In this work, various morphologies of SrFe12O19 (SrFe) nanostructures were synthesized via a simple sol–gel method. The effect of concentration, temperature and various surfactants on the morphology and particle size of the magnetic seeds was investigated. The prepared magnetic products were characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy techniques. Alternating gradient force magnetometry reveals that the samples exhibit hard magnetic property with the coercivity up to 5300 Oe. Strontium ferrite was added to poly vinyl alcohol to prepare the magnetic polymeric matrix thin film nanocomposites. The saturation magnetization and coercivity decreased due to agglomeration of magnetic nanoparticles in polymer matrix. 相似文献
Spray pyrolysis has been used to produce X-ray amorphous precursors with the nominal composition SrFe12O19 · 6SrB2O4 in the form of spherical particles 0.3 to 2 μm in diameter. Heat treatment of the precursors at temperatures from 650 to
900°C has produced platelike strontium hexaferrite particles embedded in a SrB2O4 matrix. With increasing annealing temperature, the average dimensions of the hexaferrite particles increase from 80 × 20
to 450 × 100 nm and the coercivity of the material rises from 240 to 440 kA/m. 相似文献
A new type of Ni-coated strontium ferrite powder was prepared with electroless plating enhanced by ultrasonic wave at room
temperature. The morphology, crystal structure and microwave absorption properties of the Ni-coated powder were investigated
with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), EDS and vector network analyzer. The results
show that the powder possesses excellent microwave absorption properties. The maximum microwave loss of the composite powder
reaches −41.3 dB. The bandwidth with the loss above −10 dB reaches 8 GHz. 相似文献
The strontium hexaferrite (SrFe12O19) nanoparticles have been successfully synthesized by co-precipitation route. The effect of various parameters such as calcination temperature and chelating agents were screened to achieve optimum condition. Different chelating agents such as amino acids (proline, alanine, aspartic acid) and surfactants (SDBS, PVP, and EDTA) were used. Compared with the amino acids, the surfactants increase the particle size and the best result was observed for alanine. The SrFe12O19 nanoparticles showed enhanced photocatalytic activity in the degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 220 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 32 emu/g. The SEM images proposed that the particles are almost spherical with an average particle size of 90 nm. 相似文献
Magnetically separable TiO2-coated SrFe12O19 electrospun nanofibers were obtained successfully by means of sol–gel, electrospinning, and coating technology, followed
by heat treatment at 550–650 °C for 3 h. The average diameter of the electrospun fibers was 500–600 nm. The fibers were characterized
by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and vibrating sample
magnetometer (VSM). The optimized calcining temperature was determined by XRD and the analysis of decolorizing efficiency
of methylene blue (MB) under UV–vis irradiation. The photocatalytic activity of the TiO2-coated SrFe12O19 fibers was investigated using ultraviolet–visible absorbance by following the photooxidative decomposition of a model pollutant
dye solution, MB in a photochemical reactor. In contrast to pure TiO2 fibers, the TiO2-coated SrFe12O19 fibers have higher absorption in 250–750 nm wavelength regions. The presence of SrFe12O19 not only broadened the response region of visible-light, but also enhanced the absorbance for UV light. The decolorizing
efficiency of MB under UV–vis irradiation was up to 98.19%, which was a little higher than that of Degussa P25 (97.68%). Furthermore,
these fibers could be recollected easily with a magnet in a photocatalytic process and had effectively avoided secondary pollution
of treated water. 相似文献
Strontium hexaferrite (SrFe12O19) which crystallizes in the hexagonal system and has a uniaxial magnetoplumbite structure, displays distinctive magnetic characteristics,
good chemical stability, good tribological properties and a weak temperature dependent coercivity at about room temperature.
In the present work the synthesis conditions for the solid-state preparation of the chromium-doped hexaferrite SrCr0.3Fe11.7O19 were optimised and the effect on the magnetic properties of this compound of additions of nanosized SrFe12O19 was studied. The nanosized SrFe12O19 additive, synthesized by the citrate–nitrate reaction, was substituted in varying amounts for a commercial calcium silicate
borate sintering additive mixture. A combination of 0.75 wt% of nano-sized SrFe12O19 with 0.75 wt% of the commercial additive increases the intrinsic coercivity, remanence magnetization and rectangularity ratio
and results in superior magnetic properties than obtained with 1.5 wt% of nanosized SrFe12O19 or the commercial sintering additive alone. 相似文献
Strontium aluminates are important compounds with interesting properties such as long-duration phosphorescence and elastico-deformation luminescence. They have potential application in flexible light emitting panels. Since there are serious discrepancies in available thermodynamic data for these compounds, a redetermination of their Gibbs energies of formation was undertaken using solid-state electrochemical cells incorporating single-crystal SrF2 as the electrolyte in the temperature range from 1000 to 1300 K. However, the measurements were restricted to SrAl12O19 and SrAl4O7 because of the formation of strontium oxyfluoride phase between SrAl2O4 and SrF2. For the reactions, SrO + 6 Al2O3 → SrAl12O19, ΔGo/J mol?1 (± 280) = ?83386 ? 25.744 (T/K), and SrO + 2Al2O3 → SrAl4O7, ΔGo/J mol?1 (± 240) = ?80187 ? 25.376 (T/K). The high entropy of SrAl4O7 and SrAl12O19 can be partly related to their complex structures. The results of this study are consistent with calorimetric data on enthalpy of formation of other Sr-rich aluminates and indicate only marginal stability for SrAl4O7 relative to its neighbours, SrAl12O19 and SrAl2O4. The thermodynamic data explain the difficulty in direct synthesis of phase pure SrAl4O7 and the formation of SrAl2O4 as the initial ternary phase when reacting SrO and Al2O3 or crystallizing from amorphous state, irrespective of composition. 相似文献
Nickel substituted strontium hexaferrite, SrFe11.2Ni 0.8O19 nanoparticles having super paramagnetic nature were synthesised by co-precipitation of chloride salts using 7.5 M sodium
hydroxide solution. The resulting precursors were heat treated (HT) at 900 and 1,200 °C for 4 h in nitrogen atmosphere. During
heat treatment, transformation proceeds as a constant rate of nucleation and three dimensional growth with activation energy
of 183.724 kJ/mole. The hysteresis loops showed an increase in saturation magnetization from 1.045 to 65.188 emu/g with increasing
HT temperatures. The ‘as-synthesised’ particles have size in the range of 20–25 nm with spherical and needle shapes. Further,
these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plates with increase in HT temperatures.
The effect of such a systematic morphological transformation of nanoparticles on dielectric (complex permitivity and permeability)
and microwave absorption properties were estimated in X band (8.2–12.2 GHz). The maximum reflection loss of the composite
powder reaches −24.92 dB at the thickness of 2.2 mm which suits its application in RADAR absorbing materials. 相似文献
Ce-substituted BaFe12O19 (BaCexFe12−xO19, x = 0, 0.01, 0.03, 0.05) was prepared by citrate sol–gel method. The thermal decomposition process of precursor was investigated
by TG-DSC. The phase composition of the BaCexFe12−xO19 was characterized by X-ray powder diffraction analysis (XRD) which reveals that the BaCexFe12−xO19 crystallizes in a hexagonal structure. The lattice parameter of BaCexFe12−xO19 increases slightly when Ce was substituted into BaFe12O19. The average crystallite size calculated from the XRD line broadening is about 30–33 nm and no intermediate phases are detected
in the XRD patterns. The transmission electron microscope (TEM) analysis indicates that the particles of samples obtained
are the rod-like morphology. 相似文献
The nanocrystalline SrFe12O19 materials were prepared by a sol-gel auto-combustion method using different fuels such as citric acid, dextrose, aniline, and hexamine. The combustion product obtained from all the fuels except from that of aniline show a single phase of SrFe12O19 materials upon annealing at 1000 °C/2 h. The combustion product obtained from aniline as fuel shows SrFe12O19 as the main phase with α-Fe2O3 as impurity. No notable change in lattice parameters is observed due to variation in fuels for SrFe12O19 materials. With a little change in the NIR relative reflectance (72–85 %) on fuels, the different SrFe12O19 materials display high NIR reflectance in the wavelength range, 1500–2500 nm. The photoluminescence emission spectra of SrFe12O19 materials reveal a broad emission peak at ~350 nm which is reminiscent to the Ba-based hexaferrite, BaFe12O19. The FESEM images expose quite dissimilar morphology for the various fuels used in the synthesis of SrFe12O19 materials. Hysteresis loops for all the nanocrystalline SrFe12O19 materials observed under the applied field of ±1.5 T at room temperature exhibit hard ferromagnetic property. The SrFe12O19 materials produced from glycine and aniline as fuels exhibit highest and lowest Ms values of 61.3 and 50.5 emu/g, respectively. 相似文献
The SrFe12O19/SiO2/TiO2 nanostructures with hard magnetic core were successfully synthesized through the facile and efficient wet chemical processes. At first, nanocrystalline strontium hexaferrite (SrFe12O19) powder was prepared using a new co-precipitation route in ethanol/water media. In the next step, SrFe12O19/SiO2 composites were produced by well-known Stöber method using tetraethyl orthosilicate as precursor. Finally titania was coated on SrFe12O19/SiO2 composite particles using titanium n-butoxide precursor. The core/shell/shell nanostructures have been characterized by means of X-ray diffraction, vibrating sample magnetometer, Fourier transform infrared spectra, field emission scanning electron microscopy, and transmission electron microscopy equipped with an energy-dispersive X-ray spectroscopy detector. The catalytic activity of SrFe12O19/SiO2/TiO2 composites has been investigated in the degradation of methylene blue dye under UV illumination. The results indicated that the obtained SrFe12O19/SiO2/TiO2 composite has photo-catalytic properties and can be retrieved by magnetic separation. The photo-degradation of methylene blue dye was about 80% in the presence of photo-catalyst powder at irradiation time of 180 min. Recycled composite particles could be used again. 相似文献
We have studied suspensions of hard-magnetic BaFe12O19 particles in water, ethanol and 1-butanol. The surfaces of these particles were previously modified with the surfactant dodecylbenzylsulphonic
acid. The stabilities of the suspensions were estimated from their saturation concentrations and zeta potentials. We found
that the 1-butanol suspensions were more stable than the ethanol-based suspensions and much more stable than the water-based
suspensions. We analyzed the suspensions and the dispersed particles using gravimetry, conductometry and transmission electron
microscopy, measured their zeta potentials, and calculated the interparticle-attraction interaction energies due to the van
der Waals and magnetic dipole–dipole forces. The magnitudes of the attraction energies varied significantly with the particles’
sizes and the separation distances between the particles, and we found that the contribution of the van der Waals attraction
energy can be neglected with respect to the magnetic dipole–dipole attraction. The observed differences in the stability of
the suspensions were explained on the basis of the calculated electrostatic and steric repulsion energies. Electrosteric stabilization
was possible in the 1-butanol and the ethanol for particles with radii and thicknesses up to 15 nm, while a too small electrostatic
repulsion and the absence of steric repulsion in the water resulted in rapid agglomeration. 相似文献
Superexchange effects play an important role in the determination of crystal structures; however, there has been much less reported on how they determine the stability of clusters. Using evolutionary search strategies and DFT+U (density functional theory with the Hubbard U correction) calculations, we investigate the global minimum-energy structures of Fe12On clusters. Among predicted Fe12On clusters, a cage-shaped Fe12O12 cluster with unexpected stability was observed. In addition, the bare Fe12O12 cluster is shown to possess an extremely large energy gap (2.00 eV), which is greater than that of C60, Au20 and Al13?clusters. Using a Heisenberg model, we traced the origin of the unexpected stability of the bare Fe12O12 cluster to magnetic competition between the nearest-neighbor exchange constant J1 and the next-nearest neighbor exchange constant J2 that was induced by the superexchange interactions. The bare Fe12O12 cluster is thus a unique molecule that is stable and chemically inert.
Mesoporous electrode materials of spinel Co3O4 were synthesized by hydrothermal method using polyethylene glycol-6000 (PEG-6000) as dispersant and subsequent calcination
at different temperatures in air. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron
microscopy (FESEM), nitrogen adsorption and electrochemical measurements. The results showed that the dispersant PEG-6000
had a distinct effect to control the porosity, particle size and homogeneity of Co3O4; the calcination temperature had a significant influence on the crystal structure, surface area, porosity and morphology,
and indeed electrochemical performance. The resultant Co3O4 sample calcinated at 350° C possessed a narrow mesopore distribution around 4 nm and exhibited excellent electrochemical
performance. It had the specific capacitance as high as 348.7 F/g, increased by 21.5% over that of pure Co3O4 and showed good cyclical charge–discharge stability. 相似文献
Gd3Ga5O12 garnet was prepared by a solution combustion method and characterized using powder X-ray diffraction, electron paramagnetic resonance (EPR) and optical spectroscopic techniques. EPR spectrum of the samples at ambient and low temperatures exhibited resonance signal at g?≈?2 attributed to Gd3+ ions disposed in an octahedral symmetry. The optical absorption spectrum showed a band centered at 274 nm attributed to 8S7/2→6IJ transition of the Gd3+ ions. The excitation spectrum showed a maximum at 273 nm along with two relatively weaker peaks at 276 and 279 nm. These three excitation bands were assigned to the transitions 8S7/2→6IJ. The emission spectrum showed two peaks centered at 311 and 306 nm that were assigned to the transitions 6P7/2→8S7/2 and 6P5/2→8S7/2 of Gd3+, respectively. To evaluate the phosphor performance, several magnetic and thermodynamic parameters for the system were calculated adopting standard procedure. 相似文献
The nanocomposite multilayer film (NCMF) of substituted BaFe12O19 and TiO2 was prepared using sol-gel method. BaFe10.5Al1.5O19, BaFe10.1Al1.9O19 and BaFe11.4Cr0.6O19 with different absorption frequencies were selected to fabricate the multilayer film with TiO2. The morphology, crystalline structure and microwave absorption property of the NCMF were investigated with an atomic force
microscopy, X-ray diffraction and vector network analyses. The results show that the NCMF is uniform without microcracks and
it is an ideal microwave attenuation material with a broad frequency range. Its maximum loss efficiency is about −40 dB. The
frequency range with the loss above −10 dB is more than 7 GHz. The multilayer film assembles the achievements of each layer
film. Moreover, the compounding of ferrites with TiO2 is helpful to absorb more microwave energy. TiO2 particles block the growth of ferrite grains and make most of their size within nanometers. TiO2 also improves the dielectric loss efficiency of the NCMF. 相似文献
CsSmP4O12 crystals have been prepared at 300°C in molten polyphosphoric acids containing Cs, Mg, and Sm cations, and their crystal structure has been determined: sp. gr. I\(\bar 4\) 3d, a = 15.1225(8) Å, Z = 12, CsNdP4O12 structure. 相似文献
Europium-doped yttrium phosphors were successfully synthesized by combustion process using yttrium nitrate hexahydrate [Y(NO3)3·6H2O], europium nitrate [Eu(NO3)3·6H2O], and carbohydrazide [CO(N2H3)2]. The process takes only a few minutes to obtain Y2O3:Eu phosphors. The resultant powders annealed at different temperature and were investigated by X-ray diffractometer (XRD),
differential thermal analyzer/thermogravimeter (DTA/TG), Fourier transform infrared spectroscopy (FTIR), photoluminescence
excitation and emission spectra (PL), and transmission electron microscopy (TEM). The results showed that the formation temperature
of Y2O3 phase is significant low, compared to solid-state reaction route of constituent oxides. For luminescence property, the emission
intensity of Y2O3:Eu phosphors synthesized by combustion process increases steadily with increasing europium amount from 1 mol% to 5 mol%. 相似文献
Fe3O4 magnetic nanoparticles being used as seeding materials, Ag+ ions on the Fe3O4 magnetic nanoparticles reduced to the metal form by tartaric acid using heated treatment. Thus, Fe3O4/Ag composite core-shell magnetic nanoparticles were synthesized. The products were characterized by transmission electron
microscope (TEM) and x-ray diffraction (XRD). Both TEM and XRD results showed that the Ag nanoparticles were well distributed
on the surface of Fe3O4 magnetic nanoparticles. The size for Fe3O4/Ag composite magnetic nanoparticles which were spherical shape was ≃40 nm. Furthermore, the magnetic properties of samples
were characterized on a vibrating sample magnetometer. Under optimal conditions, Fe3O4/Ag composite nanoparticles showed higher magnetism than pure Fe3O4 nanoparticles.
The text was submitted by the authors in English. 相似文献