Abstract: The effect of thermal treatment on the surface properties of ultrafine amorphous NiB alloy particles has been studied by H_2 chemisorption, X-ray photoelectron spectroscopy and surface area measurments. It is found that when heating temperature is lower than 623 K the amount of H_2 chemisorbed on NiB alloy catalyst increases with increasing temperature due to the aggregation of oxidized boron species existed in the surface layers of NiB alloy particles. However, thermal treatment at temperature higher than 623K results in a remarkable decrease in the H_2 uptake. This is correlated with not only the sintering of NiB alloy particles but also the migration of boron species alloying with nickel atoms from bulk to surface caused by complete crystallization of amorphous NiB alloy catalyst.

Key words: Amorphous alloy, Ultrafine particles