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1.
We adopt an improved co-precipitation method to prepare the Fe3O4 magnetic nanoparticles (MNPs). Influence factors such as the reaction temperature, the pH value of the solution, and the Fe3+/Fe2+ molar concentration are considered. Via the transmission electronic microscope and X-ray diffractometry, we characterize the dispersibility and size of the products. The reaction temperature and the pH value of the solution have a great influence in the dispersibility and size of MNPs. The diameter of Fe3O4 MNP, produced under Fe3+/Fe2+ molar concentration of 0.25 mole/l and molar ratio of 1.9:1, the reaction temperature is 80 °C, and the pH value reaches 9, is close to 11 nm. Above all, considering the variation of molar concentrations in Fe3+/Fe2+, the linear birefringence and dichroism of the kerosene-based ferrofluids are investigated by a Stokes polarimeter.  相似文献   

2.
We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe12O19) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe3+, Fe2+ and Sr2+ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe2O3) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe2O3) by a topotactic transition. The final product of strontium hexaferrite (SrFe12O19) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.  相似文献   

3.
Phosphors of (Y0.75Gd0.25)2O3:Eu3+ (5 at.%) have been prepared through soft chemistry routes. Conversion of the starting nitrates mixture into oxide is performed through two approaches: (a) hydrothermal treatment (HT) at 200 °C/3 h of an ammonium hydrogen carbonate precipitated mixture and (b) by thermally decomposition of pure nitrate precursor solution at 900 °C in dispersed phase (aerosol) within a tubular flow reactor by spray pyrolysis process (SP). The powders are additionally thermally treated at different temperatures: 600, 1000, and 1100 °C for either 3 or 12 h. HT—derived particles present exclusively one-dimensional morphology (nanorods) up to the temperatures of 600 °C, while the leaf-like particles start to grow afterward. SP—derived particles maintain their spherical shape up to the temperatures of 1100 °C. These submicron sized spheres were actually composed of randomly aggregated nanoparticles. All powders exhibits cubic Ia-3 structure (Y0.75Gd0.25)2O3:Eu and have improved optical characteristics due to their nanocrystalline nature. The detailed study of the influence of structural and morphological powder characteristics on their emission properties is performed based on the results of X-ray powder diffractometry, scanning electron microscopy, X-ray energy dispersive spectroscopy, transmission electron microscopy, and photoluminescence measurements.  相似文献   

4.
The phase transformation of strontium hexagonal ferrite (SrFe12O19) to magnetite (Fe3O4) as main phase and strontium carbonate (SrCO3) as secondary phase is reported here. SrFe12O19 powder was obtained by a heat treatment at 250 °C under controlled oxygen flow. It was observed that the phase transformation occurred when the SrFe12O19 ferrite was heated up to 625 °C in confinement conditions. This transformation took place by a combination of three factors: the presence of stresses in the crystal lattice of SrFe12O19 due to a low synthesis temperature, the reduction of Fe3+ to Fe2+ during the heating up to 625 °C, and the similarity of the coordination spheres of the iron atoms present in the S-block of SrFe12O19 and Fe3O4. X-ray diffraction analysis confirmed the existence of strain and crystal deformation in SrFe12O19 and the absence of them in the material after the phase transformation. Dispersive X-ray absorption spectroscopy and Fe57 Mössbauer spectroscopy provided evidences of the reduction of Fe3+ to Fe2+ in the SrFe12O19 crystal.  相似文献   

5.
YAG and YIG crystals implanted respectively with 100 keV57Fe2+ ions (1 × 1017 ions.cm?2) and 50 keV27Al ions (1.1 × 1017 ions.cm?2) have been studied by conversion electron Mössbauer spectroscopy (CEMS) directly after implantation and after annealings in air at temperatures up to 1100°C. In both as-implanted samples iron is found mainly in three states: Fe2+, Fe3+ and small metallic precipitates. Annealing behaviour is divided into two stages: (i) up to 400°C the iron has become completely oxidized and (ii) between 400 and 850°C the epitaxial regrowth of the implanted layer takes place. During this process a part of iron ions are incorporated into octahedral and tetrahedral sites, thus making a Y3 (Al Fe)5 O12 compound. The remaining iron part precipitates in the form of Fe2O3 particles.  相似文献   

6.
Nanostructured nickel ferrites (NiFe2O4) were prepared by doping with Ti4+ ions using solid-state reaction route. Lowest grain size of 55 nm was achieved in the specimens with 20 mole% TiO2 doping. Magnetization in the specimens decreases with decreasing grain sizes. Lower volume fractions of ferrite phase due to dissociation of the magnetic phase into smaller particles by the disruption of super exchange interaction by the titanium substitution results a decrease in magnetizations. Coercivity showed an increasing trend. This was explained as arising due to multidomain/monodomain magnetic behavior of magnetic nanoparticles. Small polaron hopping conduction between Fe2+ and Fe3+ sites controls the dc electrical properties of the specimens. The presence of an interfacial amorphous phase between the sites is evident from Mott's analysis. Specimens containing 10 mole or more TiO2 and sintered at 1350 °C contain NiTiO3 as a secondary phase and show unusual dc conductivity.  相似文献   

7.
This article describes a method for preparing CuO nanoparticles in aqueous solution, and a demonstration of feasibility of metallic bonding with the use of the CuO particles. Colloid solution of CuO nanoparticles was prepared from Cu(NO3)2 aqueous solution (0.01 M) and NaOH aqueous solution (0.019 M) at 5–80 °C. Leaf-like aggregates with an average size of 567 nm composed of CuO nanoparticles were produced at 20 °C. The size of leaf-like aggregates decreased with increasing reaction temperature. Metallic copper discs could be bonded using the CuO nanoparticles under annealing at 400 °C and pressurizing at 1.2 MPa for 5 min in H2 gas. A shear strength required for separating the bonded discs was 25.4 MPa for the CuO nanoparticles prepared at 20 °C, whose aggregates were the largest among the CuO particles examined. These results indicated that the formation of leaf-like aggregates of CuO nanoparticles led to efficient metallic bonding.  相似文献   

8.
Stoichiometric Ni-bearing ferrite was formed by air oxidation of an iron(II) hydroxide suspension at an initial Ni : Fetot mol ratio (rNi) of 0.20 : 2.80 at pH 10.0 and 65°C. Most of products formed at rNi=0.40 : 2.60 and 0.60 : 2.40 were Ni-bearing ferrites, of which vacancies of Fe3+ ion on the lattice points may be considered. Only Ni, Zn-bearing ferrites were formed in the suspensions at initial (Ni + Zn)  : Fetot mol ratios (rNi + Zn) of 0.20 : 2.80–0.60 : 2.40 at pH 10.0 and 65°C. At higher rNi or rNi + Zn by-products containing Ni, Fe and O42− were formed. The formation of the by-products was depressed in the suspensions containing chloride ions in the place of sulfate ions.  相似文献   

9.
Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) with much improved peroxidase-like activity were successfully prepared through an advanced reverse co-precipitation method under the assistance of ultrasound irradiation. The characterizations with XRD, BET and SEM indicated that the ultrasound irradiation in the preparation induced the production of Fe3O4 MNPs possessing smaller particle sizes (16.5 nm), greater BET surface area (82.5 m2 g?1) and much higher dispersibility in water. The particle sizes, BET surface area, chemical composition and then catalytic property of the Fe3O4 MNPs could be tailored by adjusting the initial concentration of ammonia water and the molar ratio of Fe2+/Fe3+ during the preparation process. The H2O2-activating ability of Fe3O4 MNPs was evaluated by using Rhodamine B (RhB) as a model compound of organic pollutants to be degraded. At pH 5.4 and temperature 40 °C, the sonochemically synthesized Fe3O4 MNPs were observed to be able to activate H2O2 and remove ca. 90% of RhB (0.02 mmol L?1) in 60 min with a apparent rate constant of 0.034 min?1 for the RhB degradation, being 12.6 folds of that (0.0027 min?1) over the Fe3O4 MNPs prepared via a conventional reverse co-precipitation method. The mechanisms of the peroxidase-like catalysis with Fe3O4 MNPs were discussed to develop more efficient novel catalysts.  相似文献   

10.
Using conversion electron Mossbauer spectroscopy(CEMS) and slow positron beam, the chemical states of the implanted 57Fe (100KeV,3 × 10 16 ions/cm 2) in ZrO2 containing 3 mol% Y 2O 3( ZY 3) and its thermodynamic behavior during annealing process with the temperature from 200 to 500°C were studied. After annealing at 400°C the complex of Fe3+-V has been mostly dissolved, and the prior phase to α-Fe and α-Fe nano-crystalline cluster were present in the sample. Meanwhile the mixed conducting of oxygen-ions and electrons in the ZY3 containing Fe sample appeared. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

11.
Magnetic properties, arising from surface exchange and interparticle interactions of the Fe3O4 (magnetite) nanoparticles, were investigated in the temperature range of 5–300 and 120–300 K using vibrating sample magnetometer technique and electron spin resonance spectroscopy, respectively. The research was based on to figure out the origin of intraparticle interactions and the change of interparticle interactions in wide size range Fe3O4 nanoparticles. The analyses were done for samples having almost same particle size distributions. The average particle sizes were changed in between 30 ± 2 and 34 ± 2 nm. The observed magnetization values were demonstrated the mixture of single-domain size particles, exhibiting both single-domain (SD) and superparamagnetic (SPM) states. The symmetry of resonance curves changed according to the ratio of SD and SPM-stated particles in mixture under located temperature. The changes of anisotropy up to domain state were understood by freezing magnetic moment in glycerol matrix from room temperature to 120 K under 5-kG field. The shift of H R values to higher magnetic fields and the more symmetric resonance spectrum proved the effect of anisotropy and interparticle interactions fields on magnetic behave. In addition, the origin of intra-interaction was exposed from Fe3+ centers and exchange coupling in between Fe2+, Fe3+, and O, and Fe3+ centers found from g factor (g).  相似文献   

12.
In this paper, data concerning the effect of pH on the morphology of Ag–TiO2 nanocomposite during photodeposition of Ag on TiO2 nanoparticles is reported. TiO2 nanoparticles prepared by sol–gel method were coated with Ag by photodeposition from an aqueous solution of AgNO3 at various pH levels ranging from 1 to 10 in a titania sol, under UV light. The as-prepared nanocomposite particles were characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and N2 adsorption/desorption method at liquid nitrogen temperature (−196 °C) from Brunauer–Emmett–Teller (BET) measurements. It is shown that at a Ag loading of 1.25 wt.% on TiO2, a high-surface area nanocomposite morphology corresponding to an average of one Ag nanoparticle per titania nanoparticle was achieved. The diameter of the titania crystallites/particles were in the range of 10–20 nm while the size of Ag particles attached to the larger titania particles were 3 ± 1 nm as deduced from crystallite size by XRD and particle size by TEM. Ag recovery by photo harvesting from the solution was nearly 100%. TEM micrographs revealed that Ag-coated TiO2 nanoparticles showed a sharp increase in the degree of agglomeration for nanocomposites prepared at basic pH values, with a corresponding sharp decrease in BET surface area especially at pH > 9. The BET surface area of the Ag–TiO2 nanoparticles was nearly constant at around a value of 140 m2 g−1 at all pH from 1–8 with an anomalous maximum of 164 m2 g−1 when prepared from a sol at pH of 4, and a sharp decrease to 78 m2 g−1 at pH of 10.  相似文献   

13.
Ionoluminescence (IL) and photoluminescence (PL) spectra for different rare earth ions (Sm3+ and Dy3+) activated YAlO3 single crystals have been induced with 100 MeV Si7+ ions with fluence of 7.81×1012 ions cm?2. Prominent IL and PL emission peaks in the range 550–725 nm in Sm3+ and 482–574 nm in Dy3+ were recorded. Variation of IL intensity in Dy3+ doped YAlO3 single crystals was studied in the fluence range 7.81×1012–11.71×1012 ions cm?2. IL intensity is found to be high in lower ion fluences and it decreases with increase in ion fluence due to thermal quenching as a result of an increase in the sample temperature caused by ion beam irradiation. Thermoluminescence (TL) spectra were recorded for fluence of 5.2×1012 ions cm?2 on pure and doped crystals at a warming rate of 5 °C s?1 at room temperature. Pure crystals show two glow peaks at 232 (Tg1) and 328 °C (Tg2). However, in Sm3+ doped crystals three glow peaks at 278 (Tg1), 332 (Tg2) and 384 °C (Tg3) and two glow peaks at 278 (Tg1) and 331 °C (Tg2) in Dy3+ was recorded. The kinetic parameters (E, b s) were estimated using glow peak shape method. The decay of IL intensity was explained by excitation spike model.  相似文献   

14.
《Solid State Ionics》2006,177(13-14):1199-1204
Perovskite oxides of the composition BaxSr1−xCo1−yFeyO3−δ(BSCF) were synthesized via a modified Pechini method and characterized by X-ray diffraction, dilatometry and thermogravimetry. Investigations revealed that single-phase perovskites with cubic structure can be obtained for x  0.6 and 0.2  y  1.0. The as-synthesized BSCF powders can be sintered in several hours to nearly full density at temperatures of over 1180 °C. Thermal expansion curves of dense BSCF samples show nonlinear behavior with sudden increase in thermal expansion rate between about 500 °C and 650 °C, due mainly to the loss of lattice oxygen caused by the reduction of Co4+ and Fe4+ to lower valence states. Thermal expansion coefficients (TECs) of BSCF were measured to be 19.2–22.9 × 10 6 K 1 between 25 °C and 850 °C. Investigations showed further that Ba0.5Sr0.5Co0.8Fe0.2O3−δ is chemically compatible with 8YSZ and 20GDC for temperatures up to 800 °C, above which severe reactions were detected. After being heat-treated with 8YSZ or 20GDC for 5 h above 1000 °C, Ba0.5Sr0.5Co0.8Fe0.2O3−δ was completely converted to phases like SrCoO3−δ, BaCeO3, BaZrO3, etc.  相似文献   

15.
Zn/Fe oxide compound powders were obtained by the hydrothermal method using ferric nitrate Fe(NO3)3·9H2O and zinc nitrate Zn(NO3)2·6H2O at 200 °C and different precursor molar ratios x = Fe3+/Zn2+ equal to 2.8/0.2, 2.5/0.5, 1.8/1.2 and 1.5/1.5. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray analysis (SEM–EDAX). Room temperature measurements of the frequency dependence of the complex magnetic permeability and complex dielectric permittivity, over the frequency range from 0.1 to 6 GHz, were performed. For precursor molar ratios x = 2.8/0.2, x = 1.8/1.2 and x = 1.5/1.5 the obtained samples showed a ferromagnetic-like resonance behaviour. This behaviour was assigned to the prevalent compounds in the obtained samples, Fe2O3 (for x = 2.8/0.2) and ZnFe2O4 (for x = 1.8/1.2 and x = 1.5/1.5). Based on the magnetic and dielectric measurements, the microwave absorbent properties of the four samples were analysed, and the sample containing mostly of ZnFe2O4 (for x = 1.8/1.2) was found to be the best electromagnetic absorber in the frequency range 1.36–6 GHz.  相似文献   

16.
Several Co and Fe and mixed Co, Fe molydates have been studied by Mössbauer spectroscopy at 360–415°C in a flow C3H6+O2+N2 100/100/560 Torr, with and without adding Bi2 (MoO4)3. It is concluded that cobalt stabilizes Fe2+ sites and Bi2(MoO4)3 stabilizes Fe3+ in solid solution and it is proposed that Fe2+?Fe3+ pairs act as active sites in propene mild oxidation.  相似文献   

17.
《Solid State Ionics》2006,177(26-32):2413-2416
NH4PO3–(NH4)2SiP4O13 composite, a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C, was synthesized with a solid-state reaction method. Electromotive forces (emfs) as measured with hydrogen concentration cells showed that the composite was a pure proton conductor at hydrogen partial pressure from 102 to 105 Pa. Its proton transference numbers were determined to be 1.0 at 150 °C, 0.99 at 200 °C, and 0.99 at 250 °C. Fuel cells that used NH4PO3–(NH4)2SiP4O13 as electrolytes were also fabricated. Maximum power density was 6.6 mW/cm2 at 250 °C when dry hydrogen and dry oxygen were used as the fuel and oxidant, respectively. Improved cell performance is expected by increasing cathode activity, increasing the electrolyte density, and decreasing the electrolyte thickness.  相似文献   

18.
On the enzymatic formation of platinum nanoparticles   总被引:1,自引:0,他引:1  
A dimeric hydrogenase enzyme (44.5 and 39.4 kDa sub units) was isolated in a 39.5% yield from the fungus Fusarium oxysporum and purified 4.64-fold by ion exchange chromatography on Sephacryl S-200. Characterisation of the enzyme afforded pH and temperature optima of 7.5 and 38 °C, respectively, a half-life stability of 36 min and a V max and K m of 3.57 nmol min−1 mL−1 and 2.25 mM, respectively. This enzyme was inhibited (non-competitively) by hydrogen hexachloroplatinic acid (H2PtCl6) at 1 or 2 mM with a K i value of 118 μM. Incubation of the platinum salt with the pure enzyme under an atmosphere of hydrogen and optimum enzyme conditions (pH 7.5, 38 °C) afforded <10% bioreduction after 8 h while at conditions suitable for platinum nanoparticle formation (pH 9, 65 °C) over 90% reduction took place after the same length of time. Cell-free extract from the fungal isolates produced nearly 90% bioreduction of the platinum salt under both pH and temperature conditions. The bioreduction of the platinum salt by a hydrogenase enzyme takes place by a passive process and not an active one as previously understood.  相似文献   

19.
In this work, α-Al2O3 doped either with Tb3+ or Tm3+ was prepared by combustion synthesis techniques for thermoluminescent (TL) ionizing radiation dosimetry applications. In this method, the reactants (aluminum nitrate, urea and therbium or thulium nitrate) are ignited in a muffle furnace at temperatures as low as 500 °C. This synthesis route is an alternative technique to the conventional fabrication methods of materials based on α-Al2O3 (Czochralsky, Vernuil), where high melting temperatures and reducing atmospheres are required. After combustion, the samples were annealed at temperatures ranging from 1000 to 1400 °C for 4 h in order to obtain the pure α-phase structure and were then irradiated with a Co-60 gamma radiation source. The annealed samples present a well defined TL glow peak with a maximum at approximately 200 °C and linear TL response in the dose range 0.5–5 Gy. It was observed that a 0.1 mol% concentration of Tb3+ or Tm3+ and annealing at 1400 °C optimize the TL sensitivity. The highest sensitivity was found for Tm3+ doped samples which were approximately 25 times more sensitive than Tb3+ doped samples. These results strongly suggest that combustion synthesis is a suitable technique to prepare doped aluminum oxide material and that Tm3+ doped aluminum oxide is a potential material for TL radiation dosimetry.  相似文献   

20.
LiCaAlF6 (LiCAF) crystals doped with two different ions (europium and lead) have been investigated as potential new dosimetric materials. The stability of thermally stimulated luminescence (TSL) glow peaks in LiCAF:Eu was evaluated by means of the initial rise technique. The decay times at room temperature of the traps related to the dosimetric glow peaks were found to range between 40 and 2 × 104 years confirming the good dosimetric characteristics of this crystal. The glow curve of LiCAF:Pb is dominated by a peak at approximately 300 °C emitting in the UV region (3P0,11S0 transition of Pb2+) superimposed to a very broad structure at lower temperature (20–200 °C) featuring recombination at an intrinsic defect centre. The anomalous behavior of the low temperature structure during thermal cleaning procedures prevented any reliable numerical analysis of the TSL glow peak at 300 °C.  相似文献   

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