A method for the characterization of surface-modified asbestos fibres by electron energy-loss spectroscopy and electron spectroscopic imaging

A method for the characterization of surface-treated asbestos fibres with electron microscopy is presented. Electron spectroscopic imaging (ESI) of organosilane-treated chrysotile asbestos fibres has been carried out. Initially, the region below the carbon edge was inspected in ESI mode for its effectiveness as a background correction. Elemental mapping was performed on standard untreated fibres to take into account non-characteristic signals from extrapolation errors and camera artefacts. The highest resulting pixel value that results from non-characteristic signals was used as a threshold for further background correction in the net images. Samples for electron energy-loss spectroscopy were prepared in two different ways, either by gluing on grids, or by using perforated carbon foils. The results show that the use of a conducting carbon film is necessary for the analysis of such electrically insulating asbestos fibres. Focusing of the electron beam on the individual fibres results in a thermal effect promoting the evaporation of the organosilane reaction products.     

Electron energy loss near edge structure on the nitrogen K-edge in vanadium nitrides

This paper presents electron energy-loss near-edge structure (ELNES) data for the N K edges of vanadium nitrides. By rapid thermal processing of vanadium layers in pure nitrogen at high temperatures the two known vanadium nitrides, VN and V₂N, have been prepared. The phases have been checked by electron diffraction and quantitative electron energy-loss spectroscopy (EELS) analysis. Because their crystallographical structures are different, they also exhibit different ELNES features, which can be used as fingerprints for rapidly distinguishing between VN and V₂N. The experimental findings are supported by modelling the N K edge using a band structure approach (full linearized augmented plane wave method).     

Quantification of the EELS near-edge structures to study Mn doping in oxides

The L₃ to L₂ white-line intensity ratios of Mn in solid solution in yttria-stabilized zirconia and in Mn oxide standards are measured using different approaches. We show that the L₃/L₂ ratio alone cannot be used as a means of deducing the oxidation state and that a combined analysis of this ratio and the normalized white-line intensity is required to retrieve the ionicity and magnetic state of the Mn dopant with respect to reference standards. Changes as a function of composition are measured and these are discussed in terms of variations in crystal field parameters associated with possible vacancy interaction. From the oxygen near-edge structure we analyse the localization of the extra electron charge introduced by the dopant and discuss the possible effects of the association of this extra charge with oxygen vacancies in relation to the macroscopic ion conductivity.     

Contribution of energy-filtering TEM to the detection of calcium: Application to mast cells

The ultrastructural distribution and quantification of calcium in mast cells prepared by anhydrous processing was investigated by energy-filtering transmission electron microscopy (EFTEM) using a Zeiss 902 electron microscope. Optimal conditions for calcium detection were determined using inorganic (calcium phosphate) and organic (calcium-loaded chelex beads) standards with known amounts of calcium. Electron energy-loss spectroscopy (EELS) revealed calcium at the L_2,3 edge and also at the M_2,3 edge for all specimens examined. Comparison with X-ray microanalysis confirmed the results obtained with EELS. Electron spectroscopic imaging (ESI) was applied for mapping calcium both in standards and in cells and we showed that mast cell granules were the main site of calcium localization. Although, results have shown that a combination of analytical techniques is required to obtain reliable results.     

碳复合材料钻孔加工性研究

从刀具材料,几何角度,切削用量等几个方面分析了碳复合材料钻孔工艺性和表面质量,给出了改善复合材料钻孔质量的工艺参数。     

Complementary techniques for the characterization of thin film Ti/Nb multilayers

An aberration corrector on the probe-forming lens of a scanning TEM (STEM) equipped with an electron energy-loss spectrometer (EELS) and X-ray energy-dispersive spectrometer (XEDS) has been employed to investigate the compositional variations as a function of length scale in nanoscale Ti/Nb metallic multilayers. The composition profiles of EELS and XEDS were compared with the profiles obtained from the complementary technique of 3D atom probe tomography. At large layer widths (h≥7 nm, where h is the layer width) of Ti and Nb, XEDS composition profiles of Ti/Nb metallic multilayers are in good agreement with the EELS results. However, at reduced layer widths (h≈2 nm), profiles of EELS and atom probe exhibited similar compositional variations, whereas XEDS results have shown a marked difference. This difference in the composition profiling of the layers has been addressed with reference to the effects of beam broadening and the origin of the signals collected in these techniques. The advantage of using EELS over XEDS for these nanoscaled multilayered materials is demonstrated.     

High energy-resolution electron energy-loss spectroscopy study of the dielectric properties of bulk and nanoparticle LaB6 in the near-infrared region

The dielectric properties of LaB₆ crystals and the plasmonic behavior of LaB₆ nanoparticles, which have been applied to solar heat-shielding filters, were studied by high energy-resolution electron energy-loss spectroscopy (HR-EELS). An EELS spectrum of a LaB₆ crystal showed a peak at 2.0 eV, which was attributed to volume plasmon excitation of carrier electrons. EELS spectra of single LaB₆ nanoparticles showed peaks at 1.1-1.4 eV depending on the dielectric effect from the substrates. The peaks were assigned to dipole oscillation excitations. These peak energies almost coincided with the peak energy of optical absorption of a heat-shielding filter with LaB₆ nanoparticles. On the other hand, those energies were a smaller than a dipole oscillation energy predicted using the dielectric function of bulk LaB₆ crystal. It is suggested that the lower energy than expected is due to an excitation at 1.2 eV, which was observed for oxidized LaB₆ area.     

Sectionable microcarrier beads: An improved method for the preparation of cell monolayers for electron microscopy

Cross-linked dextran beads provide an excellent surface for tissue-cultured cell monolayers, and can be processed for transmission (TEM) and scanning (SEM) electron microscopy, as well as light microscopy (LM). Cells are grown to confluency on the surface of the microcarriers, where at any point aliquots can be removed and experimentally treated as desired (e.g. immunocytochemistry) providing a representative sample. Sample preparation for TEM follows standard procedures for any cell monolayer, but infiltration times must be at least doubled to allow penetration of the beads. The polymerized blocks can then be sectioned for TEM or LM with no additional steps required. SEM sample preparation involves attaching the fixed bead/cell suspension to a glass coverslip with poly-1-lysine, dehydration, critical point drying, and coating for conductivity. The fixed and dried sample can also be attached directly to the SEM stub as free beads and subsequently gold coated. These beads provide (1) an increased surface area of cells visible per area of thin section, (2) eliminates the careful orientation required for flat substrate methods of embedding, (3) decreases the amount of sample manipulation in the forms of re-embedding and gluing, and (4) decreases the amount of drying artifact seen as cracking in SEM monolayer preparations.     

Application of recording and processing of energy-filtered image sequences for the elemental mapping of biological specimens: Imaging-Spectrum

Computerized energy-filtered transmission electron microscope (EFTEM) permits the recording and the processing of energy-filtered images, allowing a part of an electron energy-loss spectrum for each picture element to be obtained. This method, called ‘Imaging-Spectrum’, uses a Zeiss CEM902 coupled to several image analysis systems. The actual configuration records sequences of 48 images, 256 × 256 pixels, in steps of the energy loss, ΔE. Processing these sequences results in part of a core-loss EELS-spectrum for each pixel. This approach produces elemental maps with a short processing time. We have implemented three kinds of background calculation for the image subtraction. The influence of the irradiation dose and of the energy selecting slit width on the quality of the spectra is investigated. The method is applied to the analysis of some biological specimens (pericellular coat behaviour during adhesion between macrophages and red blood cells and location of calcite microcrystals in dental pulp cells). The Imaging-Spectrum method appears to be suitable for the analysis of large areas.     

Analysis of the calcium distribution in predentine by EELS and of the early crystal formation in dentine by ESI and ESD

Predentine is a collagen-rich extracellular matrix between the odontoblasts and the dentine with a width of about 15–20 μm. Electron energy-loss spectroscopy of rat incisors shows a significantly higher calcium content in the predentine at the predentine-dentine border than in the middle region of the predentine. At the predentine-dentine border in the dentine, the calcium and the phosphate groups combine to form apatite crystallites. Electron spectroscopic diffraction with zero-loss filtering revealed that the earliest crystallites contain only Debye-Scherrer rings of apatite, which are fewer in number and more diffuse than the diffraction rings from the mature crystallites. We therefore conclude that the early crystallites still contain lattice defects, which are annealed out to some degree with crystal growth. Electron spectroscopic imaging with zero-loss filtering also showed that the earliest crystallites are chains of dots (or small islands); they build up strands composed of islands, which rapidly acquire a needle-like character and coalesce laterally to form ribbon- or plate-like crystallites. The parallel strands sometimes appear to reinforce the macroperiod of the collagen microfibrils (67 nm) by tiny holes without any crystal-substance lined up perpendicular to the parallel strands of the crystallites.     

Improved preservation of phospholipid-rich multilamellar bodies in conventionally embedded mammalian lung tissue—an electron spectroscopic study

Different conventional methods of tissue processing were studied to determine the extent to which phospholipid-rich multilamellar bodies of pulmonary alveolar epithelial type II cells of the pig were preserved. Prolonged treatment with half-saturated aqueous uranyl acetate yielded excellent results on the stabilization of the multilamellar substructure, irrespective of whether glutaraldehyde-paraformaldehyde or glutaraldehydetannic acid was used as a primary fixative. The lamellar periodicities were observed to be 5·5–6·1 nm. Differences in the phosphorus distribution among several types of lipid bodies of alveolar epithelial type II cells were studied by means of electron spectroscopic imaging and electron energy-loss spectroscopy. Multilamellar bodies gave phosphorus signals which were significantly higher than those obtained from granular regions of composite bodies, whereas homogeneous bodies gave phosphorus signals which were even lower than those obtained from mitochondria, endoplasmic reticulum membranes or ribosomes.     

Optimized conditions for imaging the effects of bonding charge density in electron microscopy

We report on the observability of valence bonding effects in aberration-corrected high resolution electron microscopy (HREM) images along the [0 1 0] projection of the mineral Forsterite (Mg₂SiO₄). We have also performed exit wave restorations using simulated noisy images and have determined that both the intensities of individual images and the modulus of the restored complex exit wave are most sensitive to bonding effects at a level of 25% for moderately thick samples of 20-25 nm. This relatively large thickness is due to dynamical amplification of bonding contrast arising from partial de-channeling of 1s states. Simulations also suggest that bonding contrast is similarly high for an un-corrected conventional electron microscope, implying an experimental limitation of signal to noise ratio rather than spatial resolution.     

A molecular-beam study of the tribological chemistry of carbon tetrachloride on oxygen-covered iron

Dc molecular-beam methods are used to examine the reactivity of carbon tetrachloride with oxide films grown on iron in ultrahigh vacuum. The incident CCl₄ beam flux is sufficiently low that the nature of the surface oxide is dictated by the annealing temperature allowing the reactivity of Fe₂O₃, Fe₃O₄ and FeO films to be examined. Carbon tetrachloride reacts rapidly with Fe₂O₃ and reaction with Fe₃O₄ commences at 620 K to evolve CO. The activation energy for this process is 20.6±1.0 kcal/mol. CCl₄ reacts with FeO above 790 K, also to evolve CO, and the activation energy for this reaction is 5.7±0.4 kcal/mol. X-ray photoelectron spectroscopy shows the formation of a halide after reaction at 900 K. These results are in accord with film-growth kinetics measured using a microbalance at high pressures, where it was found that it was not necessary to remove the oxide layer prior to reaction. This contrasts with the behavior of sulfur-containing molecules, where the oxide layer had to be removed before a film would grow. This effect may contribute to the additive synergies commonly found in extreme-pressure lubricant additives where one of the roles of the chloride may be to reduce the oxide layer.     

Initial experimental results on a magnetic beam separator spectrometer for the SEM

This article describes preliminary experiments to test the concept of scanning electron microscope (SEM) using a round magnetic beam separator to perform energy spectroscopy. Two experiments with an add-on attachment inside a conventional SEM were performed, one to estimate the sector image aberrations and the other to capture an energy spectrum of scattered electrons. The experiments show that the sector image aberrations lie well below 2 nm and that it is possible to capture the energy spectrum of secondary electrons.     

水润滑材料的发展状况及其趋势

由于节能及环保要求,水润滑材料在最近几年发展迅速,正成为一种很有前景的摩擦副材料.回顾了几类水润滑材料及其相关的应用,介绍了硅系陶瓷材料的特点、水润滑性能、国内外研究状况,介绍了最近几年国内外对金属陶瓷的研究及其应用.     

A comparison of two models for the characteristic X-ray fluorescence correction in thin foil analysis

It is shown that Philibert & Tixier's calculation for the contribution of characteristic fluorescence in thin foil X-ray microanalysis is in error. The calculation of Nockolds et al. for this contribution is shown to be correct.     

An experimental study on the behaviour under impact loading of metallic cellular materials

This paper presents an experimental study on the impact response of metallic cellular materials, i.e. aluminium honeycombs of various cell sizes and wall thicknesses, aluminium foams made from two different manufacturing processes (IFAM and Cymat), as well as hollow sphere agglomerates (nickel and iron). A 60 mm diameter nylon Hopkinson pressure bar is used to improve the signal/noise ratio and to host larger samples containing a sufficient number of cells. Quasi-static and classical Split Hopkinson Pressure Bar (SHPB) tests as well as direct impact Hopkinson bar tests (higher speeds up to 50 m/s) are performed. Significant rate sensitivities are observed for most of the cellular materials studied. Analyses of the potential causes of this macroscopic rate sensitivity show that the microinertia effect in the successive folding process could be an important factor.     

An experimental study on the transition criteria of open channel natural convection flows

Natural convection experiments were carried out for a wide range of the Grashof number from 10⁴ to 5 × 10⁹ or for the Rayleigh number from 10⁷ to 10¹³ in order to seek the proper transition criteria from laminar to turbulent. Using the analogy concept, heat transfer systems were simulated by corresponding mass transfer systems. The copper sulfate electroplating system was chosen as the mass transfer system. The experimental results closely reproduced the McAdams’s correlation for laminar and Fouad’s for turbulent. The Sherwood numbers obtained from the experiment were proportional to the 1/4 power of Rayleigh number or Grashof number at laminar region and the near 1/3 power at turbulent region as the well known theory. This paper concludes that the proper transition criteria of the natural convection should be the Grashof number of 10⁹. The originality of this paper comes from the fact that the study deals with very large value of Schmidt number and that by using the analogy experiment methodology, high values of Rayleigh number and Grashof number were achieved with a relatively short test facility.

     

An experimental study on the effects of lubrication in form tapping

This paper presents the results of a study of lubrication in form tapping and aims at a better understanding of its effect. It appears that lubrication is of paramount importance. Oil with efficient high pressure additives can reduce considerably the torque necessary to form the thread. Lubricants reduce the tool/work material friction during the forming process and, as a consequence, the resulting strain distribution and the strain hardening of the thread are affected. This investigation includes an analysis on the effects of additives in lubricants on the temperature during tapping, enabling correlation with the appearance of chemical elements of the oil which react with the thread material and contribute to lubrication.     

一种抛光液的化学成份分析

对一种水溶性的抛光液产品,在烘除水分后采用有机溶剂进行分离处理,对分离处理后的样品通过傅里叶变换红外光谱仪进行红外光谱测试,并对测试的红外谱图进行解析。结合红外光谱分析和电镜/能谱对元素的检测结果 ,确定样品的成分。在定性分析基础上采用原子吸收光谱法及常规化学分析方法进行定量分析,给出样品的定性和定量分析结果 。