共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Mozammel S. K. Sadrnezhaad A. Khoshnevisan H. Youzbashizadeh 《Journal of Thermal Analysis and Calorimetry》2013,112(2):781-789
Thermal oxidation of commercial ilmenite concentrate from Kahnouj titanium mines, Iran, at 500–950 °C was investigated for the first time. Fractional conversion was calculated from mass change of the samples during oxidation. Maximum FeO to Fe2O3 conversion of 98.63 % occurred at 900 °C after 120 min. Curve fit trials together with SEM line scan results indicated constant-size shrinking core model as the closest kinetic mechanism of the oxidation process. Below 750 °C, chemical reaction with activation energy of 80.65 kJ mol?1 and between 775 and 950 °C, ash diffusion with activation energy of 53.50 kJ mol?1 were the prevailing mechanisms. X-ray diffraction patterns approved presence of pseudobrookite, rutile, hematite, and Fe2O3·2TiO2 phases after oxidation of ilmenite concentrate at 950 °C. 相似文献
2.
K. S. Dhindsa A. Kumar G. A. Nazri V. M. Naik V. K. Garg A. C. Oliveira P. P. Vaishnava Z. X. Zhou R. Naik 《Journal of Solid State Electrochemistry》2016,20(8):2275-2282
We have studied LiFePO4/C nanocomposites prepared by sol-gel method using lauric acid as a surfactant and calcined at different temperatures between 600 and 900 °C. In addition to the major LiFePO4 phase, all the samples show a varying amount of in situ Fe2P impurity phase characterized by x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. The amount of Fe2P impurity phase increases with increasing calcination temperature. Of all the samples studied, the LiFePO4/C sample calcined at 700 °C which contains ~15 wt% Fe2P shows the least charge transfer resistance and a better electrochemical performance with a discharge capacity of 136 mA h g?1 at a rate of 1 C, 121 mA h g?1 at 10 C (~70 % of the theoretical capacity of LiFePO4), and excellent cycleability. Although further increase in the amount of Fe2P reduces the overall capacity, frequency-dependent Warburg impedance analyses show that all samples calcined at temperatures ≥700 °C have an order of magnitude higher Li+ diffusion coefficient (~1.3?×?10?13 cm2 s?1) compared to the one calcined at 600 °C, as well as the values reported in literature. This work suggests that controlling the reduction environment and the temperature during the synthesis process can be used to optimize the amount of conducting Fe2P for obtaining the best capacity for the high power batteries. 相似文献
3.
Shiro Kubuki Jun Iwanuma Yusuke Takahashi Kazuhiko Akiyama Zoltán Homonnay Katalin Sinkó Ernő Kuzmann Tetsuaki Nishida 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(1):1-7
A relationship between local structure and visible light activated catalytic effect of iron containing soda lime silicate glass with the composition of 15Na2O·15CaO·xFe2O3·(70-x)SiO2, x = 5–50 mass %, abbreviated as NCFSx was investigated by means of 57Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD), small angle X-ray scattering (SAXS), electrospray ionization mass spectrometry (ESI–MS) and ultraviolet–visible light absorption spectroscopy (UV–Vis). Mössbauer spectra of NCFSx glass with ‘x’ being equal to or larger than 30 after isothermal annealing at 1,000 °C for 100 min consisted of a paramagnetic doublet and a magnetic sextet. The former had isomer shift (δ) of 0.24 mm s?1 and quadrupole splitting (Δ) of 0.99 mm s?1 due to distorted FeIIIO4 tetrahedra, and the latter had δ of 0.36 mm s?1 and internal magnetic field (H int) of 51.8 T due to hematite (α-Fe2O3). The absorption area (A) of α-Fe2O3 varied from 47.2 to 75.9, 93.1, 64.8 and 47.9 % with ‘x’ from 30 to 35, 40, 45 and 50, indicating that the amount of precipitated α-Fe2O3 varied with the Fe2O3 content of NCFSx glass. The precipitation of α-Fe2O3 was also confirmed by XRD study of annealed NCFS glass with ‘x’ larger than 30. A relaxed sexted with δ, H int and Γ of 0.34 mm s?1 and 37.9 T and 1.32 mm s?1 was observed from the Mössbauer spectra of annealed NCFSx glass with ‘x’ of 45 and 50, implying that the precipitation of non-stoichiometric iron hydroxide oxide with the composition of Fe1.833(OH)0.5O2.5 having the similar structure of α-Fe2O3 and α-FeOOH. A remarkable decrease in the concentration of methylene blue (MB) from 10 to 0.0 μmol L?1 with the first-order rate constant (k) of 2.87 × 10?2 h?1 was observed for 10-day leaching test using annealed NCFS50 glass under visible light irradiation. ESI–MS study indicated that existence of fragments with m/z value of 129, 117 and 207 etc. originating from MB having m/z of 284. This result evidently showed that the MB concentration decreased due to visible light induced decomposition caused by the visible light activated catalytic effect of α-Fe2O3 and/or Fe1.833(OH)0.5O2.5 precipitated in soda-lime silicate glass matrix. 相似文献
4.
α-Fe2O3, containing small amounts of the oxides of Mg, Ni or Co, becomes ferromagnetic at 800°C, and this without any X-ray evidence for ferrite contaminations. The ferrites, and other ferromagnetic compounds, may, however, be prepared by air oxidation of Fe(OH)2. 相似文献
5.
M. A. Shuvaeva I. V. Delii O. N. Mart’yanov O. A. Bayukov E. I. Osetrov A. A. Saraev V. V. Kaichev N. S. Sakaeva G. A. Bukhtiyarova 《Kinetics and Catalysis》2011,52(6):896-906
The effect of calcination temperature on the state of the active component of iron-containing catalysts prepared by the impregnation of silica gel with a solution of FeSO4 and on their catalytic properties in selective H2S oxidation to sulfur was studied. With the use of thermal analysis, XPS, and Mössbauer spectroscopy, it was found that an X-ray amorphous iron-containing compound of complex composition was formed on the catalyst surface after thermal treatment in the temperature range of 400–500°C. This compound contained Fe3+ cations in three nonequivalent positions characteristic of various oxy and hydroxy sulfates and oxide and sulfate groups as anions. Calcination at 600°C led to the almost complete removal of sulfate groups; as a result, the formation of an oxide structure came into play, and it was completed by the production of finely dispersed iron oxide in the ?-Fe2O3 modification (the average particle size of 3.2 nm) after treatment at 900°C. As the calcination temperature was increased from 500 to 700°C, an increase in the catalyst activity in hydrogen sulfide selective oxidation was observed because of a change in the state of the active component. A comparative study of the samples by temperature-programmed sulfidation made it possible to establish that an increase in the calcination temperature leads to an increase in the stability of the iron-containing catalysts to the action of a reaction atmosphere. 相似文献
6.
A. A. Shesterkina L. M. Kozlova O. A. Kirichenko G. I. Kapustin I. V. Mishin L. M. Kustov 《Russian Chemical Bulletin》2016,65(2):432-439
The supported bimetallic Fe—Pd/SiO2 catalysts with the different Fe (0.025—8 mass.%) and Pd (0.05—3.2 mass.%) loadings were synthesized by the incipient wetness impregnation of support. The samples were heat-treated under different conditions (calcination in air at 240—350 °C or reduction in an H2 flow at 400 °C). The X-ray phase analysis revealed the formation of Pd0, α-Fe2O3 and Fe3O4 phases after calcination of the samples at 240—260 °C. The reduction of the calcined Fe—Pd samples in an H2 flow at 400 °C enables the formation of Fe0 nanoparticles of size 17—20 nm. The synthesized catalytic systems were studied in the selective hydrogenation of phenylacetylene at room temperature and atmospheric pressure in a solvent (ethanol, propanol). The catalytic properties of the Fe—Pd catalysts depend on the nature of solvent, catalyst composition, and thermal treatment conditions. The application of the Fe—Pd bimetallic catalysts with a low Pd loading of 0.05—0.1 mass.% made it possible to reach the high activity and selectivity to styrene (91%) at the complete conversion of phenylacetylene. 相似文献
7.
H. Yu C. Lu T. Xi L. Luo J. Ning C. Xiang 《Journal of Thermal Analysis and Calorimetry》2005,82(1):97-101
Summary TG-DSC-MS (thermogravimetry-differential scanning calorimetry-mass spectrometry) coupling techniques were used to make a simultaneous
characterizing study for the thermal decomposition process of the carbon nanotube (CNT)/SiO2precursor powders prepared by rapid sol-gel method. The thermal stability of the CNT and the SiO2pure gel were investigated by TG-DSC. The results showed that the oxidation of CNT began from 530 and combusted at about 678°C
at the heating rate of 10°C min-1in air. Moreover, the faster the heating rate, the higher the temperature of CNT combustion. The appropriate calcinations
temperature of the CNT/SiO2precursor powders should be held for 1 h at 500°C. 相似文献
8.
H. C. Vasconcelos 《Journal of Sol-Gel Science and Technology》2010,55(1):126-133
SiO2-TiO2-PO2,5 (STP) and SiO2-TiO2-AlO1,5 (STA) glasses were prepared by sol-gel processing. Their infrared absorption spectra (IR), differential thermal analysis
curves (DTA) and X-ray diffraction patterns (XRD) have been recorded. In the SiO2-TiO2 system, the chemical homogeneity of the sol-gel glass could be evaluated by the relative concentration of Si-O-Ti heterocondensation
comparing to Si-O-Si homocondensation. For the STA system, a gradual decrease of the Si-O-Ti/Si-O-Si band ratio (based on
IR spectra) with the addition of Al2O3 is observed, with the simultaneous formation of Si-O-Al and Ti-O-Al bounds, i.e Al3
+ ions are dissolved in the SiO2-TiO2 glass matrix and do not promote glass-in-glass phase-separation in the composition range of 0–15 mol% AlO1.5. In the STP system, on the other hand, P=O bond IR stretch in the ternary glasses indicates that P=O free PO2O2/2
− tetrahedra are formed, rather than the double bonded POO3/2 tetrahedra that usually occur in binary SiO2-P2O5 glasses. It can be concluded that SiO2-TiO2-P2O5 glass separates into a SiO2-rich phase and a TiO2(P2O5)-rich phase. During heat-treatment in STA system only anatase precipitates, even at T ~ 1,000 °C, while in for STP, anatase (TiO2) or (TiO)2P2O7 (TOP) crystals precipitate at ~600 °C, depending on the P2O5 concentration. The major crystal phase, cristobalite, precipitated at ~1,000 °C and at ~1,200 °C, the P-containing phase
melts. 相似文献
9.
Petr Brázda Daniel Nižňanský Jean-Luc Rehspringer Jana Poltierová Vejpravová 《Journal of Sol-Gel Science and Technology》2009,51(1):78-83
ε-Fe2O3/SiO2 nanocomposite was prepared by novel solgel method using single precursor for both nanoparticles and matrix. This method allows to prepare the samples free of α-Fe2O3 with 40% of Fe2O3 in SiO2. Nanoparticles of 12 nm diameter were obtained by annealing at 1,000 °C. The samples were characterized by powder X-ray diffraction and transmission electron microscopy. Mössbauer spectroscopy identified ε-Fe2O3 as the only magnetically ordered phase at room temperature. Magnetic measurements revealed progressive necking of hysteresis loops measured at 300 and 2 K. In both cases the intrinsic coercivity reaches only 0.25 T. Measurements up to 14 T shows monotonous decreasing trend of saturated magnetization with increasing temperature. 相似文献
10.
Intermetallic compounds Al13Co4, Al13Fe4, and Al13Co2Fe2 were obtained by solid-phase synthesis in air at temperatures below 600°C using precursor metals subjected to mechanochemical preactivation. The phase composition of the synthesized aluminides and composites Al13Co4/SiO2 and Al13Fe4/SiO2 was analyzed. 相似文献
11.
Maciej Chotkowski Damian Połomski 《Journal of Radioanalytical and Nuclear Chemistry》2017,312(1):87-93
The effect of the oxidation temperature of sintered UO2 pellets on the powder properties of U3O8 was studied in the temperature range 250–900 °C in air. The U3O8 was obtained at 450 °C after 180 min and its particle size and surface area are respectively, 35 µm and 0.7 m2/g. The reduction of the U3O8 powder resulted in UO2 after 30 min with a surface area of 0.8 m2/g. This value was improved more than 3.5 times by applying five alternating oxidation–reduction cycles. 相似文献
12.
S. Kubuki H. Masuda T. Nishida 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(2):1123-1128
New conductive glass with a composition of 20BaO·10Fe2O3·xWO3·(70 ? x)V2O5 (x = 10–50) was investigated by means of Mössbauer spectroscopy. A marked decrease in quadrupole splitting (Δ) was observed after the isothermal annealing at 500 °C for 1,000 min, due to the structural relaxation of 3D-network composed of FeO4, VO4, and VO5 units. After the isothermal annealing, a marked increase in the electrical conductivity (σ) was observed from 1.7 × 10?5 to 1.0 × 10?1 S cm?1 when “x” was 10, whereas comparable σ values of 1.1 × 10?4 and 2.0 × 10?4 S cm?1 were observed when “x” was 40. These results evidently show that structural relaxation of 3D-network structure involved with a marked increase in σ is intrinsic of “vanadate glass”. XRD pattern indicated several weak peaks due to needle-like BaFe2O4 and α-Fe2O3 when the glass sample with “x” of 20 was annealed at 500 °C for 1,000 min. SEM study proved the formation of needle-like BaFe2O4 just on the surface of the sample, whereas hexagonal BaFe12O19 were observed in the annealed sample with “x” of 40. Chemical durability of WO3-containing vanadate glass was investigated by immersing each glass sample into 20 %-HCl solution for 72 h. 相似文献
13.
Mingquan Liu Xiangqian Shen Fuzhan Song Jun Xiang Ruijiang Liu 《Journal of Sol-Gel Science and Technology》2011,59(3):553-560
Sr0.8La0.2Zn0.2Fe11.8O19/poly(vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol–gel assisted electrospinning. Subsequently,
the M-type ferrite Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers with diameters about 120 nm were obtained by calcination of these precursors at different heat treatment conditions.
The precursor and resultant Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive
X-ray spectrometer and vibrating sample magnetometer. With the calcination temperature increased up to 1,000 °C for 2 h or
the holding time prolonged to 12 h at 900 °C, the Sr0.8La0.2Zn0.2Fe11.8O19 particles gradually grow into a hexagonal elongated plate-like morphology due to the dimensional control along the nanofiber
length. These elongated plate-like particles will be linked one by one to form the nanofiber with a necklace-like morphology.
The magnetic properties of the Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers are closely related to grain sizes, impurities and defects in the ferrite, which are influenced by the calcination
temperature, holding time and heating rate. After calcined at 900 °C for 12 h with a heating rate of 3 °C/min, the optimized
magnetic properties are achieved with the specific saturation magnetization 75.0 A m2 kg−1 and coercivity 426.3 kA m−1 for the Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers. 相似文献
14.
Tao Yuan Zhonglei Wei Jing Yuan Longgang Yan Qingfang Liu Jianbo Wang 《Journal of Sol-Gel Science and Technology》2011,58(2):501-506
Nickel zinc ferrite (Ni0.4Zn0.6Fe2O4) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni0.4Zn0.6Fe2O4 films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface,
relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of
annealing temperature, the saturation magnetization M
s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H
c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating
rate 2 °C/min, the film shows a maximum saturation magnetization M
s of 349 emu/cc and low coercivity H
c of 66 Oe. The M
s is higher than others which prepared by this method, however, the H
c is lower. The M
s of Ni0.4Zn0.6Fe2O4 films annealed at 700 °C increases with increasing annealing time and the H
c changes slightly. 相似文献
15.
Cheng Cheng Dr. Wei Ren Fei Miao Xuantong Chen Xiaoxiao Chen Prof. Hui Zhang 《Angewandte Chemie (International ed. in English)》2023,62(10):e202218510
Generating FeIV=O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the FeIV=O generation pathway and oxidation behavior remain obscure. Employing an Fe−N−C catalyst with a typical Fe−N4 moiety to activate peroxymonosulfate (PMS), we demonstrate that generating FeIV=O is mediated by an Fe−N−C−PMS* complex—a well-recognized nonradical species for induction of electron-transfer oxidation—and we determined that adjacent Fe sites with a specific Fe1−Fe1 distance are required. After the Fe atoms with an Fe1-Fe1 distance <4 Å are PMS-saturated, Fe−N−C−PMS* formed on Fe sites with an Fe1-Fe1 distance of 4–5 Å can coordinate with the adjacent FeII−N4, forming an inter-complex with enhanced charge transfer to produce FeIV=O. FeIV=O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidation potential. 相似文献
16.
Li Yao Linlin Zhuang Zihui Yao Li Han Chengliang Han 《Journal of the Iranian Chemical Society》2016,13(12):2185-2191
In this study, a simple approach was described for the fabrication of CaSO4/Fe0 composite used as a novel adsorbent for the reductive removal of Cu2+ from aqueous solutions. The magnetic CaSO4/Fe0 composite was prepared by a solid state reaction at 550 °C in the H2 atmosphere using CaSO4·2H2O/α-FeOOH as a precursor. The structure and morphology of the as-synthesized magnetic composite were characterized by X-ray diffraction, field emission scanning electron microscopy and a superconducting quantum interference device, respectively. Results showed that the CaSO4/Fe0 composite with a rod-like shape could be easily acquired from the CaSO4·2H2O/α-FeOOH precursor with the ratio of 1:0.5 at 550 °C in the H2 atmosphere for 1 h. The CaSO4/Fe0 composite exhibited enhanced performance relevant to the reductive removal of Cu2+. The removal amount of Cu2+ increased linearly with increasing of concentration of Cu2+ in wastewater. Possible removal mechanisms were proposed as follows: (1) the formation of Cu2O by fast reduction of Cu2+ with Fe0 nanoparticles on interface of CaSO4/Fe0 composite, (2) proper adsorption of Cu2+ on the surface of CaSO4/Fe0 composite, (3) the hydrous iron oxide (HIO) such as Fe (OH)3 and FeOOH in situ generated on the rest of CaSO4/Fe0 composite could further adsorb Cu2+ from wastewater. 相似文献
17.
Nafise Modanlou Juibari Abbas Eslami 《Journal of Thermal Analysis and Calorimetry》2017,127(1):115-122
A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of Al2O3. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of Fe2O3 powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe–Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe–Al compounds during sintering at 700 °C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger’s method, could be used to optimize the fabrication of Al-Al2O3 composites by means of reactive sintering at moderate temperatures. 相似文献
18.
Zhan Jie Wang Hirokazu Usuki Toshihide Kumagai Hiroyuki Kokawa 《Journal of Sol-Gel Science and Technology》2007,42(3):375-379
(La0.7Sr0.3)MnO3 thin films were deposited on SiO2/Si substrates by a metal-organic decomposition (MOD) method, and then Pb(Zr0.52Ti0.48)O3 (PZT) thin films were grown on (La0.7Sr0.3)MnO3-coated SiO2/Si substrates by a sol-gel method. The effects of annealing temperature on the crystalline phases, microstructures and electrical
properties of the PZT films were investigated. X-ray diffraction analysis results indicated that the PZT films with a perovskite
single phase could be obtained by annealing at 650°C. The dielectric constant and the remnant polarization of the PZT films
increased with increasing annealing temperature. The remnant polarization and the coercive field of the films annealed at
650°C were 18.3 μC/cm2 and 35.5 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and
0.81, respectively. 相似文献
19.
Shiro Kubuki Koken Matsuda Kazuhiko Akiyama Tetsuaki Nishida 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):453-459
A relationship between local structure, thermal stability and electrical conductivity (σ) of xR2O·10Fe2O3·(90 ? x)V2O5 glasses (abbreviated as xRFV glasses, where R = Li, Na, K; x = 20 and 40 in mol %) was investigated by 57Fe-Mössbauer spectroscopy, X-ray diffractometry, differential thermal analysis (DTA) and DC two- and four-probe method. From DTA study, thermal stability of 20RFV glasses is lower than that of 40RFV glasses by evaluating Hruby parameter (K gl). Constant activation energy for crystallization (E a) of 2.5 eV obtained from both 20RFV and 40RFV glasses indicate that the crystallization proceeds with the cleavage of Fe–O bond having the energy of 2.6 eV. Isochronally annealed 20RFV glass at 400–450 °C resulted in the increase in electrical conductivity (σ) from the order of 10?3 to 10?1 S cm?1, whereas slight decrease in σ was observed for 20RFV glass annealed above 460 °C. A paramagnetic doublet with an identical isomer shift (δ) of 0.39 mm s?1 was observed in the 57Fe-Mössbauer spectra of 20RFV glass after isothermal annealing conducted at 400–450 °C for 100 min, which caused a decrease of quadruple splitting (Δ) from 0.67 to 0.52 mm s?1 for 20LiFV glass and from 0.66 to 0.53 mm s?1 for 20NaFV glass. On the other hand, three paramagnetic doublets with δ and Δ of 0.40 and 0.25, 0.38 and 0.60, and 0.31 and 1.11 mm s?1 respectively were observed for 20RFV glass annealed at 460–550 °C, reflecting precipitation of semiconducting FeVO4 phase having σ of 6.0 × 10?7 S cm?1. It can be concluded that isochronal annealing of 20RFV glass below 450 °C resulted in increase in σ due to the structural relaxation, while annealing above 500 °C resulted in the decrease of σ due to the precipitation of FeVO4 phase. 相似文献
20.
V. V. Patrushev S. V. Ostanova A. V. Chubarov S. V. Drozdov 《Russian Journal of Applied Chemistry》2008,81(6):1074-1077
Behavior of silver sulfide in the system Ag2S-Fe(NO3)3-HNO3-H2O was studied at 25, 55, and 80°C using the method of the simplex-lattice experiment design. The quantitative dependences of Ag2S oxidation on the concentrations of the acid and Fe3+ were determined. The isoconcentration diagrams were obtained. 相似文献