ISOKINETIC ANALYSIS OF NANOCRYSTALLINE NICKEL ELECTRODEPOSITS UPON ANNEALING

The grain growth kinetics of nanocrystalline nickel electrodeposits wa s studied by transmission electron microscopy and differential scannin g calorimetry at different heating rates. It was found that, upon anne aling, the nanocrystals in the nickel electrodeposits appeared to grow abnormally and released about 415.7 +/- 3.5 J/mol of heat. The mechan ism of the abnormal grain growth was attributed to the subgrain coales cence. The method for determination of the grain growth activation ene rgy as well as all the other kinetic parameters in the Johnson-Mehl-Av rami equation was proposed based on an isokinetic analysis. This metho d is applicable to general types of transformation process governed by a single activation energy under the isokinetic condition. The activa tion energy for the grain growth of nanocrystalline nickel electrodepo sits was found to be about 131.5 kJ/mol using this method. The differe nce between the present method and the Kissinger and Ozawa method was addressed in terms of their physical backgrounds. (C) 1997 Acta Metall urgica Inc.