共查询到20条相似文献,搜索用时 15 毫秒
1.
F. A. Kulikov A. S. Vanetsev G. P. Murav'eva A. L. Il'inskii N. N. Oleinikov Yu. D. Tret'yakov 《Inorganic Materials》2003,39(10):1074-1075
Fine-particle Fe2O3 is prepared via microwave processing of Fe(NO3)3 · nH2O, followed by low-temperature annealing. The particle size of the resulting -Fe2O3 is 5–6 nm after microwave processing and 80–110 nm after subsequent low-temperature heat treatment. 相似文献
2.
Iron(II) carboxylato-hydrazinates: Ferrous fumarato-hydrazinate (FFH), FeC4H2O4·2N2H4; ferrous succinato-hydrazinate (FSH), FeC4H4O4·2N2H4; ferrous maleato-hydrazinate (FEH), FeC4H2O4·2N2H4; ferrous malato-hydrazinate (FLH), Fein4H4O5·2N2H4; ferrous malonato-hydrazinate (FMH), FeC3H2O4·1.5N2H4·H2O; and ferrous tartrato-hydrazinate (FTH), FeC4H4O6·N2H4·H2O are being synthesized for the first time. These decompose (autocatalytically) in an ordinary atmosphere to mainly γ-Fe2O3, while the unhydrazinated iron(II) carboxylates in air yield α-Fe2O3, but the controlled atmosphere of moisture requires for the oxalates to stabilize the metastable γ-Fe2O3. The hydrazine released during heating reacts with atmospheric oxygen liberating enormous energy, N2H4 + O2 → N2 + H2O; ΔH2O = −621 kJ/mol, which enables to oxidatively decompose the dehydrazinated complex to γ-Fe2O3. The reaction products N2 + H2O provide the necessary atmosphere of moisture needed for the stabilization of the metastable oxide.
The synthesis, characterization and thermal decomposition (DTA/TG) of the iron(II) carboxylato-hydrazinates are discussed
to explain the suitability of γ-Fe2O3 in the ferrite synthesis. 相似文献
3.
Yassine El Mendili Nirina Randrianantoandro Jean-Marc Greneche Fabien Grasset 《Science and Technology of Advanced Materials》2016,17(1):597-609
The effects of laser irradiation on γ-Fe2O3 4 ± 1 nm diameter maghemite nanocrystals synthesized by co-precipitation and dispersed into an amorphous silica matrix by sol-gel methods have been investigated as function of iron oxide mass fraction. The structural properties of γ-Fe2O3 phase were carefully examined by X-ray diffraction and transmission electron microscopy. It has been shown that γ-Fe2O3 nanocrystals are isolated from each other and uniformly dispersed in silica matrix. The phase stability of maghemite nanocrystals was examined in situ under laser irradiation by Raman spectroscopy and compared with that resulting from heat treatment by X-ray diffraction. It was concluded that ε-Fe2O3 is an intermediate phase between γ-Fe2O3 and α-Fe2O3 and a series of distinct Raman vibrational bands were identified with the ε-Fe2O3 phase. The structural transformation of γ-Fe2O3 into α-Fe2O3 occurs either directly or via ε-Fe2O3, depending on the rate of nanocrystal agglomeration, the concentration of iron oxide in the nanocomposite and the properties of silica matrix. A phase diagram is established as a function of laser power density and concentration. 相似文献
4.
《Materials Research Bulletin》1987,22(4):513-520
The dehydration process of lepidocrocite, γ-FeOOH, induced by wet grinding procedures has been studied. Microcrystals of maghemite, γ-Fe2O3, are found in the product of ball-milling in hexane and cyclohexane media. In contrast, grinding in air leads to hematite α-Fe2O3. This change is accompanied by the development of a characteristic texture in which a slit-shaped porous system is present. On the other hand, mechanochemically prepared maghemite increases in its thermal stability. This fact has been attributed to the higher crystallinity of ground microcrystals as revealed by the values of crystallite size and microstrains. 相似文献
5.
K. S. Rane V. M. S. Verenkar R. M. Pednekar P. Y. Sawant 《Journal of Materials Science: Materials in Electronics》1999,10(2):121-132
Direct current electrical conductivity () measurements as a function of temperature have been carried out on -Fe2O3 prepared from precursors, iron (II) carboxylatohydrazinates, -FeOOH and hydrazinated -FeOOH. The conductivity variation obeys an Arrhenius equation, I = \oe- E / kT and the plots of log versus 1/T of the as prepared -Fe2O3, which are in general linear, during the very first heating up to 350°C and cooling to room temperature (RT) do not overlap. This indicates a hysteresis behavior of conductivity, thereby suggesting involvement of two different conductivity mechanisms. When the heat treated sample was equilibrated in a known partial pressure of moisture at 200°C and then conductivity measured from RT, the log plots during heating and cooling did not overlap and a hysteresis behavior similar to the as prepared -Fe2O3 is observed again in the conductivity. Water is considered to be crucial during the synthesis of -Fe2O3 through magnetite, Fe3O4. Protons, H+, are thought to be introduced in the spinel Fe3O4 making it defective and the oxidation product of this is -Fe2O3 which retains few protons in its spinel structure. From the structural similarity of such proton incorporated -Fe2O3 and lithium ferrite, LiFe5O8, (Fe3+)8 [Fe3+
12 Li1+
4]O32, a formula HFe5O8, (Fe3+)8 [Fe3+12H1+4]O32 is suggested. A hydrogen iron oxide of formula H1-xFe5+x3O8, where x 0.1 is probably formed as a maximum limit. Protons are removed during the very first heating of the as prepared sample in the present studies and hence the conductivity of proton free -Fe2O3 is different and therefore a hysteresis behavior is observed. Moisture equilibration reintroduces the protons. The lithiated samples in the present studies were found to substitute for protons in -Fe2O3 and no hysteresis behavior is observed in such samples even after moisture equilibration. 相似文献
6.
D. Andreeva T. Tabakova I. Mitov A. Andreev 《Journal of Materials Science: Materials in Electronics》1991,2(4):199-203
The influence of the main reaction parameters (temperature, pH and concentration) in the oxidative hydrolysis of iron (II) sulphate in an acid medium on the properties of the obtained -Fe2O3 and its applicability in ferrite production has been studied. The addition of manganese(II) ions catalyses the process in the homogeneous phase, probably by activation of oxygen. The obtained results are discussed within the framework of the assumed reaction mechanism, which includes an homogeneous reaction and a heterogeneous one with the participation of the oxidative hydrolysis product -FeOOH. 相似文献
7.
Titanium-doped -Fe2O3 has been prepared by the calcination of a solid formed by the addition of aqueous ammonia to an aqueous solution of titanium- and iron-containing salts and boiling the precipitate under reflux. As compared to pure -Fe2O3 made by similar methods, titanium-doped -Fe2O3 showed a higher surface area and a greater stability to reduction, thermal conversion to an -Fe2O3-related structure and the maintenance of a higher surface area during oxidation-reduction cycling. 相似文献
8.
K. S. Rane V. M. S. Verenkar P. Y. Sawant 《Journal of Materials Science: Materials in Electronics》1999,10(2):133-140
Electro-magnetic properties and microstructural characterization of MgFe2O4 synthesized by a ceramic technique at 1000°C from iron oxides, consisting of mainly -Fe2O3 and traces of alpha-Fe2O3, prepared from iron ore rejects, are compared with the ferrite obtained from commercial alpha-Fe2O3. The sources of -Fe2O3 are hydrazinated iron (II) carboxylates and iron oxyhydroxides which autocatalytically decompose giving mainly -Fe2O3 of uniform particles of 10–30 nm (by scanning electron microscopy (SEM) studies) having high surface area. The ferrite synthesized from such nanoparticle size -Fe2O3 gave a porosity of 25% with grains ranging from 0–3 m. On the other hand, MgFe2O4 obtained from commercial alpha-Fe2O3 grains (of 1–2 m size) gave particles of 0–6 m with a porosity 42%. Saturation magnetization values 922–1168 G are found for MgFe2O4 from -Fe2O3 source while the alpha-Fe2O3 source gave the lowest value, 609. The Curie temperature, Tc, from magnetic susceptibility, initial permeability and resistivity measurements indicated a highest Tc of 737 K for MgFe2O4 from alpha-Fe2O3, while lower values are found for the ferrite prepared from -Fe2O3. 相似文献
9.
Chernomordik BD Russell HB Cvelbar U Jasinski JB Kumar V Deutsch T Sunkara MK 《Nanotechnology》2012,23(19):194009
Undoped hematite nanowire arrays grown using plasma oxidation of iron foils show significant photoactivity (~0.38 mA cm(-2) at 1.5 V versus reversible hydrogen electrode in 1 M KOH). In contrast, thermally oxidized nanowire arrays grown on iron exhibit no photoactivity due to the formation of a thick (>7 μm Fe(1-x)O) interfacial layer. An atmospheric plasma oxidation process required only a few minutes to synthesize hematite nanowire arrays with a 1–5 μm interfacial layer of magnetite between the nanowire arrays and the iron substrate. An amorphous oxide surface layer on hematite nanowires, if present, is shown to decrease the resulting photoactivity of as-synthesized, plasma grown nanowire arrays. The photocurrent onset potential is improved after removing the amorphous surface on the nanowires using an acid etch. A two-step method involving high temperature nucleation followed by growth at low temperature is shown to produce a highly dense and uniform coverage of nanowire arrays. 相似文献
10.
T. C. Rojas J. C. Sánchez-López J. M. Greneche A. Conde A. Fernández 《Journal of Materials Science》2004,39(15):4877-4885
Nanocrystalline iron powders have been prepared by the inert gas evaporation method. After preparation the material has been passivated by pure oxygen and air exposure. In the present paper we describe new characterization studies of this sample by Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), X-ray Absorption Spectroscopy (XAS), Electron Energy Loss Spectroscopy (EELS) and Mössbauer Spectroscopy (MS), giving a complete chemical and structural characterization of the nanocomposite material in order to correlate its microstructure with its singular magnetic behavior.This nanocomposite was later heated following different thermal treatments. It was found that the sample heated successively in high vacuum (10–7 torr) at 383 K for 1 h and under a residual oxygen pressure of 4 × 10–4 torr at 573 K for 3 h, results in a powder formed by nanoparticles of -Fe2O3 as stated from XRD, XAS and MS. This material is stable during several years and behaves almost totally like superparamagnetic at room temperature. 相似文献
11.
XRD and TG reduction analysis show that -Fe2O3 Fe-Cr catalysts, which contains 0.0 to 14.0 wt %. Cr2O3 and prepared by coprecipitating method, consist of crystalline -Fe2O3 and non-crystalline Fe2O3. Between 150–450 °C, three reduction stages are observed in the catalyst. The first stage is non-crystalline Fe2O3 reduced to non-crystalline Fe3O4, the second is crystalline -Fe2O3 to crystalline Fe3O4 and the third is non-crystalline Fe2O3 reduced to non-crystalline FeO. About 5 wt %. Cr2O3 can enter the lattices of -Fe2O3 to form solid solution. With the increasing of Cr2O3 content, the relative abundance of non-crystalline Fe2O3 and the amount of soluble Cr2O3 in non-crystalline increases, while the crystalline size of -Fe2O3 decreases. 相似文献
12.
Gao Yue Hongwei Ni Rongsheng Chen Ziyang Wang Chao Zhang Weiting Zhan Youwei Li Jihui Li 《Journal of Materials Science: Materials in Electronics》2013,24(9):3324-3329
SnO2 nanorod arrays were fabricated on hematiete nanotube arrays by an efficient hydrothermal method. The hematiete nanotube arrays were prepared by anodization of pure iron foil in an ethylene glycol solution. SnO2 nanorod arrays grew from the bottom of hematite nanotubes and were firmly combined with the iron foil substrate. The morphology and microstructure of SnO2 nanorod arrays are investigated by field-emission scanning electron microscopy, grazing incidence X-ray diffraction and UV–Vis absorbance spectra. The sample presented typical SnO2 nanorod arrays (reacted for 2 h) generally of 400 nm in length and 50 nm in side width showed the best photocatalytic activity and photoelectrochemical response under the UV illumination. It should be attributed to the effective electron–hole separation and the excellent electron transfer pathway along the 1D SnO2 nanorod arrays and hematiete nanotube arrays. 相似文献
13.
I. I. M. Tijburg H. De Bruin P. A. Elberse J. W. Geus 《Journal of Materials Science》1991,26(21):5945-5949
Sintering of pseudo-boehmite, acicular-Al2O3 produced by dehydration of pseudo-boehmite, and-Al2O3 ex alum was investigated. The sintering process was studied by X-ray diffraction, transmission electron microscopy with selected area electron diffraction and BET surface area measurements. The solid state reaction to-Al2O3 causes a steep drop of the surface area to less than 10 m2g–1. The acicular pseudo-boehmite and-Al2O3 supports exhibit an intermediate state where the acicular particles assume a rod-like shape and the surface area falls from about 300 to 100 m2g–1. It was established that reaction to -Al2O3 and, hence, sintering proceeds via a nucleation and growth mechanism. The rate-limiting step is nucleation of -Al2O3. Consequently, the contacts between the elementary alumina particles dominate the sinter process. The contact between the acicular elementary particles of pseudoboehmite and-Al2O3 studied leads to the reaction to -Al2O3 to be almost complete after keeping samples for 145 h at 1050 °C. Decomposition of alum produces very small particles showing negligible mutual contacts. Consequently an elevated thermal stability is exhibited. Treatment of the alumina ex alum with water and drying results in a xerogel in which contact between elementary particles is much more intimate. Accordingly, treatment at 1050 °C causes a sharp drop in surface area. 相似文献
14.
With same procedure and same starting materials, nearly monodispersed α-Fe2O3, γ-Fe2O3 and Fe3O4 nanoparticles were synthesized on an large scale of about 60 g in a single reaction through a low temperature sol–gel route. The simple preparation process includes the reactions between FeCl2 and propylene oxide in ethanol solution at boiling point to form a sol and the following drying of the sol. The different iron oxide phases can be obtained just by changing of the drying conditions for the sol solution. The strategy developed in this study offers important advantages over the conventional routes for the synthesis of α-Fe2O3, γ-Fe2O3 and Fe3O4 nanoparticles, showing potential for its application in industrial production of iron oxides. 相似文献
15.
Zhang Tianfeng Wang Zhumei Feng Xiaoxia Xie Zhixiang Li Yueming 《Journal of Materials Science: Materials in Electronics》2021,32(11):14149-14155
Journal of Materials Science: Materials in Electronics - In this paper, Na–β"–Al2O3 is prepared using a conventional solid-state method and cost-effective burying and... 相似文献
16.
-Fe2O3 particles with BaO additives (up to 20 mol%) have been crystallized by solid state reaction of the stoichiometric compositions containing 20 mol% B2O3 as a sintering aid. This markedly effects the crystallization and magnetic properties of -Fe2O3. The microstructure of the samples shows growth of crystallites of considerably smaller sizes and with fairly sharp size distribution after the additions. Crystallites as small as 5 m size (normally 25 m) were obtained using 15 to 20 mol% BaO additives in the reaction performed at 1230 °C/20h. This leads to a variation in coercivity over a wide range from 35 to 3500 Oe. Measurements of X-ray diffractometry, magnetization, microstructure and magnetic resonance have been carried out to characterize the magnetic applications of the material. The results are all consistent and elucidate promotion by thermal-treatment of the incorporation of Ba2+ into the -Fe2O3 particle cores. 相似文献
17.
-Fe2O3 synthesized from ferrous fumarate half-hydrate was studied by measurements of D.c. electrical conductivity, Seebeck coefficient, initial magnetization and magnetic hysteresis, and by Mössbauer spectroscopy and scanning electron microscopy. The phase transformation observed by electrical conductivity measurements matched well with the phase transformation observed by the variation with temperature of initial magnetization measurements of -Fe2O3; this magnetic study also established the single-domain character of -Fe2O3. The magnetic hysteresis values of the -Fe2O3 synthesized indicated improved values over that of a -Fe2O3 sample synthesized by established procedures. The scanning electron micrographs showed that the -Fe2O3 particles were acicular in shape and the Mössbauer spectrum showed a well-resolved six-band spectrum. The presence of a hydrogen ferrite phase was also confirmed by the electrical and magnetic measurements.Deceased, 10 October, 1985. 相似文献
18.
A. Venkataraman Vijay A. Hiremath S. K. Date S. D. Kulkarni 《Bulletin of Materials Science》2001,24(6):617-621
A new combustion route for the synthesis of γ-Fe
2
O
3
is reported by employing purified a-Fe
2
O
3
as a precursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves
fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the
reaction is completed in a single step yielding magnetic iron oxide i.e. γ-Fe
2
O
3
.The as synthesized γ-Fe
2
O
3
is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on
magnetic properties is also presented. 相似文献
19.
In order to explore the fundamental properties of one-dimensional nanostructured high-temperature superconductors and enhance their promising applications, a universal and general method for the synthesis of high-quality YBa(2)Cu(3)O(7-δ) (YBCO) nanowire arrays is developed, which involves the combination of a novel sol-gel process to lower the crystallization temperature of YBCO, and porous anodic alumina (PAA) as an effective morphology-directing hard template. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results indicate that the as-prepared YBCO nanowires have average diameters of about 50?nm and lengths up to several microns. The structures of the samples were analysed by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray spectroscopy (EDX) and inductively coupled plasma (ICP) analysis, which indicate that the nanowires are well crystallized with orthorhombic YBCO-123 structure. The magnetization measurement under zero-field-cooled (ZFC) mode indicates that the superconducting transition temperature (T(c)) of the nanowires is about 92?K, which is in agreement with that of a bulk YBCO sample. 相似文献
20.
Acicular -FeOOH particles with a particle length of about 0.35 m and an axial ratio of about 7 were synthesized by the coprecipitation method using the reaction of FeCl2-NaOH. The (Co, Zn)-modified -F2O3 particles were produced by absorbing Co2+ and Zn2+ ions on the surfaces of -FeOOH particles followed by dehydration, reduction and oxidation. The saturation magnetization and thermal stability of the coercivity of (Co, Zn)--Fe2O3 particles were all higher than those of Co--F2O3 particles. For the same (Co+Zn) content, the saturation magnetization of (Co, Zn)--Fe2O3 particles increased with increasing zinc content but the coercivity decreased. 相似文献