共查询到20条相似文献,搜索用时 15 毫秒
1.
利用乙酰丙酮(AcAcH)络合溶胶-凝胶法合成了Ni0.5Zn0.5Fe2O4(NZFO)尖晶石型软磁铁氧体。采用傅里叶变换红外光谱(FTIR)技术研究了Fe、Zn、Ni 3种溶胶中AcAcH与Fe3+、Zn2+、Ni2+的结合形式,通过比较Fe、Zn、Ni溶胶与未添加AcAcH的Fe、Zn、Ni甲醇溶液的红外光谱发现,分别在1 532 cm-1、1 520 cm-1和1 520 cm-1处多了一个吸收峰,说明AcAcH都能与3种离子发生螯合反应。采用X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、物性测量系统(PPMS)分别表征NZFO铁氧体的相组成、微结构以及磁性能。XRD测试结果表明,NZFO铁氧体为单一尖晶石相结构;HRTEM透射结果表明,NZFO为片状,大小均匀,尺寸45 nm左右;PPMS研究结果表明,NZFO铁氧体的饱和磁化强度(Ms)和矫顽力(Hc)分别为36 emu.g-1和167 Oe。 相似文献
2.
采用静电纺丝技术制备了添加0~20wt%Al2O3的Ni0.5Zn0.5Fe2O4纳米纤维。通过XRD、FESEM、TEM和VSM对样品的物相结构、形貌和磁性能进行了表征。结果表明,所合成的复合纳米纤维的直径都分布在40~150 nm之间,添加到纤维中的Al2O3主要以非晶态形式分布于铁氧体晶粒边界;随着Al2O3添加量的增加,可观察到γ-Fe2O3相逐渐析出,Ni-Zn铁氧体的晶格常数单调减小,说明有一些Al2O3进入到尖晶石晶格中取代了B位的Fe3+离子,Ni-Zn铁氧体的平均晶粒尺寸先增大后减小,在Al2O3添加量为8wt%时达到最大值39.2 nm;比饱和磁化强度和矫顽力随Al2O3添加量的增加呈现出相同的变化规律,先减小后增大,当Al2O3添加量超过5wt%时又开始变小。 相似文献
3.
采用差示扫描量热法(DSC)、热重和微分热重(TG-DTG)及固相原位反应池/快速扫描傅立叶变换红外联用技术(hyphenated in situ thermolysis/RSFTIR)研究了纳米结晶体Ni 0.5Zn 0.5Fe 2O 4与高氯酸铵(AP)组成的混合物的热行为和分解反应动力学。结果表明:Ni 0.5Zn 0.5Fe 2O 4使得AP的低、高温分解放热峰温分别提前17.44 K和27.74 K,并使得对应的分解热分别增加3.7 J·g -1和193.7 J·g -1。Ni 0.5Zn 0.5Fe 2O 4并不影响AP的晶转温度和晶转热。Ni 0.5Zn 0.5Fe 2O 4使得AP的TG曲线出现3个阶段,并使得后2个失重阶段的初始和终止温度都有所提前。凝聚相分解产物分析表明Ni 0.5Zn 0.5Fe 2O 4加速了凝聚相AP的分解及氨气的释放。含Ni 0.5Zn 0.5Fe 2O 4的AP的高温分解反应的动力学参数 Ea=238.88 kJ·mol -1, A=1018.59 s -1,动力学方程可表示为d α/d t=10 18.99(1- α)[-ln(1- α)] 3/5e -2.87×104T。始点温度( Te)和峰顶温度( Tp)计算得出AP的热爆炸临界温度值分别为:574.83 K和595.41 K。分解反应的活化熵(Δ S≠)、活化焓(Δ H≠)和活化能(Δ G≠)分别为:109.61 J·mol -1·K -1、236.49 kJ·mol -1及172.58 kJ·mol -1。 相似文献
4.
The solid–liquid equilibria of the ternary system H 2O–Fe(NO 3) 3–Co(NO 3) 2 were studied by using a synthetic method based on conductivity measurements. Two isotherms were established at 0 and 15 °C, and the stable solid phases which appear are the iron nitrate nonahydrate (Fe(NO3)3·9H2O), the iron nitrate hexahydrate (Fe(NO3)3·6H2O), the cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and the cobalt nitrate trihydrate (Co(NO3)2·3H2O). 相似文献
5.
A synthetic route for advanced perovskites is elucidated that consists of a combined EDTA/citrate complexing of metal cations and the subsequent drying and firing at moderate temperatures. A fine-scale intermixing of cations is maintained during all the processing steps. The perovskite-type oxide is formed already in an intermediate step at 700 °C by the reaction of an ultra-finely dispersed powder consisting of a mixed barium–strontium carbonate, a zinc–iron spinel, and zinc oxide. The process yields powders of good sinterability and finally dense ceramics composed of stoichiometric perovskite grains of the type (Ba,Sr)(Zn,Fe)O 3−δ. 相似文献
6.
通过静电纺丝技术制备了多孔软硬磁Ni 0.5Zn 0.5Fe 2O 4/SrFe 12O 19复合纤维,利用综合热重分析仪(TG-DSC)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线能谱仪(EDS)和矢量网络分析仪(VNA)等对复合纤维的晶体结构、微观形貌和电磁性能进行了表征,研究了不同软硬磁质量比对纤维结构和性能的影响。结果表明:900℃下制备的复合纤维具有立体多孔结构,软硬磁质量比为1∶3时,复合纤维的比表面积达到55 m 2·g -1。吸波性能测试结果显示,当吸波剂涂层厚度为3.5 mm时,复合纤维在10.6 GHz处反射损失( RL)值达到-31.9 dB,在2~18 GHz频率范围内, RL值小于-10 dB的吸收带宽达到10.5 GHz,覆盖了整个X波段(8.2~12.4 GHz)和Ku波段(12.4~18 GHz),显示出优异的宽波段吸收性能。 相似文献
7.
Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu 2P 2O 7 and Cu 3(P 2O 6OH) 2. α-Cu 2P 2O 7 is reversibly transformed to β-Cu 2P 2O 7 at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol −1. Enthalpies of formation from oxides of α-Cu 2P 2O 7 and Cu 3(P 2O 6OH) 2 are −279.0 ± 1.4 kJ mol −1 and −538.8 ± 2.7 kJ mol −1, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol −1 and −4302.7 ± 6.7 kJ mol −1, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu 3(P 2O 6OH) 2, thus decreasing its thermodynamic stability. 相似文献
8.
Ab initio-TST calculations were carried out to study the kinetics of the title reaction. The H atom and the OH abstraction paths leading to the same products HO 2 and OH have been considered. The ZPE and BSSE corrected classical barrier heights were predicted to be 7.4 and 17.3 kcal/mol, respectively. Calculated thermal rate constants over the temperature range 300–5000 K showed that the H-abstraction path was the most likely to occur for temperatures below 2500 K which confirms the result found in a previous study [Y. Tarchouna, M. Bahri, N. Jaïdane, Z. Ben Lakdar, J. Mol. Struct. (Theochem), 189 (2003) 664]. The contribution of OH abstraction path to the reaction was predicted to be important for high temperatures. 相似文献
9.
A synthetic method for the fabrication of silica-based mesoporous magnetic (Fe or iron oxide spinel) nanocomposites with enhanced adsorption and magnetic capabilities is presented. The successful in situ synthesis of magnetic nanoparticles is a consequence of the incorporation of a small amount of carbon into the pores of the silica, this step being essential for the generation of relatively large iron oxide magnetic nanocrystals (10 ± 3 nm) and for the formation of iron nanoparticles. These composites combine good magnetic properties (superparamagnetic behaviour in the case of SiO 2–C–Fe 3O 4/γ–Fe 2O 3 samples) with a large and accessible porosity made up of wide mesopores (>9 nm). In the present work, we have demonstrated the usefulness of this kind of composite for the adsorption of a globular protein (hemoglobin). The results obtained show that a significant amount of hemoglobin can be immobilized within the pores of these materials (up to 180 mg g −1 for some of the samples). Moreover, we have proved that the composite loaded with hemoglobin can be easily manipulated by means of an external magnetic field. 相似文献
10.
This work is devoted to a detailed analysis of the interconnection between composition, cation distribution and acidic properties of the surface of nanocrystalline ferrites Ni xZn 1−xFe 2O 4 obtained by aerosol pyrolysis. The detailed analysis of the Mössbauer spectra allows us to determine the distribution of cations between tetrahedral and octahedral positions in spinel structure. Depending on samples composition, the tetrahedral positions can be occupied by only Fe 3+ cations (inverse spinel, x≥0.4) or by Fe 3+ and Zn 2+ cations (mixed spinel, x=0, 0.2). Increasing the nickel concentration in the ferrite leads to decrease in the number of strong acid centers on the surface. It was found that the decrease in the contribution of strong surface acid sites leads to an increase in sensory sensitivity of the ferrite towards ammonia. For ethanol detection an inverse relationship between sensor signal and surface acidity was observed. 相似文献
11.
The structure, magnetism, transport and thermal expansion of the perovskite oxide LaNi 0.5Fe 0.5O 3 were studied over a wide range of temperatures. Neutron time-of-flight data have shown that this compound undergoes a first-order phase transition between ∼275 and ∼310 K. The structure transforms from orthorhombic ( Pbnm) at low temperatures to rhombohedral ( R3¯ c) above room temperature. This phase transition is the cause for the previously observed co-existence of phases at room temperature. The main structural modification associated with the phase transition is the change of tilting pattern of the octahedra from a+b−b− at low temperatures to a−a−a− at higher. Magnetic data strongly suggests that a spin-glass magnetic state exists in the sample below 83 K consistent with the absence of magnetic ordering peaks in the neutron data collected at 30 K. At high temperatures the sample behaves as a small polaron electronic conductor with two regions of slightly different activation energies of 0.07 and 0.05 eV above and below 553 K, respectively. The dilatometric data show an average thermal expansion coefficient of 14.7×10 −6 K −1 which makes this material compatible with frequently used electrolytes in solid oxide fuel cells. 相似文献
12.
High-temperature proton conductors have wide applications in the areas of fuel cells, electrolysis and hydrogen separation. Barium zirconate-based materials are of interest due to their good stability and high protonic conductivity. The reported conductivity of these ceramic materials is generally less than 10 −2 S/cm, even at high temperatures. This is not high enough for an electrolyte-supported device to achieve an ASR of less than 0.2 Ω cm 2 therefore thin film electrolytes are required for successful application. As BaZrO 3-based materials have to be sintered at temperatures as high as 1700 °C, this makes it difficult to find a suitable supporting electrode which will not undergo significant chemical reaction with the BaZrO 3-based electrolyte during fabrication of the required electrode supported electrolyte. In this paper, proton-conducting BaZr 0.8Y 0.2O 2.9 was successfully sintered at 1325 °C with a relative density of 96% via addition of 1 wt% ZnO. Fabrication of electrochemical cells using proton-conducting BaZr 0.8Y 0.2O 2.9 as the electrolyte thus becomes possible. The formula of the 1 wt% ZnO added sample is Ba 0.97Zr 0.77Y 0.19Zn 0.04O 3−δ which exhibits a tetragonal structure with space group P4/ mbm (127); a=5.9787(1) Å, c=4.2345(1) Å, V=151.36(1) Å 3. It was found that a solid solution was formed for a limited range of Zn doping. Conductivity has been studied as a function of atmosphere (air, dry and wet 5% H 2/Ar) with the changes in bulk and grain boundary on changing atmosphere being monitored as a function of time. The total conductivity of Ba 0.97Zr 0.77Y 0.19Zn 0.04O 3–δ is 1.0×10 −3 S/cm above 600 °C therefore it may be used as a proton-conducting thin film electrolyte for efficient electrochemical devices at such temperatures. The grain boundary resistance is insignificant at high temperature for the well-sintered sample. 相似文献
13.
Mesoporous YSZ–γ-Al 2O 3 membranes were coated on α-Al 2O 3 (Ø2 mm) tube by dipping the α-Al 2O 3 support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al 2O 3 support. The quality of the mesoporous YSZ–γ-Al 2O 3 membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ -Al 2O 3 content became more than 40%. Addition of γ-Al 2O 3 inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N 2 permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al 2O 3 layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al 2O 3 composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al 2O 3 layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H 2 flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al 2O 3 by elevation of temperature. 相似文献
14.
The germanate compound Cu 2Sc 2Ge 4O 13 has been synthesized by solid-state ceramic sintering techniques between 1173 and 1423 K. The structure was solved from single-crystal data by Patterson methods. The title compound is monoclinic, a=12.336(2) Å, b=8.7034(9) Å, c=4.8883(8) Å, β=95.74(2), space group P2 1/ m, Z=4. The compound is isotypic with Cu 2Fe 2Ge 4O 13, described very recently. The structure consists of crankshaft-like chains of edge-sharing ScO 6 octahedra running parallel to the crystallographic b-axis. These chains are linked laterally by [Cu 2O 6] 8− dimers forming a sheet of metal-oxygen-polyhedra within the a- b plane. These sheets are separated along the c-axis by [Ge 4O 13] 10− units. Cooling to 100 K does not alter the crystallographic symmetry of Cu 2Sc 2Ge 4O 13. While the b, c lattice parameter and the unit cell volume show a positive linear thermal expansion ( α=6.4(2)×10 −6, 5.0(2)×10 −6 and 8.3(2)×10 −6 K −1 respectively), the a lattice parameter exhibits a negative thermal expansion ( α=−3.0(2)×10 −6 K −1) for the complete T-range investigated. This negative thermal expansion of a is mainly due to the increase of the Cu-Cu interatomic distance, which is along the a-axis. Average bond lengths remain almost constant between 100 and 298 K, whereas individual ones partly show both significant shortages and lengthening. 相似文献
15.
The adsorption of Saccharomyces cerevisiae mandelated dehydrogenase (SCMD) protein on the surface-modified magnetic nanoparticles coated with chitosan was studied in a batch adsorption system. Functionalization of surface-modified magnetic particles was performed by the covalent binding of chitosan onto the surface of magnetic Fe 3O 4 nanoparticles. Characterization of these particles was carried out using FTIR spectra, transmission electron micrography (TEM), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Magnetic measurement revealed that the magnetic Fe 3O 4–chitosan nanoparticles were superparamagnetic and the saturation magnetization was about 37.3 emu g −1. The adsorption capacities and rates of SCMD protein onto the magnetic Fe 3O 4–chitosan nanoparticles were evaluated. The adsorption capacity was influenced by pH, and it reached a maximum value around pH 8.0. The adsorption capacity increased with the increase in temperature. The adsorption isothermal data could be well interpreted by the Freundlich isotherm model. The kinetic experimental data properly correlated with the first-order kinetic model, which indicated that the reaction is the adsorption control step. The apparent adsorption activation energy was 27.62 kJ mol −1 and the first-order constant for SCMD protein was 0.01254 min −1 at 293 K. 相似文献
16.
The electric and magnetic properties of the perovskites Nd 0.8Na 0.2Mn (1−x)Co xO 3 (0 x0.2) prepared by the usual ceramic procedure were investigated. The insulator-to-metal-like (IM) transition, closely related to a ferromagnetic arrangement, was revealed for the composition of x=0.04 and a similar tendency was detected for x=0. The insulating behavior persists down to low temperatures for higher contents of cobalt ions in spite of the transition to the bulk ferromagnetism. The properties are interpreted in terms of the steric distortion, tilting of the Mn(Co)O 6 octahedra and the double-exchange interactions of the type Mn 3+–O 2−–Mn 4+and Mn 3.5+δ–O 2−–Co 2+, respectively. Presence of antiferromagnetic domains in the ferromagnetic matrix for the most of cobalt-substituted samples is supposed. 相似文献
17.
A detailed study has been made of the different steps involved upon the preparation of γ-Al 2O 3-supported Ni-Mo HDS catalyst precursors by urea–matrix combustion (UMxC) method. Catalyst performance was evaluated using a tubular fixed-bed reactor and the hydrodesulfurization of thiophene under normal pressure as a model reaction. The oxidic and sulfurized states of the HDS catalysts were characterized by X-ray diffraction (XRD), laser Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and high resolution transmission electron microscopy (HRTEM) in order to correlate their oxidic and sulfurized properties with the catalytic behaviour. During the UMxC process several consecutive stages such as melting, dissolution and chemical reactions occurred. There was no evidence of residual carbon and well-dispersed Ni- and Mo-oxo-species supported on alumina were formed. Urea employed as fuel not only increases the combustion rate, but also undergoes a decomposition process (endothermic reaction) that could contribute to the reduction of the combustion temperature. The urea–matrix combustion method permit to synthesize highly active γ-Al2O3-supported Ni-Mo HDS catalysts with a comparable promoter effect than that of corresponding catalyst prepared by impregnation method. In addition, an opposite relation between the activity and the hydrogenation properties was observed indicating that highly active HDS catalyst requires low consumption of hydrogen. Finally, both the ignition temperature and the urea-oxidizer ratio produce no significant changes in the HDS catalytic properties of Ni-Mo-based catalysts. 相似文献
18.
In the present work temperature dependence of heat capacity of cesium tantalum tungsten oxide has been measured first in the range from 7 to 350 K and then between 330 and 630 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity Cp° ( T), enthalpy H°( T) − H°(0), entropy S°( T) − S°(0) and Gibbs function G°( T) − H°(0), for the range from T → 0 to 630 K. The structure of CsTaWO 6 is refined by the Rietveld method: space group F d3 m, Z = 8, a = 10.3793(2) Å, V = 1118.14(4) Å 3. The high-temperature X-ray diffraction was used for the determination of temperature of phase transition and coefficient of thermal expansion. 相似文献
19.
Effect of H 2S on the catalytic performance of the reduced and sulfided Ni–Mo/Al 2O 3 catalysts in hydrodeoxygenation of benzofuran is studied. The steady-state reaction experiments showed a decrease in activity for both reduced and sulfided catalysts when H 2S was introduced into the feed. The reaction conversion of benzofuran over the reduced catalyst still remained superior to that of the sulfided catalyst in the presence of H 2S, however, at high reaction temperatures, the product distribution over the pre-reduced catalyst is similar to the sulfided catalyst. The studies with temperature-programmed desorption (TPD), temperature-programmed reaction (TPRxn) and X-ray photoelectron spectroscopy (XPS) techniques showed a partial sulfidation of the reduced catalysts when exposed to H 2S under reaction conditions, however, the catalyst does not go through a complete conversion to a molybdenum sulfide phase. Instead oxygen–sulfur exchange on the surface leaves behind oxisulfide species, with catalytic activity closely resembling that of the reduced catalysts. The effect of H 2S on the reaction performance is mainly coming from the competitive adsorption between H 2S and benzofuran and the formation of SH groups with decomposition of H 2S at high temperatures. 相似文献
20.
Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCF) hollow fibers were fabricated using a phase inversion/sintering method. As oxygen permeation of BSCF hollow fibers is controlled by the rate surface exchange kinetics, catalytic Ag particles were coated on both inner and outer surfaces using chemical deposition method, as verified by SEM and EDX. The Ag coated BSCF membranes showed up to 100% increase in oxygen permeation at 700 °C, and improvements lower than 10% were measured at 950 °C as compared with unmodified membranes. It was found that Ag catalyst surface loading was non-homogenous and concentrated on the perovskite grain boundaries. As a result, lighter Ag surface loading delivered improved oxygen flux while oxygen flux reached a maximum even though in the presence of excess catalyst loading. The catalytic activity of Ag was beneficial in enhancing surface reaction kinetics up to 850 °C attributed to the spillover effect. Above this temperature, the increase in oxygen permeation rate was marginally diminished due to the reduction of the spillover effect. 相似文献
|