Abstract: The crystallization behavior of the uhrafine amorphous Ni-P alloy particles prepared by chemical reduction has been studied by TEM, XRD, XPS and surface area measurments. It is found that neither sintering nor redispersion of the ultrafine par-ticles occurred during thermal treatment, but the surface and bulk structure of the amorphous alloy (sample a)were changed. For the case of the sample treated at 573 K, the alloy was partially segregated to Ni microcrystallites dispersed on the amorphous martrix (sample b). The increase in the surface area of the sample indicates the higher surface beterogeneity of the partially crystallized alloy. Increasing the temperature of thermal treatment to 773 K, the amorphous alloy was completely crystallized and segregated to Ni and Ni_3P alloy (sample c), and the surface area of the particles was decreased due to the aggregation of Ni crystallites at higher temperature.

Key words: Amorphous, Ni-P alloy, Ultrafine particles, Crystallization