Dendrite Formation during Electro-Deposition of Titanium on SiC fibres

Kurzfassung

To develop an electrolytic production route for titanium matrix composites, experimentswere performed to deposit pure titanium on carbon coated SiC-fibres using molten LiCl-KCl-K2TiF6 as the electrolyte. At least 4 different types of dendrites and particulate could be observed, instead of the expected coherent layers. Dendrite formation is well known in titanium electrolysis, especially in all chloride melts [1]. Fluoride addition, however, should help to improve the coherence of the deposit [2]. Besides the fact that the fluoride content was apparently too low to unfold its advantageous influence on crystal growth, the following reasons may be responsible for dendrite and powder formation: The concentration of approx. 0.1mol-% K2TiF6 was comparably low and the cathodic overvoltage was certainly higher than the critical values (ηi, ηc) for dendrite or even powder formation respectively (see e.g. [3]). Some of the i-t curves indicate that there may be an induction time before dendrite formation starts. The same reasons can be responsible for the fact that it was not possible to observe nucleation phenomena in the chronoamperogram as described by [4]. In further experiments, it is planned to improve the quality of the deposits by increasing the K2TiF6 concentration and to stabilize the trivalent titanium complexes (TiF6 3-) by raising the F/Ti ratio, e.g. by adding KF. The electrical parameters will have to be carefully adjusted to make sure that the critical value ηi will not be exceeded. In the poster, typical SEM pictures are depicted and the current vs. time curves of the corresponding electrolysis are discussed. Literature: [1] Ehrlich, P. and Kühnl, H., Über die schmelzelektrolytische Abscheidung von Titanmetall. Z. anorg. allg. Chem., 1959. 298(3-4): p. 176-192. [2] Ene, N. and Zuca, S., Role of free F- anions in the electrorefining of titanium in molten alkali halide mixtures. J. Appl. Electrochem., 1995. 25(7): p. 671-676. [3] Popov, K.I., et al., Dendritic electrocrystallization and the mechanism of powder formation in the potentiostatic electrodeposition of metals. J. Appl. Electrochem., 1981. 11(2): p. 239-246. [4] Haarberg, G.M., et al., Electrodeposition of titanium from chloride melts. J. Appl. Electrochem., 1993. 23(3): p. 217-224.