Flaky carbonyl iron particles with both small grain size and low internal strain for broadband microwave absorption

Abstract Controlling the microstructures such as particle shape, grain size (〈 D 〉) and internal strain (〈 e 〉) of magnetic absorbents are of importance for the construction of broadband microwave absorbing materials (MAMs). Here we have developed a heating wet ball-milling method to tune the aspect ratio ( a r ), 〈 D 〉 and 〈 e 〉 of the flaky carbonyl iron powders (CIPs) so as to achieve optimized microwave absorbing properties. In our protocol, when the milling temperature ( T ) exceeds 250 °C, the heat effects dominate over the deformation effects, deteriorating the electromagnetic performances due to the rapid growth up of 〈 D 〉. When T is below 250 °C, the deformation effects play a dominant part. In this condition, the 〈 e 〉 constantly accumulate and a r decrease with T , decreasing the relative complex permeability. As a result, controlling T cannot enlarge 〈 D 〉 and 〈 e 〉, but only increase a r . This comes from the competition of the grain growth effect and deformation effect at different temperatures. The as-obtained flaky CIPs are a good candidate absorbent for broadband MAMs of thin thickness. The heating wet ball-milling method proposed here, as a simple and effective way to control the particle shape, grain size and internal strain of CIPs, can be easily extended to the fabrication of other high performance magnetic absorbents.