Synthesis and characterization of yttrium iron garnet nanoparticles doped with cobalt

In this work, we have synthesized and characterized yttrium iron garnet nanoparticles doped with cobalt. The X-ray diffraction data showed a single phase, belonging to the cubic structure of Y₃Fe₅O₁₂. Rietveld refinement revealed variation of the angles and interionic distances (Fe³⁺(a)-O^2-Y³⁺(c) and Fe³⁺(d)-O^2--Y³⁺(c) when Fe³⁺ ions are replaced by Co³⁺ ions in the tetrahedral (d) and octahedral (a) sites of YIG. In addition, the lattice parameter a, decreases from 12.3846?Å to 12.3830?Å with the increasing of cobalt concentration. The analysis by Infrared and Raman spectroscopies has shown a slight stretching at lower wave numbers as the dopant concentration increased. The magnetic measurements confirm the substitution of Fe³⁺ by Co³⁺ in the a-sites and d-sites with the reduction of the saturation magnetization from 26.63?emu/g to 24.92?emu/g, for 0.000?≤?y?≤?0.030. Changes in the coercive field varying the dopant concentration were related to the particle size and pinning centers existence.     

Local atomic disorder and temperature dependence of saturation magnetization in yttrium iron garnet

In the present work experimental data for saturation magnetization at low temperatures, of yttrium iron garnet nanoparticles are different from that expected by the T^3/2 Bloch's Law. This result is mainly conditioned by the local atomic disorder induced during the nanoparticles preparation by using the sol gel method. To correctly describe the experimental curves, a fitting using Cojocaru's theory was performed because the model uses geometric and other conditions in agreement with our experimental results. The magnetic ions localized at the nanoparticles surface, outside the crystalline periodicity, are the responsible by the saturation magnetization behavior presented here.     

Competitive effect of dopants on magnetic and structural properties in yttrium iron garnet co-doped with Er and Cr

In the present work, we have studied the competitive effect of Er and Cr dopants on the structural and magnetic properties of yttrium iron garnet (YIG) nanoparticles synthesized by the sol gel method. The YIG single phase was obtained for all samples and the variations of structural parameters were associated to the dopants influence. Fourier transform infrared spectroscopy showed typical absorption peaks of YIG, with small displacements for larger wavenumbers corresponding to vibrational modes (Fe–O) belonging to the tetrahedral sites. The behavior of the Raman vibrational modes as a function of dopant concentration confirms the insertion of Er in dodecahedral sites and Cr in the octahedral and tetrahedral sites. A frequency shifting of some Raman modes was observed as the Cr concentration increased. The powder morphology was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), evidencing agglomerated particles with irregular shapes. The Er and Cr incorporation in YIG promote random fluctuations in the saturation magnetization, coercivity and the magnetocrystalline anisotropy constants of the synthesized compound.     

Treatment of wastewater containing oil using phosphorylated silica nanotubes (PSNTs)/polyvinylidene fluoride (PVDF) composite membrane

PVDF membranes are broadly applied in many fields owing to their good physicochemical stability, resistance to oxidation and chlorine. However when treating with wastewater, PVDF membranes are easily contaminated by pollutant, degrading their properties due to the hydrophobicity and poor anti-compaction capabilities, which can result in the decline of flux and lifespan of the membrane and limit their application in large scale. To enhance the integrative capabilities of PVDF membrane, phosphorylated silica nanotubes (PSNTs) were doped to PVDF to prepare a novel PSNTs/PVDF composite membrane through a phase inversion technique. The PSNTs/PVDF composite membranes were exposed to wastewater containing oil, and the effects of doped materials, operating pressure and operating temperature on fluxes were researched. The optimum parameters are: operating pressure is 0.1 MPa, operating temperature 25 °C. Through physical flushing and chemical cleaning, the PSNTs/PVDF membranes could still keep a high permeation flux and long lifetime. Finally, the interaction mechanism between PSNTs and PVDF membrane, the anti-fouling mechanism of PSNTs/PVDF composite membrane were explored and analyzed. The results show that the hydrophilicity, anti-fouling and anti-compaction properties of composite membrane can be obviously enhanced and hence the PSNTs/PVDF composite membrane is desirable in the treatment of wastewater containing oil and sewage.     

Dielectric and microwave properties of carbon nanotubes/carbon black filled natural rubber composites

Abstract

Natural rubber (NR) based nanocomposites containing a constant amount (50 phr) of standard furnace carbon black and carbon nanotube (CNT) at a concentration from 1 to 5 phr have been prepared. Their dielectric (dielectric permittivity and dielectric loss) and microwave properties (coefficients of absorption and reflection of the electromagnetic waves and electromagnetic interference shielding effectiveness) have been investigated in the 1–12 GHz frequency range. The results achieved allow recommending CNTs as second filler for NR based composites to afford specific absorbing properties.     

Synthesis,thermal, dielectric,and microwave reflection loss properties of nickel oxide filler with natural fiber-reinforced polymer composite

Fabrication of hybrid composite of nickel oxide (NiO) combined with oil palm empty fruit bunch (OPEFB) reinforced with polycaprolactone (PCL) has been done by using thermal Haake blending machine, which ensured mixture homogeneity. All hybrid composites' characterizations were carried out using X-ray diffraction (XRD), Fourier transform infrared spectrometry, differential thermogravimetry, thermogravimetric analysis, and scanning electron microscopy. The results showed that the XRD profile patterns of the composites clearly changed as the filler loading amount was increased. Fourier transform infrared spectra illustrated a slight change in the frequencies and positions of the peaks after adding NiO, indicating that some interactions occurred between C=O and O–H or among the fiber, NiO, and PCL. The microwave electromagnetic properties, such as reflection loss (dB), relative complex permittivity (ε_r =–j), and permeability (−j) were calculated at various microwave frequencies in the X-band (8–12 GHz) range. It was observed that the thermal stability, magnetic, and dielectric properties of NiO:OPEFB:PCL composites were modified significantly with NiO addition. This enables the new hybrid composites to be used as engineering materials in the microwave applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46998.     

In situ sol-gel co-synthesis at as low hydrolysis rate and microwave sintering of PZT/Fe2CoO4 magnetoelectric composite ceramics

Pb(Zr_0.53Ti_0.47)O₃/Fe₂CoO₄ (PZT/Fe₂CoO₄) diphase particulate composites were prepared in an 80:20 M ratio by the in situ sol-gel co-synthesis method. Controlling the hydrolysis rate of the metal-organic reagents used in the formation of the sol was essential to obtain a nanostructured system with a highly homogeneous and immiscible two-phase distribution. The compact diphase powders were densified throughout the microwave-assisted sintering methods for controlling grain growth, and to evaluate this new nanostructure and effect on the physical properties of this material. The characterizations revealed that the new in situ sol-gel co-synthesis method was successful in producing highly homogeneous nanopowders without secondary phases. The powders processed at low hydrolysis rates showed the formation of a core-shell particle architecture. After microwave-assisted sintering, the samples showed uniform distribution of the cobalt ferrite phase in the PZT phase, with an average nanograin size of about 300 nm, while the same material sintered conventionally had an average cobalt ferrite grain size of about 6 µm. Innovative PZT/Fe₂CoO₄ nanostructures were obtained with magnetoelectric response.