The Detailed Mechanism of Oxidation of Ni-P Alloys

Abstract

DTA in conjuction with X-ray diffraction analysis with a high-temperature camera and infrared spectroscopy was employed to determine the mechanism of oxidation of Ni-P alloys. Amorphous Ni-P powders were obtained from a nickel(II) sulphate bath as a nickel source and sodium dihydrophosphate(I) as a reducing agent. The crystallization product is composed of two phases: (f.c.c.) Ni and (b.c.t.) Ni₃P. The amorphous to crystalline transformation takes place in the temperature range 280–330°C. Ni₃P samples were heated from room temperature to 1050°C in air atmosphere at 5°C min⁻¹. It was found that the first stage of oxidation of Ni₃P goes through the intermediate phase of Ni₁₂P₅ formation to Ni₂P. Some exothermic reactions were observed. Heating runs were interrupted after each reaction for crystal structure determination by IR spectrometry. Infrared spectra are reported and it is shown that the structure units present in the amorphous products at about 700°C were the oxoanions PO₃ ⁻ and P₂O₇ ⁻. The final products of the oxidation process are NiO and Ni₃(PO₄)₂.