Structure and Magnetic Properties of Nickel–Zinc Ferrite Nanoparticles Prepared by Glass Crystallization Method

Summary. The magnetic and microstructure properties of Fe₂O₃–0.4NiO–0.6ZnO–B₂O₃ glass system, which was subjected to heat treatment in order to induce a magnetic crystalline phase (Ni_0.4Zn_0.6-Fe₂O₄ crystals) within the glass matrix, were investigated. DSC measurement was performed to reveal the crystallization temperature of the prepared glass sample. The obtained samples, produced by heat treatment at 765°C for various times (1, 1.5, 2, and 3 h), were characterized by X-ray diffraction, IR spectra, transmission electron microscopy, and vibrating sample magnetometer. The results indicated the formation of spinel Ni–Zn ferrite in the glass matrix. Particles of the ferrite with sizes ranging from 28 to 120 nm depending on the sintering time were observed. The coercivity values for different heat-treatment samples were found to be in the range from 15.2 to 100 Oe. The combination of zinc content and sintering times leads to samples with saturation magnetization ranging from 12.25 to 17.82 emu/g.     

Structure and Magnetic Properties of Nickel–Zinc Ferrite Nanoparticles Prepared by Glass Crystallization Method

The magnetic and microstructure properties of Fe₂O₃–0.4NiO–0.6ZnO–B₂O₃ glass system, which was subjected to heat treatment in order to induce a magnetic crystalline phase (Ni_0.4Zn_0.6-Fe₂O₄ crystals) within the glass matrix, were investigated. DSC measurement was performed to reveal the crystallization temperature of the prepared glass sample. The obtained samples, produced by heat treatment at 765°C for various times (1, 1.5, 2, and 3 h), were characterized by X-ray diffraction, IR spectra, transmission electron microscopy, and vibrating sample magnetometer. The results indicated the formation of spinel Ni–Zn ferrite in the glass matrix. Particles of the ferrite with sizes ranging from 28 to 120 nm depending on the sintering time were observed. The coercivity values for different heat-treatment samples were found to be in the range from 15.2 to 100 Oe. The combination of zinc content and sintering times leads to samples with saturation magnetization ranging from 12.25 to 17.82 emu/g.     

Electrochemical study of manganese and iron compounds at carbon paste electrodes with electrolytic binder. Application to the characterization of manganese ferrite

An electrochemical study of several solids, such as MnCl₂ · 4 H₂O_(s), MnF_3(s), Fe₂O_3(s), Fe₃O_4(s) and MnO_2(s), using carbon paste electrodes with electrolytic binders, is described. Results obtained have been compared with results of earlier electrochemical experiments to carry out the characterization of technological material, such as manganese ferrite. The voltammograms obtained represent the “electrochemical spectra” of solid or dissolved substances that can be used to characterize the material without previous solubilization, as charge transfer processes can proceed in the solid or dissolved state, depending on the solubility in the binder used. Received: 9 December 1996 / Accepted: 14 April 1997     

Reactivity of nanoparticles; interaction between zinc and copper oxide nanoparticles and iron ions in an alkaline medium

The reactivity of zinc and copper oxide nanoparticles was investigated upon their interaction with iron oxides. It was ascertained that, depending on the reaction conditions, nanoparticles of zinc and copper ferrites (ZnFe₂O₄ and CuFe₂O₄) or core/shell nanoparticles (Fe₃O₄/ZnO) are produced. Size, composition, and structure of the resulting nanoparticles were determined by transmission electron microscopy and X-ray diffraction analysis. The average size of zinc and copper ferrite nanoparticles was ascertained to be 9–10 and 2–3 nm, respectively. For core/shell Fe₃O₄/ZnO nanoparticles, the average size is 20 nm. It was experimentally proved that the photoluminescence radiative characteristics of ZnO nanoparticles are retained in core/shell Fe₃O₄/ZnO nanoparticles.     

Synthesis and Properties of Complexes of Lead(II), Cadmium(II), and Zinc(II) with N-Phosphonomethylglycine

Summary.  Sparingly water soluble complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine (glyphosate, NPMG) of the general formulae C₃H₆O₅NPPb, C₃H₆O₅NPCdċ2H₂O, and C₃H₆O₅NPZn were synthesized. The complexes were also precipited from a dilute Roundup solution, and their solubility in water was determined. Thermal, diffractometric, and IR spectrophotometric analyses were carried out. It was found that the metal is bonded to glyphosate through the oxygen atoms of the carboxylic and phosphonate groups; metal-nitrogen binding is absent in the above compounds. Studying the complexing behaviour in solution by UV spectrophotometry pointed out that a complex of the composition Pb(II) : NPMG=1:1 with an absorption band at 232 nm is formed. Its stability constant as determined by Job’s method is logK=5.9±0.1. Using potentiometric techniques, the dissociation constant of N-phosphonomethylglycine and the stability constants of its complexes with cadmium (II) and zinc (II) were determined. Received June 30, 1999/Accepted July 21, 1999.     

Solubility Measurements of Crystalline Cu<Subscript>2</Subscript>O in Aqueous Solution as a Function of Temperature and pH

The equilibrium solubility of crystalline cuprous oxide, cuprite, was measured in liquid water and steam using two flow-through reactors and a conventional batch autoclave. These measurements were carried out from 20 to 400 °C. Different batches of pretreated cuprite were thoroughly characterized prior to and following each set of experiments. Metallic copper beads were added to the inlet end of the reactors and to the solid charge in the autoclave to preserve the Cu(I) oxidation state, although one series of experiments produced some results which were only compatible with CuO(cr) as the solubility limiting phase. Comparison of the solubility data for Cu₂O(cr) in aqueous solution with those from the only available high-temperature dataset (Var’yash, Geochem. Int. 26:80–90, 1989) showed that in near-neutral solutions the new data are lower by about four orders of magnitude at 350 °C. Moreover, the dominant species in solution at temperatures ≥100 °C were found to be only Cu⁺ and Cu(OH)₂^-\mathrm{Cu(OH)}_{2}^{-} with Cu(OH)⁰ occurring over a narrow pH range at ≤75 °C rather than the reverse trend reported previously. Solubility equations were developed as a function of temperature and pH, based on these new results, which showed increased solubility with temperature in acidic and basic solutions. The solubility of Cu₂O(cr) in steam decreased slightly with temperature and as expected increased with increasing pressure to supercritical conditions where limited, compatible data were available in the literature. The solubility at subcritical conditions was on the order of one to several parts per billion, ppb. A simple empirical fit was derived for the solubility in steam as a function of temperature and pressure.     

Enhancing the Photo and Biomedical Activity of ZnO by Incorporation with Zinc Silicate Nanocomposites

Highly active and non-toxic ZnO incorporated with zinc silicate (zinc silicate/ZnO) nanocomposites are synthesized via a simple and low-cost hydrothermal method followed by heat treatment. Different molar ratios from Si to Zn [1:20], [1:10], [1:8] and [1:6] are used to prepare different zinc silicate/ZnO nano composite materials which are assigned to ZS1, ZS2, ZS3 and ZS4 samples, respectively. The effect of calcination times and temperatures have been investigated on the crystallographic and morphological properties of the synthesized nano composite materials. The XRD analysis show that at very low molar ratios, zincite (ZnO) is the most predominant phase. However, at higher molar ratios, there are two phases coexist; hemimorphite (Zn₄Si₄O₇) and zincite. The TEM images show a uniform nanoplate-like shaped morphology from ZnO with well dispersed Zn₂SiO₄ nanoparticles. The S_BET is remarkably increased from 18.14 to 176.5 m².g⁻¹ by calcination up to 400 °C and then decreased to 72.2 m². g⁻¹ by further increasing in the calcinations temp up to 1,000 °C. The bio and photocatalytic activities of the composite nanomaterials have been investigated. Compared with the pure ZnO, the nano composites have been demonstrated as better photocatalysts for the degradation of Levafex golden yellow (LGY) dye as a model of organic dye pollutant under simulated sunlight irradiation. Moreover, the nano composites were evidenced to possess better and non-toxic antitumor activity towards hepatocellular carcinoma cell lines with (IC₅₀ = 11.2 μg.ml⁻¹ and LD₅₀ ˃ 50 mg. Kg⁻¹).     

Low-temperature synthesis and characterization of the Mn–Zn ferrite

Nanocrystalline ferrite with the composition: Mn_0.6Zn_0.4Fe₂O₄ was synthesized by two-stage route: the precipitation of Zn, Mn and Fe hydroxides from sulphates solution and the synthesis of a precursor by the sol–gel auto-combustion method. The ferrite powder obtained from the gel by ashing was sintered under air at a temperature of 720, 1150 and 1300 °C. The composition and morphology of the as-obtained phases were examined by ICP-AES, TG/DTA, XRD, FTIR, SEM and low-temperature nitrogen adsorption (BET). It was found that the spinel phase forms after gel combustion. The nanometric ferrite powder obtained as a result of the combustion is soft-agglomerated. The zinc content in the ferrite during ashing and auto-combustion is lower by about 21 mol% than the assumed one and the final product turn out to be Mn_0.68Zn_0.32Fe₂O₄.     

Thermogravimetric investigation of the effect of annealing conditions on the soft ferrite phase homogeneity

In the present work, the conventional method of increasing the efficiency of solid-phase synthesis of lithium–zinc ferrites that involves multiple intermediate grinding of briquetted reaction mixtures annealed at high temperatures is compared with a new radiation-thermal (RT) method using a high-power pulsed beam of accelerated electrons for heating of reaction mixtures. An analysis of the TG(M)/DTG(M) curves recorded in a magnetic field demonstrates that the efficiency of Li_0.3Zn_0.4Fe_2.3O₄ synthesis from Li₂CO₃–Fe₂O₃–ZnO mechanical mixture at a temperature of 700 °C during 120 min is equivalent to thermal annealing at 800 °C, but with the triple annealing duration.     

Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn_0.5Ni_0.5Fe₂O₄/Fe type were synthesized starting from nanocrystalline Mn_0.5Ni_0.5Fe₂O₄ (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn_0.5Ni_0.5Fe₂O₄/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn_0.5Ni_0.5Fe₂O₄/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe_1?xMn_xFe₂O₄/Ni–Fe composite type. The new formed ferrite of Fe_1?xMn_xFe₂O₄ type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe_1?xMn_xFe₂O₄, Ni structure, FeO, and (NiO)_0.25(MnO)_0.75 phases.     

Effects of strontium silicate on structure and magnetic properties of electrospun strontium ferrite nanofibers

The composite nanofibers of xSrSiO₃/(100 − x)SrFe₁₂O₁₉ (x = 0–13 wt%) with diameters around 110 nm have been prepared by calcination of the electrospun SrSiO₃/SrFe₁₂O₁₉/poly (vinyl pyrrolidone) (PVP) composite fibers at 800–900 °C. The composite nanofibers were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. After calcined at 800° the M-type strontium ferrite is formed and the strontium silicate exists as an amorphous state when the calcination temperature below about 950 °C. The addition of SrSiO₃ has an obvious suppression effect on the strontium ferrite grain growth and the ferrite grain size decreases from 66.9 to 33.5 nm corresponding SrSiO₃ content from 0 to 9 wt% in the composite. The specific saturation magnetization (Ms) of the xSrSiO₃/(100 − x)SrFe₁₂O₁₉ composite nanofibers exhibits a continuous reduction from 58.0 to 45.6 A m² kg⁻¹ with the increase of SrSiO₃ content from 0 to 13 wt%. With addition of SrSiO₃ from 0 to 13 wt%, the coercivity of the composite nanofibers obtained at 900 °C initially increases, reaching a maximum value 501.1 kA m⁻¹ at the silicate content 7 wt%, and then shows a reduction tendency with the strontium silicate content increase further up to 13 wt%. This influence on the coercivity by strontium silicate can be attributed mainly to the ferrite grain growth suppression and the non-magnetic phase barrier for the domains misalignment.     

Physico-chemical Studies on Zinc Hexa(formato)ferrate(III) Decahydrate

Thermal analysis of zinc hexa(formato)ferrate(III) decahydrate, Zn₃ [Fe(HCOO)₆]₂ 10H₂O has been investigated up to 800°C in static air atmosphere employing TG, DSC, XRD, IR, ESR and Mössbauer spectroscopic techniques. After dehydration at 160°C, the anhydrous complex decomposes into α-Fe₂ O₃ and zinc carbonate in successive stages. Subsequently the cations remix to yield fine particles of zinc ferrite, ZnFe₂ O₄ , as a result of solid state reaction between α-Fe₂ O₃ and zinc carbonate at a temperature (600°C) much lower than for ceramic method.     

Electrochemical properties of perovskite and A<Subscript>2</Subscript>MO<Subscript>4</Subscript>-type oxides used as cathodes in protonic ceramic half cells

Three selected materials have been prepared and shaped as cathode of half cells using the proton-conducting electrolyte BaCe_0.9Y_0.1O_3 − δ (BCY10): two perovskite compounds, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ (BSCF) and La_0.6Sr_0.4Fe_0.8Co_0.2O_3 − δ (LSFC), and the praseodymium nickelate Pr₂NiO_4 + δ (PRN) having the K₂NiF₄-type structure. The electrochemical properties of these compounds have been studied under zero current conditions (two-electrode cell) and under polarization (three-electrode cell). Their measured area-specific resistances were about 1–2 Ω cm² at 600 °C. Under direct current polarization, it appears that the three compounds show almost similar values of current densities at 625 °C; however, at lower temperatures, BSCF appears to be the most efficient cathode material.     

Low-temperature sol-gel synthesis of modified nickel ferrite

A low-temperature method has been developed for preparing nickel ferrite doped with cobalt and copper (Ni_0.9Co_0.1Cu_0.1Fe_1.9O_{4 − δ}). This method provides the target product at 170–200°C with nanosized particles. The role of ammonium nitrate in the considerable reduction of ferrite synthesis temperature was studied.     

Mechanism of NiZn ferrite formation

The regularities in the change of character of the ferrite formation process as a function of Ni_1?xZn_xFe₂O₄ solid solution and of the degree of zinc oxide saturation of the Ni_1?xZn_xO solid solution (x = 0.14; 0.29; 0.43) are established in the temperature range 1220–1305°C. It is shown that in the reaction zone of interacting NiO, (Ni, ZnO), or ZnO with Fe₂O₃ the ferrite phase crystallizes only on iron oxide. The distribution of the Fe, Ni, and Zn concentrations over the reaction layer thickness using electron probe and X-ray spectrum analysis is obtained. The interdiffusion coefficients over the investigated temperature range calculated in the (Ni, Zn, Fe)O and ferrite phases change from (0.8 – 7.0) × 10^?9 to (1.0 – 12.0) × 10^?10 cm²/sec, respectively. The interaction of (Ni, Zn)O with Fe₂O₃ takes place by the mechanism of interaction of interdiffusion of Fe³⁺, Fe²⁺ and Ni²⁺, Zn²⁺ along with a current of Zn²⁺ ions and electrons or oxygen ions directed to the $\text{ferrite}\text{Fe}{}_2\text{O}{}_3$ interface.     

New Measurements of the Solubility of Zinc Oxide from 150 to 350°C

The solubility of zincite (ZnO) has been re-evaluated in noncomplexing solutions over a wide range of pH and from 150 to 350°C at pressures ranging from slightly above saturation vapor pressure to significantly higher pressures in NaOH, NH₃, F₃CSO₃H/F₃CSO₃ Na (HTr/NaTr), CH₃COOH/NaOH, and HTr/NH₃ solutions using a hydrogen-electrode concentration cell (HECC) and a flow-through cell with downstream acid injection. The new results, coupled with our earlier results at 75–100°C, indicate that the solubility of zinc oxide is higher than we recently reported,⁽¹⁾ but substantially lower than previous estimates available in the scientific literature. It is believed that deposition of ZnO or a zinc hydroxide phase must have occurred near the solubility minimum in the HECC sample lines in our earlier study; a problem that is overcome in the flow cell by injecting acid into the sample line before the solution is depressurized and cooled to room temperature.     

Phase Equilibria in the Ternary System Fe-Gd-Mo at 600 °C

 Phase equilibria in the ternary system Fe-Gd-Mo at 600 °C were determined. The phase composition for different element concentrations were quantitatively determined from the diffraction patterns by means of the multi-phase Rietveld-refinement as well as through evaluation of the microstructure images obtained by the scanning electron microscopy. Both methods are compared with each other with respect to their precision and limitations. The complete isothermal section at 600 °C includes one ternary phase τ (ThMn₁₂-type of structure), four pseudo-binary phases (Fe,Mo)₁₇Gd₂, (Fe,Mo)₂₃Gd₆, (Fe,Mo)₃Gd and (Fe,Mo)₂Gd and binary phases Fe₂Mo and μ-(Fe,Mo). The ternary phase τ forms the tie-lines with the solid solutions α-Fe, (Mo)-, Fe₂Mo and μ-(Fe,Mo) phases as well as with the pseudo-binary Fe-Gd compounds. Three phases (Fe,Mo)₂Gd, (Mo) and Gd coexist in a wide concentrations range. The homogeneity region of the ternary phase τ as well as the solubilities of the third element in the binary phases were determined.     

Thermal Characterization and Physico-Chemical Properties of Fe2O3−Mn2O3/Al2O3 Systems

The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al₂O₃ and Fe₂O₃/Al₂O₃ systems has been studied separately. The pure and doped mixed solids were thermally treated at 400–1000°C. Pyrolysis of pure and doped mixed solids was investigated via thermal analysis (TG-DTG) techniques. The thermal products were characterized using XRD-analysis. The results revealed that pure ferric nitrate decomposes into Fe₂O₃ at 350°C and shows thermal stability up to1000°C. Crystalline Fe₃O₄ and Mn₃O₄phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al₂O₃ phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al₂O₃ phase at1000°C. Crystalline MnAl₂O₄ and MnFe₂O₄ phases were formed at 1000°C as a result of solid–solid interaction processes. The catalytic behavior of the thermal products was tested using the decomposition of H₂O₂ reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation of Cr2O3-Al2O3 Solid Solutions by Reactive Magnetron Sputtering

 (Al,Cr)₂O₃ layers were deposited on cemented carbide insert tips at a substrate temperature of 500 °C by means of reactive magnetron sputtering. An Al target was sputtered in RF mode and a Cr target in DC mode simultaneously in an oxygen/argon plasma. The influence of the Al and Cr sputter power and of the oxygen partial pressure on composition and structure of the (Al,Cr)₂O₃ layers as well as on the binding states of their components were investigated. Special attention was paid to the interpretation of the O ls and O-KLL fine structure and peak shifts. For the binary phases γ-Al₂O₃ and Cr₂O₃, a good agreement with literature values was observed in each case. In case of the ternary phases a continuous shift of the energetic position of the O1s peak, the O-KL₂₃L₂₃ transition and the modified Auger parameter α ′ of oxygen between the two binary phases γ-Al₂O₃ and Cr₂O₃ could be detected, indicating a wide range of solid solubility between Al₂O₃ and Cr₂O₃. As revealed by grazing incidence X-ray diffraction, the crystallinity of the ternary phases is less pronounced as compared to the binaries and increases with increasing oxygen flow rate.     

Optimization on fabrication and performance of A-site-deficient La0.58Sr0.4Co0.2Fe0.8O3-δ cathode for SOFC

A-site-deficient perovskite cathode material La_0.58Sr_0.4Co_0.2Fe_0.8O_3 − δ (L58SCF) is coated on the yttria-stabilized zirconia electrolyte by screen-printing technique. Several key fabrication parameters including selection of additives (binder and pore former), effect of coating thickness, sintering temperature and time on the microstructure, and electrochemical performance of cathode are investigated by scanning electron microscopy and electrochemical impedance spectroscopy. We study the microstructure and the electrochemical property of the cathode with different kinds of additives. Results show that the cathode possesses fine microstructure, enough porosity, and ideal electrochemical property when polyvinyl butyral serves as both binder and pore former in the cathode. The cathode with three screen-printing coats (thickness 28 ± 7 μm, weight 6.07 ± 0.72 mg cm⁻²) sintering at 1,000 °C for 2 h shows lower polarization resistance of 0.183 Ω cm² at 800 °C. Based on the optimized parameters, the polarization resistances of the L58SCF–Ce_0.8Gd_0.2O_{1.9 – δ} composite cathode display the R _p values of 0.067 Ω cm² at 800 °C, 0.106 Ω cm² at 750 °C, 0.225 Ω cm² at 700 °C, and 0.550 Ω cm² at 650 °C.