Hollow Ceramic Microsphere Coated with Co by Electroless Plating and Its Electromagnetic Properties

Functional microspheres with size of 1–20 μm were produced by plating Co on hollow ceramic microspheres for the application of lightweight microwave absorbers. Using Sn-Pd solution as active agent, the surface of hollow microspheres was activated. Co plating was carried out in an alkaline bath with sodium hypophosphite as a reducing agent. The coating of Co was characterized by field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). The electromagnetic properties were improved by adjusting the molar ratio of main salt to complexing agent and the concentration of the main salt in a certain range. Furthermore, the processing conditions such as pH value and plating temperature were optimized. Due to the conductive and ferromagnetic behavior of Co coating which is dense and uniform, high dielectric constant can be obtained in the microwave frequency range of 2–18 GHz and the functional hollow micorsphere has certain microwave absorption performance.