Formation of Nanocrystalline Phases During Thermal Decomposition of Amorphous Ni-P Alloys by Isothermal Annealing

Abstract

The microstructure and the average grain size were investigated by x-ray diffraction and transmission electron microscopy for nanocrystalline (n) Ni-P alloys with 18, 19, and 22 at.% P. A detailed study of the nanocrystalline states obtained along different heat treatment routes has been performed: (1) a-->ni by isothermal annealing of the melt-quenched amorphous (a) Ni-P alloys; (2) ni-->nii by isothermal annealing of the nanocrystalline ni state; (3) ni-->nii by linear heating of the ni state. The heats evolved during the structural transformations were determined by differential scanning calorimetry. From these studies, a scheme of the structural transformations and their energetics was constructed, which also includes previous results on phases obtained by linear heating of the as-quenched amorphous state of the same alloys. Grain boundary energies also have been estimated. In some cases it was necessary to assume a variation of the specific grain boundary energy during the phase transformation to understand the enthalpy and microstructure changes during the different heat treatments.

The Microstructure of Ni Layer on Single-Walled Carbon Nanotubes Prepared by an Electroless Coating Process

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“…As it was shown by Révész et al, 27 in different states containing the same phases, a "virtual" heat release can be introduced, which is equal to the enthalpy difference between the two states, and afterwards ␥ can be determined. According to Table II, the difference in the total enthalpy release, ⌬H 1 iso + ⌬H 2 iso , between annealing temperatures of 285 and 277.5°C is 17.6 J/g.…”