Developing a Thermodynamic Database for Lead-Based Alloys

The availability of advanced thermodynamic databases and software and the CALPHAD method allow different phenomena, i.e. phase transformations, and chemical reactions, to be evaluated mathematically by means of thermodynamic calculations. These calculations require internally consistent and reliable thermodynamic databases, such as the MTOX (metal-oxide-sulphide-fluoride) database. MTOX covers the thermodynamic data of the systems related to metal smelting and refining processes, where lead is often considered as an impurity coming from the primary and secondary raw materials. Better knowledge of the thermodynamic behaviour of lead and its alloys can help in developing the smelting, refining and slag cleaning processes where lead often exists as a component. In this thesis, the mutual solubilities of molten lead and solid metallic foils (Ni, Fe, Cu, Fe-Ni) were measured by means of an isothermal equilibration technique at elevated temperatures, in specially formed quartz ampoules. The chemical compositions of the saturated metals were analysed with an ICP spectrometer and by EPMA. Literature surveys of the experimental data of the respective systems were performed with the aim of covering all the published data from the early 20th century until today. The critically evaluated and selected experimental literature data together with the data obtained from my own experiments were used to optimize the thermodynamic interaction parameters of the solution phases with the CALPHAD method. These phases were described in terms of a simple substitutional solution model. For the pure elements the SGTE Unary data were used. The systems were assessed with MTDATA software and the experimental data were fitted by a least square method. The new experimental data obtained within this thesis enabled the determination of more accurate thermodynamic description of the present systems. In particular, the lead solid solubility in the solid metals, below the monotectic temperature, had not been determined experimentally before with this accuracy. The metal solubilities in molten lead of these systems are rather well known and are in agreement with the results obtained in this thesis. The thermodynamic description of the Ni-Pb, Fe-Pb, Cu-Pb and Fe-Ni-Pb systems have been improved/established. The overall agreement of the calculated phase diagrams with the critically selected experimental data is good. The thermodynamic assessment of these lead-alloy systems can be used together with the MTOX database to calculate the thermodynamic properties and phase equilibria of multicomponent systems and consequently, to solve practical problems related to materials engineering and metallurgy.