Activation mécanique d'oxydes de fer et de vanadium en vue d'une synthèse de ferrite de vanadium nanométrique similaire au composé issu de la chimie douce

Co-milling of iron and vanadium oxides allows us to obtain an intimate oxide mixture at a nanoscale, similar to a coprecipitate elaborated by soft chemistry. Reduction of such a mixture in the same temperature and oxygen partial pressure conditions (500 °C and 10⁵ Pa) as the Pa) as the soft chemistry products leads to a nanometric vanadium ferrite with only a spinel phase. Homogeneity of grain size and chemical composition is reached if the initial oxides have similar grain sizes.     

Investigation of a “Plasmatron” as a tool for spectrochemical analysis of powdered samples of complex composition

A plasma jet produced by a plasmatron with non-consumed electrodes has been developed into a promising analytical tool. The temperature of the plasma does not depend on the chemical composition of the sample. The presence of an excess of an easily ionized element in the plasma results in the intensification of the lines of analyte elements. The main cause of the effect of sample composition on the intensity of spectral lines is a change in the electron pressure.The evaporation conditions were optimized. Analysis of samples of widely varying composition may be performed using a single set of reference samples with an accuracy meeting the requirements of quantitative analysis. The errors caused by the grain size of the samples are eliminated by grinding the samples to a particle size of 0·01 mm.Under optimum conditions of excitation the detection limits of elements are in a range between 10^?5 and 10^?7%. Many elements may be determined simultaneously.     

Interaction of hydrogen chloride with ice surfaces: the effects of grain size, surface roughness, and surface disorder

Characterization of the interaction of hydrogen chloride (HCl) with polar stratospheric cloud (PSC) ice particles is essential to understanding the processes responsible for ozone depletion. The interaction of HCl with ice was studied using a coated-wall flow tube with chemical ionization mass spectrometry (CIMS) between 5x10(-8) and 10(-4) Torr HCl and between 186 and 223 K, including conditions recently shown to induce quasi-liquid layer (QLL) formation on single crystalline ice samples. Measurements were performed on smooth and rough (vapor-deposited) polycrystalline ice films. A numerical model of the coated-wall flow reactor was used to interpret these results and results of studies on zone-refined ice cylinders with grain sizes on the order of several millimeters (reported elsewhere). We found that HCl adsorption on polycrystalline ice films typically used in laboratory studies under conditions not known to induce surface disordering consists of two modes: one relatively strong mode leading to irreversible adsorption, and one relatively weak binding mode leading to reversible adsorption. We have indirect experimental evidence that these two modes of adsorption correspond to adsorption to sites at crystal faces and those at grain boundaries, but there is not enough information to enable us to conclusively assign each adsorption mode to a type of site. Unlike what was observed in the zone-refined ice study, there was no strong qualitative contrast found between the HCl uptake curves under QLL versus non-QLL conditions for adsorption on smooth and vapor-deposited ices. We also found indirect evidence that HCl hexahydrate formation on ice between 3x10(-7) and 2x10(-6) Torr HCl and between 186 and 190 K is a process involving hydrate nucleation and propagation on the crystal surface, rather than one originating in grain boundaries, as has been suggested for ice formed at lower temperatures. These results underscore the dependence of the HCl-ice interaction on the characteristics of the ice substrate.     

纳米氧化锌的合成与表征

纳米氧化锌的合成与表征何勇宁，沈孝良，马礼敦（复旦大学分析测试中心上海２００４３３）关键词纳米材料，氧化锌，合成，表征制备纳米材料的方法很多，如蒸发冷凝法、化学气相沉积法、溶胶－凝胶法、超临界法、水热法及各种热分解法等。Ｌｉｕ等［２］用超声雾化热分解...     

感光乳剂颗粒中杂质中心在感光过程各阶段的演变及其诠释——(Ⅰ)感光乳剂颗粒中最大潜影中心相对大小频率分布的测定

本文根据显影过程电极理论的基本概念和单个乳剂颗粒显影过程的若干动力学特征,认为在特定的条件下,单个乳剂颗粒的显影过程可以分作两个阶段:自催化阶段和快速还原阶段。在自催化阶段,决定过程速度的是显影液/潜影中心界面上电子转移的步骤,这时过程的速度与显影中心表面积的大小成正比,反应具有自催化的性质。在快速还原阶段,乳剂颗粒内部填隙银离子向显影中心附近的迁徙成为决定过程速度的步骤;这一阶段与自催化阶段相比,持续的时间极短。在这种假设的基础上,通过乳剂颗粒显影时间的频率分布求出颗粒中最大潜影中心相对大小的频率分布。该方法适用于在同样的原始乳剂和显影的条件下比较乳剂颗粒中最大潜影中心的相对大小频率分布的情况。     

Spectrophotometric method for the determination of paraquat in water, grain and plant materials

A sensitive spectrophotometric method for the determination of paraquat using ascorbic acid (an easily available reducing agent) is described. Paraquat is reduced with ascorbic acid in alkaline solution to give a blue radical ion with an absorbance maximum at 600 nm. Beer's law is obeyed in the range 12-96 micrograms of paraquat in 10 ml of the final solution (1.2-9.6 ppm). The important analytical parameters and the optimum reaction conditions were evaluated. The method was applied successfully to the determination of paraquat in water, grain and plant materials.     

Central role of TiO2 anatase grain boundaries on resistivity of CaCu3Ti4O12-based materials probed by Raman spectroscopy

This study focuses on characterization and control of grain boundaries to enhance the properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics capacitors for industrial applications. A novel factor deals with TiO₂ anatase revealed by Raman scattering in grain boundaries, found as a dominant parameter of largest sample resistivity, consistent with higher grain boundary resistivity and higher breakdown voltage. Four selected samples of CCTO-based compositions showing very different properties in terms of permittivity ranging from 1000 to 684 000 measured at 1 kHz, capacitance of grain boundaries ranging from 8 10⁻¹⁰ to 4.5 10⁻⁷ F cm⁻¹, grain boundary resistivity ranging from 193 to 30,000,000 Ω cm and sample resistivity extending from 450 to 10¹¹ Ω cm. The relationship between permittivity weighted by grain size and capacitance of grain boundaries confirms the internal barrier layer capacitance model over 5 orders of magnitude.     

Surface structural characterization of highly porous activated carbon prepared from corn grain

A novel corn grain precursor was used for the preparation of activated carbon by chemical activation. The detailed investigation of the porosity development in the prepared activated carbon was done by altering the various activation conditions such as the activation temperature, activation time and ratio between the powdered form of carbonized corn grain char and KOH. The surface characteristics including the surface roughness of all the activated carbon samples were evaluated from the analysis of nitrogen (N₂) adsorption isotherm data. At the maximum of 2978 m²/g, a super surface area having the corn grain‐based activated carbon (CG‐AC) was synthesized by using the following conditions: 1/4 ratio of powdered form of carbonized corn grain char/KOH; 800 °C; and 4 h. The possibility of preparing highly porous activated carbons with controlled porosity by varying different activation conditions was found from the pore size distribution results. In particular, the domination of the ratio between the powdered form of carbonized corn grain char and KOH on the porosity development was high compared to the activation temperature and activation time. In addition, the surface roughness calculated from the surface fractal dimension indicates the decrease of surface roughness with increasing activation conditions. Copyright © 2009 John Wiley & Sons, Ltd.     

粒径可控的纳米铁酸铋的制备及其光催化性能

采用改进的聚丙烯酰胺凝胶法制备了BiFeO3纳米颗粒,利用热重-差热、红外光谱及X射线衍射等手段研究了干凝胶的热分解及BiFeO3的成相过程.结果表明,在600℃煅烧可制备出高纯的BiFeO3纳米颗粒.同时发现,随着双丙烯酰胺含量的增加,所得样品晶粒尺寸逐渐减小,从而制备出平均粒径约52～110nm的系列BiFeO3颗...     

Effect of Ion Energy on Structure and Composition of Cathodic Arc Deposited Alumina Thin Films

The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α- and γ-phase above 700 ^oC, and γ-phase dominated films at temperatures as low as 200 ^oC. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ-alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ-alumina growth at temperatures as low as 200 ^o C.     

流动注射化学发光测定甲基对硫磷

首次研究了农药甲基对硫磷在碱性介质中（ｐＨ：１１．５～１２．０）与鲁米诺和过氧化氢产生化学发光的行为及反应机理,并发现水溶性高分子聚乙二醇对该反应具有显著的增效作用,据此建立了流动注射化学发光测定甲基对硫磷的新方法。甲基对硫磷的浓度在 ５×１０－８～１．０ ×１０－５ｇ／ｍＬ范围内与化学发光强度呈良好的线性关系;检出限为 ２×１０－８ｇ／ｍＬ;对 １．０×１０－６ｇ／ｍＬ甲基对硫磷进行了１１次平行测定,相对标准偏差小于４％;标准加入回收率为８３％～９４％。该法应用于谷物中农药残余量的测定,结果满意。     

高碘酸钾氧化酚藏花红催化光度法测定痕量钴(Ⅱ)

在HAc-NaAc(pH=4.0)缓冲溶液中,以氨三乙酸为活化剂,痕量钴(Ⅱ)可催化KIO4氧化酚藏花红褪色反应。研究了反应的最佳条件,测得反应表观活化能为65.23kJ.moL-1,据此建立了一种测定痕量钴(Ⅱ)的新方法。方法线性范围为0.010～1.20μg/25mL,检出限为8.84×10-10 g.mL-1,回收率为94%～103%,相对标准偏差(RSD)为3.6%～5.1%。该法用于粮食样品中钴(Ⅱ)的测定,结果满意。     

Growth control of homogeneous pulsed electrodeposited Co thin films on n-doped Si(1 1 1) substrates

Cobalt thin films were deposited by pulsed electrodeposition on n-doped silicon substrates. We show that the morphology and the magnetic properties of the samples can be controlled by a careful choice of the deposition conditions. Atomic force microscopy measurements reveal a granular growth with grain size and homogeneity strongly dependent on the total deposition time and pulse frequency of the applied signal. Magnetic force microscopy and magnetization measurements indicate the formation of magnetically correlated grain systems with a maximum magnetic correlation and homogeneity for samples with grain diameters of about 40 nm.     

[Fe(CN)6]4-在溴碘化银T-颗粒乳剂中的掺杂

本文研究了K₄[Fe(CN)₆]掺杂对溴碘化银T-颗粒乳剂感光性能的影响.结果表明,掺杂剂的掺杂量以及掺杂位置对乳剂的感光性能都有影响.K₄[Fe(CN)₆]的掺杂量在每克乳剂31×10^-9-31×10^-11mol之间时,乳剂感光度都有提高.最佳掺杂量为每克乳剂31×10-10mol.掺杂位置接近表面时效果相对较好,表明K₄[Fe(CN)₆]是浅电子陷阱掺杂剂.当掺杂剂的掺杂量大于每克乳剂31×10^-8mol,且掺杂位置在乳剂颗粒较深内部时,乳剂的感光度反而下降.     

Finite element simulation of diffusion into polycrystalline materials

Diffusion in polycrystalline materials is investigated by means of numerical finite element simulations for constant source conditions. The grain boundaries are assumed to provide fast diffusion paths. Main emphasis is put on situations that typically occur for nanocrystals, viz. on situations in which (i) the diffusion length is significant compared with grain size, (ii) the influence of boundaries that are parallel to the surface become important in addition to the perpendicular ones. Furthermore, we treat the influence of blocking space charge layers sandwiching the core pathways and thus channeling grain boundary diffusion.     

Electrical properties of the protonic conductor 1 mol% Y-doped $$ {\hbox{BaZr}}{{\hbox{O}}_{{3 - \delta }}} $$

Much attention has been paid to barium zirconates because their high protonic conductivity and chemical stability are excellent properties for solid electrolytes. However, most studies have focused on highly doped materials such as 10 or 20 mol% Y-doped barium zirconates. In this study, the bulk and the grain boundary electrical properties of 1 mol% Y-doped barium zirconate are investigated as a function of temperature, water partial pressure, and oxygen partial pressure. At low temperatures and in wet atmospheres, the bulk of the barium zirconate predominantly conducts protonic defects, whereas, at high temperatures and in dry conditions, it is mixed oxygen ionic and electron-hole conducting. In the grain boundary, the protonic conductivity is a few orders of magnitude lower than the protonic conductivity in the bulk. In this study, possible causes for the low protonic conduction at the grain boundaries are considered.     

Influence of grain orientation on zinc enrichment and surface morphology of an Al?Zn alloy

Zinc is an important alloying element in the 7000 series aluminium alloys. It is also an element that may enrich near the alloy surface during treatments of aluminium alloys by processes such as electropolishing, alkaline anodic etching and alkaline etching. The enrichment may occur since the change in Gibbs free energy per equivalent for formation of ZnO is less negative than that for formation of Al₂O₃. The enriched alloying element is present in an alloy layer up to ～5 nm thick located immediately beneath the alloy/film interface. In the present study, the dependence of the enrichment of zinc on the grain orientation of the alloy is investigated for a solid solution Al‐1.1at.%Zn alloy. The enrichment of the zinc is developed by alkaline etching of the alloy. The grain orientation is determined by electron backscattering diffraction, with enrichments quantified on selected grains by Rutherford backscattering spectroscopy and medium energy ion scattering. The morphologies of the surfaces of the etched grains are characterised by scanning electron microscopy and atomic force microscopy. The findings reveal that the zinc enrichment ranges from 1.7 × 10¹⁵ atoms/cm² to 3.9 × 10¹⁵ atoms/cm², with the greatest enrichment occurring on a grain of (100) orientation, while differing surface topographical textures are developed on the various grains. Copyright © 2009 John Wiley & Sons, Ltd.     

Wurtzite-to-rocksalt structural transformation in nanocrystalline CoO

Hexagonal CoO nanocrystals are coarsened under hydrothermal conditions to investigate the effect of particle size on phase transformation and stability property. Structural stability and phase transformation of the hexagonal CoO phase have been investigated by X-ray powder diffraction with Rietveld refinement, transmission electron microscopy, X-ray absorption fine structure, and differential scanning calorimeter. It is found that the hexagonal CoO phase is a metastable phase, which increases its grain size from 50 to 250 nm for refluxing times from 1 to 6 h at 200 degrees C. After 12 h, cubic-structured CoO grains with an average grain size of 20 nm are observed, which spread around big hexagonal CoO grains. After about 24 h, only the cubic CoO phase with an average grain size of 25 nm is detected. The onset temperature of hexagonal-to-cubic phase transformation in CoO is estimated to be 378 degrees C by DSC, using a heating rate of 20 deg/min. The results obtained indicate that the hexagonal-to-cubic phase transformation in nanocrystalline CoO is by nucleation and growth mechanism, starting from the surface to the center of the hexagonal grains.     

Dielectric Properties of Colossal-Dielectric-Constant Na1/2La1/2Cu3Ti4O12 Ceramics Prepared by Spark Plasma Sintering

In the current study, we report on the dielectric behavior of colossal-dielectric-constant Na_1/2La_1/2Cu₃Ti₄O₁₂ (NLCTO) ceramics prepared by mechanochemical synthesis and spark plasma sintering (SPS) at 850 °C, 900 °C, and 925 °C for 10 min. X-ray powder diffraction analysis showed that all the ceramics have a cubic phase. Scanning electron microscope observations revealed an increase in the average grain size from 175 to 300 nm with an increase in the sintering temperature. SPS NLCTO ceramics showed a room-temperature colossal dielectric constant (>10³) and a comparatively high dielectric loss (>0.1) over most of the studied frequency range (1 Hz–40 MHz). Two relaxation peaks were observed in the spectra of the electrical modulus and attributed to the response of grain and grain boundary. According to the Nyquist plots of complex impedance, the SPS NLCTO ceramics have semiconductor grains surrounded by electrically resistive grain boundaries. The colossal dielectric constant of SPS NLCTO ceramics was attributed to the internal barrier layer capacitance (IBLC) effect. The high dielectric loss is thought to be due to the low resistivity of the grain boundary of SPS NLCTO.     

A novel theoretical model for calculating the effective diffusivity of gases in a porous pellet composed of two different grains

Effective diffusivity of gases is an important property when modeling the physicochemical processes occurring in a pellet. Calculating effective diffusivity in a pellet composed of a mixture of particles is a difficult task. In this paper, a theoretical model is presented in order to describe the diffusion of gases in a porous pellet made up of a mixture of two kinds of solid grain. Solid grains can either be fully dense and thus non-porous or contain pores, with a grain being sub-divided into sub-grains. The results predicted by the model have been evaluated and validated by use of experimental data obtained by reduction of cuprous sulfide in the presence of lime. Finally, the effects of structural properties and operating conditions on the effective diffusivity of the gases in the pellet have been evaluated.