Chapters authored
Spinel‐Structured Nanoparticles for Magnetic and Mechanical Applications
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
Synthesis of High-Purity Ceramic Nano-Powders Using Dissolution Method
A set of ceramic powders has been synthesized using a “bottom-up” approach which is denoted here as the dissolution method. The raw materials were metal powders or minerals. The dissolution media were strong acid or base solutions. In the case of metallic raw materials, magnesium and titanium powders were separately dissolved in hydrochloric acid to obtain their precursors. They were then dried, washed, and calcined in air at various temperatures to produce pure MgO and TiO2 nano-powders. Pure MgTiO3 nano-powders by mixing the precursors at the stoichiometric ratio and calcining the dried mixture at a temperature as low as 700°C have also been successfully synthesized. In the mineral case, local zircon sand was used as the raw material. A standard procedure to extract the “clean” and pure zircon powder was applied which included washing, magnetic separation, and reactions using hydrochloric acid and sodium hydroxide. A pure zircon nano-powder was obtained by applying mechanical ball-milling to the zircon powder. The zircon powder was also chemically dissociated to give amorphous silica (SiO2), cristobalite, amorphous zirconia (ZrO2), and nanometric tetragonal zirconia powders.
Part of the book: Ceramic Materials
Ferrite-Based Nanoparticles Synthesized from Natural Iron Sand as the Fe3+ Ion Source
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