Synthesis, structural, and microwave absorption properties of hematite (α-Fe2O3) and maghemite (γ-Fe2O3)

This work demonstrated the synthesis, structural, and microwave absorption properties of hematite (a-Fe2O3) and maghemite (?-Fe2O3) nanopowders. The desired samples are successfully synthesized from the natural ironstone of Indonesia by using the coprecipitation method. The variations of acidic environments during the synthesis process (i.e., pH 6 and 7) were done to obtain the maghemite and hematite phases. The combination of x-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements was used to investigate the crystal and microstructure, respectively. Meanwhile, the vector network analyzer (VNA) was performed to examine the microwave absorption properties at x-band frequency. The structural measurements of the samples confirmed the formation of single-phase maghemite and hematite phases for precipitation pH 6 and 7, respectively, which showed the change in morphology after the precipitation process and sphere-like agglomerated particles of samples. The results Debye-Scherrer equation indicates that the crystal size of precipitated samples is on the order of nanometers. The microwave absorption characteristics through VNA measurements showed enhanced microwave absorption properties after the precipitation process; the RL (max) of natural ironstone increased from -4.39 dB to -10,99 and -11,72 dB for S6 and S7 samples, respectively. Generally, the hematite and maghemite reveal the same pattern of absorption peaks. The RL (max) of natural ironstone, S6, and S7 samples were observed at 10.52, 11.04, and 11,06 GHz, respectively. These results revealed that the variation of acidic environments during the synthesis process influenced the structure and microwave absorption.