Tape casting technology, followed by debinding and sintering at very high temperature (~2200 °C) has been used. In Europe H2 generation processes are being studied under the project HycycleS1, that focuses at the qualification and enhancement of materials and components, in particular ceramics of the SiC family, for key steps of thermochemical cycles for solar or nuclear hydrogen generation. SiC-based materials for applications in extreme environments are developed within the European project ExtreMat. This project has identified the generation of hydrogen as a possible spin off of research activities. HycycleS (Materials and components for Hydrogen production by sulphur based thermochemical cycles) is a project funded under 7th Framework Programme. ExtreMat is funded within the 6th Framework Programme and it targets on the creation of new multifunctional materials. The aim of this research is to develop multilayer SiC for applications in hydrogen generation plants based on thermochemical cycle "S-I" or cycle hybrid thermochemical-electrolytic. The structured components of such facilities (tanks, tubular heat exchangers, etc) should have excellent thermal stability at high temperature, corrosion resistance (in the presence of corrosive agents such as sulphuric acid, sulphur dioxide, sulphur dioxide and hydrogen iodide) and good thermal conductivity. The proposed method will provide almost pure silicon carbide products with multilayer laminate structure. Compared with other fabrication processes, this manufacturing approach for SiC-based ceramics has some advantages: the absence of secondary components (as is the case of bonded reaction infiltrated SiC) that expose the material to corrosion, easy-forming components, and a good toughness due to the laminate structure. The integration of porous layers in the multilayer structure as well as the integration of chopped carbon fibres, placed within the SiC sheets constituting the multilayer core, can provide better thermal management. Porous layers are suitable for lowering down the thermal conductivity through the thickness, while the fibres (aligned with the casting direction) are expected to increase the conductivity in the plane of the sheets and to drive the heat far from the hot spots. Finally both of them are suitable for improving the multilayer toughness, provided that suitable interfacial bonds between the layers as well as between the matrix and the fibres form. Toughness should be improved by exploiting de-bonding, pull-out and delamination phenomena, without decreasing too much the overall strength of the material. Then a compromise between strength and toughness should be achieved. Accordingly, three kinds of specimens were tested: · Multilayered SiC integrating porous layers, · Multilayered SiC integrating SiC and C long fibres layer. · Multilayered composites made by stacking Cf/SiC composite layers. Two kinds of chopped carbon fibres (polyamide coated and uncoated) were used for the manufacture of the composite sheets. Dense SiC was always used as a reference. The main concern in the design of ceramic laminates containing either porous layers or composite Cf/SiC layers deals with the risk of decreasing the oxidation resistance. In this research will be detailed the effects of different heat treatments (oxidation and/or corrosion) applied to different kinds of multilayer SiC. To this purpose the microstructure and the main mechanical properties will be compared before and after heat treatment.
JRC Directorate:Nuclear Safety and Security

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