TiB2 Deposited on Graphite by Suspension Plasma Spray as Al Wettable Cathode

In developing wettable TiB2-based cathodes for Al production, the main problem encountered for decades is the difficulty to sinter or melt this refractory material. Here, suspension plasma spray (SPS) is used as this process makes it possible to use micrometric TiB2 particles to favor a high heat transfer per particle. In addition, an argon gas shield is used to protect the inflight TiB2 particles from oxidation with air during spraying. Our results confirm the efficiency of the argon shroud to limit TiB2 oxidation when compared with a TiB2 coating obtained without shroud. The SPS TiB2 coatings show a good adhesion to the graphite substrate. However, their high porosity indicates an insufficient TiB2 melting during the spraying, suggesting that the transit time spent by the TiB2 particles in the plasma is too short. The SPS TiB2 coatings present a good wettability for molten Al. However, Al infiltration through the porous coating results in the direct contact of molten Al with the graphite substrate, which may be detrimental for its mechanical integrity.