Microwave absorption properties of microporous CoNi@(NiO-CoO) nanoparticles through dealloying

Abstract

CoNi alloy is an important absorber and it can combine characteristics of transition metals Co and Ni with various advantages of strong magnetic loss, low cost and easy morphology control. The microporous CoNi@(CoO-NiO) nanoparticles (NPs) of about 45 nm are obtained by using hydrogen plasma metal reaction (HPMR) and dealloying methods. The Al element in Al9Co2, Al70Co15Ni15 and Al14Co3Ni3 phases can be dealloyed by NaOH at 323 K. The CoNi surface would oxidize to CoO and NiO, leading to the core@shell structure. The CoNi@(CoO-NiO)-paraffin wax composite displays high microwave absorption performance with minimum reflection loss (RL) of −38.1 dB at matching thickness of 5.0 mm. The effective absorption bandwidth (RL < −10 dB, at thickness of 2.0 mm) is 5.9 GHz. The RL values below −10 dB cover frequencies of 4.6–18.0 GHz with thickness ranging from 2.0 to 5.0 mm. The effective permittivity modification for a mixture of air and microporous CoNi host, and the large interfacial polarization relaxation of the CoNi@(CoO-NiO) structure contribute much to the enhanced microwave absorption performances.