The objective of this work was to study the electrodeposition of silicon in molten KF-LiF (eut)-K2SiF6 (5 mol%) on Ag and Si substrates at 550oC and 800oC. In addition electrochemical studies of the system were performed on silver, tungsten and glassy carbon substrates at 800oC. The electrochemical measurements confirmed that the reduction of Si is diffusion controlled and occurs in two steps. On silver, dense, coherent films with good adhesion and no inclusions of salt were obtained at 800oC at the growth rate 52 µm/hour. On silicon, the microstructure seemed to consist of small "randomly" oriented crystals. At 550oC, the deposit became porous and powderish both on silver and silicon substrates. The low temperature combined with the relatively high current densities applied was believed to hinder crystal growth.

Concentrations of dissolved rare earth metal oxides, Nd2O3, and Pr2O3 or their mixtures in different fluoride electrolytes composed of NdF3, PrF3, and LiF at ca. 1040 °C were monitored using a graphite probe inserted into the electrolyte during the dissolution process. Fast voltage sweeps of 100 V/s were applied to the graphite probe, and the current response was measured. As the oxide concentration in the diffusion layer towards the electrode depletes, a passive layer is, at a certain point, formed on the probe, resulting in a current drop. The magnitude of the peak current attained before the formation of the passive layer reflects the concentration of the dissolved oxide and, thus, is applied to determine the oxide concentration. The oxide concentration in the electrolyte samples determined using the inert gas fusion technique showed a good correlation to the peak current determined by the probe.

No abstract

The electrochemical de-oxidation process, also called FFC-Cambridge process, has been proposed previously to produce reactive metals and their alloys through reduction of their metal oxides. The process works by introducing metal oxides into a molten salt bath where it is electrolysed to form metal powders offering both economic and environmental benefits over the traditional metal production methods. Within the frame of the EU-financed project SCALE (GA 730105), SINTEF is investigating the optimal parameters of the direct electrolytic reduction of Sc2O3 and Sc2O3-Al2O3 precursors (dross from Al-Sc alloy production), giving Sc and Al-Sc metallic powders, respectively, in a molten CaCl2-based electrolyte at a working temperature of ca. 900 °C. The influence of the applied cathodic potential in the reduction mechanism and in the metal product has been studied.

No abstract