Challenges of Electrolytic Titanium Extraction and Deposition

Abstract

Modern civil aircrafts contain an increasing amount of titanium as structural material. Besides mechanical properties the electrochemical compatibility with carbon fibre reinforced materials is the main driving force for new titanium applications in aeronautics. Researchers in industry and academia are spurred by high demand and high costs to develop new affordable processes for the extraction of the attractive light metal. Established industrial scale processes are based on chlorination of the titanium dioxide and reduction of titanium tetra chloride with magnesium or sodium. Processes based on electrolysis are promising for the replacement of common titanium extraction routes. However, many different process alternatives were proposed in the past but due to up-scaling restrictions none of them has been industrialised yet. Nevertheless, it is worth to examine new attempts with lower energy consumption and carbon dioxide emissions for ecological and economical reasons. The difficulty of titanium winning is its strong affinity to oxygen and hydrogen. Electrolytic processes require detailed knowledge on the electrolyte as well as on the behaviour of the titanium ions and its species in the electrolytic cell. Higher energy efficiency is the main driver for the development of an electrolytic process. Worldwide several processes based on the extraction of titanium in molten salts are under investigation. The electrolytic processes can be divided in direct reduction of cathodes on the one hand and several technologies to dissolve different titanium compounds in the electrolyte on the other hand. Table 1 provides an overview on the major international known developments, which will be discussed in the presentation. Further challenges of the electrolysis of titanium in molten salts are referred to the deposition on substrates to form dense coatings. Electrochemical routes have the potential to replace energy and time consuming PVD processes for special applications. Once an electrolytic titanium coating process is developed new applications e.g. for corrosion protection and titanium matrix composites will arise. Opportunities and challenges of new coating technologies by molten salt electrolysis will be presented.