Formation of fine skeletal Co-Ag by chemical leaching of Al-Co-Ag ternary alloys

The formation of skeletal silver-cobalt structures was attempted by means of chemical leaching of Al atoms from various ternary Al-Ag-Co alloys which were prepared by rapid solidification or mechanical alloying. Almost all Al atoms were removed for rapidly solidified alloys and their crystallographic structure was changed from fcc of Al into fcc of Ag during chemical leaching. The microstructures of the leached specimens were observed by transmission electron microscopy. TEM observation showed that the leached specimens had a skeletal structure composed of finely distributed particles and fine pores. The particles were classified into two groups by size. The first one was rather large and about 30 nm in size. The other was fine and a few nanometers. No detectable diffraction peaks corresponding to the Co phase were observed but they were detected after annealing at 1073 K for 3.6 ks. The saturation magnetization of the leached specimens gradually increased with increasing temperature and approached to the maximum. A part of this variation was due to the precipitation of Co from the supersaturated Ag(fcc) phase. The chemical leaching of Al-Co-Ag alloys might open the possibility to form a skeletal material with a metastable state in which a few cobalt atoms dissolved into the silver phase.