Changes in morphology and local chemical composition due to various
methods of modification of surfaces of Cu-Zr, Cu-Hf, and Cu-Ti
amorphous alloys (caused by aging in air/dry corrosion or hydrogen
charging) were investigated. These modification/activation
procedures transform the original amorphous ribbons of low surface area
into efficient and stable catalysts, due to the segregation of a
distinct amount of Cu and the development of a large specific surface
area of Cu on a ZrOx or HfOx
support. It was found that aging in air resulted in the formation of a
bilayer of rough copper (containing small Cu particles indispensable
for catalysis) on top of a rather smooth oxide underlayer
(ZrOx, HfOx). Careful
examination of the cross sections of the modified Cu-based ribbons
revealed that, even after prolonged aging in air, only the first few
microns of the surface layer was modified. Cu-Ti alloy was stable in
air and did not undergo the expected modification. Hydrogenation
followed by air exposure resulted in a disintegration of the ribbons
into small pieces. Each piece was covered with many small Cu clusters
0.1–0.5 μm in diameter formed on an oxide underlayer.
High-energy resolution Auger spectroscopy allowed identification of the
underlayers (ZrO2, HfO2, or
TiOx), identification of small Cu clusters,
determination of the degree of surface oxidation of them, and mapping
of the surface to identify the Cu-covered and “naked” heavy
metal.