原子吸收光谱分析中石墨炉的原子化效率

本文评述了原子吸收光谱分析中石墨炉原子化效率的研究进展，叙述了基础理论、各种原子化效率公式以及βm,βi(exp),βi(cal)间的关系，讨论了原子化效率研究中需要进一步改善的问题。     

石墨炉内原子化过程的热力学研究——Ⅰ.氩气氛的计算以及铜原子化机理的研究

我们对石墨炉内氩气氛中杂质分压的计算,得到了与其他作者明显不同的结论。在原子化过程中,如果样品中的组分以氧化物形式热分解,则石墨管内氧的分压主要取决于样品中组分的氧化物热分解释放出的氧量。在常用原子化温度范围内(1000—2500K),常规样品分析所用氩气中氧的分压低于10~(-12)atm。我们首次提出了CO分压的变化特性。杂质主要以CO存在,也就是说,气氛中CO的分压近似等于除去H_2、N_2以外杂质总的分压。     

石墨炉原子化器中氧在原子化过程的作用

石墨炉中氧的来源石墨炉中氧分压一直认为是决定于下列反应。2C(s)+O_2→2CO (1) 按照这个假定,除了最稳定的金属氧化物(B,La,Ta,Th,U,Zr)之外,一般认为在高温石墨炉中氧化物解离是完全的,同时自由氧分压是很低的。例如,假定CO分压为100Pa,那么在1400—2500°K范围Po_2将为3×10~(-19)—2×10~(-15)Pa。近年来,许多实验资料表明,石墨炉中自由氧分压的实际值大于按反应(1)计算的数值。这说明基于反应(1)估计Po_2是不够全面的。对基于反应(1)获得的有关元素的原子化机理,值得重新考虑。     

石墨炉原子吸收分光光度法中钼的原子化机理

平台技术与X光衍射,扫描电镜,X光能量色散以及俄歇电子能谱相结合应用于石墨炉原子吸收法中钼的原子化机理的研究。已发现,钼的氧化物(MoO_2,MoO_3,Mo_4O_(11))和Mo,MoC以及Mo_2C在预原子化阶段以凝聚相凝结在热解石墨及电解石墨表面上。     

用于石墨炉原子吸收分析的钽化-热解石墨管的研究

一些金属,在高温下,能与碳元素形成耐高温、热稳定性好的金属碳化物,碳化钽就是其中之一种。它具有很高的熔点,(4270°K),很低的蒸气压,能导电,化学上惰性,是理想的涂层碳化物。本文讨论了用于石墨炉原子吸收分析的钽化-热解石墨管的处理技术及其分析性能,比较了不同类型涂层石墨管的分析效果。实验表明,钽化-热解管具有热解涂层管和碳化钽涂层管的优点,分析灵敏度高,重现性好,使用寿命长。钽化-热解管制作简单,价格低廉,可在一般分析实验室中推广应用。     

ICP-AES、石墨炉原子吸收光谱法及X射线荧光光谱法测定土壤中钒的比较

研究了土壤中钒的3种测定方法,ICP-AES、石墨炉原子吸收光谱法和X射线荧光光谱法.其中ICP-AES选用谱线V 311.1nm,用干扰系数法,干扰系数用多个土壤标样的标准值和测定值的最小二乘法来确定;石墨炉原子吸收光谱法用新、旧石墨管(热解涂层),加与不加基体改进剂(硝酸镁)分别进行测试;X射线荧光光谱法样品无需前处理、无需做校准曲线,测定前仪器用自带校正钢片单点法进行校正.通过测试结果的比较得出:ICP-AES测定土壤标样中的钒,精密度高,准确度好,适合土壤中钒的实验室分析;石墨炉原子吸收光谱法灵敏度过高(高一个数量级),信号稳定性较差,对高温元素钒的测定最好加硝酸镁机体改进剂消除基体干扰且每只石墨管分析次数不超过100次;X荧光光谱法较适合于野外监测或土壤样品无损检测,操作方便快速.     

石墨炉原子化器的温度

本文用光谱纯铜粉考察了P-E HGA-500型石墨炉的管壁温度,首次研究了此石墨炉内原子蒸气的激发温度,证明了用双线法测定的激发温度为区域平均激发温度,真正的等温区域只存在于原子化开始的瞬间。通过研究激发温度的变化,我们认为当内气流速不小于20ml/min时,样品耗散主要由内气流的迁移作用决定。     

Effects of synthesis methods of vanadium oxide nanotubes on the inter layer distances

Vanadium oxide nanotubes were synthesized via two methods: (1) Adding a template to vanadium oxide gels, (2) Grinding mixture of a template and vanadium oxide by using a ball mill. Influence of preparation method on structure of vanadium oxide nanotubes has been investigated. Vanadium oxide nanotubes has been characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) techniques.     

SIMS,EID and flash-filament investigation of O2, H2, (O2 + H2) and H2O interaction with vanadium

Comparative investigations of secondary ion emission, electron induced ion emission and flash filament signals from polycrystalline vanadium surfaces exposed to well-defined O₂, H₂, H₂O and (O₂ + H₂) doses (<500 L) have been carried out. The vanadium target could be heated and bombarded by either electrons (300 eV) or ions (3 keV) under ultra high vacuum conditions (<10^?10 Torr). The investigations were carried out with a computer controlled ultra high vacuum mass spectrometer. The experimental results establish exact reproducible spectra of well defined surface layers. They give detailed insight into the reactions between H₂, O₂ H₂O and vanadium, and some interactions between these species. They further indicate the importance of bulk and surface diffusion as well as the influence of the probing ion and electron bombardment. A clear distinction between bulk oxygen, surface oxides, and adsorbed oxygen for the vanadium-oxygen interaction at room temperature could be established. For the interaction of hydrogen with clean and oxygen covered vanadium surfaces the formation of adsorbed hydrogen, bulk solution of hydrogen, and the formation of OH groups and H₂O could be demonstrated. A detection limit below 10^?5 of one single monolayer for metal bonded hydrogen could be established.     

Surface modification of porous poly(tetrafluoroethylene) film via cold plasma treatment

In this study, cold plasma technology was applied for the surface modification of porous polytetrafluoroethylene (PTFE) film to improve the hydrophilicity. The surface properties of PTFE, modified by air, helium (He) or acrylic acid (AAc), were investigated with scanning electron microscopy (SEM), scanning probe microscope (SPM), in situ X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. The changes of the surface property before and after plasma treatment were discussed. According to SEM and SPM measurements, the surface roughness increased at different levels after plasma treatment. Compared to air and AAc plasma treatment, the He plasma treatment introduced large amounts of oxygen into the surface, as known from XPS results. Contact angle measurements revealed that the hydrophilicity of the PTFE film surface was greatly improved due to the surface roughness and changes of chemical elements on the PTFE surface.     

STM characterization of size-selected V1, V2, VO,and VO2 clusters on a TiO2(110)-(1 × 1) surface at room temperature

We use ultra-high vacuum scanning tunneling microscopy (UHV–STM) to probe, at the atomic level, the structure of mass-selected isolated V₁, V₂, VO and VO₂ clusters deposited on rutile TiO₂(110) by ion soft landing. All four species interact differently with the TiO₂ surface and the ultimate binding site and configuration strikes a balance between the gas-phase structure and the ligation of this cluster by the TiO₂ surface. Our results show that vanadium atoms prefer to bind in the upper threefold hollow sites on the surface and have a slight tendency to pair along the [1–10] direction, while vanadium dimers bind to the surface oriented along the [001] direction exclusively. VO clusters bind with the vanadium atom in the upper threefold hollow site and with the oxygen atom bound to an adjacent fivefold coordinated Ti atom (5c-Ti). The VO₂ cluster also binds with the vanadium atom in the upper threefold hollow site and with both oxygen atoms bound to adjacent 5c-Ti atoms or with only one oxygen bound to the surface and the other directed out of the plane of the surface.     

硫化廿二酸中氧与硫在菜籽油中的协同减摩抗磨作用研究

采用低温硫化工艺和复分解反应制备了无臭硫化廿二酸,在四球摩擦磨损试验机上考察了其在菜籽油中的减摩抗磨行为及承载能力,并对钢球磨损表面进行了扫描电子显微（ＳＥＭ）、电子探针（ＥＰＭＡ）以及Ｘ射线光电子能谱（ＸＰＳ）分析。通过与廿二酸和硫化异丁烯的对比研究发现,在廿二酸中引入硫后,氧与硫产生了明显的协同减摩抗磨及承载作用。钢球磨损表面ＸＰＳ分析结果表明,在摩擦过程中硫化廿二酸发生了摩擦化学变化,表面Ｅ     

Is a coating part of the substrate? The case of vanadium carbide on steel

Metallic surfaces, especially that of steel, are generally protected by various types of coatings. This paper presents some of the results of CEMS studies currently being made on mild steel substrate coated with a thin layer of vanadium carbide (VC). CEMS studies were done before and after coating. The internal magnetic field was found to be oriented at an angle of 48 degrees with respect to the transverse surface of the steel sample. After coating with VC at 950 °C, this value was reduced to 39 degrees. Molecular orbital calculations indicated that the electron density along the surface of the steel is significantly changed when the VC layer is formed, which leads to the changes in the magnetic field directions that are observed. The experimental data therefore reveal that vanadium from the coating diffuses into the iron substrate.     

Initial interaction of oxygen with aluminium single crystal faces: A LEED,AES and work function study

Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and work function (Kelvin probe) measurements have been used to study the initial interaction of clean Al(111), (100) and (110) surfaces with oxygen at room temperature. The oxidation process was found to be surface orientation dependent, but a common feature has been always observed on the three low-index surfaces: they show two distinct phases, i.e. a chemisorbed phase followed then by an oxidized phase. From analysis of AES, LEED and Kelvin probe results, an adsorption mechanism of O on Al for each surface orientation is proposed.     

Phase transition kinetics of vanadium pentoxide II. Theoretical results

Experimental data on the phase transformation kinetics in vanadium pentoxide due to surface oxygen loss are analyzed theoretically. A model for the process as a one-dimensional problem with oxygen loss from the surface and coupled interface and diffusion controlled growth modes is described. This model appears to match well the experimental data with reasonable numbers for the surface loss rate and diffusion constant. In particular, the model reproduces changes in the number of phase fronts as a function of electron beam flux. In addition, the analysis confirms that the effective diffusion constant is electron beam flux dependent.     

Characterization of tetravalent vanadium functional centres in metal oxides derived from a spin-Hamiltonian analysis

The electronic and structural characterization of vanadium functional centres in metal oxides by means of electron paramagnetic resonance (EPR) defines an important topic in solid-state research. In that respect, transfer of determined spin-Hamiltonian parameters into electronic and structural information often imposes a ‘bottleneck’ to interpret the obtained EPR spectra. Using two semi-empirical models, EPR spin-Hamiltonian parameters for tetravalent vanadium can be analysed first to distinguish between either V⁴⁺ and vanadyl VO²⁺-centres and second to determine the location of the corresponding centre either in the ‘bulk’ or at the surface region of metal oxide particles.     

Assessing the structure and function of single biomolecules with scanning transmission electron and atomic force microscopes

The scanning transmission electron microscope (STEM) and the atomic force microscope (AFM) have provided a wealth of useful information on a wide variety of biological structures. These instruments have in common that they raster-scan a probe over a sample and are able to address single molecules. In the STEM the probe is a focused electron beam that is deflected by the scan-coils. Detectors collecting the scattered electrons provide quantitative information for each sub-nanometer sized sample volume irradiated. These electron scattering data can be reconstituted to images of single macromolecules or can be integrated to provide the mass of the macromolecules. Samples need to be dehydrated for such quantitative STEM imaging. In contrast, the AFM raster-scans a sharp tip over a sample surface submerged in a buffer solution to acquire information on the sample's surface topography at sub-nanometer resolution. Direct observation of function-related structural changes induced by variation of temperature, pH, ionic strength, and applied force provides insight into the structure-function relationship of macromolecules. Further, the AFM allows single molecules to be addressed and quantitatively unfolded using the tip as nano-tweezers. The performance of these two scanning probe approaches is illustrated by several examples including the chaperonin GroEL, bacterial surface layers, protein crystals, and bacterial appendices.