Investigating the interaction of oxide cathode core of nickel-rhenium lanthanum or nickel-tungsten-lanthanum alloys with its surface coating

The reactions at the base-coating interface using a Ni-Re-La alloy containing 10 % Re and 0.1 % La and an analogous Ni-W-La alloy as cathodes were investigated. The cathodes were coated with a fine-grained BaCO3-SrCO3-CaCO3 layer 40-50 μ thick. The phase composition of the cathode bases was studied by microscopy, x-ray diffraction and electron diffraction. A new phase was formed at the grain boundaries at the coating-base interface. On the basis of thermodynamic calculations, it is likely that this consists of a mixture of BaO, SrO, CaO, La2O3, and a Ba-CaC2-Sr alloy. The formation of oxides and carbides of alkaline earth elements can be explained by the high thermodynamic activity and affinity for O and C of these elements compared with Ni and Rh