Metal Dusting of Nickel and its Alloys

Abstract

Pure nickel, Ni-Cu binary alloys, Types 304 and 310 stainless steels and Alloy 800H were all reacted with carbon- supersaturated CO/H2/H2O at 680oC. In general, the reaction led to growth of an external deposit, together with graphitization at both external surfaces and interior grain boundaries. By independently controlling the supersaturated carbon activity and pCO, it was demonstrated that the reaction of pure nickel was determined by parallel, independent reaction paths, and the carbon uptake rate was well described by Rate = k1pCOpH2 + k2p2CO - k3p2H2 leading to a maximum rate at about pCO ~ 0.7 atm. The surface graphite layer thickened, growing into the metal, while graphite particle clusters and nanofilaments formed on the surface. Each particle cluster and filament contained metal nanoparticles. Addition of copper to the nickel suppressed graphite particle cluster formation, thereby decreasing greatly the overall dusting rate. This phenomenon is interpreted in terms of graphite nucleation and copper interference with nucleation sites involving multiple nickel atoms. Reaction conditions used were such as to stabilize Fe3C and chromium carbides, Cr2O3 and spinel, but not iron or nickel oxides. Under these conditions, all three alloys, 304SS, 310SS and 800H, dusted, with 304SS experiencing the greatest metal wastage. Additions of copper had no effect on the dusting rate of 304SS, but greatly decreased the dusting of 310SS and 800H.