Quantitatively Evaluating the Effect of Oxygen/Fuel Ratio on Fe super(2+) Content in HVOF-Sprayed Ni-Zn Ferrite Coatings

This article quantitatively describes the dependence of Fe super(2+) content in Ni-Zn ferrite coatings on the oxygen-fuel (O/F) ratio in high velocity oxy-fuel (HVOF) spraying. Fe super(2+) 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 Fe super(2+) content. The results show that the atomic percentage of the Fe super(2+) 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 Fe super(2+) was produced only by the reduction of Fe super(3+) and that oxygen and zinc losses by the decomposition of ZnO in fact increased the percentage of oxygen in the coatings.