INVESTIGATION OF NI-P-B ULTRAFINE AMORPHOUS ALLOY PARTICLES PRODUCED BY CHEMICAL-REDUCTION

Ni-P-B ultrafine amorphous alloy particles have been prepared by chemical reaction of nickel chloride, sodium hypophosphite, and potassium borohydride in aqueous solution. Two samples prepared at different initial pH values (pH = 5 and 9) have been characterized by different experimental methods. X-ray and electron diffraction indicated that both samples were amorphous in nature, and transmission electron microscopy gave average diameters of 50 and 30 nm for particles prepared at pH = 5 and 9, respectively. X-ray photoelectron spectroscopy revealed that nickel and phosphorus existed exclusively in their elemental states, while boron existed mainly in its elemental state but with some trace of its oxide on the surface. The crystallization process of the amorphous samples was investigated by differential scanning calorimetry and by x-ray diffraction after annealing the samples at various temperatures. The results are correlated with the microstructure of the as-prepared samples. It is found that when the initial pH of the reaction mixture is adjusted to 9, the pH value can be maintained automatically throughout the reaction and the sample thus formed has a fairly homogeneous microstructure.