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Organisationseinheit der BAM
For the determination of main and minor components in silicon-based ceramic powders, a decomposition by a combustion with elemental fluorine and separation of the volatile fluorination products by a carrier-gas distillation with a subsequent detection by quadrupole mass spectrometry is described. The necessity and success of the separation step is demonstrated for the determination of boron as a minor constituent in SiC, where the spectral interferences of silicon on the boron signals are decreased considerably. The method developed is shown to be directly applicable to determination of silicon in Si3N4, SiC, and SiO2. The determination of nitrogen in Si3N4 requires additional effort, to separate nitrogen from the excess of fluorine. For the determination of boron, a complete mobilization of BF3 is assured by the presence of an adequate amount of GeF4. Analysis results obtained with different types of calibration show a precision of 30 g for boron at the milligram-per-gram level and a precision between 0.5 and 2% (m/m) for the main components, silicon and nitrogen. Within these standard deviations, the results agree well with the values expected from the stoichiometry, with the results for silicon and boron obtained by wet chemical decomposition and slurry techniques in combination with ICP-OES and with the results for nitrogen obtained by carrier gas heat extraction.
Isotope amount ratios of krypton were measured on subsamples from one large batch of high purity krypton separated from the atmosphere. Synthetic mixtures of enriched krypton isotopes were used to calibrate the measurements with small uncertainties. The result is a primary isotopic gas standard (PIGS) IRMM-2030 with certified values for isotope ratios, isotopic composition, and molar mass of krypton with small combined uncertainties uc, evaluated according to the ISO/BIPM Guide (GUM). It is commercially available from IRMM-Geel or from MESSER (Duisburg, D). The certified krypton isotope amount ratios in the PIGS IRMM-2030 are as follows: n(78Kr)/n(84Kr)=0.006 232 5(55), n(80Kr)/n(84Kr)=0.040 107(17), n(82Kr)/n(84Kr)=0.203 43(12), n(83Kr)/n(84Kr)=0.201 79(11), and n(86Kr)/n(84Kr)=0.303 205(59) with expanded uncertainty U=kuc and coverage factor k=2. The molar mass of Kr in this sample is M(Kr)=83.798 02(16) g/mol. These values are in good agreement with published measurements of atmospheric krypton but have smaller combined uncertainties and are calibrated by means of synthetic isotope mixtures. The values of the PIGS are traceable to the SI. Measurements of isotope amount ratios of krypton in other samples can be linked to SI using this PIGS.
Spatially resolved X-ray fluorescence analysis using synchrotron radiation (SR-XRF) at the wavelength shifter beamline, BAMline, at BESSY was used to investigate Renaissance silverpoint drawings as it is extremely sensitive, non-destructive and can be carried out in air using an excitation spot in the hundred micrometer range.
This paper deals with first results of the study of silverpoint drawings of Albrecht Dürer (14711528) belonging to the sketchbook that Albrecht Dürer used during a travel to the Netherlands in 1520/21. These results are compared to a PIXE study performed on drawings from the same sketchbook.
The minor element composition of the silverpoint used for the drawings in the sketchbook was (10.6 ± 3.5) wt.% of Cu and traces of Zn. Mercury was found in the marks but does not belong to the initial composition of the silverpoint as it is attributed to an alteration phenomenon. One drawing of the sketchbook represents an exception. It consists of silver marks containing an additional minor element, Zn, in the marks and was, therefore, created with another silverpoint, probably at a different time than the other drawings.
Synchrotron-induced X-ray fluorescence (Sy-XRF) analysis was used to study the chemical composition of precious Renaissance silverpoint drawings. Drawings by famous artists such as Albrecht Dürer (14711528) and Jan van Eyck (approximately 13951441) must be investigated non-destructively. Moreover, extremely sensitive synchrotron- or accelerator-based techniques are needed since only small quantities of silver are deposited on the paper. New criteria for attributing these works to a particular artist could be established based on the analysis of the chemical composition of the metal points used. We illustrate how analysis can give new art historical information by means of two case studies. Two particular drawings, one of Albrecht Dürer, showing a profile portrait of his closest friend, Willibald Pirckheimer (1503), and a second one attributed to Jan van Eyck, showing a Portrait of an elderly man, often named Niccolò Albergati, are the object of intense art historical controversy. Both drawings show inscriptions next to the figures. Analyses by Sy-XRF could reveal the same kind of silverpoint for the Pirckheimer portrait and its mysterious Greek inscription, contrary to the drawing by Van Eyck where at least three different metal points were applied. Two different types of silver marks were found in this portrait. Silver containing gold marks were detected in the inscriptions and over-subscriptions. This is the first evidence of the use of gold points for metal point drawings in the Middle Ages.
This work is part of an effort to develop chelating agents for stable binding and easy conjugation of Re-188 to biologically interesting structures. Starting from the well-known in vivo stability of [188ReO(DMSA)2]-, we want to exploit this coordination system for the design of 188ReO(V) chelates, which are stable toward reoxidation to perrhenate and toward ligand exchange under all conditions of radiopharmaceutical development. Therefore, a new type of tetradentate ligand has been synthesized by bridging two molecules of N,N'-diisobutyl-2,3-dimercaptosuccinamide with N-(3-aminopropyl)propane-1,3-diamine. The resulting stereoisomeric tetrathiolato S4 ligand of composition (iBu)2N(O)C-C(SH)-C(SH)-C(O)NH-(CH2)3-NH-(CH2)3-NHC(O)-C(SH)-C(SH)-C(O)N(iBu)2 forms anionic five-coordinate oxorhenium(V) complexes by a ligand-exchange reaction of NBu4[ReOCl4] in methanol. In the absence of a base, the compounds were isolated as "betaine", [ReO(S4)], with the protonated nitrogen of the bridge serving as an internal "counterion". Two representatives have been fully characterized in both the solid and solution states and found to adopt the expected square-pyramidal coordination geometry. The equatorial plane is formed by four thiolate sulfur atoms, whereas the oxygen occupies the apical position. The orientation of the metal oxo group is exo in relation to the carbamido groups in both isomers. Both complexes are stereoisomeric regarding the junction of the triamine chain.
A new approach was developed for quantitative calibration in GD-MS which can afford reliable and metrologically traceable results for many trace elements and was exemplified for pure copper and pure iron. It can be assumed that the technique can be further improved and applied to the analysis of other pure metals. Pressed copper and iron powder samples were used to calibrate the glow discharge mass spectrometry applied to the analysis of pure copper and iron. The new type of glow discharge mass spectrometerthe Element GD (Thermo Electron Corporation)was used with a Grimm-type discharge cell for flat samples. Two series of powder samples were prepared for each of the copper and iron matrixes. The powders were quantitatively doped with solutions of graduated and defined concentrations of 40 or 20 analytes, respectively. The mass fractions of the analytes in the dried and homogenized metal powder samples ranged from µg/kg levels up to 10 mg/kg levels. A special technique was developed to press the samples and to form mechanically stable pellets with low risk of contamination. Ion beam ratios of analyte ions to matrix ions were used as measurands. The calibration curves were determined and the linear correlation coefficients were calculated for different intervals of the curves. The linear correlation coefficients are very satisfactory for most of the calibration curves, which include the higher segments of mass fractions; however, they are less satisfactory for the lower segments of the calibration curves. Nevertheless, in many cases rather acceptable and rather promising values were achieved even for these lower segments, representing mass fractions of analytes at ultra-trace level. The comparison of the certified values of different reference materials with the measured values based on calibrations with the pressed powder samples led to deviations less than 30% for most of the considered examples.
Coarsening of grain-refined semi-solid Al-Ge32 alloy: X-ray microtomography and in situ radiography
(2007)
The International Temperature Scale of 1990 (ITS-90) is based on thermodynamic equilibrium states of ideally pure substances. The largest contribution to the uncertainty budgets of most metallic fixed points is the influence of impurities on the fixed-point temperature. Therefore, a traceable chemical analysis of the remaining impurities with small uncertainty is the basis of further progress. Further requirements are better knowledge of the phase diagrams at very low impurity contents, impurity segregation, and the quantification and correction of thermal effects during a fixed-point realization. In this article, current and future activities at PTB and BAM in order to develop improved metallic fixed-point cells of the ITS-90 are reviewed.
Rocks are commonly very heterogeneous materials. Randomly distributed micro-flaws inside the rock are believed to initiate tensile cracks from which shear fractures develop and coalescence through en echelon interactions leads to fracture. In this paper, we describe the results of applying high-resolution X-ray tomography to samples of greywacke and limestone experimentally deformed under unconfined axial shortening at various loads equivalent to different fractions of the sample strength. Mineral grains, pores, micro-cracks and other voids were imaged with a resolution of 10 µm. 3D image analysis enabled us to monitor the initial state of the samples and the changes in them due to compression. Crack morphology is characterized and compared to the micro-structure of the sample before and after deformation. In the greywacke, formation of a macro-crack ~10° oblique to the stress direction is observed. It initiated in fine intergranular material at the top tip of the sample and is composed of tensile fractures connected by wing cracks. None of the voids defined in the initial state fractured, and the crack is interpreted to have started either as a micro-crack which was smaller than the resolution of the tomography, or, as a completely new crack. In the limestone, cracks are observed to initiate in features that are too small to be imaged by the tomography, or also in newly created cracks.
X-ray topography is a well known imaging technique to characterise strain and extended defects in single crystals. Topographs are typically collected on X-ray films. On the one hand such photographic films show a limited dynamic range and the production of films will be discontinued step by step in the near future. On the other hand new imaging detectors improved for X-ray tomography become more and more attractive even for topography because of increasing resolution, dynamic range, speed and active area. In this paper we report about the upgrade of the TOPOTOMO beamline at the synchrotron light source ANKA, Research Centre Karlsruhe, with a high resolution digital camera for the topography use.