SOLID SOLUTION BEHAVIOR OF Y2−x−yGdxEuyO3 NANOPOWDERS DURING PROCESS OF PREPARATION AND THEIR LUMINESCENCE PROPERTIES

用柠檬酸螯合法制备Y_2-x-yGd_xEu_yO₃纳米粉体(x+y≤ 2), 通过FTIR, XRD和SEM分析了制备过程中的物相变化以及pH值对粉体 形貌的影响. 测试了Y_2-x-yGd_xEu_yO₃ 晶格常数和晶胞体积, 分析了Gd与Eu在Y₂O₃中的固溶行为及其发光性能. 结果表明: 在pH<3的体系中制备Y_2-x-yGd_xEu_yO₃粉体较为适合, 经900 ℃煅烧2 h可完全合成出立方相的Y_2-x-yGd_xEu_yO₃; 在pH=1时, 加入少量乙二醇 (5%, 体积分数) 时得到粉体形貌最佳, 粒径约90 nm, 近球形. 样品的发光性能和Y, Gd的配比以及Eu的含量有关, 当化学配比为Y_0.2Gd_1.65Eu_0.15O₃时样品发光强度最高,y值超过0.15会发生浓度猝灭, 导致发光强度降低.     

Cu2+−Ni2+−NH3−NH4+−C2O42−−H2O体系金属离子沉淀行为热力学分析

针对反应体系Cu2+?Ni2+?NH3?NH4+?C2O42??H2O中Cu2+和Ni2+的反应行为,根据物质守恒原理,建立热力学数学模型.模拟计算结果表明,该体系中金属离子的沉淀是一个复杂的动态平衡过程;在高pH条件下,Cu2+和Ni2+与NH3配合分别形成[Cu(NH3)n]2+(n=3?5)和[Ni(NH3)m]...     

A systematic study on the synthesis of Ca, Gd codoped cerium oxide by combustion method

Co-doped of CeO₂ nanopowders are ideal electrolyte materials for intermediate temperature solid oxide fuel cells. In this work, Ce_1−(x+y)Gd_xCa_yO_2−(0.5x+y) nanopowders are successfully synthesized by a glycine-nitrate combustion process. Then calcination was carried out at 450, 700, 850, 950 and we found that calcined powders were single phase by room temperature X-ray diffraction (XRD) and have an average crystallite size of 45 nm (based on Scherrer formula). Scanning electron microscopy (SEM) was employed to characterize the morphology of powder. Finally we studied the effect of fuel to nitrate ratio on the properties of resulting powders.     

缓冲溶液和分散剂对共沉淀法制备纳米级ITO粉体的影响

用化学共沉淀法制备ITO粉体。制备过程中,分别将NH_4Cl-NH_3H_2O、(NH_4)_2SO_4-NH_3H_2O和NH_4AC溶液作为缓冲溶液,保持反应过程中pH值基本不变。采用可溶性淀粉、PVP、十二烷基磺酸钠作为分散剂。借助XRD、TEM、BET及四探针电阻仪,研究缓冲溶液和分散剂对制得粉体的物相、形貌、分散性及导电性能的影响。结果表明:采用缓冲溶液制备出的粉体为单相In_2O_3粉体。采用NH_4AC作为缓冲溶液,用淀粉作为分散剂,当pH值为6~7时,所制粉体的粒径在10 nm左右,颗粒为立方体形,粒度均匀,分散性能好,电阻率相对较低。     

Composite of polyaniline containing iron oxides with nanometer size

A composite of polyaniline (PANI) containing iron oxides with nanometer size was synthesized by a chemical method. The structure, electrical and magnetic properties of the resulting PANI-Fe_xO_y composites depend on the pH value of the reaction medium and temperature. For the basic preparation conditions (e.g. pH 14), the resulting PANI-Fe_xO_y, composite can be attracted by a magnet at room temperature, and its magnetization with the applied magnetic field exhibits a hysteresis loop with H_c = 0. It has been demonstrated that nanocrystalline ferromagnetic particles of Fe₃O₄ with 14.0 nm size correspond to super-paramagnetic properties observed from PANI-Fe_xy composites. For the acidic conditions (e.g. pH1), on the other hand, the electrical properties of the resulting PANI-Fe_xO_y composite show a semiconducting behavior. By comparison with PANI-Cl⁻¹, the lower conductivity (about 10⁻⁴ S/cm) for PANI-Fe_xO_y composite may be due to the presence of iron oxides in the composite, although its doping degree is the same as that of PANI-Cl⁻.     

Preparation and property of spinel LiMn2O4 material by co-doping anti-electricity ions

1 Introduction At present, LiCoO2 is almost the only cathode material of Li-ion batteries, which can be used in large-scale commercialization, because such material possesses high specific capacity, ease of preparation, high discharging flat and favorable…     

Recovery of valuable elements from spent YBa2Cu3O7-x/Ag composite superconductor bulks

Silver as a highly conductive metal is usually doped in YBa₂Cu₃O_7–x superconductor bulks to improve critical current density of YBa₂Cu₃O_7–x superconductor. The valuable metal elements silver, yttrium, barium and copper in waste YBa₂Cu₃O_7–x/Ag composite superconductor bulks were recovered, respectively. Silver was recovered with process at first, the waste was dissolved by nitric acid and silver chloride was precipitated by adding chloride acid, then silver pig was obtained by melting silver chloride together with sodium carbonate at 1 000 °C. The effective factors on recovery ratio and purity of silver were studied. The chemical analysis proves that the purity of silver ingot is 95.86%. The recovery ratio of silver is calculated to be 92.56%. The loss of silver may be due to the loss of silver chloride during filtering and the volatilization of silver when silver chloride and sodium carbonate are smelted at high temperature. For other three metal elements, Y³⁺, Ba²⁺ and Cu²⁺, in the surplus waste liquid after recovering silver, they were separated with the sequence of barium, copper and then yttrium step by step. First, sulfate acid was used to precipitate barium sulfate. Then, sodium sulfide was added to the surplus solution so that copper could be separated as copper sulfide. During this separation procedure, it was important to control the pH value to be 1–2. After that, oxalic acid was added into the surplus solution to obtain yttrium oxalate. Finally, yttrium oxide was formed by burning yttrium oxalate. The XRD results indicate that the final products are all single-phase compounds as BaSO₄, CuS and Y₂O₃, respectively.     

Combustion synthesis of FeAl−Al2O3 composites with TiB2 and TiC additions via metallothermic reduction of Fe2O3 and TiO2

Combustion synthesis involving metallothermic reduction of Fe₂O₃ and TiO₂ was conducted in the mode of self-propagating high-temperature synthesis (SHS) to fabricate FeAl-based composites with dual ceramic phases, TiB₂/Al₂O₃ and TiC/Al₂O₃. The reactant mixture included thermite reagents of 0.6Fe₂O₃+0.6TiO₂+2Al, and elemental Fe, Al, boron, and carbon powders. The formation of xFeAl−0.6TiB₂−Al₂O₃ composites with x=2.0−3.6 and yFeAl−0.6TiC−Al₂O₃ composites with y=1.8−2.75 was studied. The increase of FeAl causes a decrease in the reaction exothermicity, thus resulting in the existence of flammability limits of x=3.6 and y=2.75 for the SHS reactions. Based on combustion wave kinetics, the activation energies of E_a=97.1 and 101.1 kJ/mol are deduced for the metallothermic SHS reactions. XRD analyses confirm in situ formation of FeAl/TiB₂/Al₂O₃ and FeAl/TiC/Al₂O₃ composites. SEM micrographs exhibit that FeAl is formed with a dense polycrystalline structure, and the ceramic phases, TiB₂, TiC, and Al₂O₃, are micro-sized discrete particles. The synthesized FeAl−TiB₂−Al₂O₃ and FeAl−TiC−Al₂O₃ composites exhibit the hardness ranging from 12.8 to 16.6 GPa and fracture toughness from 7.93 to 9.84 MPa·m^1/2.     

Thermoelectric properties of n-type Ca1−xDyxMn1−yNbyO3−δ compounds (x = 0, 0.02, 0.1 and y = 0, 0.02) prepared by spray-drying method

We report the high temperature thermoelectric properties of Ca_1−xDy_xMn_1−yNb_yO_3−δ (x = 0, 0.02, 0.1 and y = 0, 0.02) synthesized by spray-drying method. A maximum power factor (PF) value of 2.65 μW K⁻² cm⁻¹ is obtained at 1100 K for CaMn_0.98Nb_0.02O_3−δ. This represents an improvement of about 75% with respect to undoped CaMnO_3−δ sample at the same temperature. We also provide a complete structural characterization of the samples.     

Corrosion-electrochemical properties of α-Fe + Fe3C + TiC nanocomposites in neutral environments

The corrosion-electrochemical properties of α-Fe + Fe₃C + TiC three-phase nanocrystalline composites in borate solutions with pH 6.3–9.0 both with and without NaCl are studied. α-Fe + Fe₃C + TiC composites are found to have heightened resistances at active-oxidation potentials of α-Fe and cementite due to the formation of xFeO · yTiO₂ mixed surface oxides. The protective properties of passive films based on xFeO · yTiO₂ and their resistance to local activation are worse than those of Fe₃O₄/γ-Fe₂O₃ (γ-FeOOH) passive films formed on iron and α-Fe + Fe₃C composites.     

Shape-controlled synthesis of nanocubic Co3O4 by hydrothermal oxidation method

The nanocubic Co3O4 was synthesized by hydrothermal oxidation method. The effects of cobalt salt, precipitating agent, surfactant, solvent, pH value of the suspension and the amount of oxidant H2O2 on the morphology and structure of Co3O4 were investigated. The Co3O4 powders were characterized by transmission electron microscope and X-my diffraction. The results show that the morphology of Co3O4 is closely dependant on the anion in cobalt salts, but it is not so sensitive to the precipitating agents and solvents. The amount of H2O2 is the key factor to obtain Co3O4 with spinel crystal structure. The optimum synthetic conditions of uniform shape-controlled Co3O4 nanocubes are as follows： Co（CH3COO）2·4H2O as cobalt salt, KOH as precipitating agent, polyethylene glycol with relative molecular mass of about 20 000 as surfactant, water-n-butanol as solvent system, pH value of 8-9, the molar ratio of H2O2 to Co^2＋ above 2.5：1.0, hydrothermal temperature of 160 ℃ and hydrothermal holding time of 10 h. The tap density and apparent density of nanocubic Co3O4 obtained with the average particle size of 20 nm are 1.01 g/cm^3 and 0.70 g/cm^3, respectively.     

One-step chemical synthesis of doped polythiophene by use of copper(II) perchlorate as an oxidant

A reaction of 2,2′-bithiophene with copper(II) perchlorate in acetonitrile achieved polymerization and doping in one step, and yielded polythiophenes, [(C₄H₂S)(ClO₄)_x·yH₂O]_n. The polymers with x ∼ 0.17 and y ∼ 0.3 exhibited a high electrical conductivity in the range 3 – 8 S cm⁻¹ at 300 K and a small activation energy of 0.04 eV. The i.r. and e.s.r. spectra showed the characteristics of doped polythiophenes.     

Spectroscopic and crystal field analysis of absorption and photoluminescence properties of red phosphor CaAl12O19:Mn modified by MgO

The spectroscopic properties of a series of red phosphors with general composition of CaAl₁₂O₁₉:yMn⁴⁺ and (Ca_1−xAl₁₂O₁₉, xMgO):yMn⁴⁺ (x = 0-1, y = 0.001-1.5%) synthesized by a modified solid state method in air have been investigated in detail. Addition of MgO is necessary for Mn⁴⁺ charge compensation and leads to the formation of separate crystal phases of Al₂O₃ and MgAl₂O₄, which was confirmed by the XRD studies. Enhancement of Mn⁴⁺ luminescence with increasing content of MgO was observed and a mechanism for explanation of this phenomenon is suggested. For an analysis of the crystal phases and luminescent efficiency of the phosphors in the prepared series, crystal field calculations of the Mn⁴⁺ energy levels have been performed. This theoretical approach allowed for assigning the observed excitation and emission spectra. Red shift of the Mn⁴⁺ luminescence with increasing concentration of Mg ions is explained from the point of view of enhanced nephelauxetic effect after doping.     

A novel aqueous co-precipitation process to prepare indium tin oxide nanopowders

In this paper, a novel aqueous co-precipitation process for preparing ITO (indium tin oxide) nanopowders was investigated. In this process, the solutions of In³⁺-Sn⁴⁺ ions and 25% NH₃·H₂O were simultaneously added into the solution of (NH₄)₂SO₄-NH₃·H₂O, NH₄Cl-NH₃·H₂O and NH₃·H₂O to make different reaction solutions. When (NH₄)₂SO₄-NH₃·H₂O solution was used as the primary reaction liquid with pH value in the range of 6.5-7.0, spherical ITO particles with uniform particle size (10-20 nm), low agglomeration and large specific surface were obtained. The ITO particles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and energy-dispersive spectrometer (EDS). The EDS analysis indicated that the distribution of In and Sn elements in the ITO powders was uniform and their mass ratio was close to 9:1, which would result from the co-precipitation process that provided a stable chemical circumstance for In³⁺ and Sn⁴⁺ to be co-precipitated.     

利用赝电容效应提高Se修饰MnO/Mn3O4复合负极材料的储锂容量及倍率性能(英文)

为了提高锰氧化物负极材料的倍率和循环性能,采用沉淀法及热处理法,通过调控Mn₂O₃与Se粉的反应温度,制备Mn O/Mn₃O₄/Se O_x(x=0,2)复合负极材料。Mn O/Mn₃O₄/Se O_x负极在3 A/g电流密度下经过560次充放电循环后放电比容量为1007 m A·h/g。循环伏安法定量分析结果表明,在2.0 m V/s的扫描速率下赝电容贡献率高达89.5%。研究结果表明,Mn O与Mn₃O₄之间存在明显的协同效应。     

Heat capacity measurements and XPS studies on uranium-lanthanum mixed oxides

Heat capacity measurements were carried out on (U_1−yLa_y)O_2±x (y = 0.2, 0.4, 0.6, and 0.8) using differential scanning calorimeter (DSC) in the temperature range 298-800 K. Enthalpy increment measurements were carried out on the above solid solutions using high temperature drop calorimetry in the temperature range 800-1800 K. Chemical states of U and La in the solid solutions of mixed oxides were determined using X-ray photoelectron spectroscopy (XPS). Oxygen to metal ratios of (U_1−yLa_y)O_2±x were estimated from the ratios of different chemical states of U present in the sample. Anomalous increase in the heat capacity is observed for (U_1−yLa_y)O_2±x (y = 0.4, 0.6 and 0.8) with onset temperatures in the range of 1000-1200 K. The anomalous increase in the heat capacity is attributed to certain thermal excitation process, namely, Frenkel pair defect of oxygen. The heat capacity value of (U_1−yLa_y)O_2±x (y = 0.2, 0.4, 0.6, and 0.8) at 298 K are 65.3, 64.1, 57.7, 51.9 J K⁻¹ mol⁻¹, respectively. From the XPS investigations, it was observed that the O/M ratios at the surface are higher than that in the bulk. In uranium rich mixed oxide samples, the surface O/M ratios are greater than 2 whereas that in La rich mixed oxides, they are less than 2, though the bulk O/M in all the samples are less than 2.     

Synthesis of Li excess LiFePO4/C using iron chloride extracted from steel scrap pickling

Olivine-type Li rich Li_1+xFePO₄/C composites are synthesized by a solid state reaction process using premilled Li₂CO₃ and pre-synthesized amorphous FePO₄·xH₂O powders. The amorphous FePO₄·xH₂O powders are prepared from an industrial waste liquid (by-product), a FeCl₃ (38%) solution, via a precipitation process. In addition, lithium carbonate is pre-milled using a high energy nano mill to control particle sizes and shape differences for enhancing the reaction activity in the starting materials. The main purpose of this study is to investigate the effect of excess Li on the electrochemical properties of LiFePO₄ cathode materials. The pre-synthesized FePO₄ powders are mixed with pre-milled lithium carbonate and glucose (8 wt%) using a ball-mill process. The structural characteristics of the Li_1+xFePO₄/C composites are examined by XRD and SEM. To investigate the effect of excess Li content on the electrochemical properties in Li_1+xFePO₄/C composites, a Li[LiPF₆ (Ethylene carbonate + Dimethyl carbonate)] Li_1+xFePO₄/C model cell is used. It is demonstrated that the 1% Li rich Li/[Li_1.01FePO₄/C] cell exhibits the best electrochemical performance and delivers an initial discharge capacity of 161 mAhg^?1, which is 25 mAhg^?1 higher than that of the Li/[LiFePO₄/C] cell.     

Synthesis and characterization of Ba(CoxNb1-x)O3 nanoparticles by hydrothermal processing

The nanosized Ba(Co_xNb_1–x)O₃(BCN) particles were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. Ba(Co_xNb_1–x)O₃ powders were obtained in the temperature range of 170–210 °C for 6 h. The results show that the average size of the synthesized particles increases with increasing reaction temperature. The average size of the synthesized particles is about 10 nm. The crystalline phase of the synthesized particles is found to be Ba(Co_xNb_1–x)O_3. Ceramics derived from the nano BCN powders could achieve high sintering density at a relatively low sintering temperature.     

Cyclic voltammetry studies on 4 V and 5 V plateaus of non-stoichiometric spinel Li1＋xMn2-yO4

1 Introduction As one of the most promising cathode materials for lithium ion batteries, spinel LiMn2O4 has received much attention in recent years. This material has reversible capacities at both 3 V and 4 V plateaus[1]. However, the Li insertion and ex…     

Influence of Nd-Co Substitution on Structural,Electrical, and Dielectric Properties of X-Type Hexagonal Nanoferrites

A series of single phase X-type hexagonal ferrites with concentration Sr_2?x Nd _x Ni₂Fe_28?y Co _y O₄₆ (x = 0.02, 0.04, 0.06, 0.08, 0.10 and y = 0.1, 0.2, 0.3, 0.4, 0.5) has been prepared by sol-gel method sintered at 1250 °C for 6 h. The x-ray diffraction analysis reveals the single phase of X-type hexagonal ferrites. The particle size was calculated by using SEM and TEM. The ferrite substituted with Nd³⁺ and Co²⁺ has average particle size in the range of 40-50 nm. The room temperature electrical resistivity experiences the significant enhancement from a value of 1.1 × 10⁷ to 2.03 × 10⁸ Ωcm with the increase in Nd³⁺ and Co²⁺ concentration. The dielectric constant exhibits high value at low frequencies and decreases with the increase of frequency. The tangent dielectric loss shows the abnormal behavior which can be explained on the basis of hopping between the Fe²⁺ and Fe³⁺ ions on octahedral sites. The maximum value of tangent loss at low frequencies reflects the application of these materials in medium frequency devices (MF).