Chemical state of phosphorus in amorphous Ni-Fe-P electroplates

High-quality Fe-Ni-P coatings on copper plates were prepared by electrodeposition from solutions containing simultaneously Ni(II) and Fe(II) cations and hypophosphite-anions. The structure of Fe-Ni-P deposits was compared to Fe-P and Ni-P coatings prepared under similar conditions. All as-prepared deposits showed amorphous or very fine nanocrystalline structure as no Bragg peaks of any crystalline phase were detected. Quantitative analysis of valence-to-core X-ray emission (vtc-XES) spectra of amorphous coatings showed that majority of phosphorus atoms are chemically bonded to the atoms of iron and nickel. These results prove that the structure of amorphous coatings formed during electrodeposition does not contain a significant amount of elemental (or so-called “free” or “intermediate”) phosphorus. Thermal treatment in vacuum of Fe-Ni-P coatings (as well as Fe-P and Ni-P) resulted in their complete crystallization. Comparison of vtc-XES spectra of original and thermally treated samples allows one to conclude that the concentration of phosphorus chemically bonded to metals increases only slightly (by 1-2 at.%) further confirming very low concentration (or the absence) of elemental phosphorus in the original structure.