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51.
52.
Hugo M. Ortner Wilhelm Blödorn Gernot Friedbacher Manfred Grasserbauer Viliam Krivan Alois Virag Peter Wilhartitz Gerold Wünsch 《Mikrochimica acta》1987,91(1-6):233-260
It is first shown what effects trace impurities generally exert on metal properties and why trace analysis is essential to modern applications of refractory metals in today's high technology. The effect of trace impurities in metals on complex systems like microelectronic components is also discussed.It is then shown, what principal analytical requirements are mandatory for trace characterization of refractory metals at levels of rising purity (4 N to 6 N). A survey of analytical methods for trace and ultratrace characterization of refractory metals is given including the following methods: flame and graphite furnace atomic absorption spectrometry, ICP and DCP-atomic emission spectrometry, X-ray fluorescence spectrometry, activation analysis, mass spectrometric methods, especially SIMS and GDMS. 相似文献
53.
Using instrumental neutron activation analysis (INAA), graphite furnace atomic absorption spectrometry (GFAAS), flame atomic absorption spectrometry (FAAS) and combustion elemental analysis, green coffees of the Arabica species produced in crop year 1987/88 in Colombia, Costa Rica, Cuba, El Salvador, Mexico, Nicaragua, Panamá and Papua New Guinea were analysed for the elements Ba, Br, C, Ca, Co, Cr, Cu, Cs, Fe, H, K, La, Mg, Mn, N, Na, Rb, Sc, Sr and Zn. In accordance with the concentrations determined, the elements could be ranked into five groups: Sc (sub-ppb level); Br, Co, Cr, Cs and La (ppb level); Ba, Cu, Fe, Mn, Na, Rb, Sr and Zn (ppm level); Ca and Mg (%o level); and C, H, K and N (% level). On the basis of the results obtained, an attempt was made to establish the origin of the green coffee via its elemental composition. Among the investigated elements, manganese was found to be best suited as an indicator for this purpose. However, the elements C, Co, Cs, Na and Rb proved to be of interest too. 相似文献
54.
A direct solid sampling electrothermal atomic absorption spectrometric method for determination of Cd, Co, Cr, Cu, Fe, Li, Mn, Ni and Zn in zirconium dioxide has been developed. Using optimised experimental conditions, very effective in-situ analyte/matrix separation was achieved without any chemical modification. After the measurement, the matrix residue could easily be tipped out from the platform. In the determination of Cr, before sampling, the platform bottom was covered with carbon powder. Quantification was performed using calibration curves measured with aqueous standard solutions pipetted onto the matrix residue from a previous sample run. Sample amounts between 0.5 and 40 mg were applied for each analysis cycle. The accuracy was determined by comparison of the results with those obtained by radiochemical neutron activation analysis and by electrothermal atomic absorption spectrometry using liquid sampling of digests and slurry sampling. For the nine elements assayed, the limits of detection achievable by this method are between 0.06 ng g–1 (Cd) and 2.3 ng g–1 (Fe).Dedicated to the memory of Wilhelm Fresenius 相似文献
55.
Findeisen A Kolivoska V Kaml I Baatz W Kenndler E 《Journal of chromatography. A》2007,1157(1-2):454-461
The exudates of conifers consist mainly of diterpenoic acids of the abietane and pimarane type (abietic, neoabietic, dehydroabietic, palustric, pimaric, isopimaric, levopimaric and sandaracopimaric acid) and larixol acetate. These natural resins were used as adhesives, coatings, varnishes or plasticizers in artistic and historic works since ancient times. For the purpose of conservation and restoration and for art historic examination of such museum objects the identification of the binding media used is undoubtedly of paramount importance. In the present paper, the characterization of these resins based on the pattern of their diterpenoid constituents is carried out by capillary electrophoresis. For separation a background electrolyte which has been initially introduced for the analysis of chlorinated and natural resin acids in waste water was modified and the experimental conditions were adjusted in terms of resolution and analysis time. Separation was carried out in borate buffer at pH 9.25 (ionic strength 20 mmol L(-1)) with methyl-beta-cyclodextrin and sulfobutylether-beta-cyclodextrin as additives to increase selectivity and enhance the solubility of the analytes. With this electrophoretic system the resin acids of interest and larixol acetate--all as anionic cyclodextrin complexes--were separated within 5 min and detected at 200, 250 and 270 nm with a diode array detector. The electrophoretic patterns served for the characterisation of the relevant diterpenoic resins, balsams and copals. Sample pre-treatment was limited to sonication in methanol at 55 degrees C for 30 min. This enables the identification of the resins in mixtures with other binders like plant gums, animal glues or drying oils, even when these media are present in excess. Colophony was identified as resinous constituent of a modelling mass for gilded frames originating from the 19th century. 相似文献
56.
P. Tarapčík Ján Labuda Blandine Fourest Viliam Pätoprstý 《Accreditation and quality assurance》2001,6(8):352-359
A complete and accurate evaluation of measurement uncertainty requires the knowledge of the uncertainty distributions. The
latter are rarely determined or verified experimentally, and hence up to now only crude estimates or assumptions based on
intuition have been used. The simulation of experimental results is readily accessible and provides a more relia-ble solution
to this problem. When using an appropriate model of measurement and after determina-tion of input value parameters by present
state-of-the-art techniques, simulation data supply reliable information about the distribution of the output results of a
complex measurement. The method permits simple variation of preposition and therefore ready analysis of various features influencing
the measurement of uncertainty intervals. In the paper we described examples of such evaluations related to the preparation
of certified reference materials, where there is excellent agreement between the traditional and simulation approaches. And
evaluation of more complex measurements of diffusion coefficients by the open capillary method, where uncertainty of the simulated
result is more realistic than the re-sult from the traditional error method due to non-linearity and probably Cauchy distribution
in some steps.
Received: 17 March 2000 Accepted: 25 July 2000 相似文献
57.
Vladimír Luke Viliam Laurinc Stanislav Biskupi
《International journal of quantum chemistry》1999,75(2):81-88
A many‐body perturbation theory based on the partitioning of the dimer Hamiltonian, formulated in an orthogonalized basis set, is used for the calculation of interaction energies at the Hartree–Fock (HF) level. Numerical results for the (HF)2 and (H2O)2 systems in selected geometries are presented. The interaction‐energy components are compared with the results obtained from the standard supermolecular approach and the intermolecular perturbation theory based on the biorthogonal basis set. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 81–88, 1999 相似文献
58.
Importance of the Anchor Group Position (Para versus Meta) in Tetraphenylmethane Tripods: Synthesis and Self‐Assembly Features 下载免费PDF全文
Marcin Lindner Dr. Michal Valášek Jan Homberg Kevin Edelmann Dr. Lukas Gerhard Prof. Dr. Wulf Wulfhekel Dr. Olaf Fuhr Tobias Wächter Prof. Dr. Michael Zharnikov Dr. Viliam Kolivoška Dr. Lubomír Pospíšil Dr. Gábor Mészáros Dr. Magdaléna Hromadová Prof. Dr. Marcel Mayor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(37):13218-13235
The efficient synthesis of tripodal platforms based on tetraphenylmethane with three acetyl‐protected thiol groups in either meta or para positions relative to the central sp3 carbon for deposition on Au (111) surfaces is reported. These platforms are intended to provide a vertical arrangement of the substituent in position 4 of the perpendicular phenyl ring and an electronic coupling to the gold substrate. The self‐assembly features of both derivatives are analyzed on Au (111) surfaces by low‐temperature ultra‐high‐vacuum STM, high‐resolution X‐ray photoelectron spectroscopy, near‐edge X‐ray absorption fine structure spectroscopy, and reductive voltammetric desorption studies. These experiments indicated that the meta derivative forms a well‐ordered monolayer, with most of the anchoring groups bound to the surface, whereas the para derivative forms a multilayer film with physically adsorbed adlayers on the chemisorbed para monolayer. Single‐molecule conductance values for both tripodal platforms are obtained through an STM break junction experiment. 相似文献
59.
P J Vlok J L Coetzee D Banjevic A K S Jardine V Makis 《The Journal of the Operational Research Society》2002,53(2):193-202
This paper describes a case study in which the Weibull proportional-hazards model is used to determine the optimal replacement policy for a critical item which is subject to vibration monitoring. Such an approach has been used to date in the context of monitoring through oil debris analysis, and this approach is extended in this paper to the vibration monitoring context. The Weibull proportional-hazards model is reviewed along with the software EXAKT used for optimization. In particular the case considers condition-based maintenance for circulating pumps in a coal wash plant that is part of the SASOL petrochemical company. The condition-based maintenance policy recommended in this study is based on histories collected over a period of 2 years, and is compared with current practice. The policy is validated using data that arose from subsequent operation of the plant. 相似文献
60.
The interactions of selected zirconium alloys used as special construction materials (Zr-pure, Zry-2, E-110) with the molten system of (LiF—NaF—KF)(eut.) with additions of K2ZrF6 or Na7Zr6F31 were studied. Corrosion losses of pure zirconium decrease sharply with 5 mole% addition of K2ZrF6 to (LiF—NaF—KF)(eut.). The presence of alloying additives (Sn, Nb) has a positive influence on corrosion resistance in the eutectic mixture — up to 60% increase in corrosion resistance in comparison with pure zirconium. The mass losses of pure zirconium indicate an increasing corrosion attack with increasing Na7Zr6F31 content in (LiF—NaF—KF)(eut.) mixtures. 相似文献