AbstractPublished in the seriesAir Monitoring Methods, Vol. 10 (2007)The article contains sections titled:General principlesEquipment, chemicals and solutionsEquipmentChemicals and solutionsSampling and preparation of samplesPreparation of the filterSamplingPreparation of the samplesOperating conditionsAnalytical determinationDetermination of the blank valueDetermination of organic carbonDetermination of elemental carbonDetermination of total carbonCalculation of the analytical resultReliability of the methodPrecisionRecoveryLimit of detection and limit of quantificationInterferenceResults from comparative measurementsDiscussion of the method

AbstractVeröffentlicht in der ReiheAnalytische Methoden zur Prüfung gesundheitsschädlicher Arbeitsstoffe: Luftanalysen, 15. Lieferung, Ausgabe 2006Der Artikel enthält folgende Kapitel:Grundlage des VerfahrensGeräte, Chemikalien und LösungenGeräteChemikalien und LösungenProbenahme und ProbenaufbereitungVorbereitung der FilterProbenahmeProbenaufbereitungArbeitsbedingungenAnalytische BestimmungBestimmung des BlindwertesBestimmung des organisch gebundenen KohlenstoffsBestimmung des elementaren KohlenstoffsBestimmung des GesamtkohlenstoffsBerechnung des AnalysenergebnissesBeurteilung des VerfahrensPräzisionWiederfindungsrateNachweis‐ und BestimmungsgrenzeStöreinflüsseErgebnisse von VergleichsmessungenDiskussion

OBJECTIVES:Starting shortly after the reunification of Germany and lasting up to the end of the 1990s, an extensive series of retrospective exposure investigations for the East German uranium mining industry was performed in order to provide information about the exposure situation of the miners towards respirable dust, inhalable dust, crystalline silica and heavy metals. It should provide the necessary information for legal compensation of miners with potential industrial diseases as well as for epidemiological research.METHODS:Extensive side-by-side measurements using original historic equipments as well as comprehensive evaluation of the time increments of specific jobs with respect to exposure relevant tasks were performed. After attributing average exposures to the tasks, shift exposures for the jobs could be calculated.RESULTS:By the end a comprehensive job exposure matrix for all underground jobs of the German uranium mining industry was developed for the components mentioned, including arsenic where relevant. In the early days of SAG/SDAG Wismut dust and silica exposures were extremely high with respirable dust up to 20 mg/m(3) and respirable crystalline silica well above 2 mg/m(3) as shift averages. Beginning from about the early 1960s dust control measures started to improve conditions dramatically.CONCLUSIONS:It is absolutely necessary to invest sufficient effort for the estimation of exposure situations of past technological environments. Especially, the situation of early mechanised mining, characterised by low ventilation, dry drilling techniques and generally lacking dust control measures was characterized by extreme shift exposures. It is important to keep these in mind when metal mining exposure in different environments is considered.

Rapidly quenched ribbons of a Mg65Y10Cu25 metallic glass were electrochemically charged up to a maximum hydrogen content of about 3.7 wt.%. The hydrogen content was determined by hot extraction. The microstructure of different hydrogen-charged samples was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal behaviour was studied by differential scanning calorimetry (DSC) and thermal desorption analysis (TDA). Samples heated to selected temperatures were characterised by XRD. With increasing hydrogen content a change from a single-phase amorphous to a very fine nanocrystalline microstructure was observed, which is a consequence of hydride-forming reactions at room temperature. This strongly affects the thermal behaviour. With increasing fraction of nanocrystalline phases in the hydrogenated samples, grain growth processes are more pronounced than crystallisation of the residual amorphous phase for temperatures up to 623 K. Correspondingly, the fraction of nanocrystalline products of hydride-forming reactions, i.e. YH3, MgH2 and Cu2Mg, increases. Significant hydrogen desorption occurs at temperatures above 623 K and is mainly related to the reverse of those hydriding reactions.

An attempt has been made to understand the correlation between the interface structure and the giant magnetoresistance (GMR) properties of electrodeposited Co–Cu/Cu multilayers by measurements performed on a series produced by galvanostatic electrodeposition under the application of different capacitances connected parallel to the electrochemical cell, and this was expected to increase the width of the chemically intermixed interface between the magnetic and non-magnetic layer. In contrast to expectation, the GMR values of multilayers electrodeposited in the presence of a capacitance remained nearly unchanged even at the highest applied capacitance value, as a consequence of immiscibility of alloying elements.

The maximum room-temperature giant magnetoresistance (GMR) of electrodeposited Co–Cu/Cu multilayers produced during this work was approximately 9% at 8 kOe, and it was found to decrease with increasing bilayer repeat number. A transmission electron microscopy study has revealed the fine details of the microstructure formed during growth. At the beginning of the deposition very small, nano-sized crystallites formed with both hexagonal close-packed (hcp) and face-centred cubic (fcc) crystal structures containing a high level of internal stress. The Cu-content of these small crystallites was found to depend strongly on their crystal structure (fcc or hcp). After this initial polycrystalline region, the size of crystallites increases, forming an fcc superlattice with increasing average Cu concentration at the first hundreds of repeat periods. This increase is not monotonous across the whole sample thickness. As another effect, the bending of layer planes becomes more remarkable as the growth progresses. The above inhomogeneities formed during the deposition of hundreds of bilayers could be responsible for the decrease in GMR with increasing total thickness of the multilayered samples.

Composite layers, which consist of TiC and hard amorphous carbon (a-C), have been prepared by plasma-enhanced chemical vapour deposition (PACVD). It is shown using high-resolution transmission electron microscopy (HRTEM) that the carbon phase forms a matrix, in which nano-crystalline TiC particles are embedded. The layers were characterized by X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS) with respect to the binding state of the carbon. According to the XPS and EELS measurements, the carbon was found to be largely sp3 hybridized (>70%). The hydrogen content of the carbon phase amounted to 8–10 at.%. As-prepared pure carbon layers are nearly stress relaxed, as it is demonstrated by use of the substrate curvature method.

Abstract Initial permeability measurements on nanocrystalline soft magnetic Fe73.5Si13.5B9Nb3Cu1 and Fe86Zr7B6Cu1 alloys revealed that, in agreement with previous studies, in the optimum annealed state, the Fe –Si–B–Nb–Cu alloy exhibits much better soft magnetic behaviour than the Fe –Zr – B–Cu alloy. On the other hand, the density remained almost unchanged upon the amorphous– nanocrystalline transformation in Fe – Zr –B–Cu whereas a significant increase (~ 2%) occurred in Fe – Si–B–Nb – Cu. From X-ray diffraction and transmission electron microscopy studies, the amount of the residual amorphous phase, the lattice parameter, the internal stresses, and the grain morphology of the crystallized phase were found to evolve differently with increasing annealing temperature for the two alloys whereas their grain sizes were nearly the same for a given annealing temperature. It is pointed out that all these observed differences may also contribute to the differences in their soft magnetic behaviour. Furthermore, an analysis of the phases in the fully annealed state gave some hints to explain the different behaviour of density upon crystallization.

Nanoscale multilayers have microstructural and compositional properties which may differ widely from those of bulk materials. Such changes were investigated by EELS in the analytical TEM for different binary multilayer systems. Nanoscale Co/Cu multilayers showed a chemical mixing depending on the preparation technique. A trend to demixing was observed at annealing. The fine structure of the O–K edge on nanoscale Fe/Al layers enables the localized distinction between O bonding at Fe and Al.

At first a survey of the methodic state of the art in analytical transmission electron microscopy is given. This concerns both the lateral and the analytical resolution, contrast phenomena and electron-solid interactions. The efficiency of the analytical techniques electron nanodiffraction, energy dispersive X-ray spectroscopy (EDXS), and electron energy loss spectroscopy (EELS) is discussed.The possibilities and the limitations of analytical TEM are demonstrated at cross-sections of nanometer scaled multilayers of relevant functional materials. Concentration profiles are taken from EDX and EEL spectra of Fe-Cr and Co-Cu multilayers, which are standard systems for the investigation of giant magnetoresistance (GMR). Furthermore, from the course of the electron energy loss near edge structure (ELNES) conclusions concerning the chemical bonding are possible. This will be discussed for the oxygen bonding in interface regions of the system Al2O3-TiN. The results allow to distinguish between different oxide phases in thin functional layers. (C) 2001 Elsevier Science B.V. All rights reserved.

A structural study has been performed on the La0.8Sr0.2FexCo1-xO3 (x = 0.025 to 0.3) system displaying large magnetoresistance (MR) at room temperature. A detailed analysis of the crystal structure and microstructure was done by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM). The atomic resolution TEM images and the appearing superreflections in the corresponding SAED patterns revealed that a superstructure is formed due to the presence of iron. The correlation between the ordered microstructure and the observed large MR ratio is discussed. 57Fe Mössbauer spectroscopy was utilized to gain information on the valence state of iron in the sample with x = 0.3. The lattice parameters of Fe- doped La0.8Sr0.2FexCo1-xO3 compounds were found to increase monotonously with increasing Fe content. The valence state of iron was found to be Fe3+.

Amorphous (Zr65Al7.5Cu17.5Ni10)100−xFex alloys (0≤x≤20) prepared by rapid quenching were investigated by DSC, X-ray diffraction, TEM and magnetization measurement. The short-range order of the bulk glass is found to be similar to that of amorphous binary Zr66M33 alloys (M=Cu, Ni, Fe). For x=20at.% Fe a small contribution of magnetic clusters is observed. The amorphous Zr65Al7.5Cu17.5Ni10 alloy crystallizes eutectically into CuZr2 and Zr6NiAl2. Fe addition leads to a changed crystallization sequence. A metastable f.c.c. phase (NiTi2-type) is formed for x≥1at.% iron. With increasing iron content the metastable cubic phase becomes stabilized and the microstructure in the first stage of crystallization changes into a nanocrystalline state.

Nanoscale multilayers show properties completely different from bulk materials and are of great interest in the modern materials science. The characterisation of their structure and composition requires methods with spatial resolution of only few nanometers. The analytical transmission electron microscopy on cross sections is one of the most suitable methods. imaging and spectroscopy of the same specimen details lead to essential information about correlation of structure and properties. The use of the analytical TEM with possibilities and limitations in the scanning mode will be demonstrated on four materials problems: oxygen bond in thin resistivity films (CuNi/NiCr), hard coating multilayers (TiN/Al2O3), and Fe/Al multilayers, as well as the degree of mixing within nanoscale Co/Cu multilayers.

The influence of the synthesis parameters on the mean characteristics of single-wall carbon nanotubes in soot produced by the laser vaporization of graphite has been analyzed using optical absorption spectroscopy. The abundance and mean diameter of the nanotubes were found to be most influenced by the furnace temperature and the cobalt/nickel catalyst mixing ratio. Via an analysis of the fine structure in the optical spectra, the existence of preferred nanotube diameters has been established and their related fractional abundance could be determined. The results are consistent with nanotubes located mainly around the armchair axis.

We show optical spectroscopy to be fast and useful for the analysis of the relative diameter distribution and nanotube yield in SWNT soot. The optical spectra revealed a fine-structure consisting of several overlapping absorption bands. While the energy positions of these subpeaks remained constant upon variation of the synthesis conditions, their relative intensities varied considerably. This allowed the determination of SWNT diameters grouped around preferred values and related, the determination of variations of the fractional abundance.

We study the metal-insulator transition in two sets of amorphous Si_{1-x}Ni_x films. The sets were prepared by different, electron-beam-evaporation-based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission spectroscopy, and Rutherford back scattering. Investigating the logarithmic temperature derivative of the conductivity, w = d ln sigma / d ln T, we observe that, for insulating samples, w(T) shows a minimum increasing at both low and high T. Both the minimum value of w and the corresponding temperature seem to tend to zero as the transition is approached. The analysis of this feature of w(T,x) leads to the conclusion that the transition in Si_{1-x}Ni_x is very likely discontinuous at zero temperature in agreement with Mott's original views.

Synthesis of bundles of single-wall carbon nanotubes in the laser ablation process was studied under different laser irradiation conditions. Surprisingly high nanotube net yield was found when the laser operated near the threshold of the free-running generation regime.

A detailed investigation of the grain size dependence of the magnetic properties has been performed for intensively milled, nanocrystalline single-phase NdFeB-powder. These powders were prepared with grain sizes in the range of 20–90 nm by controlled annealing. Phase evolution and microstructure have been studied by means of X-ray diffraction, including Rietveld analysis, and transmission electron microscopy. The reduced remanence of the Isotropic powders is clearly above the Stoner-Wohlfarth limit and shows the typical grain size dependence expected for exchange-coupled nanograins. The coercive field of our samples remains almost constant at a value of μ0Hc = 1T in contradiction to earlier experimental studies on rapidly quenched ribbons, where a pronounced drop in Hc is reported for grain sizes below 40 nm. We, therefore, support the findings of more recent micromagnetic calculations which predict an improvement of the magnetic properties of exchange-coupled nanocrystalline NdFeB-powders by a further decrease in grain size.

Wear resistant multilayers consisting of the components TiN and Al2O3 are deposited on WC-Co-hardmetal substrates by plasma assisted chemical vapour deposition (PACVD) using different variants. Cross sections of the layered system are investigated by means of analytical transmission electron microscopy (TEM). Correlations between the layer formation and the nanostructure of the layers are revealed. Electron energy loss spectroscopy (EELS) in the scanning mode is used for the investigation of nanoscale interface regions, whereby both element- and bonding specific signals are used for characterization.