Process and Magnetic Properties of Iron Powders Clad with Phosphorus and Nickel–Phosphorus

Abstract

Composite materials based on iron powders clad with nickel and nickel-phosphorus are developed using modified methods such as thermal chemical decomposition of diammoniumphosphate, thermochemical method in a vibrating layer, chemical phosphating and nickel salt reduction with a sodium hypophosphite solution in both acid and alkaline media. Cladding of iron powder with phosphorus is shown to promote materials with improved magnetic characteristics: magnetic induction increased by 20% on average and permeability by 25% and higher electric resistance, which results in decrease of magnetic losses. The coating partially remains on iron powder particles in composite materials based on powders clad with phosphorus in a vibrating layer or with nickel-phosphorus in an acid medium after high-temperature sintering. This also decreases magnetic losses. Laboratory tests are conducted to determine the corrosion resistance of the initial and clad iron powders using an accelerated drop analysis. It is established that phosphorus and nickel-phosphorus coatings increase the corrosion resistance by 2.5 to 3.0 times probably because protective phosphide layers form on iron particles. The materials based on iron powders clad with phosphorus and nickel-phosphorus differ from conventional ones by high magnetic characteristics, high corrosion resistance, and low magnetic losses at a frequency of 50 Hz and may be recommended for manufacture of soft magnetic articles operating in both constant and alternating fields of the power line frequency.