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Electrically insulating phosphate coatings for iron powder based electromagnetic core applications

Powdered metals, such as iron, are a common building block for electromagnetic cores. An iron powder was reacted with phosphoric acid to create a layer of iron phosphate on each particle. This electrically insulating phosphate layer could lead to significant reductions in eddy current losses in alternating current applications. The electro-magnetic properties of this phosphatecoated powder material were examined as a function of heat treatment. Additionally, SEM and EDS were used analyze the particle interfaces and composition in compressed bar-shape samples that were heat treated at temperatures ranging from 315'C to 5400C. The bulk composition of oxygen and phosphorus are also tested for each heat treatment. Results indicate that after high temperature heat treatments (required for stress reduction, sintering, increased magnetic permeability, and decreased coercivity), the bulk resistivity is reduced. Correlation of interface structure and composition with these trends in resistivity is discussed. Ultimately, this analysis will aid in the development of coatings that withstand higher temperatures and yield ideal properties for electromagnetic core applications. Thesis Supervisor: Christopher A. Schuh Title: Associate Professor of Metallurgy