Multi-layer cathode structures

A process of producing multi-layer cathode structures. In one aspect, the process comprises providing a carbonaceous cathode substrate, and forming at least one layer of a metal boride-containing composite refractory material over the substrate, wherein the surface of the carbonaceous substrate to be coated is roughened prior to the formation of the layer overlying the said surface. The roughening of the surfaces reduces the tendency of the layers to separate in high temperature operating conditions. In another aspect, the process comprises providing a carbonaceous cathode substrate, and forming at least two coating layers of a metal boride-containing composite refractory material successively over the substrate, wherein the content of metal boride in the coating layers increases progressively as the distance of the layer from the substrate increases. By graduating the content of metal boride among several coating layers, the effect of differences in thermal expansion rates between carbon and metal boride are attenuated. The metal of the metal boride is selected from the group consisting of titanium, zirconium, vanadium, hafnium, niobium, tantalum, chromium and molybdenum.