The dealloying behaviour of Ni 38Mn 62 binary alloy was investigated in Li 2SO 4 and NH 4H 2PO 4 solutions under different electrochemical conditions. Ni-Mn alloy ribbons with a thickness of 20 μm were prepared through arc melting followed by melt spinning. The melt-spun Ni-Mn alloy comprised of NiMn and NiMn 2 phases. The NiMn phase, a few hundred nanometers across, preferentially precipitated along the grain boundary. After electrochemical dealloying treatment in 0.16 M Li 2SO 4 solution under open circuit potential and anodic polarization at -0.6 V, selective dissolution of the Ni-Mn alloy was observed at the grain boundary and also in the interfacial region between the NiMn phase and NiMn 2 phases. The Ni-Mn alloy formed a nanoporous structure in 0.17 M NH 4H 2PO 4 solution due to its high pH buffer ability under open circuit potential. Two types of nano-pores were formed under -0.45 V and -0.4 V, one with dimensions of a few hundred nanometers and the other only tenths of nanometers. Unlike the NiMn 2 phase, the NiMn phase remained stable along the grain boundaries and exhibited noble electrochemical properties. Since different nanoporous structures were formed in regions where the microstructure was heterogeneous, we propose that a homogeneous microstructure is a key factor in the formation of uniform nanoporous structures during the electrochemical dealloying of the alloys.
ASJC Scopus subject areas
- 化学 (全般)