Quantitatively Evaluating the Effect of Oxygen/Fuel Ratio on Fe2+ Content in HVOF-Sprayed Ni-Zn Ferrite Coatings

This article quantitatively describes the dependence of Fe2+ content in Ni-Zn ferrite coatings on the oxygen-fuel (O/F) ratio in high velocity oxy-fuel (HVOF) spraying. Fe2+ is detrimental to the magnetic properties of ferrites and should be tightly controlled. Methods were developed for calibrating energy dispersive x-ray analysis and for calculating Fe2+ content. The results show that the atomic percentage of the Fe2+ decreased from 25 to 15 at.% by increasing the O/F ratio from 80 to 110% of the stoichiometric ratio. The effect of O/F ratio has also been observed on in flight particle temperature, microstructure, and deposition efficiency. Simulations on the chemical reactions during HVOF spraying demonstrated that Fe2+ was produced only by the reduction of Fe3+ and that oxygen and zinc losses by the decomposition of ZnO in fact increased the percentage of oxygen in the coatings.