Iron Oxide Ceramics Research Articles

Size-modulated electromagnetic properties and highly efficient microwave absorption of magnetic iron oxide ceramic opened-hollow microspheres

Hollow structured nanomaterials are considered as one of the most promising candidates of thin broadband absorbers due to the potential multiple scattering and resonance of electromagnetic waves. Here, magnetic iron oxide ceramics opened-hollow microspheres with tunable size were fabricated based on hydrothermal route and carbothermal reduction method. The electromagnetic parameters are obviously dependent on microsphere size due to size-dependent relaxation time of polarization and magnetization. The opened-hollow microspheres with diameter of 500 nm achieve the −10 dB absorption bandwidth of 6.1 GHz covering 7.5–13.6 GHz at only 2 mm thickness, which is the widest bandwidth in all reported nanostructures of magnetic iron oxide composites. Moreover, the broadband absorption covering the X band at such thin thickness is competitive in all absorbing materials. Such excellent microwave absorption benefits from the outstanding impedance matching caused by the multiple scattering of electromagnetic waves in large size open-hollow microspheres. This work provides a physical insight for obtaining high-performance microwave absorber.

Virus removal by iron oxide ceramic membranes

Nanoporous iron oxide ceramics were studied for the removal of virus contamination from water. Supported and unsupported iron oxide nanostructured hematite was fabricated by a green chemistry route from ferroxane nanoparticles. The material had a surface area of approximately 30m2/g and a mean pore size of 65nm. Bacteriophage P22 was chosen as a model for human virus. The kinetics and equilibrium of the attachment process was investigated. P22 adsorption isotherms on iron oxide were described by the Freundlich equation. Batch experiments resulted in 1.5LRVs. Removal proceeded rapidly for the first 7h; next, a diffusion-limited stage occurred. Dynamic attachment experiments demanded extensive recirculation to achieve significant reduction levels. Up to 3LRV were observed. The enhanced performance can be explained by the higher iron oxide area available and the facilitated access to inner porosity sites that were previously unavailable due to slow diffusion. The role of electrostatic interactions in the attachment mechanisms was confirmed by the dependence of the isotherm on the ionic strength of the suspension medium. P22 bacteriophage is expected to attach to the iron oxide by electrostatic forces up to a pH of 6.5. DLVO theory predicts moderately well the interaction energies between P22 particles themselves and between the phage and the ceramic. However, a slight underestimation of the P22–P22 repulsive forces was evident by comparison to the experimental data.

特別講演-2 古くて新しい酸化鉄材料の新展開 : 備中吹屋ベンガラ,備前焼緋襷模様,そして微生物が作る酸化鉄(特別講演)

特別講演-2 古くて新しい酸化鉄材料の新展開 : 備中吹屋ベンガラ,備前焼緋襷模様,そして微生物が作る酸化鉄(特別講演)

Double-pulse laser-induced breakdown spectroscopy for trace element analysis in sintered iron oxide ceramics

Double-pulse laser-induced breakdown spectroscopy (LIBS) is an emerging technique for accurate compositional analysis of many different materials. We present a systematic study of collinear double-pulse LIBS for analysis of the trace and side elements boron, manganese, copper, aluminum, titanium, silicon, chromium, nickel, potassium, and calcium in sintered iron oxide targets. The samples were ablated in air by single-pulse and double-pulse Nd:YAG laser radiation (6 ns pulse duration, laser wavelength of 532 nm) and spectra were recorded with an Echelle spectrometer equipped with an ICCD camera. We investigated the evolution of atomic and ionic line emission intensities for different interpulse delay times between the laser pulses (from 100 ns to 50 μs) and gate delays after the second laser pulse. We also varied the energy partition between the first and second laser pulse and the size of the irradiated spot at the sample surface. For the trace and side elements, we observed double-pulse LIBS signals that were enhanced as compared to single-pulse measurements depending on the interpulse delay time, the energy partition between the pulses, and the spot size. For the elements boron, copper, aluminum, titanium, chromium, potassium, and calcium limits of detection below 10 ppm were achieved.

Synthesis of porous iron oxide ceramics using Greek wooden templates and mill scale waste for EMI applications

The scope of this study is the synthesis of low cost iron oxide ceramics with porous structure for lightweight Electromagnetic Interference (EMI) shielding applications, using mill scale waste as the initial material, utilizing Greek wood templates. These wood-templated iron oxide (Fe 2O 3) ceramics were prepared by impregnation of inorganic precursor solution, derivated from mill scale waste, into four different kinds of Greek native wood templates; pine, fir, poplar and beech, followed by thermal treatment. Scanning Electron Microscopy (SEM) was used to investigate the microstructure of the prepared wood-templated iron oxide specimens. Their iron and oxygen contents were validated by Scanning Electron Microscopy–Energy-Dispersive X-ray Spectroscopy (SEM–EDX) and their mineralogical composition by X-ray Powder Diffractometry (XRD). The wooden substances were found to be completely removed and the synthesized Fe 2O 3 (hematite) was confirmed by XRD, as a single phase. It is also demonstrated that the structures of the iron oxide were hierarchically porous developed according to the wood templates. Moreover, the pore shape and size distribution showed a dependence on the calcination temperature and wood template. Specifically, the temperature increase from 1000 °C to 1200 °C created larger but less pores in μm scale. Finally these low cost iron oxide ceramics exhibited electrical (mainly) and magnetic properties suitable for electromagnetic shielding applications.

Combination of RF-plasma jet and Laser-induced plasma for breakdown spectroscopy analysis of complex materials

Laser-induced breakdown spectroscopy method is modified using an external radiofrequency (RF) plasma jet that overlaps spatially with the laser-induced plasma. Short UV laser pulses (wavelength 193 nm) are employed to ablate iron oxide ceramics, zinc oxide ceramics and polyethylene pressed pellets in ambient air background. An RF generator (frequency 13.56 MHz, power ≤1 kW) and a gas nozzle system are employed to generate a continuous jet of argon and nitrogen plasma expanding into air. The optical emission of the overlapped plasma is analyzed using an Echelle spectrometer equipped with an intensified CCD camera. The time dependence of optical emission intensities and of plasma parameters is investigated by varying the spectrometer delay time with respect to the laser pulse. The emission intensities of major (Fe, Zn) and minor (Mn, Al) elements are moderately increased with the RF plasma jet (≤2×). The intensities of atomic lines and molecular bands from ablated polymer material are increased also.

Processing and properties of Yb-doped BiFeO3 ceramics

The authors prepared Yb-doped bismuth iron oxide ceramics (Bi1−xYbxFeO3, with 0⩽x⩽0.20) by rapid liquid phase sintering method and investigated the material’s structures and electrical properties. The x-ray diffraction measurements showed that the doping of Yb has induced noticeable lattice distortion in the ceramics, and a largest distortion was observed when the concentration of Yb was 15%. By doping electrical resistivity, ferroelectric and dielectric properties of the ceramics were improved. Among all samples, BiFeO3 doped with 15% Yb was found to have the smallest leakage current density (<10−7A∕cm2) and the largest remnant polarization (8.5μC∕cm2).

Chemically Bonded Phosphate Ceramics: III, Reduction Mechanism and Its Application to Iron Phosphate Ceramics

In this, the last of a series of three papers, we discuss a method of forming iron phosphate ceramics by a reduction process. We report the formation of iron oxide ceramics by reducing hematite with iron in a phosphoric acid solution. The reaction results in a rapid‐setting ceramic (at room temperature) with a compressive strength of 3700 psi and a density of 1.7 g/cm3. Although the exact mineral form of the binder is difficult to determine because it is mostly amorphous and hence is not amenable to X‐ray diffraction analyses, this material is expected to consist of iron hydrophosphates. The reduction process is very useful in recycling several industrial wastes that are rich in hematite, including iron mine tailings, red mud (a caustic waste from the alumina industry), and machining swarfs. Formation of ceramics with red mud and swarfs is also discussed.

CO2 Decomposition by Oxide Ceramics Intercalated in Layered Compound

Iron oxide polymers intercalated and/or loaded within täniolite have been studied as a CO2 decomposition medium. Fe2+ was exchanged for Li+ in täniolite, oxidized by air‐bubbling at 60°–70°C. The basic d‐spacing (13.75 Å in the Li+ form) was expanded to give 14.86 Å in the Fe2+ form. Oxidation by air in the form of suspension gave a 15.3‐Å phase, which was ascribed to formation of magnetite within the interlayer. The interlayer distance of the intercalated phase remained the same upon heating at 300°C. The magnetite–intercalated täniolite was heated to activate in a H2 and/or H2O steam. CO2 decomposition reactivity at 300°C has been evidenced by evolution of CO gas. The high reactivity for CO2 decomposition is ascribed to the highly dispersed iron oxide ceramics within the interlayer of täniolite Li[(Mg2Li)(Si4O10)]F2nH2O.

Thershold Switching in Iron Oxide Ceramics

Thershold Switching in Iron Oxide Ceramics