共查询到20条相似文献,搜索用时 16 毫秒
1.
V. V. Korolev A. S. Romanov I. M. Aref’ev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(3):464-466
The magnetocaloric effect (MCE) and heat capacity of magnetite-based magnetic liquids and suspensions of magnetite in cyclohexane and water were studied calorimetrically at various temperatures and magnetic inductions. It was found that the magnetocaloric effect in the systems under study increases nonlinearly with the magnetic induction. In contrast to monocrystalline magnetite, the inverse temperature dependence was observed for the MCE in the nanosystems studied over the entire temperature range covered; i.e., the effect decreases with increasing temperature. It was found that the dependence of the specific heat on the magnetic induction passes through a maximum for all the systems at all temperatures tested; its height increases with the temperature. The extremal character of the dependence can be explained by the formation of chain structures of magnetite nanoparticles in the presence of a magnetic field. 相似文献
2.
Ling Hu Aurelien Percheron Denis Chaumont Claire-Helene Brachais 《Journal of Sol-Gel Science and Technology》2011,60(2):198-205
A simple, rapid, one-step synthesis way of pure iron oxide nanoparticles: magnetite (Fe3O4), maghemite (γ-Fe2O3) and hematite (α-Fe2O3) was investigated. Nanoparticles were prepared by microwave synthesis, from ethanol/water solutions of chloride salts of
iron (FeCl2 and FeCl3) in the presence of sodium hydroxide NaOH. X-ray powder diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier
transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize these nanoparticles. 相似文献
3.
Xiaoqi Fu Shuang Wang Qian Zhao Tingshun Jiang Hengbo Yin 《Frontiers of Chemistry in China》2011,6(3):206-212
A new kind of nonmetallic nanosensors based on surface-enhanced Raman spectroscopy (SERS) have been successfully prepared
by the assembly of α-Fe2O3 nanoparticles (NPs) onto clean quartz surface via the cross-linker of hexamethylene diisocyanate (HDI). The resultant substrates
have been characterized by electron micrographs, which show that the α-Fe2O3 NPs distribute on the modified surface uniformly with a monolayer or sub-monolayer structure. 4-mercaptopyridine (4-Mpy)
and 2-mercaptobenzothiazole (2-MBT) molecules have been used as SERS probes to estimate the detection efficiency of the α-Fe2O3 thin films. The SERS experiments show that it is possible to record high quality SERS spectra from probe molecules on the
α-Fe2O3 thin films at sub-micromolar ( < 10−6 mol/L) concentration. These results indicate that the highly ordered, uniformly roughed, highly sensitive and low-cost α-Fe2O3 thin films are excellent candidates for nonmetallic SERS-active nanosensors. 相似文献
4.
The oxidation of magnetite yields the lacunar phase γ-Fe2O3, for sizes less than 5000 Å and the rhombohedral phase, α-Fe2O3, for sizes above 10 000 Å. For intermediate sizes, oxidation kinetics and X-ray analysis have confirmed that the γ-Fe2O3 phase forms at the beginning of the reaction, followed by phase α-Fe2O3 forming from γ-Fe2O3 and then directly from the still-unoxidized magnetite. Influence of size could be accounted for in terms of structure and stresses at the crystal lattice level. 相似文献
5.
The wet mixtures of ammonium hexacyanoferrate, (NH4)4[Fe(CN)6], and cupric nitrate, Cu(NO3)2, react explosively when heated at 220 ?C. Among the solid products studied by chemical analysis, magnetic measurements and X-ray diffraction there are magnetite (Fe3O4), iron nitride (Fe4N), gamma iron oxide (γ-Fe2O3), cuprous oxide (Cu2O), alpha iron oxide (α-Fe2O3), cupric oxide (CuO), cuprous ferrite and metallic copper. Furthermore cupric hexacyanoferrate (Cu2[Fe(CN)6]) and ferric ferrocyanide (Fe4[Fe(CN)6]3) have been found in weakly ferromagnetic products. The presence of these phases and their quantitative contribution depend upon the proportion of the initial salts and air supply. 相似文献
6.
Studies were undertaken of phase transitions of iron oxide obtained from iron oxide-hydroxides of type α-, β-, γ- and δ-FeOOH,
and used as a support of ruthenium catalysts Ru/Fe2O3, employed in the water-gas shift reaction. In asprepared pure supports and ruthenium catalysts the main phase was α-Fe2O3. After use in the water-gas shift reaction, the support showed the presence of different phases of iron oxide. The most active
Ru/Fe2O3 catalysts prepared on the basis of α- and δ-FeOOH, after use in the water-gas shift reaction, revealed the presence of Fe3O4 or a mixture of phases Fe3O4 and γ-Fe2O3. The least active catalysts, prepared on the basis of β- and γ-FeOOH, contained a solid solution of Fe3O4-γ-Fe2O3 with traces of α-Fe2O3. 相似文献
7.
Xiaojie Zhang Wanzhong Ren Hongtao Cui 《Journal of Sol-Gel Science and Technology》2011,58(1):232-237
A general sol–gel strategy was established for the synthesis of metal ions doped γ-Fe2O3 nanoparticles with narrow particle size distribution. The unique chemistry of the route guarantees the simple preparation
procedure for the preparation of doped γ-Fe2O3 nanoparticles, which includes the boiling of the ethanolic solution of precursor salts after the addition of gelation agent,
and the following drying of the obtained sol solution. On the other hand, it guarantees the production of the nanoparticles
with nearly monodispersed state and median size of about 5 nm on an ultra large scale of about 60 g in a single reaction.
The doping of metal ions in γ-Fe2O3 allows the great promotion of phase transformation temperature from γ-Fe2O3 to α-Fe2O3. Due to the advantages of this strategy over other routes, it is very promising to be applied in the industrial production
of undoped and doped γ-Fe2O3 nanoparticles as a general route. 相似文献
8.
Kojima Kunihiko Miyazaki Mitsuharu Mizukami Fujio Maeda Kazuyuki 《Journal of Sol-Gel Science and Technology》1997,8(1-3):77-81
The structure of iron oxide was controlled by regulating the hydrolytic polymerization of aquo iron complexes with organic
polydentate ligands such as diols. Iron oxides were prepared by calcining the precursor polymers obtained from iron nitrate
nonahydrate and diols. When the diols were 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol, α-Fe2O3 with corundum structure appeared exclusively or as the main crystalline phase, in spite of the amount of diol used and the
calcination temperature. In the case of 1,2-decanediol and 1,2-dodecanediol, when five moles of the diols were used to one
mole of iron nitrate and the calcination temperatures were below 400°C, ψ-Fe2O3 with spinel structure appeared as the main phase and, when less than five moles of the diols were used, α-Fe2O3 appeared exclusively or as the main phase, irrespective of the calcination temperature. This tendency was also observed in
thin films. Thus, a transparent magnetic film composed of γ-Fe2O3 could be prepared by applying a benzene solution of the iron polymer, obtained with 5 equivalents of 1,2-decanediol, on quartz
and calcining the gel film at 350°C. 相似文献
9.
S. M. Eyubova V. D. Yagodovskii 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(13):2362-2366
The oxidation of CO on α-Fe2O3 was studied in a flow reactor. The conversion was complete at 650–660 K. The catalytic activity of iron oxide was higher
than that of the ferrite-containing xMgOyFe2O3 catalyst. The adsorption of CO on iron oxide and the kinetics of interaction of carbon monoxide with oxygen atomically adsorbed
on the surface of α-Fe2O3 were studied. The kinetic parameters of the oxidation of CO are evidence of the participation of adsorbed oxygen atoms, whose
binding energy on the surface of α-Fe2O3 is lower than that on the surface of the magnesium ferrite-containing catalyst. 相似文献
10.
The thermolysis of zinc bis(citrato)ferrate(III)dodehydrate has been investigated from ambient temperature to 600 °C using various physico-chemical techniques, i.e., simultaneous TG-DTG-DTA, XRD, Mössbauer and I.R. spectroscopy. After dehydration at 200 °C, the anhydrous complex undergoes oxidative decomposition to yield -Fe2O3 and ZnO at 350 °C. Subsequently, the cations remix to yield fine particles of zinc ferrite, ZnFe2O4 as a result of solid state reaction between -Fe2O3 and ZnO at a temperature (450 °C) much lower than for ceramic method. 相似文献
11.
B. S. Randhawa 《Journal of Radioanalytical and Nuclear Chemistry》1995,196(1):57-63
The thermal decomposition of cesium tris(oxalato) ferrate(III) dihydrate, Cs3 Fe(ox)3 2H2O has been studied at various temperatures in air, employing Mössbauer and infrared spectroscopies, and thermogravimetric methods. The complex undergoes reduction to an iron(II) intermediate at 473 K. The particle size of -Fe2O3 formed during thermolysis increases with increasing decomposition temperature. Finally, a solid state reaction between -Fe2O3 and cesium carbonate/oxide occurs, leading to the formation of fine particles of cesium ferrite (CsFeO2). 相似文献
12.
α-Fe2O3 films as inorganic red color filter were synthesized through a simple procedure, epoxide assisted sol–gel route. The sol
was prepared through reaction of FeCl2 in boiling ethanol solution with propylene oxide. The films were formed by the dip-coating of sol on substrate, drying and
the following annealing steps. The obtained α-Fe2O3 films were composed of homogeneous distributed α-Fe2O3 nanoparticles with size of 30–50 nm. The film shows strong absorption to the light below 600 nm and high transparency to
the red light (87% at 630 nm). As inorganic red color filter, the optic behavior of this film is nearly as same as the organic
color filter made of dye. 相似文献
13.
M. Josse O. Bidault F. Roulland E. Castel A. Simon D. Michau R. Von der Mühll O. Nguyen M. Maglione 《Solid State Sciences》2009,11(6):1118-1123
Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln = La, Pr, Nd, Sm, Eu, Gd) with the “tetragonal tungsten bronze” (TTB) structure have been synthesised by conventional solid state methods. The neodymium, samarium and europium compounds are ferroelectric with Curie temperature ranging from 320 to 440 K. The praseodymium and gadolinium compounds behave as relaxors below 170 and 300 K respectively. The praseodymium, neodymium, samarium, europium and gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these materials as composites multiferroic. Based on crystal-chemical analysis we propose some relationships between the introduction of Ln3+ ions in the TTB framework and the chemical, structural and physical properties of these materials. 相似文献
14.
C. Sikalidis T. Zorba K. Chrissafis K.M. Paraskevopoulos 《Journal of Thermal Analysis and Calorimetry》2006,86(2):411-415
Phase changes of iron containing solid wastes from steel mill pickling
lines after thermal treatments were investigated aiming the determination
of the appropriate conditions for its transformation to be useful for industrial
raw materials. Above 275°C, the thermally treated wastes contain a mixture
of α-Fe2O3 (hematite)
and γ-Fe2O3 (maghemite)
in different proportions, depending on the maximum heating temperature of
the thermal treatment. Increasing the maximum temperature the maghemite participation
is decreased through its transformation to hematite. Above 850°C hematite
is the main constituent, suggesting that thermal treatment of the wastes in
this temperature will give a product that could be used as red iron pigment. 相似文献
15.
Ferrous gluconate dihydrate (FeC12H22O14⋅2H2O), was prepared and its thermal decomposition was studied by means of simultaneous thermal analysis, supplemented with a
two probe d.c. electrical conductivity measurements under the atmospheres of static air, dynamic air and dynamic nitrogen.
Under all the atmospheres final product was found to be α-Fe2O3 with FeO, γ-Fe2O3, Fe3O4 etc. as probable intermediates. γ-Fe2O3 was formed under the atmosphere of dynamic air containing water vapour. γ-Fe2O3 thus synthesised was characterised for its structure, morphology, thermal and magnetic behaviour.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
B. S. Randhawa K. Prabhjinder Sweety Kamaljeet 《Journal of Radioanalytical and Nuclear Chemistry》1966,214(3):255-262
Thermal decomposition of cobalt hexa(formato)ferrate(III) decahydrate, Co3[Fe(HCOO)6]2. 10H2O, has been studied up to 973 K in static air atmosphere, employing TG, DTG, DSC, XRD, ESR, Mössbauer and infrared spectroscopic techniques. Dehydration occurs in two stages in the temperature range of 340–430 K. Immediately after the removal of the last water molecule the anhydrous complex undergoes decomposition till -Fe2O3 and cobalt carbonate are formed at 588 K. In the final stage of remixing of cations, a solid state reaction between -Fe2O3 and cobalt carbonate leads to the formation of CoFe2O4 at a temperature (953 K) much lower than for the ceramic method. A saturation magnetization value of 2310 Gauss of ferrite (CoFe2O4) shows its potential to function at high frequencies. 相似文献
17.
High energy ball-milling methods were employed in the synthesis of anatase-doped hematite xTiO2(a) · (1−x)α-Fe2O3 (x = 0.1, 0.5, and 0.9) ceramic system. The thermal behavior of as obtained ceramic system was characterized by simultaneous
DSC–TG. The pure anatase phase was found to be stable below 800 °C, but there is a 10.36% mass loss due to the water content.
Two exothermic peaks on DSC curves of pure anatase indicate the different crystallization rates. The pure hematite partially
decomposed upon heating under argon atmosphere. Ball-milling has a strong effect on the thermal behaviors of both anatase
and hematite phases. For x = 0.1 and 0.5, there is gradual Ti substitution of Fe in hematite lattice, and the decomposition of hematite is enhanced
due to the smaller particle size after ball-milling. The crystallization of hematite was suppressed as the enthalpy values
decreased due to the anatase-hematite solid–solid interaction. For x = 0.9, most of the anatase phase converted to rutile phase after long milling time. The thermal behavior of xTiO2(a) · (1−x)α-Fe2O3 showed smaller enthalpy value of the hematite transformation to magnetite and anatase crystallization due to the small fraction
of hematite phase in the system and hematite–anatase interaction, while the mass loss upon heating increased as a function
of milling time due to more water content absorbed by the smaller particle size. 相似文献
18.
The reduction of α-Fe2O3 and Li0.5Fe2.5O4 by hydrogen has been studied to characterise the stages of reduction. The course of reduction as followed by TGA and M?ssbauer
spectroscopy indicates that (i) in the case of α-Fe2O3, the reduction to metallic iron goes through the intermediate formation of Fe3O4, and (ii) in the case of Li0.5Fe2.5O4 the reduction proceeds in a single step to give a mixture of LiFeO2 and Fe. 相似文献
19.
T.M. Kwon M.S. Jhon H.J. Choi T.E. Karis 《Colloids and surfaces. A, Physicochemical and engineering aspects》1993,80(1)
Single-domain magnetic particles are the essential ingredient of magnetic tapes, particulate recording disks and magnetic stripes. The particles are single-domain γ-Fe2O3, CrO2 or barium ferrite, and non-magnetic α-Fe2O3 mixture. Each of these particles has intrinsic coercivity, which should be matched with the magnetic field strength of the writing element of a particular device. In this study a magnetic inductance measurement with low field strength was employed to obtain the magnetic permeability of suspensions containing two of the particle types mixed together as a function of composition and volume fraction of particles. The bulk magnetic property B is a linear combination of the contributions from each particle type such that the “excess” inductance is L − Ls = ΣφiBi where φi is the volume fraction and Bi, is the magnetic property of particle type i. For the non-magnetic α-Fe2O3, Bi = 0. This allows the formulation of mixed particle suspensions to obtain a desired property for custom-designed magnetic particle coatings. However, mixing magnetic particle types will broaden or produce a bimodal switching field distribution. This may affect the squareness of the magnetic hysteresis loop. These properties should be taken into account for the design of a practical magnetic coating with mixed particle suspension. Another requirement of the magnetic particle suspensions is that they remain well dispersed, even though strong magnetic forces between the particles promote flocculation. An extension of the inductance measurement technique is employed to study the flocculation of a suspension containing magnetic γ-Fe2O3 and non-magnetic α-Fe2O3. The presence of the α-Fe2O3 decreases the flocculation state of the suspension. Thus the suspension stability is enhanced by incorporating a small amount of non-magnetic particles in addition to surfactant. 相似文献
20.
Yu Liu Hongbing Yu Sihui Zhan Yi Li Zhenning Lv Xiaoqing Yang Yunjiang Yu 《Journal of Sol-Gel Science and Technology》2011,58(3):716-723
The α-Fe2O3 fibers have been prepared by electrospinning the corresponding sol–gel precursor, then these fibers were characterized by
TGA, SEM, XRD, BET and FT-IR respectively, indicating that the hierarchical α-Fe2O3 nanostructured fibers came into being. Photocatalytic degradation of methylene blue (MB) in water was carried out under ultraviolet
(UV) light, showing that the fibers had better efficiency for removing MB than other catalysts. And several process parameters
have also been studied, which showed that the removal effect of MB was influenced by the process parameters, such as the initial
dye concentration, catalyst amounts, inorganic anions, and so on. 相似文献