Electrodeposited TiB2 on graphite as wettable cathode for Al production

Titanium diboride (TiB2) is considered as a promising cathode material for Al production. However, the manufacture of TiB2 cathodes is facing numerous challenges. In this study, electrodeposition of TiB2 on graphite was performed in molten fluoride (FLiNaK) electrolyte at 600°C by using a periodically interrupted current technique for various electrodeposition times (from 10 to 75 minutes) and at two different current densities (−0.12 and −0.5 A/cm2). It is shown that the TiB2 coating morphology/microstructure strongly depends on the applied current density. Denser coatings were obtained at jon = −0.12 A/cm2 with a growth rate of ca. 0.7 µm/min. The thicker films display a preferential crystallographic orientation along the [110] plan. At jon = −0.5 A/cm2, TiB2 coatings are deposited at a growth rate of ca. 6 µm/min with no crystallographic texture. They present a porous and stratified morphology with numerous transversal macrocracks. All TiB2 coatings show excellent wettability for molten Al as confirmed by sessile drop experiments. However, significant molten Al infiltration occurs in the TiB2 coatings, which accumulates at the coating/graphite interface, inducing the coating delamination.