Project Details
Projekt
Thermodynamics and phase diagrams of refractory composites
Applicants
Dr. Peter Franke; Professor Dr. Hans Jürgen Seifert
Subject Area
Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
Glass, Ceramics and Derived Composites
Glass, Ceramics and Derived Composites
Term
since 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 416817512
In the frame of subproject 7, funding period 2, the thermodynamics and phase diagrams of the refractory composites will be investigated by combination of CALPHAD-type modeling with selected key experiments. In the focus during second funding period is the investigation of the influence of element silicon on the thermodynamics and heterogeneous phase equilibria of Tantalum-Al2O3 and Niobium-Al2O3 composites, respectively. Thus, the quaternary systems Ta-Al-Si-O and Nb-Al-Si-O will be studied. This requires the modelling of the ternary subsystems, especially of Ta-Al-Si, Ta-Si-O, Nb-Al-Si, Nb-Si-O and Al-Si-O. For these systems, and their quasibinary subsystems, analytical descriptions of the Gibbs Free Energy functions for all solid and liquid phases and gas species will be developed by using CALPHAD approaches. The generated computer datasets for these ternary systems will be combined with the thermodynamic datasets as developed during the first funding period (systems Ta-Al-O and Nb-Al-O). Based on this, calculations of the ternary and quaternary systems are performed and required key experiments will be derived from the results to refine the modeling and phase diagram calculations. By using commercially available databases, additional thermodynamic calculations will be conducted to find out the influence of carbon and other elements (e.g. calcium) on phase formations of Ta-Al2O3 and Nb-Al2O3 composites, respectively. The thermodynamic properties for the system phases will be measured by differential scanning calorimetry (DSC) and high temperature drop solution calorimetry. The heat capacities of single phases, their transformations as well as formation enthalpies will be determined. Samples as provided by subprojects 1 and 2 in FOR 3010 will be investigated regarding oxidation behavior and other physico-chemical properties (e.g. by dilatometry). Additionally, silicon containing tantalum and niobium coatings, respectively, will be produced by magnetron sputtering. The coatings will be deposited on sapphire substrates, heat treated and subsequently characterized by X-ray diffraction and electron probe microanalysis (EPMA). These samples will then be investigated within subproject 5 by atom probe and electron microscopy to analyse both phase and grain boundary developments.
DFG Programme
Research Units
