Yolk–shell Fe3O4@ZrO2 prepared by a tunable polymer surfactant assisted sol–gel method for high temperature stable microwave absorption

Highly-dispersed Fe3O4@ZrO2 yolk–shell structures with a ZrO2 shell of homogeneous shell thickness was successfully prepared via a polymer surfactant (hydroxypropyl cellulose) assisted sol–gel method. By using HPC as a surfactant, highly dispersed particles with Zirconia shells of about 25–30 nm thickness were obtained. The yolk–shell Fe3O4@ZrO2 structure was characterized by several techniques, including transmission electron microscopy (TEM), scanning electron microscopy, (SEM) and X-ray diffraction (XRD), which indicated that the particles had a ZrO2 shell 500 nm in diameter and 25–30 nm in thickness, and a Fe3O4 core of 300 nm in diameter. An in situ TEM heating experiment from 20 °C to 1000 °C demonstrated that the obtained yolk–shell Fe3O4@ZrO2 structure was stable, without any distinguishable structural damage below 700 °C. This material has great potential as a high temperature stable microwave absorber. Even at temperatures of 500 °C, this material still preserved over 90% of its reflection loss (RL) value compared to its room temperature properties. These findings may shed light on the development of novel microwave absorbers for high temperature operation.