THERMAL-STABILITY OF NANOCRYSTALLINE NI

Thermal stability of electroplated nanocrystalline Ni of 10 and 20 nm grain size was investigated by differential scanning calorimetry (DSC) . The temperature dependence and heat release Delta H during grain gro wth have been determined by linear anisothermal measurements (linear h eating at 10 K min(-1)). The corresponding change in microstructure ha s been monitored in the temperature range between 373 K and 693 K usin g transmission electron microscopy (TEM). The TEM and DSC studies iden tified three exothermic reactions: ''nucleation'' and abnormal grain g rowth (353-562 K), normal grain growth (562-593 K) and growth towards equilibrium (643-773 K). The grain growth behaviour, and the similar h eat releases Delta H = 18 J g(-1) and 16 J g(-1) measured for the 10 n m and 20 nm Ni nanocrystals respectively in the DSC experiments may be related to the observed sulphur segregation at grain boundaries and t riple junctions.