Preparation and microwave absorption properties of electroless Co–P-coated nickel hollow spheres

Co–P-coated nickel hollow spheres (NHSs) were prepared by electroless plating technology. The morphology and component content of Co–P coating varies with the change of sodium citrate concentration in elctroless plating solution. And as phosphorus content increases in coatings, resulting in smaller grain, coercivity of microspheres decreases. The microwave absorption properties of spheres–wax composite were investigated in the range of 2–18 GHz. Both permittivity and permeability increase with an increase of cobalt content in coatings. For composite layer, a minimal reflection loss (RL, −36.9 dB) of was predicted at 8.1 GHz with a thickness of 3 mm.