Electroplating silicon and titanium in molten fluoride media

The electrolytic reduction mechanisms of K₂SiF₆ and K₂TiF₆ solutions in LiF-KF and LiF-NaF-KF eutectic mixtures have been studied at temperatures between 550 and 850°C. The reduction of K₂SiF₆ proceeds by two successive electron transfers, $$Si(IV) + 2e to Si(II) + 2e to Si$$ coupled with an antidisproportionation reaction $$Si(IV) + Si underset{{k_b }}{overset{{k_b }}{longleftrightarrow}} 2Si(II)$$ Very pure thin silicon layers, up to 300 μm thick, were obtained on a silver substrate. The cathodic reduction of TiF ₆ ^2? ions occurs in two well separated reversible steps, $$TiF_6^{2--} + e to TiF_6^{3--} + 3e to Ti + 6F^--$$ Adherent coatings of pure titanium were found to be linked to the copper substrate by an interdiffusion sublayer comprising Ti₂Cu, TiCu, Ti₂Cu₃ and TiCu₄ which were formed in a narrow potential domain preceding titanium deposition.