University of Limoges developing composite ceramics for aeronautics applicationsPublished on August 4th, 2011 | By: Martin Grolms
New advanced materials are often drivers of technologies, especially for aeronautics applications. Many materials have been developed to resist severe working conditions, which usually couple high-temperature and mechanical-stress corrosion resistance. For these applications, non-oxide ceramics are promising materials, particularly transition metal carbides, such as zirconium carbide, because of their high melting point.
Unfortunately, ZrC exhibits low oxidation resistance. However, a ZrC–SiC composite material may be a way to overcome this drawback, as silicon carbide forms a passive silica layer at high temperature under oxidizing conditions. The coupling of these properties could lead to ceramics that are resistant to high temperatures in oxidizing atmospheres.
A polymer-derived ceramic route has already been used successfully for the synthesis of ZrB2–SiC composites, and it seems that this synthesis route is also applicable for ZrC-SiC. The method rests on the synthesis of a hybrid material in which a powder of ZrC first is coated by a SiC precursor polymer. Subsequent pyrolysis yields a composite with a homogeneous microstructure.
However, until just recently, systems of these organic–inorganic interactions, as well as mechanisms of polymerizations and thermal/chemical cross-linking, have not been investigated. Now scientists of the University of Limoges report (10.1002/adem.201000336) they have implemented a polymer-derived ceramics route approach to obtain new ZrC-SiC composites.
Some background on this work: Limoges has a long porcelain tradition dated back to 1768. Today, more than 50% of all porcelain made in France comes from Limoges. At the school’s renowned “Laboratoire Science des Procédés Céramiques et de Traitements de Surface,” the researchers selected different SiC precursor polymers to generate the composite and to study the material. They investigated the mechanisms of thermal and chemical cross-linking, as well as the thermal behaviour of the polymers. Apparently, the key to this approach was the use the polymers synthesized from a vinylsilane monomer, which enhances organic-inorganic interactions between the ZrC mineral phase and the polymer.
The French researchers obtained a promising yield and microstructural homogeneity of the materials. XRD analysis indicated the formation of a β-SiC phase in presence of ZrC. SEM observations emphasized the role of the polymer structure on the final microstructure. Further investigations are presently under to understand the sinterability of these systems.
Editor’s note: Martin Grolms is a writer for Materials Views.
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