Nanoparticles of Fe3O4 have been successfully synthesized using a simple coprecipitation technique from natural iron sands, employing HNO3 and NH4OH as dispersing and precipitating agents, respectively. The substitution of Fe with Mn to result in Fe3-xMnxO4 (0 ≤ x ≤ 3) was conducted to control the magnetic strength of this nano‐sized spinel powder. It is shown that magnetic properties depend not only on the particle size and Mn doping but also on the particles clustering. The applications for magnetic fluids, gels, and coating are extensively described. Meanwhile, the spinel MgAl2O4 nanoparticles have also been prepared by the same simple method from commercial starting materials. This powder was used as a nano‐reinforcer of Al‐matrix composites. In addition, MgAl2O4 micro‐sized powder forming a thick layer was successfully grown by electroless plating on the interface of matrix‐filler in Al/SiC composites. The strengthening of mechanical properties with respect to the varying uses of these MgAl2O4 powders is discussed.
Part of the book: Magnetic Spinels
Polyvinyl alcohol (PVA)/Fe3O4 magnetic hydrogels had been fabricated by freezing-thawing (F-T) cycle technique, employing natural iron sand as the raw material for the magnetic micro- and nano-sized fillers. An exploration of the durability and magnetoelasticity as well as PVA hydrogel applications in the assessment of human brain tumor was also intensively conducted. The performance of the PVA and magnetic hydrogels mainly depends on the structural dynamic properties, such as polymeric crystallization and particle size. The durability of PVA/Fe3O4 magnetic hydrogels affecting the magnetoelasticity is determined by the concentration ratio of PVA and water, number of F-T cycles, and the concentration of Fe3O4 particles. By controlling those parameters, it was found that hydrogels had PVA: water ratio of 23:100 and four times F-T cycles possessed good mechanical properties. Due to the biocompatible character, the PVA hydrogel was used in the assessment of the human brain tumor, analyzed from the apparent diffusion coefficient (ADC) value representing the diffusion coefficient of a biological tissue. It was found that the abnormal tissue has a low ADC value compared with the normal one. Moreover, the higher b-value of the diffusion-weighted magnetic resonance imaging (DW-MRI) measurement is more preferred in obtaining a good contrast of the data imaging.
Part of the book: Hydrogels
Ferrite-based nanoparticles, namely, bismuth ferrite (BiFeO3) and calcium ferrite (CaFe4O7), have been synthesized via sol-gel and chemically dissolved method, respectively, employing hematite (α-Fe2O3) as the Fe3+ ion source. Firstly, α-Fe2O3 nanoparticles were prepared from natural iron sand containing mostly magnetite (Fe3O4) phase through coprecipitation technique continued by sintering process at 800°C for 2 h. Higher BiFeO3 phase content was achieved after Bi-Fe gel being annealed at 650°C for 1 h in air atmosphere. Furthermore, major phase of CaFe4O7 was formed with molar ratio of Fe3+/Ca2+ = 6 and sintering temperature of 800°C for 3 h. Interestingly, the powders with dominant CaFe4O7 phase, known as calcium biferrite, exhibit higher ferromagnetism at room temperature. The magnetic properties of the calcium biferrite are comparable to those of barium hexaferrite which can be applied for radar-absorbing material. Meanwhile, BiFeO3 powders also show weak room temperature ferromagnetism. It has also demonstrated that Ni doping in the bismuth ferrite (BiFe1−xNixO3 with x = 0.1) nanoparticles results in enhancement of the magnetic properties. Moreover, a ferroelectric hysteresis loop and a trend of frequency dependence of the dielectric constant have been observed, which were enhanced by Pb doping (Bi1−yPbyFeO3 with y = 0.1). These results suggest a multiferroic behavior in the BiFeO3 nanoparticles.
Part of the book: Nanocrystalline Materials