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AFM investigation of the in situ-formed oxide layer at the interface of Al2O3-C/steel melt in terms of adhesion force and roughness in a model systemWednesday (07.10.2020) 13:40 - 14:00
Ceramic foam filters are used in metal melt filtration to increase metal pureness by separation of inclusion particles like alumina. These non-metallic inclusions can considerably effect the mechanical properties of cast products, there-fore high filtration efficiencies are desirable. It has been observed prevoiusly that an in situ-formed oxide layer can be generated on ceramic fil-ters based on MgO-C, Al2O3-C and Al2O3-MgO-C after immersion in liquid steel. In liquid 42CrMo4 steel at 1650 °C, crystal structures are formed at the filter surface that are based on alumina and spinel and strongly impact the chemistry and surface morphology of the filter.
As part of the CRC 920, in situ layers of the material used by Zienert et al.  have been investigated in this study via atomic force microscopy (AFM) in a water-based model system. These samples have been exposed to the melt at different contact times. Surface morphologies of the samples and colloidal probe particles (model inclusions) have been recorded via contact mode AFM and a MatLAB script has been used subsequently to describe roughness pa-rameters depending on the size of the scanned area. Adhesion force measurements between samples and colloidal probe particles were done by using colloidal probe AFM under variation of wetting properties (hydrophilic and hydrophobic surfaces) for all samples. Poor wetting leads to larger adhesive forces due to insufficient immersion and the generation of small bubbles that causes capillary interactions. In case of good wetting, samples exposed for a longer time period show larger adhesive forces than the ones exposed for a shorter period, but this is vice versa under poor wetting conditions. The behavior under poor wetting conditions has been further proved indirectly with drop probe AFM using a mercury droplet. For good wetting conditions, capillary interactions can be neglected in the experimental setup. Here, van der Waals interactions are responsible for adhesion. Therefore, experimental results have been compared with an AFM data-based MatLAB script that calculates van der Waals forces for the different samples.
 T. Zienert, S. Dudczig, P. Malczyk, N. Brachold, C. G. Aneziris, Adv. Eng. Mater. 2020, 22, 1900811