Fabrication of Mn1-x Zn x Fe2O4 ferrofluids from natural sand for magnetic sensors and radar absorbing materials

Exploring the role of Mn2+ in the structure, magnetic properties, and radar absorption performance of MnxFe3-xO4-DEA/MWCNT nanocomposites

Iron oxide/carbon-based nanocomposites are known as an ideal combination of magnetic-conductive materials that were recently developed in radar absorption application; one example is the Fe3O4/multiwalled carbon nanotubes (MWCNTs). In this study, we try to boost their radar absorption ability by Mn-ion doping. Mn is an appropriate Fe substitute that is predicted to alter the magnetic properties and enhance the conductivity, which are crucial to developing their radar absorption properties. Diethylamine (DEA) is also used as a capping agent to improve the size and shape of the nanocomposite. In this study, a MnxFe3-xO4-DEA/MWCNT nanocomposite is successfully prepared by the coprecipitation method using a variation of x = 0, 0.25, 0.5, 0.75, and 1. We found that the sample's magnetic saturation (Ms) decreases, while the reflection loss (RL) increases with increasing the molar fraction of Mn. The enhancement of the radar wave absorption in the sample is dominated by dielectric losses due to the increase of electrical conductivity and interfacial polarization with the addition of Mn in the nanocomposites. We believe that our finding could shed light on the role of doping elements to develop the radar absorption properties, and further pave the way for the real implementation of iron oxides/graphene-based nanocomposite as radar-absorbing materials (RAMs).

Approaches on Ferrofluid Synthesis and Applications: Current Status and Future Perspectives

Ferrofluids are colloidal suspensions of iron oxide nanoparticles (IONPs) within aqueous or nonaqueous liquids that exhibit strong magnetic properties. These magnetic properties allow ferrofluids to be manipulated and controlled when exposed to magnetic fields. This review aims to provide the current scope and research opportunities regarding the methods of synthesis of nanoparticles, surfactants, and carrier liquids for ferrofluid production, along with the rheology and applications of ferrofluids within the fields of medicine, water treatment, and mechanical engineering. A ferrofluid is composed of IONPs, a surfactant that coats the magnetic IONPs to prevent agglomeration, and a carrier liquid that suspends the IONPs. Coprecipitation and thermal decomposition are the main methods used for the synthesis of IONPs. Despite the fact that thermal decomposition provides precise control on the nanoparticle size, coprecipitation is the most used method, even when the oxidation of iron can occur. This oxidation alters the ratio of maghemite/magnetite, influencing the magnetic properties of ferrofluids. Strategies to overcome iron oxidation have been proposed, such as the use of an inert atmosphere, adjusting the Fe(II) and Fe(III) ratio to 1:2, and the exploration of other metals with the oxidation state +2. Surfactants and carrier liquids are chosen according to the ferrofluid application to ensure stability. Hence, a compatible carrier liquid (polar or nonpolar) is selected, and then, a surfactant, mainly a polymer, is embedded in the IONPs, providing a steric barrier. Due to the variety of surfactants and carrier liquids, the rheological properties of ferrofluids are an important response variable evaluated when synthesizing ferrofluids. There are many reported applications of ferrofluids, including biosensing, medical imaging, medicinal therapy, magnetic nanoemulsions, and magnetic impedance. Other applications include water treatment, energy harvesting and transfer, and vibration control. To progress from synthesis to applications, research is still ongoing to ensure control of the ferrofluids' properties.