Gewinnung kostengünstiger Titanwerkstoffe durch modifizierte Erzeugung von Titanschlacke, aluminothermische Reduktion und pfannenmetallurgische Raffination
Zusammenfassung der Projektergebnisse
The proposed production route for cost-affordable titanium alloys from ilmenite consists of three main steps, two of which have been studied until now. The first step is the production of a modified titania slag from ilmenite. This titania slag is subsequently reduced by aluminium to produce Ti-Al-O pre-alloy, which in equilibrium with Al2O3 contains high amounts of oxygen and aluminium. The third steps deals with the refinement of this pre-alloy under CaO saturation in order to decrease the Al- and O-content to acceptable levels. The investigations on modified titania slag productions indicate that an efficient process can be developed to produce a titania slag and separate it from the iron in ilmenite. This process begins with pelletizing ilmente and the carbothermal reduction of iron in solid state. The reduced pellets are then melted with the help of CaO and MgO as slag formers. The iron will melt and form a metal pool while Ti oxide combines with CaO and MgO and joins the slag. This way, two valuable products are produced: a low-iron Ti slag and a liquid iron with the potential to be converted to steel. The aluminothermic reduction of slag in liquid state is still to be done. However, the result is only useful if the refinement of the Ti-Al-O alloy could be successfully performed in the subsequent third step. In refinement step, there is a big lack of data available in literature. First, the equilibrium between Ti-Al alloys and Al2O3 has not been studied well. Thus the state of the alloy from the second steps is not clear. More importantly, there is almost no research conducted on Ti-Al-O alloys with Alcontents lower than 15 wt% in contact with pure CaO and/or CaO saturated slags. The investigations performed on this step indicated that the oxygen content of the alloy molten in CaO crucible is significantly and even more that 10 times lower than that of in contact with Al2O3. Therefore, the third and decisive step of the process route seems really promising. However, difficulties in the experiments lead into uncertainty and scatter in the results. The main problem is the penetration of the melt into the crucible. A series of experiments to make a more resistant crucible was also conducted, which improved the performance of the crucible. Nevertheless, more investigation is needed to obtain a suitable crucible by which a highly reliable experiment can be done. Modelling of the equilibrium of Ti-Al-Ca-O melts saturated with pure Al2O3 and CaO, respectively, was done in parallel. The calculation results strongly depend on the precision of the experimental data and the applied model. The investigations within the present research project proved the high degree of difficulty to conduct experiments with reasonable accuracy on Ti-Al-O alloys at the temperatures 1700 - 1800°C. This might be the reason why there is not much available literature data for this system at low Al-contents. Now that the present research has shown that the refinement of Ti-Al-O alloy in CaO crucible is promising and has the potential to lead into cost-affordable Ti alloys, this creates a strong motivation to continue research with the focus on: Further studying the equilibrium between Ti-Al-Ca-O melts and Al2O3 at the low Al content. - Further studying the equilibrium between Ti-Al-Ca-O melts and CaO. - Studies to make a crucible and eventually a refractory resistant against metal and slag penetration, while providing CaO-saturation condition. Such a refractory material could also be used for a possible production process. Success in conducting these researches can lead into a great step forward for mass production of cost-affordable Ti alloy for automotive and other more common applications. In brief, the present study indicates that the proposed process route is really promising and is worth to spend more investigation. The conducted research has also led into a more clear view on the problems and main challenges in investigations, which makes the further researches more effective and solution oriented. We have to admit that from scientific point of view neither the experimental nor the modelling results achieved in this project can be considered to be well-validated and sufficiently reliably. Nevertheless, after performing this project, the envisaged process is assessed to be more feasible than before, even though there are still a lot of open crucial questions.
