Temperature-Induced Changes in the Microstructure of the Metal Melt Filters and Non-metallic Inclusions

Abstract

The functionalization of ceramic foam filters aims typically at the enhancement of the thermal shock resistance and the reactivity of the filters with respect to specific inclusions and impurities. For this purpose, thermodynamically metastable phases are utilized that have a strongly defective crystal structure and/or nanocrystalline character. Such phases possess frequently better or even unique properties in comparison with their thermodynamically stable counterparts. However, the stability of metastable or defect-rich phases is usually impaired by microstructural changes, which occur during the contact of these phases with the metallic melt at high temperatures and which speed up finally the degradation of the functionalized filters. In general, the first step towards the stabilization of the thermodynamically metastable and/or defect-rich phases is the understanding of their microstructure and the microstructure changes accompanying the transition to the thermodynamically stable state. In this chapter, the thermally induced microstructure changes are illustrated on the examples of selected carbon containing binders and metastable alumina phases. In order to be able to describe the crystal structure and microstructure of these compounds in more details, which is required for the targeted development of the functional filter materials, complementary methods of crystal structure and microstructure analysis like X-ray and electron diffraction, X-ray and nuclear magnetic resonance spectroscopy and electron microscopy were combined and further developed.