Processing and magnetic properties of iron powders clad with phosphorus and nickel–phosphorus

Abstract

Composites based on iron powders clad with nickel and nickel–phosphorus are developed using modified methods such as thermochemical decomposition of diammonium phosphate, thermochemical synthesis in a vibrating layer, chemical phosphating, and reduction nickel salt with a sodium hypophosphite solution in both acid and alkaline media. The cladding of iron powders with phosphorus increases the magnetic flux density by 20% on average and permeability by 25% and promotes higher resistivity, thus decreasing magnetic losses. The coating partially remains on iron particles in composites based on powders clad with phosphorus in a vibrating layer or with nickel–phosphorus in acid media after high-temperature sintering. This decreases magnetic losses as well. Laboratory tests are performed to determine the corrosion resistance of iron powders before and after cladding using an accelerated drop analysis. It is established that phosphorus and nickel–phosphorus coatings increase the corrosion resistance by a factor of 2.5 to 3.0 apparently because protective phosphide layers form on iron particles. The materials based on iron powders clad with phosphorus and nickel–phosphorus differ from conventional ones in high magnetic properties, high corrosion resistance, and low magnetic losses at a frequency of 50 Hz and may be recommended for the manufacture of soft magnetic articles operating in both constant and alternating fields of power line frequency.