Overheating and undercooling of Ni polycrystalline nanowires

The thermal stability of Ni polycrystalline nanowires (PNWs) enclosed in Ni oxide shells has been studied via differential scanning calorimetry (DSC) and the Kissinger equation. The influences of the oxide shells and the grain size on the thermal stability of the Ni PNWs were investigated. The critical temperature (TC, the peak temperature of the DSC curve) increases as the diameter of the PNWs decreases when the grain size is the same, whereas TC decreases with the grain size if the diameter of the Ni PNWs remains unchanged. When both the diameter and the grain size change, the grain size dominates the thermal stability. These findings are explained by the bond-order–length–strength correlation theory.