Investigation on magnetic and microwave behavior of magnetite nanoparticles coated carbon fibers composite

Radar absorbing materials, i.e. magnetite (Fe3O4) coated carbon fibers (MCCFs) were fabricated by electro-deposition technique. Black-colored single spinel phase Fe3O4 nanoparticles was easily synthesized by hydrothermal method using reduction of a Fe (III) - Triethanolamine complex in an aqueous alkaline solution at 60-80 ◦C. Uniform and compact Fe3O4 films were fabricated on nitric acid treated carbon fibers. A correlation between magnetic and absorption properties of specimens was made. It was found that the deposition time, and the sequences of the coating process have a significant effect on the reflection loss characteristics of the MCCFs. On the other hand, the temperature of the coating process affects strongly the composition of the thin film. MCCFs prepared at 80 ◦C possesses a much higher loss factor than the one prepared at 60 ◦C. The morphology, phases in the coating layer, magnetic properties and absorption behaviors of the MCCFs were examined using FESEM, XRD, permagraph, vector network analyzer (VNA), respectively. The highest reflection loss that is −10 dB at 12.27 GHz was observed in the sample deposited for four minutes. It was also found out that a uniform deposition layer can be observed in the sample deposited in three steps in which each step takes four minimums

Effect of various parameters on the microstructure and magnetic properties of sintered Sr-hexaferrite

Sr-hexaferrite powders with Fe/Sr molar ratio of 11 was synthesized via conventional ceramic route. Powders were milled for 5–25 h, then pressed to make green compacts by applying a pressure of 100–400 MPa. In other series, K2CO3 was used in starting materials. K2CO3/SrCO3 mixing molar ratio was 0.05 and 0.5. First series were calcined at 1250 °C, and the second series were calcined at 1000 °C for 2 h. The XRD characterization results revealed Sr-hexaferrite structure has been produced in both series; Crystallite size is constant then increases while lattice strain rises by variation of milling time from 5 h to 25 h. (BH)max and Br increase by increasing milling time to 25 h and (BH)max reaches to optimized value of 24.75 kJ/m3. SEM was used for microstructure investigation; particle morphologies are hexagonal shape. Addition of slight amount of K2CO3 makes SrFe12O19 crystallites get less platelet shape and more regular shape. By increasing pressure morphology of the grain enhances in regularity. Magnetic properties were measured via permagraph; By increasing sintering temperature from 1150 °C to 1200 °C, density increases from 3.38 g/cm3 to 4.85 g/cm3. Maximum energy product varies from 9.54 kJ/m3 to 25.27 kJ/m3. Between the sintering temperatures of 1200–1250 °C maximum energy product stays at the highest values, But after 1250 °C drops to 3.82 kJ/m3. As density increases, remanence (Br) and maximum energy product [(BH)max] first increase at the pressure range of 100–200 MPa until it reaches to a optimize value of 15.20 kJ/m3 at 200 MPa. Keywords: Sr-hexaferrite, Lattice strain, Williason-Hall, Salt-melt, Sinter-aid, Milling time, Demagnetization curv

Effect of Heat-Treatment Temperatures on Magnetite Oxidation in 20SiO2.50FeO.30CaO Glass Ceramic Prepared by the Sol-Gel Method

Abstract The effect of different heat-treatment temperatures on the magnetic, crystallization, and structural properties of 20SiO2.50FeO.30CaO (mol%) glass ceramics was studied. The initial glass was synthesized by the sol-gel method at 25℃  with a precursors to solvent ratio of 1/5. After aging the resulted gel for 24 h at room temperature, it was dried in an electric dryer at 110 ℃ . By heat treatment at different temperatures, different phases such as magnetite, maghemite, and hematite were crystallized in the glass. The maximum stability temperature of magnetite and maghemite were 360℃  and 440℃  respectively. By increasing the heat treatment temperature to higher than 440℃ , the oxidation of maghemite to hematite was occureds. The highest magnetization amount (1.9 emu/g) belonged to sample heat treated at 680℃ . By increasing the heat treatment temperature to 840℃ , the magnetization decreased to 0.8 emu/g, due to the oxidation of maghemite. By increasing the heat treatment temperature from 440℃  to 680℃ , crystalline size of maghemite was increased from 40 to 200 nm. By forther increment of temperature to 840℃ , the size of maghemite crystals decreased to 17nm, due to the oxidation of maghemite to hematite. Abstract The effect of different heat-treatment temperatures on the magnetic, crystallization, and structural properties of 20SiO2.50FeO.30CaO (mol%) glass ceramics was studied. The initial glass was synthesized by the sol-gel method at 25℃  with a precursors to solvent ratio of 1/5. After aging the resulted gel for 24 h at room temperature, it was dried in an electric dryer at 110 ℃ . By heat treatment at different temperatures, different phases such as magnetite, maghemite, and hematite were crystallized in the glass. The maximum stability temperature of magnetite and maghemite were 360℃  and 440℃  respectively. By increasing the heat treatment temperature to higher than 440℃ , the oxidation of maghemite to hematite was occureds. The highest magnetization amount (1.9 emu/g) belonged to sample heat treated at 680℃ . By increasing the heat treatment temperature to 840℃ , the magnetization decreased to 0.8 emu/g, due to the oxidation of maghemite. By increasing the heat treatment temperature from 440℃  to 680℃ , crystalline size of maghemite was increased from 40 to 200 nm. By forther increment of temperature to 840℃ , the size of maghemite crystals decreased to 17nm, due to the oxidation of maghemite to hematite

Nanostructured soft magnetic materials synthesized via mechanical alloying: a review

Soft magnetic materials are widely used in electrical and electronic industries due to their desirable electromagnetic features, i.e. relatively high electrical resistivity and low eddy current loss at high frequencies. From industrial point of view, once the size of grains is reduced to micron scale regimes, their performance is only narrowed to a few megahertz frequencies, due to their higher conductivity and domain wall resonance. Thus, one way to resolve this issue and utilize these materials at high frequency applications, is to reduce the size of grains from micron to sub or nanoscale before they are being compacted for sintering. In this aspect, however, several methods are employed to synthesize these nanoparticles, a mechanical alloying is found to be a proven route to produce a vast variety of materials with both non-equilibrium and equilibrium phases in a controlled size and shape of powder particles at desired tonnages. Mechanical alloying (MA) is a solid-state powder metallurgy route which involves a repeated action of fracturing and re-welding of powder particles in a high-energy ball mill. The final products characteristics are strongly dependent on the variable parameters of the process, i.e. milling time, ball-to-powder weight ratio, rotation speed, grinding media and milling atmosphere. Thus, this work reviews the key role of these parameters on the structure and magnetic behaviors of soft magnetic materials. Eventually, the mechanism of mechanical alloying and effect of diffusivity are also highlighted

Green synthesis of superparamagnetic magnetite nanoparticles: effect of natural surfactant and heat treatment on the magnetic properties

A facile and eco-friendly synthetic approach was employed to synthesize superparamagnetic magnetite (Fe3O4) nanoparticles with cubic lattice structure. Zucchini and pomegranate peel-extracts were used as natural stabilizer and surfactant. The X-ray diffraction patterns revealed that the green synthetic technique was successful in formation of highly distributed Fe3O4 nanoparticles using both of the above extracts. The infrared (IR) analysis further confirmed the phase formation and the binding of extracts with Fe3O4 nanoparticles. Based on UV–Vis analysis, the samples showed the characteristic of surface plasmon resonance in the presence of Fe3O4 nanoparticles. The as-synthesized samples were heated at 550 °C for 2 h. It was found that the particles however grew, their sizes remained in nanoscale regime, indicating their thermal stability. The VSM analysis indicated that the as-synthesized samples have a saturation magnetization of 21.4 emu/g (using zucchini peel extract) and 13.3 emu/g (using pomegranate peel extract), which increased respectively to 45.8 emu/g and 38.1 emu/g after the heating process. A negligible coercivity in the samples with the particle sizes of less than 10 nm suggests superparamagnetic behavior of the samples

Cytotoxicity characteristics of green assisted-synthesized superparamagnetic maghemite (γ-Fe2O3) nanoparticles

Magnetic nanoparticles such as Fe3O4 and γ-Fe2O3 are extensively used in medical application, i.e. drug delivery, MRI, etc. Chemical toxicity and side-effect behaviors always play an important role in such applications. Thus, synthesis of such less-toxic compounds with green technology is privilege. In this study, the extract prepared from mango leaves was used for the preparation of iron oxide nanoparticles (γ-Fe2O3) using FeSO4 as iron source with the green-assisted route. The X-ray diffraction pattern indicated single-phase formation with the average crystallite size of 7 ± 2 nm. HRTEM micrographs indicated a dot-cloud-surrounded like particles ranging from 1 to 12 nm. Fourier Transform Infrared (FT-IR) spectroscopy showed two absorption bands at 457 and 634 cm−1, which are attributed to octahedral and tetrahedral sites of Fe–O band, respectively. A vibrating sample magnetometer (VSM) indicated a saturation magnetization (Ms) value about 53 emu/g with negligible coercivity (Hc), suggesting superparamagnetic behavior of the synthesized nanoparticles. The cytotoxicity was evaluated by exposing the breast cancer cell type (MCF7) to different concentrations of the γ-Fe2O3 nanoparticles. MTT assay results revealed that the growth and survival of MCF7 cells directly depend on the concentration of synthesized iron oxide nanoparticles. It was found that up to concentration of 200 µg/mL, cell survival has not yet reached 50%, which indicates the safety of nanoparticles and lack of toxicity

Mechanochemically synthesized NiCo2O4/Vulcan/PANI nanocomposite and investigation of its electrochemical behavior as a supercapacitor

Wet-mechanical alloying was used to synthesize NiCo2O4 (Ni-Co) nanoparticles. XRD results showed that single phase nanoparticles were formed after 1 h of milling and a minimum crystallite size of 3 nm was obtained for 3 h-milled sample. The 3-h-milled sample was mechanically alloyed with Vulcan (Vu) to fabricate NiCo2O4/Vulcan (Ni-Co/Vu). The Ni-Co/Vu sample was thoroughly mixed with aniline (ANI), and the mixture was then polymerized to polyaniline (PANI). The microscopic evaluations showed the change in shape of Ni-Co particles from spherical to worm-liked after the polymerization process. Their structure was evaluated using FT-IR and Raman spectroscopies. The electrochemical studies through cyclic voltammetry (CV) and chronopotentiometry (CP) showed the highest capacitance for the 3-h-milled Ni-Co, in comparison with other milled samples. The capacitance of 341 F g−1 of the 3-h-milled sample, was enhanced to 455 and 644 F g−1, upon introducing Vu and Vu/ PANI, respectively

Facile and scalable synthesis of ultrafine MnCo2O4 nanoparticles via mechanical alloying as supercapacitive materials

The possibility of synthesizing MnCo2O4 nanoparticles from MnCl2·4H2O and CoCl2·6H2O via mechanical alloying was investigated and sampled after 1, 2, 3, and 4 h of milling. X-ray diffraction (XRD) analysis showed that the initial materials were changed to MnCo2O4 after 1 h of milling and calcination. The broadening of the XRD lines showed that MnCo2O4 crystallites were on the order of nanometers. Fourier-transform infrared spectroscopy spectra of the MnCo2O4 samples indicated the cation distribution of Co-O (~ 567 cm−1) and Mn-O (~ 665 cm−1) in octahedral and tetrahedral sites, respectively. The morphology of the samples is spherical, according to field emission scanning electron microscopy results. Electrochemical measurements, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy, were performed to evaluate specific capacitance, cyclic stability, and charge transfer resistance, respectively. The highest capacitance of about 546 F/g and efficiency of 103% were obtained for the 3-h-milled MnCo2O4 sample