Microwave-assisted synthesis of CaMoO4 nano-powders by a citrate complex method and its photoluminescence property

Nano-sized CaMoO₄ powders, which have scheelite type structure, were successfully synthesized at low temperatures by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 700 °C for 3 h. Crystallizations of the CaMoO₄ nano-sized powders were detected at 400 °C, and entirely completed at a temperature of 500 °C. Almost nano-powders of CaMoO₄ heat-treated between 400 and 600 °C showed primarily spherical and homogeneous morphology. The average crystalline sizes of CaMoO₄ were 12–27 nm at temperatures of 400–700 °C, showing an ordinary tendency to increase with the temperatures. The CaMoO₄ powders prepared at 600 °C showed the strongest photoluminescence intensity.     

Preparation of nano-sized SrAl2O4 using an amorphous hetero-nucleus complex as a precursor

Nano-crystalline SrAl₂O₄ with spinel structure was successfully prepared at 700 °C using amorphous SrAl₂(diethylenetriaminepentaacetic acid (DTPA)_1.6)(H₂O)₄ as precursor. The precursor was synthesized by a simple inorganic reaction and decomposed into SrAl₂O₄ at temperatures above 500 °C, which was proved by DTA–TGA and X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction (XRD) results illustrated that a crystalline SrAl₂O₄ phase can form at 700 °C, which is about 600 °C lower than that used in the traditional method. The crystalline SrAl₂O₄ prepared at 900 °C for 2 h had a crystal size of about 28 nm and a grain size of about 80 nm, and its BET surface area can reach 28.056 m²/g. Calcination temperature and time had a weak effect on crystal size.     

La0.9Sr0.1Ga0.8Mg0.2O3−δ sintered by spark plasma sintering (SPS) for intermediate temperature SOFC electrolyte

The La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) powders for intermediate temperature SOFC electrolyte have been synthesized by glycine-nitrate combustion process. The as-synthesized powders show almost pure perovskite phase. And then, the as-synthesized powders were sintered by SPS at 1300 °C to prepare electrolyte. The SEM, XRD and AC impedance were employed to characterize the microstructure, phase and electrical conductivities. Results show that the grain size is very fine, less than 1 μm, and the relative density of the pellet after sintering by SPS is about 94.7%. There is very little amount of secondary phases after SPS and the grain boundary and secondary phase resistance is very small. The electrolyte sintered by SPS shows higher conductivities than that sintered by conventional method at the same temperature. The activation energy at lower temperatures (400–700 °C) and higher temperatures (700–800 °C) is about 0.94 and 0.49 eV, respectively. Spark plasma sintering is a promising and effective method to sinter the LSGM electrolyte.     

Ionic conductivity and Raman investigations on the phase transformations of Na4P2O7

The ionic conductivity and thermo-Raman spectra of anhydrous sodium pyrophosphate Na₄P₂O₇ were measured dynamically in the temperature range from 25 to 600 °C with a heating rate of 2 °C min⁻¹ to understand the structural evolution and phase transformation involved. The DSC thermogram was also measured in the same thermal process for the phase transformation investigation. The spectral variations observed in the thermo-Raman investigation indicated the transformation of Na₄P₂O₇ from low temperature phase () to high temperature phase () proceeded through pre-transitional region from 75 to 410 °C before the major orientational disorder at 420 °C and minor structural modifications at 511, 540 and 560 °C. The activation energies and enthalpies of the proposed phase transformations were determined. The possible mechanism for temperature dependent conductivity in Na₄P₂O₇ was discussed with the available data.     

Effect of annealing on the morphology evolution and densification of LiMn2O4 film from chitosan-containing solution

Dense LiMn₂O₄ films deposited on a Pt-coated silicon substrate were obtained by annealing the deposited Li–Mn–O-chitosan films under a two-stage heat-treatment procedure. It was demonstrated that the heat-treatment at 300 °C plays an important role in the subsequent densification of LiMn₂O₄ films. This is attributed to the formation and rearrangement of the nano-sized LiMn₂O₄ crystallites. The surface morphology of the calcined Li–Mn–O-chitosan films was highly related to the annealing temperature. Ridge-like bumps formed on the surface of the films after being heated at 200 °C for 1 h. With calcination at 400 °C or higher, the surface morphology turned into a wrinkle-like microstructure. This morphology transformation is ascribed to the flowing characteristics of the Li–Mn–O-chitosan films during heat-treatment and subsequent thermal decomposition of the precursor at higher temperatures. Moreover, the electrochemical tests showed that the 700 °C-annealed LiMn₂O₄ film possesses the highest discharge capacity of 56.3 μA h/(cm² μm) and best capacity retention of 90.7% after 50 charge/discharge cycles of all annealed films.     

Study on phase formation and sintering kinetics of BaTi0.6Zr0.4O3 powder synthesized through modified chemical route

BaTi_0.6Zr_0.4O₃ powder was prepared from barium oxalate hydrate, zirconium oxy-hydroxide and titanium dioxide precursors. Barium oxalate hydrate and zirconium oxy-hydroxide were precipitated from nitrate solution onto the surface of suspended TiO₂. Phase formation behaviour of the materials was extensively studied using XRD. BaTiO₃ (BT) and BaZrO₃ (BZ) start forming separately in the system upon calcinations in the temperature range 600–700 °C. BT–BZ solid solution then forms by diffusion of BT into BZ from 1050 °C onwards. The precursor completely transforms into BaTi_0.6Zr_0.4O₃ (BTZ) at 1200 °C for 2 h calcination. The activation energy (AE) of BT (134 kJ mol⁻¹) formation was found to be less than that of BZ (167.5 kJ mol⁻¹) formation. BTZ formation requires 503.6 kJ mol⁻¹ of energy. The sintering kinetics of the powder was studied using thermal analyzer. The mean activation energy for sintering was found to be 550 kJ mol⁻¹.     

Pore morphology in sintered ZrO2–8 mol% Y2O3 ceramic: a small-angle neutron scattering investigation

Pore morphology and pore size distribution in yttria-stabilized zirconia (ZrO₂–8 mol% Y₂O₃) have been investigated, for two sintering temperatures, namely 1200 and 1270 °C, using small-angle neutron scattering. The results show that the reduction in the porosity, at 1270 °C compared to that at 1200 °C, occurs by the elimination of the pores at the lower end of the pore size distribution. In addition, the polydispersity is also lower at 1270 °C and the nature of the distribution is altered significantly near the smaller radius range. The average pore size shifts towards the higher radius range. The specific surface area of the pores is also diminished at 1270 °C because of the elimination of the finer pores.     

Structural changes of Co70Fe5Si10B15 amorphous alloy induced during heating

In this study we present the results on complex structural changes of the Co₇₀Fe₅Si₁₀B₁₅ amorphous alloy induced during heating in the temperature range between 20 and 1000 °C. The structural and phase transformation changes were correlated with DTA, XRD and SEM properties. It is shown that initial Co₇₀Fe₅Si₁₀B₁₅ alloy during heating undergoes complex crystallochemical changes. In the range between ambient temperature and near 400 °C, investigated alloy retains the solid-state amorphous properties. Prolonged heating induces complete transformation to crystalline solid state. The solid–solid amorphous to crystalline state transformation process is completed at 500 °C, when two nanocrystalline phase alloy systems are formed. Prolonged thermal treatment between 600 and 1000 °C, influenced further elemental segregation and phase transition. At 1000 °C, the composite material consisting of two FCC cobalt-rich alloys and a hexagonal unidentified alloy are formed.     

Sm0.5Sr0.5CoO3 cathode material from glycine-nitrate process: Formation, characterization, and application in LaGaO3-based solid oxide fuel cells

Cathode material Sm_0.5Sr_0.5CoO₃ (SSC) with perovskite structure for intermediate temperature solid oxide fuel cell was synthesized using glycine-nitrate process (GNP). The phase evolution and the properties of Sm_0.5Sr_0.5CoO₃ were investigated. The single cell performance was also tested using La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolyte and SSC as cathode. The results show that the formation of perovskite phase from synthesized precursor obtained by GNP begins at a calcining temperature of 600 °C. The single perovskite phase is formed completely after sintering at a temperature of 1000 °C. The phase formation temperature for SSC with complete single perovskite phase is from 1000 to 1100 °C. The SrSm₂O₄ phase appeared in the sample sintered at 1200 °C. It is also found that the sample sintered at 1200 °C has a higher conductivity. The electrical conductivity of sample is higher than 1000 S/cm at all temperature examined from 250 to 850 °C, and the highest conductivity reaches 2514 S/cm at 250 °C. The thermal expansion coefficient of sample SSC is 22.8 × 10⁻⁶ K⁻¹ from 30 to 1000 °C in air. The maximum output power density of LSGM electrolyte single cell attains 222 and 293 mW/cm² at 800 and 850 °C, respectively.     

Preparation of neodymium sulphides by the reaction of Nd2(So4)3 with carbon disulphide

The reaction to synthetize neodymium sulphides from neodymium sulphate octahydrate in a stream of carbon disulphide gas was studied. The dehydration of the octahydrate in vacuum was finished at 300 °C. At 1050–1100 °C in air neodymium oxysulphide, Nd₂O₂SO₄, was formed. Neodymium oxysulphide, Nd₂O₂S, was formed upon heating with a reducing agent such as annealed carbon. The reaction of neodymium sulphate with carbon disulphide commenced at 500–600 °C, resulting in formation of the disulphide, NdS₂. The crystal structure of NdS₂ heated at 500 °C was, however, different from that of the sample heated at 600 °C. In the temperature range 800–900 °C -Nd₂S₃ was obtained as a single phase after heating for at least 3 h in high flow rates of gas mixtures of nitrogen and high concentrations of carbon disulphide. The sesquisulphide, γ-Nd₂S₃ (or Nd₃S₄), was formed at temperatures as high as 1100 °C. The reaction conditions for the compounds mentioned above are discussed together with the analysis of their crystal structures by X-ray powder diffractometry.     

A facile route to VN and V2O3 nanocrystals from single precursor NH4VO3

V₂O₃ and VN nanocrystals have been synthesized by the decomposition of the precursor NH₄VO₃ and following nitridation in an autoclave with metallic Na flux at 450–600 °C. X-ray powder diffraction (XRD) recorded the evolution process of the reaction from precursor NH₄VO₃ to hexagonal V₂O₃ and then to NaCl-type VN. In addition, the products were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).     

Existence, structure and valence properties of the skutterudites CeyFe4−xCoxSb12

We report on sample preparation, annealing effects, electron microprobe analysis in the series Ce_yFe_4−xCo_xSb₁₂ which shows that a phase separation occurs for substituted samples (0<x<4) annealed at 650 and 550 °C. Single phase samples are obtained for either Ce_yFe₄Sb₁₂ or Ce_yCo₄Sb₁₂ samples annealed at 650 °C and for all compositions when annealed at 700 °C. The valence state of Ce in homogeneous samples has been studied using X-ray absorption spectroscopy (XAS). Ce ions are trivalent throughout the series and the XAS spectra does not show effect of the crystal field on the 5d-final state.     

Structural and electrical properties of SrBi2(Ta0.5Nb0.5)2O9 thin films

SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBTN) thin films were obtained by polymeric precursor method on Pt/Ti/SiO₂/Si(1 0 0) substrates. The film is dense and crack-free after annealing at 700 °C for 2 h in static air. Crystallinity and morphological characteristic were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The films displayed rounded grains with a superficial roughness of 3.5 nm. The dielectric permittivity was 122 with loss tangent of 0.040. The remanent polarization (P_r) and coercive field (E_c) were 5.1 μC/cm² and 96 kV/cm, respectively.     

The characteristics of Li(CoxNi1 − x)O2 cathode powders formed from the fine-sized Co3O4/NiO precursor powders

Li(Co_xNi_1 − x)O₂ (0 ≤ x ≤ 1) cathode powders were prepared by solid state reaction method using Co₃O₄/NiO precursor powders obtained by spray pyrolysis. The effect of the ratios of cobalt and nickel components on the characteristics of Co₃O₄/NiO precursor and Li(Co_xNi_1 − x)O₂ cathode powders were investigated. The Co₃O₄/NiO precursor powders with the ratios of cobalt and nickel components as 1/0, 0.75/0.25 and 0.5/0.5 had submicron size and regular morphologies. On the other hand, the Co₃O₄/NiO powders with the high contents of nickel component had aggregated morphologies of submicron size primary powders. The fine-sized precursor powders formed the fine-sized LiCoO₂ and Li(Co_0.75Ni_0.25)O₂ cathode powders by solid state reaction with LiOH powders. However, the high contents of the nickel component of the Co₃O₄/NiO precursor powders formed the Li(Co_xNi_1 − x)O₂ (0 ≤ x ≤ 0.5) cathode powders with aggregated morphologies and large sizes. The discharge capacities of the powders increased with increasing the nickel content into the Li(Co_xNi_1 − x)O₂ cathode powders up to 188 mAh/g.     

Preparation and luminescent properties of europium-activated YInGe2O7 phosphors

Effects of precursor milling on phase evolution and morphology of mullite (3Al₂O₃·2SiO₂) processed by solid-state reaction have been investigated. Alumina and silica powders were used as starting materials and milling was taken place in a medium energy conventional ball mill and a high-energy planetary ball mill. Milling in a conventional ball mill although decreases mullite formation temperature by 200 °C, but does not considerably change mullite phase morphology. Use of a planetary ball mill after 40 h of milling showed to be much more effective in activating the oxide precursors, and mullitization temperature was reduced to below 900 °C. Whisker like mullite was formed after sintering at 1450 °C for 2 h and volume fraction of this structure was increased by increasing the milling time. XRD results showed that samples mechanically activated for 20 h in the planetary ball mill were fully transformed to mullite after sintering at 1450 °C, whereas Al₂O₃ and SiO₂ phases were still detected in the samples milled in the conventional ball mill for 20 h and then sintered at the same conditions.     

Toughened ZrO2 ceramics sintered with a La2O3-rich glass as additive

In this study, the influence of the glass addition and sintering parameters on the densification and mechanical properties of tetragonal zirconia polycrystals (3Y-TZP) ceramics were evaluated. High-purity tetragonal ZrO₂ powder and La₂O₃-rich glass were used as starting powders. Two compositions based on ZrO₂ and containing 5 wt.% and 10 wt.% of La₂O₃-rich glass were studied in this work. The starting powders were mixed/milled by planetary milling, dried at 90 °C for 24 h, sieved through a 60 mesh screen and uniaxially cold pressed under 80 MPa. The samples were sintered in air at 1200 °C, 1300 °C, 1400 °C for 60 min and at 1450 °C for 120 min, with heating and cooling rates of 10 °C/min. Sintered samples were characterized by relative density, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Hardness and fracture toughness were obtained by Vickers indentation method. Dense sintered samples were obtained for all conditions. Furthermore, only tetragonal-ZrO₂ was identified as crystalline phase in sintered samples, independently of the conditions studied. Samples sintered at 1300 °C for 60 min presented the optimal mechanical properties with hardness and fracture toughness values near to 12 GPa and 8.5 MPa m^1/2, respectively.     

Temperature and loading time dependence of hardness of LaB6, YB6 and TiC single crystals

The temperature and loading time dependence of Vickers’ microhardness of LaB₆, YB₆ and TiC single crystals prepared by the floating zone method have been investigated under various temperatures from 25 to 1000 °C and loading time 5–60 s. Clear inflection points at 700 °C for LaB₆ and YB₆, and at 600 °C for TiC can be seen in the plot of log hardness versus the temperature. A series of straight lines with various slopes were obtained in the plot of log hardness versus log loading time of all samples. As the temperature is above the inflection temperature, the present data confirm our previous observation of ZrB₂ single crystals that .     

基于纳米NiO颗粒敏感电极的NO2气敏特性研究

利用浸渍技术在YSZ多孔层中制备NiO纳米颗粒材料,并以其为敏感电极组成新型的电流型NO2传感器。采用X射线衍射仪、扫描电子显微镜表征了NO2传感器物相和形貌结构,应用IM6e型电化学工作站测试了其气敏性能。实验结果表明:NiO颗粒粒度约50nm,且分布均匀。在500~600℃时,传感器对NO2有良好的敏感性,其响应电流值与NO2的浓度之间呈良好的线性关系。传感器对NO2响应时间短且响应信号稳定。O2和CO2的存在对传感器响应信号几乎没有影响。     

低品位钒渣在碳酸钠存在下的氧化过程

利用XRD,SEM/EDS和TG-DSC等手段对低品位钒渣在Na2CO3存在条件下的氧化过程进行检测。结果表明：钒渣的氧化温度范围为273至700°C,橄榄石相与尖晶石相彻底分解的温度分别是500和600°C,大部分水溶性的钒酸盐在500与600°C之间形成。当温度达到700°C以上时,钒酸盐富集相明显可见,但焙烧温度在800°C以上时,样品发生烧结,并且钒被形成的玻璃相包裹,导致其浸出率下降。同时,研究不同焙烧温度对钒浸出率的影响,并对浸出残渣进行分析。     

Hydrothermal synthesis of CeO2 nano-particles

Nano-crystalline particles of CeO₂ have been synthesized via a low temperature hydrothermal synthesis process. Two types of precursors were studied—cerium hydroxide and ceria acetate. The precursors were adjusted to a basic (pH 10) and acidic (pH 4) medium before hydrothermal treatment at various durations of 6, 12, 18, and 24 h at 250 °C using a Teflon-lined hydrothermal bomb. The synthesized samples were characterized using DTA/TGA, XRD and TEM. Based on the characterization results, both precursor systems produced crystalline ceria nano-particles after 6 h of hydrothermal synthesis at 250 °C. The average crystallite sizes were 6 and 15 nm for the hydroxide and acetate system, respectively. The acetate precursor system appeared to produce better particles in terms of crystallinity and morphology. Based on the DTA/TGA analysis, hydrothermal synthesis had been effective in reducing the amount of intermediate products. With increasing hydrothermal treatment duration of up to 24 h, the samples did not exhibit a remarkable improvement in properties. The synthesized nano-particles were subsequently heat treated at 500 and 1000 °C for 2 h. After the heat treatment, enhanced crystallinity and growth in crystallite size was observed, but particles appeared more agglomerated.