Ferrite Coating on Iron Particles in Aqueous Solution: Effect of Surface Functionalization

Abstract

International audienceWith the growth of miniaturization requirement for application such as transformers, computers, and inductors or motors, soft magnetic composites (SMC) with high flux density, high permeability and low magnetic loss are under development [1-5]. These powders are composed of an iron (or its alloys) core coated with a thin electrically insulating layer. This insulating layer is generally made of a polymer [6,7] or oxides [8-10]. In these cases, as the insulating layer is a nonmagnetic material, it leads to a decrease of the magnetic permeability or of the magnetic induction. One way to avoid or to reduce these properties decrease is to replace the non-magnetic layer by a magnetic electrically insulating layer. NiZn ferrite can appear as a good candidate. Abe have developed a process to deposit NiZn ferrite onto particles by an aqueous route using metal salt [11]. They reported that 1) the ferrite coating occurs thanks to the presence of hydroxyl groups (-OH) on the surface of the substrate and 2) the increase of the –OH group concentration on the surface of particles, after acid treatment, leads to an increase of the substrate reactivity. In this work, Abe et al. apparatus and process have been simplified and optimized and the effect of chemical surface treatments, of Fe particles, followed using X-ray photoelectron spectroscopy (XPS) analysis. This study demonstrates that surface reactivity of Fe particles on NiZn ferrite coating, using electroless process, is strongly link with OH groups chemically linked on Fe particles. Five different acid treatments have been tested onto Fe particles and the evolution of the XPS C1s and O1s followed. Finally the morphology and the adhesion strength of the NiZn ferrite coating, electroless deposited onto acid treated Fe particles, have been analyzed and correlated with the experimental procedures