Effects of aqueous ethanol solutions on the structural and magnetic properties of NiZn ferrite thin films prepared by spin-spray deposition

Although substrate wettability greatly impacts deposition processes using the spin-spray technique, there are few substrates suitable for the deposition of spin-sprayed ferrite thin films. To tune substrate wettability without changing the type of substrate, we demonstrate a Ni_0.17Zn_0.52Fe_2.31O₄ ferrite film deposited by the spin-spray technique on a 0.2 mm glass substrate with 0–5% aqueous ethanol solutions. All samples showed (222) preferential orientation and triangular grain morphology. The effects of aqueous ethanol solutions on the microstructure and magnetic properties of ferrite thin films were also investigated. When the ethanol volume percent concentration equaled 3%, the columnar morphology of the microstructure was most evident and the saturation magnetization and the real permeability reached their maximum values. Because of the shape anisotropy of the columnar structure, the coercivity of the parallel magnetic field increased, whereas the coercivity of the perpendicular magnetic field decreased. First-order inversion curve measurements revealed that ethanol-containing ferrite thin films had a more uniform grain size.     

Electrical and electrochemical studies of nanocrystalline mesoporous MgFe2O4 as anode material for lithium battery applications

Nanocrystalline mesoporous spinel magnesium ferrite (MgFe₂O₄) particles with high surface area were prepared by urea assisted modified citrate combustion process. The prepared sample was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field-emission scanning electron microscope (FE-SEM), BET surface area analyzer and impedance spectroscopy techniques. XRD results confirmed the formation of a single phase of nanocrystalline spinel magnesium ferrite sample. FTIR and Raman spectroscopy (FTIR) results confirmed the structural co-ordination of the magnesium ferrite sample. The spherical shape morphology of the prepared magnesium ferrite particles was confirmed from the FE-SEM images. Specific surface area and porosity of the MgFe₂O₄ sample were obtained from N₂ adsorption–desorption isotherms results. The D.C. and A.C. electrical conductivities of the MgFe₂O₄ sample as a function of temperature and frequency were investigated by analyzing the measured impedance data. The activation energy for the migration of the carriers in the MgFe₂O₄ sample was found to be 0.607 eV. The dielectric studies revealed that the dielectric constant of the mesoporous MgFe₂O₄ sample increases with increase in temperature. Further, lithium battery was fabricated using the developed nanocrystalline mesoporous spinel MgFe₂O₄ as anode material and investigated its electrochemical performance. The charge-discharge studies revealed that the fabricated lithium battery using the developed nanocrystalline mesoporous MgFe₂O₄ as anode exhibited high capacity and good cycleability in the voltage range 0.005–3 V. The results show that the developed nanocrystalline mesoporous spinel magnesium ferrite could be a better anode material for lithium battery applications.     

Green hydroelectrical energy source based on water dissociation by nanoporous ferrite

Dissociation of water molecule occurs on octahedrally coordinated unsaturated suface cations and oxygen vacancies created by lithium substitution in magnesium ferrite. Lower synthesis temperature of ferrite has generated nanopores in microstructure. Dissociated hydronium and hydroxyl ions are transported through surface and capillary diffusion in porous ferrite network towards attached Zn and Ag electrodes. Water molecule dissociation ability of nanoporous ferrite has been exploited to develop a green electrical energy cell, which is a combination of material science and electrode chemistry. The innovated cell has been nomenclatured as hydroelectric cell (HEC). When HEC is partially dipped in deionized water, spontaneously hydroxide and hydronium ions are produced by water molecule dissociation. Hydronium ions trapped in nanopores develop enough electric field that further dissociates physisorbed water molecules. Thereby, the process of water molecule dissociation is accelerated in a bigger way to increase ionic current in the cell. Oxidation of Zn electrode by hydroxide ion and reduction of H₃O⁺ at Ag electrode develop voltage and electric current in the cell. The HEC cell of a 17 cm² area is able to generate a short circuit current of 82 mA and 920 mV emf with a maximum output power of 74 mW, which is three order higher than reported output power 1.4 μW/cm² produced by water in cement matrix. Hydroelectric cell performance is repetitive, stable and possesses potential to replace traditional ways of generating renewable energy in terms of cost and safety. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrospray‐deposited nickel ferrite thin film electrode for hydrogen production in PV‐assisted water electrolysis system

Nanocrystalline Ni ferrite thin film was prepared by electrospray deposition technique and characterized by different analytical techniques at different annealing temperatures. All these films were studied by photovoltaic‐assisted water electrolysis system for solar to hydrogen production efficiency measurement. Highly dense and uniform surface morphology was observed in as‐deposited film, which changed into agglomerated nanocrystalline grains of irregular size and shape with change in annealing temperature. The X‐ray photoelectron spectroscopy study showed that the as‐deposited film was a mixture of an oxyhydroxide form of iron and an Ni₂O₃ form of nickel, whereas it changed into ferrite phase with change in annealing temperature. The as‐deposited film was observed to be of amorphous phase, which changed to crystalline cubic spinel structure with change in annealing temperature. The solar to hydrogen production efficiency was found to increase in a film with an increase in annealing temperature. The film annealed at 500°C showed a high solar to hydrogen production efficiency (8.29%) with constant performance of up to initial 500 h. Thereafter, the performance slowly declined by 11% when up to 1000 h. Copyright © 2011 John Wiley & Sons, Ltd.     

Nanograin Mn-Zn ferrite smart cores to miniaturize electronic devices

Conventional ceramic and sol-gel auto combustion routes were adopted to develop Mn-Zn ferrite cores. To control high frequency (>500 kHz) losses, zirconia (0.2 wt%) and calcia (0.04 wt%) were added in Mn_0.57Zn_0.35Fe_2.08O₄. The results revealed that Mn-Zn ferrite smart cores synthesized by auto combustion process have superior properties than conventionally prepared cores. It is believed that the presence of unique properties such as nanograin microstructure, light weight and short height (thickness) dimensions have played their role to enhance the magnetic impedance of smart core to manifold. Fabricated smart core excellently performed in a test frequency band of 3-15 MHz.     

尖晶石型铁氧体CaxZn1-xFe2O4的制备及其光催化性能研究

采用改进的溶胶-凝胶法制备CaxZn1-xFe2O4粉体。用X射线粉末衍射仪(XRD)对样品进行结构表征,随着Ca2+掺杂量的增加,样品出现CaFe2O4的衍射峰。使用扫描电子显微镜(SEM)对样品进行形貌表征,结果表明样品的形貌呈不规则的颗粒状,且颗粒大小为2μm,并显现出片层堆叠情况。通过对甲基橙进行光催化降解实验,对CaxZn1-xFe2O4粉体的光催化活性进行了研究。结果表明,经过Ca2+掺杂的CaxZn1-xFe2O4样品,光催化活性明显提高。     

Mechanosynthesis of hydroxyapatite–ferrite composite nanopowder

In the present work, an investigation of the mechanosynthesis of calcium hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) from a mixture of calcium oxide (СаО) and ammonium hydrophosphate ((NH₄)₂HPO₄) and mechanotreatment of HA in a planetary mill with the use of steel drums and milling body has been performed. The obtained results have shown that the mechanosynthesis of crystalline nanodisperse HA proceeds through the stage of formation of an amorphous material. The temperature treatment of HA powders at 1000 °C has enabled us to establish the influence of the treatment time on the phase composition of the powders and establish the following sequence of phase transformations: Ca₁₀(PO₄)₆(OH)₂→β-Ca₃(PO₄)₂ (t_milling~2 h), β-Ca₃(PO₄)₂→α-Ca₃(PO₄)₂ (t_milling~5 h), β-,α-Ca₃(PO₄)₂→Ca₁₀(PO₄)₆(OH)₂ (t_milling~7 h).The mechanosynthesis and mechanotreatment of hydroxyapatite in steel drums with steel balls is accompanied by the contamination of hydroxyapatite by their wear debris (iron + manganese). A large part of oxidized iron forms superparamagnetic inclusions distributed in HA powder. A small part of Fe³⁺ and Mn²⁺ ions from the steel wear debris enters into the hydroxyapatite lattice, substituting Ca²⁺ ions. As a result, a nanocomposite powder consisting of hydroxyapatite, alloyed by Fe³⁺ and Mn²⁺ ions and ferrite inclusions forms. The phase composition of HA powders, the degree of their alloying by Fe³⁺ and Mn²⁺ ions, and the content of ferrite inclusions can be controlled by changing the time of mechanotreatment.