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Oxide Ceramic Fiber Development at ITCF Denkendorf

Oxide Ceramic Fiber Development at ITCF Denkendorf Ceramic fibers are key components for ceramic fiber-reinforced composites (CMCs), which form a new class of light-weight high temperature resistant materials with exceptional properties such as non-brittle fracture behavior, resistance against extreme thermo-shocks and very good corrosion resistance. These materials are predestined for many applications in technical fields like aerospace, power engineering and automotive but have also potential in medical fields like bone reconstruction and tissue engineering.

Fundamental research in the field of oxide ceramic fibers started at ITCF Denkendorf as early as in 1989. The complete production process of this fiber type has been studied intensively comprising the development of spinning dopes, the dry spinning process as well as pyrolysis and sintering. Both alumina and mullite type fibers with excellent high temperature properties have been developed. Currently, the transfer of the technology into industrial scale is under progress. New developments focus on the improvement of creep resistance and the reduction of grain growth in long time applications of oxide fibers, i.e. YAG fibers (yttrium aluminum garnet) and structure-optimized alumina fibers (ZTA, zirconia toughened alumina). Another research field is the production of fibers, e.g., of Ca-phosphates, and of the corresponding scomposite materials for medical applications.

         

    

YAG fibers Oxidic ceramic fibers are a fundamental component of high-temperature resistant fiber-matrix composites and are increasingly used in rockets, combustion chambers and engines, gas turbines, etc., thereby replacing highly legated steel. Generally, the creep rate of polycrystalline ceramic fibers increases with decreasing grain size and the creep resistance of these fine-grained fibers is not very high in contrast to their strength. Particularly under mechanical stress and at high temperatures exceeding 1100°C, they tend to creep and brittleness increases due to grain growth, which can ultimately lead to failure of the entire device. Yttrium-Aluminum-Garnet (YAG) fibers are high performance fibers with outstanding features such as high temperature stability, high modulus and strength, high oxidation resistance and excellent creep resistance. As YAG is characterized by a very high melting point of almost 2000°C it is very attractive for high temperature applications. Furthermore, it is chemically inert in reducing and oxidizing atmosphere and it is the oxide with the highest creep resistance. For these reasons, YAG fibers satisfy the growing requirements especially in terms of chemical and mechanical stability in long-term, high-temperature applications in oxidizing atmospheres and are therefore the most promising materials to outperform the so far developed ceramic fibers in this area.