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- EXAFS (3)
- Dielectric spectroscopy (2)
- Disorganized bone (2)
- Electrochromism (2)
- Local structure (2)
- Metallo-supramolecular polyelectrolytes (2)
- Micro-computed tomography (2)
- Rhodium (2)
- Silicon nitride (2)
- X-ray topography (2)
Organisationseinheit der BAM
For the first time, an international comparison was conducted on the determination of the purity of a high purity element. Participants were free to choose any analytical approach appropriate for their institute’s applications and services. The material tested was a high purity zinc, which had earlier been assessed for homogeneity and previously used in CCQM-K72 for the determination of six defined metallic impurities. Either a direct metal assay of the Zn mass fraction was undertaken by EDTA titrimetry, or an indirect approach was used wherein all impurities, or at least the major ones, were determined and their sum subtracted from ideal purity of 100 %, or 1 kg/kg. Impurity assessment techniques included glow discharge mass spectrometry, inductively coupled plasma mass spectrometry and carrier gas hot extraction/combustion analysis. Up to 91 elemental impurities covering metals, non-metals and semi-metals/metalloids were quantified. Due to the lack of internal experience or experimental capabilities, some participants contracted external laboratories for specific analytical tasks, mainly for the analysis of non-metals. The reported purity, expressed as zinc mass fraction in the high purity zinc material, showed excellent agreement for all participants, with a relative standard deviation of 0.011 %. The calculated reference value, w(Zn) = 0.999 873 kg/kg, was assigned an asymmetric combined uncertainty of + 0.000025 kg/kg and – 0.000028 kg/kg. Comparability amongst participating metrology institutes is thus demonstrated for the purity determination of high purity metals which have no particular difficulties with their decomposition / dissolution process when solution-based analytical methods are used, or which do not have specific difficulties when direct analysis approaches are used. Nevertheless, further development is required in terms of uncertainty assessment, quantification of non-metals and the determination of purity of less pure elements and/or for those elements suffering difficulties with the decomposition process.
The present study is dealing with the basic physics for a novel way to generate a free-formed ceramic body, not like common layer by layer, but directly by Selective Volume Sintering (SVS) in a compact block of ceramic powder. To penetrate with laser light into the volume of a ceramic powder compact it is necessary to investigate the light scattering properties of ceramic powders. Compared with polymers and metals, ceramic materials are unique as they offer a wide optical window of transparency. The optical window typically ranges from below 0.3 up to 5 µm wave length. In the present study thin layers of quartz glass (SiO2) particles have been prepared. As a function of layer thickness and the particle size, transmission and reflection spectra in a wave length range between 0.5 and 2.5 µm have been recorded. Depending on the respective particle size and by choosing a proper relation between particle size and wave length of the incident laser radiation, it is found that light can penetrate a powder compact up to a depth of a few millimeters. With an adjustment of the light absorption properties of the compact the initiation of sintering in the volume of the compact is possible.
Short-range order has been investigated in Zr69.5Cu12Ni11Al7.5 and Zr41.5Ti41.5Ni17 metallic glasses using X-ray absorption spectroscopy and ab initio molecular dynamics simulations. While both of these alloys are good glass formers, there is a difference in their glass-forming abilities (Zr41.5Ti41.5Ni17 > Zr69.5Cu12Ni11Al7.5). This difference is explained by inciting the relative importance of strong chemical order, icosahedral content, cluster symmetry and configuration diversity.
Within the National Metrology Institutes (NMIs) and designated laboratories, an interlaboratory comparison, CCQM-P107, was conducted to verify the degree of international comparability concerning the results of purity analysis. The mass fractions of Ag, Bi, Cd, Cr, Ni, Tl at the lower mg/kg-level in a high purity zinc material were determined, but the real measurand in metrological sense was the sum of the six mass fractions. Homogeneity was investigated by glow discharge mass spectrometry, reference values were obtained using isotope dilution mass spectrometry. Six NMIs participated, contributing eight independent data sets. The agreement amongst the results of the participants, their median and the agreement with the reference values were usually excellent and in almost all cases below the target uncertainty of 30% relative. In this manner, the accuracy of results and the comparability between the participants was demonstrated to be established.
The first hard X-ray beamline at BESSY II will be installed by BAM and PTB at a superconducting 7 T wavelength shifter. The main optical elements of the beamline are a Double-Multilayer-Monochromator and a Double-Crystal-Monochromator. The two devices can be used separately or in-line. Main applications of monochromatic radiation with photon energies up to 50 keV are X-ray fluorescence analysis, micro-computed tomography, X-ray topography, detector calibration and reflectometry. Calculable undispersed radiation up to 200 keV will be available for radiometric applications.
The impact of very high cycle fatigue (VHCF) load conditions on the microstructure of specimens consisting of nodular cast iron is analyzed by means of micro-computed tomography (µCT) utilizing both monochromatic synchrotron radiation and polychromatic X-ray tube radiation. Using 3D µCT, the microstructure in the region of the smallest cross-sections of shouldered round specimens is imaged in different stages of the VHCF loading. By digital image correlation (DIC) of these tomograms strain fields are analyzed three-dimensionally. Strain levels in the range of a few percent were detected. It is proven that a localization of strain allows to predict the site of the crack which precedes and induces the macroscopic failure of the specimens.
A new instrument for simultaneous microbeam small- and wide-angle X-ray scattering and X-ray fluorescence (SAXS/WAXS/XRF) is presented. The instrument is installed at the microfocus beamline at BESSY II and provides a beam of 10 µm size with a flux of about 109 photons s-1. A SAXS resolution up to 500 Å d-spacing and a range of scattering vectors of almost three orders of magnitude are reached by using a large-area high-resolution CCD-based detector for simultaneous SAXS/WAXS. The instrument is particularly suited for scanning SAXS/WAXS/XRF experiments on hierarchically structured biological tissues. The necessary infrastructure, such as a cryo-stream facility and an on-site preparation laboratory for biological specimens, are available.
Local structures of amorphous and quasicrystalline phases in Zr–Ti–Ni and Zr–Ti–Ni–Cu alloys have been studied by means of x-ray absorption spectroscopy. The amorphous phases show a high degree of icosahedral short-range order. In all investigated systems local order around Cu and Ni atoms was found to be nearly identical pointing to site substitution of Ni by Cu as the reason for an improved glass forming ability when Ni is partly substituted by Cu. The results strengthen an icosahedral cluster based approach for the structure of metallic glasses and indicate the importance of the medium-range order on glass formation.
Flexible electrochromic devices (ECDs) based on Fe(II)-metallo-supramolecular polyelectrolytes (Fe-MEPE) and vanadium oxide are studied in operando by means of x-ray absorption fine structure (XAFS) spectroscopy. The ECDs are blue-purple in the colored state at 0.0 V and become light yellow when a voltage of 1.6 V is applied. The XAFS studies at the K-edge of Fe(II) reveals that the absorption edge is shifted toward higher energies by 1.8 eV in the transparent state. Comparison of two different ECDs and different charge cycles demonstrates the reversibility and repeatability of the process. We attribute the shift to a charge transfer and a change of oxidation state of the ions from Fe2+ to Fe3+. The transition is not accompanied by a noticeable structural change of the octahedral coordination geometry as confirmed by analysis of the extended x-ray absorption fine structure (EXAFS) data. (C) 2015 Elsevier B.V. All rights reserved.
Nanocomposites based on polypropylene (PP) and organically modified ZnAl layered double hydroxides (ZnAl-LDH) were prepared by melt blending and investigated by a combination of differential scanning calorimetry (DSC), small- and wide-angle X-ray scattering (SAXS and WAXS), and dielectric relaxation spectroscopy (DRS). An average number of stack size of LDH layers is calculated by analyzing the SAXS data which is close to that of pure organically modified ZnAl-LDH. Scanning microfocus SAXS investigations show that the ZnAl-LDH is homogeneously distributed in the PP matrix as stacks of 4–5 layers with an intercalated morphology. DSC and WAXS results show that the degree of crystallinity decreases linearly with the increasing content of LDH. The extrapolation of this dependence to zero estimates a limiting concentration of ca. 40% LDH where the crystallization of PP is completely suppressed by the nanofiller. The dielectric spectra of the nanocomposites show several relaxation processes which are discussed in detail. The intensity of the dynamic glass transition (β-relaxation) increases with the concentration of LDH. This is attributed to the increasing concentration of the exchanged anion dodecylbenzenesulfonate (SDBS) which is adsorbed at the LDH layers. Therefore, a detailed analysis of the β-relaxation provides information about the structure and the molecular dynamics in the interfacial region between the LDH layers and the polypropylene matrix which is otherwise dielectrically invisible (low dipole moment). As a main result, it is found that the glass transition temperature in this interfacial region is by 30 K lower than that of pure polypropylene. This is accompanied by a drastic change of the fragility parameter deduced from the relaxation map.
Organically modified ZnAl Layered Double Hydroxides (ZnAl-LDH) was synthesized and melt blended with polyethylene to obtain nanocomposites. The resulting morphology was investigated by a combination of Differential Scanning Calorimetry (DSC), Small and Wide-angle X-ray scattering (SAXS and WAXS) and dielectric relaxation spectroscopy (DRS). The arrangement (intercalation) of polyethylene chains between LDH stacks was investigated employing SAXS. The homogeneity of the nanocomposites and average number of stack size (4–6 layers) were determined using scanning microfocus SAXS (BESSY II). DSC and WAXS results show that the degree of crystallinity decreases linearly with the increasing content of LDH. The extrapolation of this dependence to zero estimates a limiting concentration of ca. 45% LDH where the crystallization of PE is completely suppressed by the nanofiller. The dielectric spectra of the nanocomposites show several relaxation processes which are discussed in detail. The intensity of the dynamic glass transition (β-relaxation) increases with the concentration of LDH. This is attributed to the increasing concentration of the exchanged anion sodium dodecylbenzene sulfonate (SDBS) which is adsorbed at the LDH layers. Therefore, a detailed analysis of the β-relaxation provides information about the structure and the molecular dynamics in the interfacial region between the LDH layers and the polyethylene matrix which is otherwise dielectrically invisible (low dipole moment).
Agglomerated superparamagnetic iron
oxide nanoparticles can easily and in large scale be
precipitated from iron salt solutions. Although the
process is well known, it is ambiguously either assumed
that magnetite or maghemite is obtained. The first part
of our study clarifies this question using X-ray absorption
spectroscopy. For further processing of the nanoparticles,
i.e., for giving them a surface functionality or
incorporating them into composites, it is important to
break the agglomerates and individualize the particles
at first. This can effectively be done with nitric acid
treatment. The influence of this process on the particles
chemistry and structure was analyzed in great detail
using X-ray diffraction, X-ray absorption, and smallangle
X-ray scattering. In contrast to our expectation,
no oxidation from magnetite (Fe3O4) to maghemite (γ-
Fe2O3) was found; the formal valence of the particles in
any case is magnetite (Fe3O4). Instead, an increase in
the particles' surface disorder was discovered from
X-ray absorption analyses and high-resolution transmission
electron microscopy. The acid treatment
roughens and distorts the surface of the nanoparticles
which is connected with an increased spin disorder.
The laboratory rat is one of the most frequently-used animal models for studying bone biology and skeletal diseases. Here we show that a substantial portion of the cortical bone of mature rats is primary endochondral bone, consisting of a disorganized arrangement of mineralized collagen fibers. We characterize the structure and mechanical properties of the cortical bone of the rat. We show that the cortical bone consists of two architecturally distinct regions. One region, consisting of well-organized circumferential lamellae (CLB), is located in the endosteal and/or the periosteal regions while another, disorganized region, is located in the more central region of the cortex. Unexpectedly, we found that the disorganized region contains many islands of highly mineralized cartilage.
Micro tomography showed different structural and compositional properties of the two primary structural elements; the CLB region has lower mineral density, lower porosity, larger but fewer blood vessels and fewer lacunae. However, no difference was found in the average lacunar volume. Additionally the mean indentation modulus of the CLB region was lower than that of the disorganized region. The islands of calcified cartilage were found to be extremely stiff, with an indentation modulus of 33.4 ± 3.5 GPa.
We conclude that though the cortical bone of rats is in part lamellar, its architecture is markedly different from that of the cortical bone of humans, a fact that must be borne in mind when using the rat as a model animal for studies of human bone biology and disease.
The results of analytical measurements performed with solid-sampling techniques are affected by the distribution of the analytes within the matrix. The effect becomes significant in case of determination of trace elements in small subsamples. In this framework we propose a measurement model based on Instrumental Neutron Activation Analysis to determine the relative variability of the amount of an analyte among subsamples of a material. The measurement uncertainty is evaluated and includes the counting statistics, the full-energy gamma peak efficiency and the spatial gradient of the neutron flux at the irradiation position. The data we obtained in a neutron activation experiment and showing the relative variability of As, Au, Ir, Sb and W among subsamples of a highly pure Rh foil are also presented.
Nanocomposites with a predominantly exfoliated morphology were prepared by melt blending of organically modified doubled layered hydroxide (LDH) and low density polyethylene (PE). The prepared materials were investigated by differential scanning calorimetry (DSC) and in detail by dielectric spectroscopy. The DSC experiments show that the degree of crystallinity decreases linearly with increasing content of the LDH. The extrapolation of this dependence to zero results in a limiting concentration of ca. 50 wt % LDH were the crystallization of PE is completely suppressed by the nanofiller. The dielectric response of pure polyethylene shows different weak relaxation processes. The intensity of dynamic glass transition (β-relaxation) increases with the concentration of LDH. This is attributed to the increasing concentration of the exchanged anion dodecyl benzene sulfonate (SDBS). The SDBS molecules are strongly adsorbed at the exfoliated LDH layers. Therefore, a detailed analysis of the β-relaxation provides information about the structure and the molecular dynamics in the interfacial region between the exfoliated LDH layers and the polyethylene matrix. This analysis shows that the β-relaxation region consists of two processes: both of them obey glassy dynamics. The difference in corresponding Vogel (ideal glass transition) temperatures is about 30 K. The relaxation process at lower frequency is assigned to polyethylene segments with a reduced molecular mobility close to LDH layers. The process at higher frequencies is related to polyethylene segments in a farer distance for the surface of the nanofiller. In the nanocomposite materials an additional process due to Maxwell-Wagner-Sillars (MWS) polarization was observed. The time constant of this MWS process can be correlated with characteristic length scales in nanocomposites and therefore provides additional information on dispersion and delamination/exfoliation of the LDH layers in these materials.
Gravimetrically prepared mono-elemental reference solutions having a well-known mass fraction of approximately 1 g/kg (or a mass concentration of 1 g/L) define the very basis of virtually all measurements in inorganic analysis. Serving as the starting materials of all standard/calibration solutions, they link virtually all measurements of inorganic analytes (regardless of the method applied) to the purity of the solid materials (high-purity metals or salts) they were prepared from. In case these solid materials are characterized comprehensively with respect to their purity, this link also establishes direct metrological traceability to The International System of Units (SI). This, in turn, ensures the comparability of all results on the highest level achievable. Several national metrology institutes (NMIs) and designated institutes (DIs) have been working for nearly two decades in close cooperation with commercial producers on making an increasing number of traceable reference solutions available. Besides the comprehensive characterization of the solid starting materials, dissolving them both loss-free and completely under strict gravimetric control is a challenging problem in the case of several elements like molybdenum and rhodium. Within the framework of the European Metrology Research Programme (EMRP), in the Joint Research Project (JRP) called SIB09 Primary standards for challenging elements, reference solutions of molybdenum and rhodium were prepared directly from the respective metals with a relative expanded uncertainty associated with the mass fraction of Urel(w)<0.05 %. To achieve this, a microwave-assisted digestion procedure for Rh and a hotplate digestion procedure for Mo were developed along with highly accurate and precise inductively coupled plasma optical emission spectrometry (ICP OES) and multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) methods required to assist with the preparation and as dissemination tools.
The local structure around Ni and La atoms in Al85Ni10La5 amorphous powder after ball milling was investigated by X-ray absorption spectroscopy. A continuous decrease in coordination number of Ni and La as a function of milling time was observed, while the nearest neighbour distance and the mean square atomic displacement did not change, pointing at the creation of free volume around the Ni and La atoms. These structural changes resemble those of a liquid upon temperature increase. The results are described by a shear band model in which the coordination numbers of Ni and La are different within and outside a shear band.
We present a new high resolution X-ray imager based on a pnCCD detector and a polycapillary optics. The properties of the pnCCD like high quantum efficiency, high energy resolution and radiation hardness are maintained, while color corrected polycapillary lenses are used to direct the fluorescence photons from every spot on a sample to a corresponding pixel on the detector. The camera is sensitive to photons from 3 to 40 keV with still 30% quantum efficiency at 20 keV. The pnCCD is operated in split frame mode allowing a high frame rate of 400 Hz with an energy resolution of 152 eV for Mn Kα (5.9 keV) at 450 kcps. In single-photon counting mode (SPC), the time, energy and position of every fluorescence photon is recorded for every frame. A dedicated software enables the visualization of the elements distribution in real time without the need of post-processing the data. A description of the key components including detector, X-ray optics and camera is given. First experiments show the capability of the camera to perform fast full-field X-Ray Fluorescence (FF-XRF) for element analysis. The imaging performance with a magnifying optics (3×) has also been successfully tested.
Pilot studies have been carried out at the BAMline at BESSY II in collaboration with the Bundesanstalt
für Materialforschung und -prüfung (BAM) on metal- and metalloid-containing compounds in biological
samples after electrophoretic protein separation. After sodium dodecylsulfate polyacrylamide gel
electrophoresis (SDS-PAGE) and transfer onto a blotting membrane the distribution of selenium among
the proteins of testis homogenate of a rat and a wallaby was determined. The comparison with the
autoradiogram of 75Se-labeled proteins separated in the same way showed that of nine seleniumcontaining
proteins found in rat testis homogenate by autoradiography four could be detected by
synchrotron radiation X-ray fluorescence analysis (SRXRF).
This key comparison aims to assess the core capabilities of the participants in gas analysis. Such competences include, among others, the capabilities to prepare Primary Standard gas Mixtures (PSMs), perform the necessary purity analysis on the materials used in the gas mixture preparation, the verification of the composition of newly prepared PSMs against existing ones, and the capability of calibrating the composition of a gas mixture. According to the Strategy for Key Comparisons of the Gas Analysis Working Group, this key comparison is classified as an RMO track A key comparison.
The artefacts were binary mixtures of propane in nitrogen at a nominal amount-of-substance fraction level of 1000 μmol/mol. The values and uncertainties from the gravimetric gas mixture preparation were used as key comparison reference values (KCRVs). Each transfer standard had its own KCRV. The results are generally good. All results are within ± 1 % of the KCRV.
CCQM-K118 was an international key comparison on natural gas composition with two types of gases, i.e., a low calorific hydrogen-enriched natural gas and a high calorific LNG type of gas. There were 14 participating laboratories. The traveling standards (i.e., 14 mixtures each) were obtained from an external source and checked for homogeneity and stability before and after the participants' measurements at the two coordinating laboratories. The data evaluation was performed using a consensus value and a laboratory effect model. The results of the participants were benchmarked against a key comparison reference value computed from the largest consistent subset (LCS) of the submitted results, adjusted for the differences between the travelling standards. For the first time in a key comparison in gas analysis, the model included a term to account for excess variability in the LCS. Most of the participants reported one or a few (slightly) discrepant results. Partly this is due to the heterogeneity and heteroscedasticity of the datasets. In all, the results in this key comparison demonstrate the good comparability of the national measurement standards for natural gas composition maintained by the participating NMIs.
Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
Background. Post-menopausal osteoporosis is a common health problem worldwide, most commonly caused by estrogen deficiency. Most of the information regarding the skeletal effects of this disease relates to trabecular bone, while cortical bone is less studied. The purpose of this study was to evaluate the influence of estrogen deficiency on the structure and mechanical properties of cortical bone.
Methods. Eight ovariectomized (OVH) and eight intact (control) Sprague Dawley rats were used. Structural features of femoral cortical bone were studied by light microscopy, scanning electron microscopy and synchrotron-based microcomputer-tomography and their mechanical properties determined by nano-indentation.
Results. Cortical bone of both study groups contains two distinct regions: organized
circumferential lamellae and disordered bone with highly mineralized cartilaginous islands. Lacunar volume was lower in the OVH group both in the lamellar and disorganized regions (182 ± 75 µm3 vs 232 ± 106 µm3 , P < 0.001 and 195 ± 86 µm3 vs. 247 ± 106 µm3 , P < 0.001, respectively). Lacunar density was also lower in both bone regions of the OVH group (40 ± 18 ×103 lacunae/mm3 vs. 47 ± 9×103 lacunae/mm3
in the lamellar region, P = 0.003 and 63 ± 18×103 lacunae/mm3
vs. 75 ± 13×103 lacunae/mm3 in the disorganized region, P < 0.001). Vascular canal volume was lower in the disorganized region of the bone in the OVH group compared to the same Region in the control group (P < 0.001). Indentation moduli were not different between the study groups in both bone regions.
Discussion. Changes to cortical bone associated with estrogen deficiency in rats require high-resolution methods for detection. Caution is required in the application of These results to humans due to major structural differences between human and rat bone.
Besides conventional scanning X-ray fluorescence imaging at synchrotron sources, full-field X-ray fluorescence (FF-XRF) imaging techniques that do not implicitly require spatial scanning of the sample have become available. FF-XRF has become achievable thanks to the development of a new type of energy dispersive CCD-based 2D detector, also referred to as a 'color X-ray camera (CXC)' or 'SLcam'. We report on different imaging schemes for biological samples using FF-XRF imaging: (a) 2D 'zoom' imaging with pinhole optics using the 'camera obscura' principle; (b) 2D 'fixed magnification' imaging using magnifying polycapillary optics; and (c) 3D-FF-XRF imaging using an X-ray sheet beam or computed tomography (CT). The different FF-XRF imaging modes are illustrated using the crustacean Daphnia magna, a model organism for investigating the effects of metals on organism/ecosystem health, and foraminifera, a class of amoeboid protist. Detailed analytical characterization of the set-up is performed through analyzing various reference materials in order to determine limits of detection (LODs) and sensitivities. Experiments were performed using the BAMline at the BESSY synchrotron (Berlin, Germany) and using the P06 Hard X-ray Microprobe at the PETRAIII synchrotron (Hamburg, Germany).
The high-resolution synchrotron-based imaging stations at the BAMline (BESSY) and TopoTomo (ANKA)
(2008)
The BAMline at the BESSY light source in Berlin and the TopoTomo beamline at the ANKA synchrotron facility in Karlsruhe (both Germany) operate in the hard X-ray regime (above 6 keV) with similiar photon flux density. For typical imaging applications, a double multilayer monochromator or a filtered white beam is used. In order to optimise the field of view and the resolution of the available indirect pixel detectors, different optical systems have been installed, adapted, respectively, to a large field of view (macroscope) and to high spatial resolution (microscope). They can be combined with different camera systems, ranging from 16-bit dynamic range slow-scan CCDs to fast CMOS cameras. The spatial resolution can be brought substantially beyond the micrometer limit by using a Bragg magnifier. The moderate flux of both beamlines compared to other 3rd generation light sources is compensated by a dedicated scintillator concept. For selected applications, X-ray beam collimation has proven to be a reliable approach to increase the available photon flux density. Absorption contrast, phase contrast, holotomography and refraction-enhanced imaging are used depending on the application. Additionally, at the TopoTomo beamline digital white beam synchrotron topography is performed, using the digital X-ray pixel detectors installed.
By means of synchrotron X-ray computed tomography, model composites consisting of silica and styrenebutadiene rubber were studied with a very high spatial resolution. By our analysis technique we were able to determine the nano- and micro dispersion from the experimental results by our numerical analysis. These results are discussed with respect to crucial advantages of the generically 3-dimensional tomography technique as compared to 2-dimensional methods. Our quantitative analysis of the 3d images demonstrates that in the case of our model composites the filler dispersion is good, independent on the filler concentration. Our new 3-dimensional results evidence that considering only 2-d pictures may lead to ambiguities that can lead to wrong conclusions.
Rigid rod-type metallo-supramolecular coordination polyelectrolytes with Fe(II) centres (Fe-MEPEs) are produced via the self-assembly of the ditopic ligand 1,4-bis(2,2':6',2''-terpyridine-4'-yl)benzene (tpy-ph-tpy) and Fe(II) acetate. Fe-MEPEs exhibit remarkable electrochromic properties; they change colour from blue to transparent when an electric potential is applied. This electrochemical process is generally reversible. The blue colour in the ground state is a result of a metal-to-ligand charge transfer at the Fe(II) centre ion in a quasi-octahedral geometry. When annealed at temperatures above 100 °C, the blue colour turns into green and the formerly reversible electrochromic properties are lost, even after cooling down to room temperature. The thermally induced changes in the Fe(II) coordination sphere are investigated in situ during annealing of a solid Fe-MEPE using X-ray absorption fine structure (XAFS) spectroscopy. The study reveals that the thermally induced transition is not accompanied by a redox process at the Fe(II) centre. From the detailed analysis of the XAFS spectra, the changes are attributed to structural changes in the coordination sphere of the Fe(II) site. In the low temperature state, the Fe(II) ion rests in a quasi-octahedral coordination environment surrounded by six nitrogen atoms of the pyridine rings. The axial Fe–N bond length is 1.94 Å, while the equatorial bond length amounts to 1.98 Å. In the high temperature state, the FeN6-site exhibits a distortion with the axial Fe–N bonds being shortened to 1.88 Å and the equatorial Fe–N bonds being elongated to 2.01 Å.
Gradient porous silicon nitride (Si3N4) was fabricated by a novel vacuum foaming and freeze drying process. Aqueous Si3N4 slurries were foamed at vacuum pressure of 50–90 kPa, the green body was obtained by the freeze drying process, a gradient pore structure with porosities of 72–90% was achieved after pressureless sintering at 1680 °C. The porosity was increased with decreasing vacuum pressure. The pore structure consists of large pores (~100 μm) on top, medium pores (~45 μm) on the wall of the large pores, and small pores (~0.7 μm) in the matrix. Such gradient porous Si3N4 with macro- and micro-pores has potential application as high temperature filters.
Porous Si3N4/SiC ceramics were rapidly prepared with Y2O3 as sintering additive and ZrO2 as nitrided catalyst, using Si and SiC as starting powders. Porous Si3N4/SiC ceramics with 5 wt% ZrO2 addition showed a complete nitridation and good mechanical properties (with a high porosity of 34.96%, flexural strength of 150±4.2 MPa, linear shrinkage of 0.02%). It was revealed that the reciprocal formation of ZrO2 and ZrN effectively enhanced nitridation by inhibiting the melting of silicon in micro-regions.
Porous Si3N4 ceramics were prepared via partial nitridation and self-propagating high temperature synthesis (SHS) process. Raw Si and additive Y2O3 were mixed and molded under 10 MPa into a compact, the compact was partial nitridation at 1300 °C to form a porous Si/Si3N4, and then it was buried in a Si/Si3N4 bed for SHS to obtain porous Si3N4 with rod-like β-Si3N4 morphology. The processing combined the advantages of the nitridation of Si and SHS with low cost, low shrinkage and time saving. Porous Si3N4 with a porosity of 47%, a strength of 143 MPa were obtained by this method.
Tapes, cast by blade deposition of a lithium aluminosilicate glass slurry, were sintered using a YAG-fiber laser, with the aim of finding suitable parameters for an additive manufacturing process based on layer-wise slurry deposition and selective laser densification. The influence of the laser parameters (output power and scan velocity) on the sintering was evaluated, by scanning electron microscopy and by X-ray diffraction, on the basis of the quality of the processed layer. Well densified samples could be obtained only in a small window of values for the output power and the scan velocity. The measurement of the width of a set of single scanned lines allowed also to estimate the minimum resolution of the system along the layer plane.
The production of agglomerate-free SiO2 particles exhibiting a monomodal distribution of particle sizes of around 300 nm by means of direct laser fuming of micrometric SiO2 powders has been successfully demonstrated. With a 12 kW cw CO2 laser system, a production rate of up to 1 kilogram powder per hour was achieved. Almost ideal spherical amorphous SiO2 particles in a broad particle size distribution between 10 nm and several 100 nm (d50 ≈ 300 nm) were synthesized. Several observations suggest weak agglomeration forces between the particles. A temperature reduction of 200 °C for sintering powder compacts was observed.
Transparent microspheres with the eutectic composition 65 Al2O3-16 Y2O3-19 ZrO2 (mol%) have been produced by laser fusing with a CO2 laser. The influence of the starting material – not pre-calcined and pre-calcined – as well as the laser power on the resulting microspheres – was investigated. After fabrication, the microspheres were analyzed by means of XRD to quantify the amorphous content of the spheres as well as to identify the residual crystalline phases, with a laser granulometer to measure the particle sizes of the starting material and the resulting microspheres, with DSC to characterize the glass transition temperature and crystallization behavior, and with SEM to investigate the microstructure of the microspheres. The laser-treated materials consist of transparent and opaque beads as well as sintered particles. The amorphous amount in the samples was detected to be ~ 85 %. Based on these results transparent beads were collected and annealed over a range of temperatures to analyze the crystallization behavior.
Porous silicon nitride ceramics were prepared via sintered reaction bonded silicon nitride at 1680 °C. The grain size of nitrided Si3N4 and diameter of post-sintered ß-Si3N4 are controlled by size of raw Si. Porosity of 42.14–46.54% and flexural strength from 141 MPa to 165 MPa were obtained. During post-sintering with nano Y2O3 as sintering additive, nano Y2O3 can promote the formation of small ß-Si3N4 nuclei, but the large amount of ß-Si3N4 (>20%) after nitridation also works as nuclei site for precipitation, in consequence the growth of fine ß-Si3N4 grains is restrained, the length is shortened, and the improvement on flexural strength is minimized. The effect of nano SiC on the refinement of the ß-Si3N4 grains is notable because of the pinning effect, while the effect of nano C on the refinement of the ß-Si3N4 grains is not remarkable due to the carbothermal reaction and increase in viscosity of the liquid phase.
KEY COMPARISON
High purity elements can serve as a realization of the SI unit amount of substance for the specific element. Solutions prepared from high purity metals by applying gravimetric preparation and the concept of molar mass are used as 'calibration' solutions in many fields of analytical chemistry and provide the metrological basis in elemental analysis. Since ideal purity does not exist for real materials, the actual purity of the high purity material must be known with a specified uncertainty. As required uncertainties around 10-4 relative on the purity statement are not accessible in almost all cases by a direct measurement of the element in itself, the indirect approach is followed, where all elements excepting the matrix element itself are measured and their sum is subtracted from the value for ideal purity, which is 1 kg/kg.
It was the aim of this comparison to demonstrate the capability of national metrology institutes and designated institutes to determine the purity of pure elements. In order to limit the effort within this comparison, only six metallic impurities (Ag, Al, Cd, Cr, Ni, Tl) in the low mg/kg range are considered in a zinc matrix. It has to be underlined here that the task was to measure the purity of zinc based on the determination of six analytes. The task is not trace analysis of specific analytes in zinc. This subtle distinction defines different measurands.
The sample, pure Zn, was cut in pieces of cubic geometry for wet chemical analysis or of pin geometry for GDMS analysis and was sent to the participants. The comparison was run under the auspices of the Inorganic analysis Working Group (IAWG) of the CCQM and was piloted by the BAM Federal Institute for Materials Research and Testing, Berlin, Germany. The majority of the participants applied ICP-MS techniques and only two participants used additionally atomic absorption spectrometry. GDMS was used only by one participant.
The observed spreads for the measurement results reported by the participants were significantly lower than those of the preceding study CCQM-P107 and were well below the target uncertainty of 30% relative. As a consequence, comparability within the participating laboratories is demonstrated to be established. The individual measurement results, mean values and medians derived were in all cases very consistent with the reference values obtained by IDMS and so the accuracy of the measurement results for the participating laboratories is as well demonstrated to be established. Especially with the results of CCQM-P62 and CCQM-P107 in mind, the outcome of CCQM-K72 can be considered as a big step forward in the community.
CCQM is aware of the difference between a characterization based on only six analytes and a complete characterization. Therefore, the pilot study CCQM-P149 has been initiated and already started, which focuses on the fit-for-purpose approaches for the purity determination of metals (here: zinc) to be used as primary standards in elemental analysis. Another follow-up in the form of a pilot study on non-metal impurities is mandatory, because non-metal impurities such as oxygen, nitrogen and sulfur often make up the largest contributions.
Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).