Structural and Thermodynamic Properties of Filter Materials: A Raman and DFT Investigation

Abstract

The contribution focuses on the accurate prediction of heat capacities for intermetallics, the estimation of reaction paths for coated and uncoated alumina foam filters in contact with metallic melts, and the investigation of thermally induced changes in various filters and filtercomponents. Density functional theory (DFT) was able to provide isobaric heat capacities for Al–Fe and Al–Fe-Si systems that outclassed the empirical Neumann–Kopp rule and matched the experimental values over a wide temperature range. Moreover, DFT calculations clarified that the formation of hercynite at the interface between alumina filters and steel melt was the result of a solid-state reaction involving high concentrations of FeO. Ex-situ Raman spectroscopy was used to compare carbon-bonded alumina filters using different bindersfrom Carbores®P to environmentally friendly lactose/tannin, as a function of heat treatment. For these carbon-bonded filters, the prominent D and G bands were used to confirm the existence of graphitization processes and determine the size of graphite clusters resulting from these processes. In order to investigate the pyrolysis processes occurring in selected binder constituents of the lactose/tannin filters, the evolution of Raman spectra with temperature was analyzed via in-situ measurements. Wherever it was appropriate, experimental Raman data were compared with DFT-simulated spectra. Further, Raman spectroscopy was used to study the thermally induced formation of metastable alumina, helping to understand the structural changes that take place during the transformation of boehmite (γ-AlO(OH)) to corundum (α-Al2O3) via metastable transition phases: γ-Al2O3, δ-Al2O3, and θ-Al2O3.