Highly efficient large-scale preparation and electromagnetic property control of silica–NiFeP double shell composite hollow particles

Abstract

Double shell composite hollow particles (DSCHPs) with silica (inner shell) and magnetic metal (outer shell) shells are prepared on a large scale through a novel cost effective strategy involving spray drying, simultaneous silicification and surface decoration with active sites, and finally directed growth of magnetic metal shells. The silica shell formed through silicification of silicate possesses good chemical durability and thermostability. The spherical shape and hollow structure are well reserved during the silicification in an acid environment and calcination at a high temperature of 1300 °C. The DSCHPs with Ni–Fe–P alloy shell exhibit a maximum reflection loss (RL) of 45.92 dB at 15.92 GHz and a broad effective absorption bandwidth (the frequency range in which the RL value exceeds 10 dB) of 4 GHz with a thin absorber layer thickness of 1.5 mm. Moreover, the hollow structure endows the DSCHPs with low real density (1.1–2.35 g cm⁻³) and makes them promising candidates as low-density magnetic materials and microwave absorbents. The new strategy reported here has the potential to be extended to the controlled preparation of various double or multishell composite hollow particles with a robust silica shell as support and various metal, alloy or metal oxides as functional shells.