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1.
Temperature-programmed thermal decomposition of γ- and α-manganese oxyhydroxide has been studied between 20 and 670°C under vacuum and under a low pressure (10 Torr) of oxygen. Solid products at various temperatures have been analyzed by X-ray diffractometry. Under vacuum γ-MnOOH decomposed below 400°C to a mixture of Mn 5O 8, α-Mn 3O 4, and water according to the reaction scheme: 8MnOOH → Mn 5O 8 + Mn 3O 4 + 4H 2O. Above this temperature Mn 5O 8 was converted to α-Mn 3O 4 as a result of oxygen removal. The vacuum dehydration at 250°C of oxyhydroxide rich in α-MnOOH led to the formation of a new modification of Mn 2O 3 isostructural with corundum (α-Al 2O 3). In oxygen both oxyhydroxides decomposed to β-MnO 2. γ-MnOOH transformed directly to β-MnO 2 while α-MnOOH appeared to transform via corundum-phase Mn 2O 3 as an intermediate. 相似文献
2.
The composite/nanocomposite powders of Mn 0.5Ni 0.5Fe 2O 4/Fe type were synthesized starting from nanocrystalline Mn 0.5Ni 0.5Fe 2O 4 ( D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn 0.5Ni 0.5Fe 2O 4/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 0.5Fe 2O 4/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 xFe 2O 4/Ni–Fe composite type. The new formed ferrite of Fe 1?xMn xFe 2O 4 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 xFe 2O 4, Ni structure, FeO, and (NiO) 0.25(MnO) 0.75 phases. 相似文献
3.
The solubility boundaries for Lu 2O 3 and Mn 3O 4 oxides and LuMn 2O 5 manganate in LuMnO 3 ± δ are determined on the basis of an X-ray phase analysis of homogeneous solid solutions and heterogeneous compositions with
molecular formula Lu 2 − x
Mn
x
O 3 ± δ (0.90 ≤ x ≤ 1.16; Δ x = 0.02) obtained by ceramic synthesis in air in a temperature range of 900–1400°C. It is found that the solubility of Lu 2O 3 in LuMnO 3 ± δ corresponds to the composition of Lu 1.03Mn 0.97O 3 ± δ and remains invariable over the investigated range of temperatures, while the solubility of Mn 3O 4 (which corresponds to the composition of Lu 0.91Mn 1.09O 3 ± δ) remains invariable in the temperature range of 995–1400°C. It is shown that lutetium manganate LuMn 2O 5 coexists with lutetium manganate LuMnO 3 ± δ at temperatures of less than 995°C in air, and its solubility in LuMnO 3 ± δ decreases as the temperature of 995°C (corresponding to the composition Lu 0.91Mn 1.09O 3 ± δ) falls to 900°C for Lu 0.97Mn 1.03O 3 ± δ. 相似文献
4.
We have studied the effect of hydrothermal conditions at constant temperature of 180 °C, varying preparation time for 15, 30 and 45 h on nanostructures of diluted magnetic semiconductor Sn 0.95Co 0.05O 2 (SC5). X-ray diffraction pattern confirm the tetragonal SnO 2 rutile phase. The transmission and scanning electron microscopy shows the resulting nanostructures i.e. nanospheres and nanorods. The proposed reaction mechanism is given. The Raman spectra show the formation of tetragonal rutile structure of SC5 nanostructures. Fourier transform infrared spectrum has been used to verify the existence of Sn–O bond. The photoluminescence spectra show that the emission spectral intensity increases gradually with decreasing grains size, increasing hydrothermal heating time of SC5 samples and exhibits an intense blue luminescence centered at a wavelength of 531 nm. The optical absorbance measurements revealed that the nanometric size of the materials influences the energy band gap. All the prepared SC5 samples exhibit room temperature ferromagnetism. 相似文献
5.
Rb 6Mn 2O 6 was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Mn 3O 4, RbN 3 and RbNO 3) were heated in a special regime up to 500 °C and annealed at this temperature for 75 h in silver crucibles. Single crystals have been grown by annealing a mixture with a slight excess of rubidium components at 450 °C for 500 h. According to the single crystal structure analysis, Rb 6Mn 2O 6 is isotypic to K 6Mn 2O 6, and crystallizes in the monoclinic space group P2 1/c with a = 6.924(1) Å, b = 11.765(2) Å, c = 7.066(1) Å, β = 99.21(3)°, 2296 independent reflections, R1 = 5.23 % (all data). Manganese is tetrahedrally coordinated and two tetrahedra are linked by sharing a common edge, forming a dimer [Mn 2O 6] 6−. The magnetic behavior has been investigated. 相似文献
6.
Single phase cubic spinel of the composition Mn 1.5Al 1.5O 4 is synthesized. Its crystal structure refinement shows that 0.4Mn+0.6Al are in the octahedral sites and 0.7Mn+0.3Al are in the tetrahedral sites. High temperature X-ray diffraction is used to analyze Mn 1.5Al 1.5O 4 behavior during heating and cooling in air. In a temperature range of 600°C to 700°C, initial spinel splits into layers, and the sample represents a twophase system: cubic spinel Mn 0.4Al 2.4O 4 and a phase based on β-Mn 3O 4. Above 900°C the sample again turns into single phase cubic spinel. The role of oxidizing processes in the decomposition of Mn 1.5Al 1.5O 4 caused by oxygenation and partial oxidation of Mn 2+ to Mn 3+ is shown. A scheme of structural transformations of manganese aluminum spinel during heating from room temperature and cooling from 950°C is proposed. 相似文献
7.
Spinel LiMn 2O 4 and Sm, La co-substituted LiSm x La 0.2-x Mn 1.80O 4 ( x?=?0.05, 0.10 and 0.15) cathode materials were synthesized by sol–gel method using aqueous solutions of metal nitrates and tartaric acid as chelating agent at 600 °C for 10 h. The structure and electrochemical properties of the synthesized materials were characterized by using thermogravimetric/differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, charge/discharge and electrochemical impedance spectroscopy studies. XRD analysis indicated that all the prepared samples were mainly belong to cubic crystal form with F d3 m space group. LiSm 0.10La 0.10Mn 1.80O 4 exhibits capacity retention of 90 % and 82 % after 100 cycles at room temperature (30 °C) and at elevated temperature (50 °C) at a rate of 0.5-C, respectively, much higher than those of the pristine LiMn 2O 4 (74 % and 60 %). Among all the compositions, LiSm 0.10La 0.10Mn 1.80O 4 cathode has improved the structural stability, high-capacity retention, better elevated temperature performance and excellent electrochemical performances of the rechargeable lithium-ion batteries. 相似文献
8.
The effect of aluminium oxide support on the thermal behaviour of manganese carbonate was investigated using TG, DTA, dDTA and XRD techniques. The concentrations of MnCO 3 were 0.025, 0.05 and 0.125 mol/mol Al 2O 3. The results obtained showed that the employed support material retards the thermal decomposition of manganese carbonate due to the formation of a manganese/aluminium adduct which decomposes readily at 350°C instead of 250°C in the absence of Al 2O 3, to give γ-MnO 2. This compound decomposed at 500°C into Mn 2O 3 (partridgeite). The produced Mn 2O 3 decomposed at 940°C yielding Mn 3O 4 which interacted with atmospheric oxygen during the cooling processes to give Mn 2O 3. However, Mn 3O 4 formed in the case of unloaded Mn 2O 3 did not interact easily with O 2 and remained stable. The results might indicate the role of Al 2O 3 in increasing the degree of dispersion of the produced manganese oxides thus increasing their reactivity towards reoxidation by O 2. The produced manganese oxide (Mn 2O 3) enhanced markedly the crystallization of aluminium oxide at 800°C into ?-Al 2O 3. Solid-solid interaction between Mn 2O 3 and Al 2O 3 occurred at 800°C giving MnAl 2O 4 which decomposed at 1000°C yielding Mn 2O 3 and α-Al 2O 3 (corundum). 相似文献
9.
Electrochemical properties of composite cathodes consisting of La 0.8Sr 0.2Mn 1?x Cu x O 3 (LSMCu, 0?≤? x?≤?0.2) and Ce 0.8Gd 0.2O 2?x (GDC) were determined by impedance spectroscopy, and conduction mechanism for the composite cathodes was investigated by a near-edge X-ray absorption fine-structure analysis (NEXAFS). LSMCu–GDC cathodes showed lower polarization resistance ( R p) than LSM–GDC up to 750 °C, whereas they exhibited better performance at higher temperature (≥800 °C). The best performance was achieved with the LSMCu10–GDC cathode: 0.27 and 0.08?Ω cm 2 at 800 °C and 850 °C, respectively. NEXAFS and refinement results confirmed that Cu doping caused the oxidation of Mn 3+ to Mn 4+ and lattice contraction. This additional Mn 4+ can lead to the formation of oxygen vacancies when Mn 4+ is converted to Mn 3+ at relatively high temperatures (above 600 °C). This in turn contributes to improved oxygen ion transport in LSM. The LSMCu–GDC composite cathode can thus be considered a suitable potential cathode for SOFC applications. 相似文献
10.
The effect of ferric and manganese oxides dopants on thermal and physicochemical properties of Mn-oxide/Al 2O 3 and Fe 2O 3/Al 2O 3 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 Fe 2O 3 at 350°C and shows thermal stability up to1000°C. Crystalline Fe 3O 4 and Mn 3O 4phases were detected for some doped solids precalcined at 1000°C. Crystalline γ-Al 2O 3 phase was detected for all solids preheated up to 800°C. Ferric and manganese oxides enhanced the formation of α-Al 2O 3 phase at1000°C. Crystalline MnAl 2O 4 and MnFe 2O 4 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 H 2O 2 reaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
The effect of the calcination temperature and composition of the MnO x–ZrO 2 system on its structural characteristics and catalytic properties in the reaction of CO oxidation was studied. According to X-ray diffraction analysis and H 2 thermo-programmed reduction data, an increase in the calcination temperature of Mn 0.12Zr 0.88O 2 from 450 to 900°C caused a structural transformation of the system accompanied by the disintegration of solid solution with the release of manganese ions from the structure of ZrO 2 and the formation of, initially, highly dispersed MnO x particles and then a crystallized phase of Mn 3O 4. The dependence of the catalytic activity of MnO x–ZrO 2 in the reaction of CO oxidation on the calcination temperature takes an extreme form. A maximum activity was observed after heat treatment at 650–700°C, i.e., at limiting temperatures for the occurrence of a solid solution of manganese ions in the cubic modification of ZrO 2. If the manganese content was higher than that in the sample of Mn 0.4Zr 0.6O 2, the phase composition of the system changed: the solid solution phase was supplemented with Mn 2O 3 and β-Mn 3O 4 phases. The samples of Mn 0.4Zr 0.6O 2–Mn 0.6Zr 0.4O 2 exhibited a maximum catalytic activity; this was likely due to the presence of the highly dispersed MnO x particles, which were not the solid solution constituents, on their surface in addition to an increase in the dispersity of the solid solution. 相似文献
12.
The crystal and pore structures of a microspherical alumina-chromium catalyst calcined at 800–1100°C were studied using a set of currently available physicochemical techniques (X-ray diffraction, lowtemperature nitrogen adsorption, diffuse reflectance UV-vis spectroscopy, Raman spectroscopy, and EPR spectroscopy); the state of its active component and the catalytic properties in isobutane dehydrogenation were examined. As the calcination temperature was increased from 800 to 900–1000°C, the properties of the catalyst were improved as a result of the formation of Cr 2O 3 clusters in an optimum amount and a decrease in the surface acidity of the catalyst due to the dehydroxylation and phase transformations of the aluminum oxide support. Calcination at 1100°C was accompanied by a decrease in the yield of isobutylene as a result of the formation of inactive macrocrystalline chromium (III) oxide and a chromium species inaccessible to reacting molecules; this chromium species was encapsulated in closed pores as the constituent of a solid solution of α-Al 2O 3-Cr 2O 3. 相似文献
13.
We have found a new compound Mn 8O 10Cl 3. It is prepared by oxidation of anhydrous or hydrated MnCl 2 in streaming (N 2 + O 2) at temperatures less than 680°C. At room temperature the compound is tetragonal, a = b = 9.2898 Å, c = 13.0247 Å. The more symmetric space group is . Mn 8O 10Cl 3 becomes cubic at 360°C with the c-axis as cubic parameter. In air, DTA and GTA have shown that Mn 8O 10Cl 3 is transformed at 580°C into Mn 2O 3 which gives Mn 3O 4 at 960°C. The exact formula has been determined only by crystal structure analysis. 相似文献
14.
Polymeric materials have been found to be ideal candidates for the synthesis of organic–inorganic nanomaterials. We have obtained Co 3O 4‐decorated graphene oxide (GO) nanocomposites by a simple polymer combustion method. Polyvinyl alcohol (PVA) of two different molecular weights, 14,000 and 125,000, was used for the synthesis. The pristine sample was annealed at 300, 500, and 800°C. PVA has played an important role in the formation of GO and Co 3O 4 nanoparticles. Synthesized Co 3O 4–GO nanocomposites were characterized by X‐ray diffraction, Fourier transform infrared, Raman, electron paramagnetic resonance, transmission electron microscopy, and vibrating sample magnetometry. Reflection peaks at 12° and 37° in an X‐ray study confirm the formation of Co 3O 4–GO. Raman study validates the presence of GO in nanocomposites of Co 3O 4–GO. Room temperature ferromagnetism was observed in all annealed samples. The highest coercivity of 462 G was observed for 300°C annealed samples as compared with bulk Co 3O 4. On the basis of the results obtained, a mechanism of formation is proposed. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
Procedures for the preparation at low temperature (80 °C) of uniform colloids consisting of Mn 3O 4 nanoparticles (about 20 nm) or elongated α-MnOOH particles with length less than 2 μm and width 0.4 μm or less, based on
the forced hydrolysis of aqueous manganese(II) acetate solutions in the absence (Mn 3O 4) or the presence (α-MnOOH) of HCl are described. These solids are only produced under a very restrictive range of reagent
concentrations involving solutions of 0.2–0.4 mol dm −3 manganese(II) acetate for Mn 3O 4 and of 1.6–2 mol dm −3 Mn(II) and 0.2–0.3 mol dm −3 HCl for α-MnOOH. The role that the acetate anions play in the precipitation of these solids is analyzed. It seems that these
anions promote the oxidation of Mn(II) to Mn(III), which readily hydrolyze causing precipitation. The evolution of the characteristics
of the powders with temperature up to 900 °C is also reported. Thus, Mn 3O 4 particles transform to Mn 2O 3 upon calcination at 800 °C; this is accompained by a sintering process. The α-MnOOH sample also experiences several phase
transformations on heating. First, it is oxidized at low temperatures (250–450 °C) giving MnO 2 (pyrolusite), which is further reduced to Mn 2O 3 at 800 °C. After this process the particles still retain their elongated shape.
Received: 19 October 1999 Accepted: 24 November 1999 相似文献
16.
LiNi 0.5Mn 1.5O 4 powders were prepared through polymer-pyrolysis method. XRD and TEM analysis indicated that the pure spinel structure was
formed at around 450 °C due to the very homogeneous intermixing of cations at the atomic scale in the starting precursor in
this method, while the well-defined octahedral crystals appeared at a relatively high calcination temperature of 900 °C with
a uniform particle size of about 100 nm. When cycled between 3.5 and 4.9 V at a current density of 50 mA/g, the as prepared
LiNi 0.5Mn 1.5O 4 delivered an initial discharge capacity of 112.9 mAh/g and demonstrated an excellent cyclability with 97.3% capacity retentive
after 50 cycles. 相似文献
17.
The thermal decompositions of pure and mixed manganese carbonate and ammonium molybdate tetrahydrate in molar ratios of 3:1,
1:1 and1:3 were studied by DTA and TG techniques. The prepared mixed solid samples were calcined in air at 500, 750 or 1000°C
and then investigated by means of an XRD technique. The results revealed that manganese carbonate decomposed in the range
300–1000°C, within termediate formation of MnO 2, Mn 2O 3 andMn 3O 4. Ammonium molybdate tetrahydrate first lost its water of crystallization on heating, and then decomposed, yielding water
and ammonia. At 340°C,MoO 3 was the final product, which melts at 790°C. The thermal treatment of the mixed solids at 500, 750 or 1000°C led to solid-solid
interactions between the produced oxides, with the formation of manganese molybdate. At 1000°C, Mn 2O 3 and MoO 3 were detected, due to the mutual stabilization effect of these oxides at this temperature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Effects of the anion type on the structure, thermal stability, and catalytic performance of La-doped Cu-Mn catalysts prepared by co-precipitation were characterized by X-ray diffraction, Brunauer-Emmett-Teller, temperature-programmed reduction, temperature-programmed reduction of oxidized surfaces, and temperature-programmed desorption. The Cu-Mn catalyst was tested for the water-gas shift (WGS) reaction. The main crystalline phase of samples prepared with sulfate, acetate, chloride, and nitrate as the starting materials was a Cu 1.5Mn 1.5O 4 spinel structure, following the WGS reaction, the main crystalline phases were transformed into Cu and MnO. The sample prepared with acetate as the starting material showed the most obvious MnCO 3 characteristic diffraction peaks, with better synergistic effects of Cu and MnO, increased adsorption of CO 2 and improved dispersion of Cu on the catalyst surface; also, the best thermal stability and the highest low temperature catalytic activity were observed. The sample prepared with nitrate as the starting material maintained high thermal stability and catalytic performance in the range of 400°C to 450°C, but CO conversion decreased below 350°C. Catalytic performance of the sample prepared with sulfate and chloride as the starting materials was poor, ranging from 200°C to 450°C. 相似文献
19.
In this work, ultrafine Cu1.5Mn1.5O4 spinel nanoparticles were successfully synthesized by a sol–gel method combined with two complexing agents, which was firstly employed in the reductive transformation from p-nitrophenol into p-aminophenol. The effect of calcination temperature on the crystal phase and microstructure of Cu1.5Mn1.5O4 nanoparticles was investigated in this article. It was found that Cu1.5Mn1.5O4 nanoparticles with pure spinel phase can be obtained at 500 °C with the help of EDTA acid–citric acid complexing agents. Below 500 °C, there exists some Mn2O3 impure phase. SEM characterization indicated that the particle size of the spinel Cu1.5Mn1.5O4 rapidly increases above 600 °C. The catalytic experimental results show that the Cu1.5Mn1.5O4 nanoparticles prepared at 500 °C exhibit the highest catalytic activity which is even superior to some precious metal catalysts. With the calcination temperature increasing, the catalytic activity of Cu1.5Mn1.5O4 spinel nanoparticles gradually degrades which can be ascribed to the particle size growth of Cu1.5Mn1.5O4. It can also be observed that all the oxide samples, namely CuO, Mn2O3 and Cu1.5Mn1.5O4, possess certain catalytic ability for the transformation from p-nitrophenol into p-aminophenol. However, the catalytic activity of Cu1.5Mn1.5O4 spinel nanoparticles is obviously higher than CuO and Mn2O3. Especially, Mn2O3 alone has very poor catalytic activity in the reduction of p-nitrophenol. 相似文献
20.
The spinel Mn 0.5Mg 0.5Fe 2O 4 was obtained via calcining Mn 0.5Mg 0.5Fe 2(C 2O 4) 3·5H 2O above 400 °C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform FT-IR, X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer, and vibrating sample magnetometer. The results showed that Mn 0.5Mg 0.5Fe 2O 4 obtained at 600 °C had a specific saturation magnetization of 46.2 emu g –1. The thermal decomposition of Mn 0.5Mg 0.5Fe 2(C 2O 4) 3·5H 2O below 450 °C experienced two steps which involved, at first, the dehydration of five water molecules and then decomposition of Mn 0.5Mg 0.5Fe 2(C 2O 4) 3 into spinel Mn 0.5Mg 0.5Fe 2O 4 in air. Based on Starink equation, the values of the activation energies associated with the thermal decomposition of Mn 0.5Mg 0.5Fe 2(C 2O 4) 3·5H 2O were determined. 相似文献
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