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Phase pure Na-β''-alumina ceramics are excellent electrolytes for molten-salt and all-solid-state batteries. However, controlled processing of this complex material is required to obtain the desired phase content, as Na-β''-alumina can accommodate variable amounts of sodium within its conduction slab. On the one hand, addition of dopant ions (e.g. Li+, Mg2+) influences stability and sodium content of Na-β''-alumina. On the other hand, β''-aluminas are prone to sodium evaporation, resulting in compositional changes during high-temperature sintering. Here, we show that while sodium evaporation indeed becomes significant at temperatures > 1300 °C, Na-β''-alumina ceramics of constant total composition can be prepared at strongly variable sintering conditions by applying an encapsulation. Nevertheless, our study reveals that the sodium content in the Na-β''-alumina crystal structure varies with the processing temperature. This is indicated by changes in the c-lattice parameter, which decreases with increasing sintering temperature, corresponding to an increase in sodium content.

The stability of the atmosphere plays a major role in the dispersion of pollutants. The meteorological conditions favoring a high-pressure situation resulting in the formation of inversion layer inhibits pollutant dispersion. The aim of the study was to obtain vertical profiles of meteorological parameters and air pollutants in order to investigate the impact of inversion on the air quality of this city. Vertical profiles help to understand the behaviour of temperature inversion, pollutants and their relationship to each other. The tethered balloon was equipped with in-situ instruments to measure Particulate Matter (PM), Black Carbon (BC), Ultra Fine Particles (UFP) as well as meteorological parameters such as air temperature, relative humidity, wind speed and wind direction of the lower troposphere. The measurements were carried out in “Schlossgarten”, a park area near the city center of Stuttgart. Vertical profiles were obtained by ascending the balloon from ground up to a height of a maximum of 470 m and then descending it back to the ground. One complete sounding (ascent and descent) took around 30–40 min. The measurement campaign took place on 8th and July 9, 2018. 43 soundings were performed during that period. During the measurement campaign, a distinct inversion was observed at nighttime, which trapped the pollutants, hence increasing the pollutant concentration near the ground within the inversion layer. PM, UFP and BC concentrations showed a decreasing trend with increasing altitude but during noon, when the atmosphere was well mixed, the concentrations were relatively constant along with increasing altitude.

The objective of this work is to determine the nitrogen oxide emission in the flue gas of a catalytic hydrogen combustion process, operating without premixed hydrogen and air supply. The study was investigated on a novel designed gas under glass stove top burner, suitable for domestic kitchen applications. The basic catalytic burner assembly consists of two platinum coated silicon carbide (SiC) foam disks with a diameter of 150 mm, a thickness of 10 mm and a porosity of 60 and 80 pores per inch (ppi) respectively. The two catalytic SiC disks are stacked with 10 mm space between for a uniform air feeding and distribution. Hydrogen is supplied from below the assembly and air is blown in between the two Pt coated catalytic SiC disks, leading to a homogeneous air distribution and thus a uniform catalytic reaction of hydrogen and air. Tests are performed at hydrogen flow rates of 5, 10 and 15 Nl/min, equivalent to 0.9, 1.8, 2.7 kW power, the hydrogen to oxygen ratios (φ) were fixed to 0.66, 0.5 and 0.33 respectively. Ultra-low nitrogen oxide emissions of 0.09 ppmv to 9.49 ppmv, equivalent to 0.007 to 0.37 mg/kWh are achieved with this novel developed catalytic combustion design. These values are significantly lower than the present EU regulation of 56 mg/kWh for combustion processes of gaseous fuels for heating applications. This result shows the very high potential of converting hydrogen to heat without harmful exhaust gases for a broad domestic application in decarbonised gas grids or stationary power to gas applications.

As for many ion conductors, the electrical conductivity of polycrystalline Na- β ″-alumina reported in literature varies by over two decades at a given temperature. This is often ascribed to a combination of variable effects related to grain size, composition, phase content, porosity and impurities, but the dominating factors are rarely identified. Based on an extensive set of Li2O-stabilized Na- β ”-alumina ceramics sintered at different conditions, we evaluate a sample series with constant composition and phase content but variable conductivity. The total conductivity of the polycrystalline samples features pronounced non-Arrhenius temperature dependence. To explain this effect, we present a simple microstructural model describing the influence of grain size effects in Arrhenius-type ion conductors with highly resistive grain boundaries as a second phase. We show that this model further predicts a linear relationship between conductivity and effective activation energy at a given temperature, which we also observe experimentally. Based on this, we are able to identify to which extent conductivity variations in a given data set may be explained by grain size effects only. As the same microstructural model relates fundamental transport properties of the corresponding grain and grain boundary phases with the experimentally observed linear relationship, we further discuss how these parameters can be extracted, e.g. by taking into account experimentally determined grain size data. Comparison with literature data indicates for which Na- β ″-alumina samples additional effects such as changes in composition and percolation of coarse grains are relevant for the transport properties. Our findings on the relation between effective conductivity and corresponding activation energy are applicable to Arrhenius-type ion conductors with highly resistive grain boundary phases in general.

Microporous, highly charged and cation exchangeable clays are interesting carriers not only for various functional molecules such as cationic dyes, surfactants, proteins, drugs and complexes, but also for water insoluble molecules. In water, swellable nanohectorite derivatives (“laponites”) with dimensions of about 25 nm in diameter and 1 nm in height delaminate to form individual nanoparticles, which proved to be very useful for applications in aqueous dispersions, but less advantageous for the use in filter systems for water treatment, membrane technology, or as catalysts. To immobilize the particles in aqueous environments and still provide accessibility and high cation exchange rates on the clays, we used an inversion process to prepare porous nanoclay polysulfone composites with high clay contents up to 60%. Successful incorporation of the clays in the matrix required clay pre-modifications with reactive silanes such as octyltriethoxysilane or octadecyltriethoxysilane. Interestingly, unmodified laponite can also be used as a template to form a porous polysulfone network due to its leakage in the inversion process. The high accessibility and activity found in composites prepared with a mixture of unmodified and modified laponite particles pave the way for further modifications with functional molecules for various applications. In this study, we characterize the nanoclay polysulfone composites via scanning electron microscopy, nitrogen gas adsorption of the dried composite, and we determine the cation exchange capacity in the wetted state.

Cities often have a problem regarding the air quality because various emissions are produced within these cities and local emission sources among others relate directly to the air quality. As an addition to stationary monitoring stations, mobile measurements can provide valuable information regarding spatial distribution of pollutants. In this research, a case study is presented to illustrate the design and implementation of mobile measurement platform with a bicycle. Different compact measuring devices were selected and installed on the bicycle for mobile measurements along a designated route in Stuttgart, Germany. The measured pollutants included Particulate Matter (PM), Ultrafine Particles (UFP), Black Carbon (BC), nitrogen oxides (NO, NO2 and NOX) and ozone (O3). Meteorological parameters such as air temperature, relative humidity, wind speed, wind direction, solar radiation and air pressure were also measured. These measured parameters were allocated to the location using a GPS device. The measurements were carried out during February 2018. The measurement route covered part of the city center with high traffic roads as well as side roads and a park. The results show a very high spatial variability and the pollutant concentration was influenced by different factors such as local traffic, measurement location, meteorological conditions, etc. For NO, NO2 and UFP, the concentrations in the park (which can be considered as urban background level) were only around 30%–50% of the measured concentrations directly on the roadside. For PM10, the differences between the concentrations on the road and in urban background were less pronounced but still clearly measurable. The mobile measurement platform with the bicycle provided an opportunity to have a spatial distribution of a larger study area and proved to be highly adaptive and flexible method.

A hydrogen based cooking stove was developed and tested in respect to efficiency, functionality and hydrogen safety. Therefore the developed novel combustion unit technology is based on the catalytic oxidation of hydrogen on a platinum coated highly porous reticulated silicon carbide foam ceramics. Compared to other works [1], premixing of hydrogen and air is avoided, thus providing the basis for safe and reliable operation. With this catalytic combustion technology, no initial hydrogen ignition is required, implying a high application security. Separate air and hydrogen supplies make regulation of temperature and power efficient, simple and save. Catalytic hydrogen oxidation is performed already at room temperature; whereby at high hydrogen load, a small hydrogen slip is detected under cold start conditions, nevertheless in operation this becomes negligible. In order to overcome this issue, a hydrogen flow regulation, based on the hydrogen combustion temperature, was introduced. A heat exchanger is integrated into the exhaust line, in order to recover heat for the incoming air, required for the catalytic combustion. This leads to a stove efficiency of up to 80%, measured according to the DIN EN 30-2-1: 2005–08 test standard and greatly exceeds the postulated standard minimum efficiency of 35%. For comfortable and save use, the combustion unit is mounted under a glass ceramic coverage, as common for conventional electrical stoves.

Microelectronic engineering 152, 6 - 9(2016). doi:10.1016/j.mee.2015.12.015, We present an improved nanofabrication method of high aspect ratio tungsten structures for use in high efficiency nanofocusing hard X-ray zone plates. A ZEP 7000 electron beam resist layer used for patterning is cured by a second, much larger electron dose after development. The curing step improves pattern transfer fidelity into a chromium hard mask by reactive ion etching using Cl2/O2 chemistry. The pattern can then be transferred into an underlying tungsten layer by another reactive ion etching step using SF6/O2. A 630 nm-thick tungsten zone plate with smallest line width of 30 nm was fabricated using this method and characterized. At 8.2 keV photon energy the device showed an efficiency of 2.2% with a focal spot size at the diffraction limit, measured at Diamond Light Source I-13-1 beamline., Published by Elsevier, [S.l.]

A solid state reaction is employed to investigate the influence of ZrO 2 , HfO 2 , Pr 6 O 11 , TiO 2 and Li 2 O doping on CeO 2 for a possible use in solar thermochemical redox cycles. Ceramics with a macroscopic interconnected porosity, necessary for high mass transport during redox cycles, are produced by the addition of spherical carbon particles prior to sintering. Partial closure of porosity is detectable when CeO 2 is doped with Pr, Zr or Hf, while Li co-doping retains interconnected porosity more effectively than other doped or pristine ceria samples. In dense ceramics, microstructures reveal a reduction of the average grain size of pristine CeO 2 with increasing Zr and Hf dopant concentration. These trends are validated using Pechini synthesized materials of the same composition. The reduction in grain size is even more pronounced for Pr doped CeO 2 and Li doped Hf 0.1 Ce 0.9 O 2 , while TiO 2 doping induces softening of samples under operating conditions (>1500 °C) limiting its use for high temperature applications. The redox performance of M x Ce 1−x O 2−δ (M = Zr, Hf; 0 ≤ x ≤ 0.2) can be increased significantly with increasing Zr and Hf dopant concentration. At x = 0.2 (Zr, Hf) the fuel production rates are doubled as compared to pristine CeO 2 . The redox performance of Hf doped CeO 2 remains stable upon co-doping with Li + .

The ambient air quality is a well-known problem for big cities with dense population and high traffic volume. The traditional way for monitoring air quality is using stationary measurement stations. However, the main disadvantages are limited spatial resolution and restricted possibility of mapping spatial distributions of air pollutants. To provide high spatial and temporal resolution, mobile measurements are necessary. This study aims to investigate the air quality of a German city i.e. Stuttgart and the impact of local traffic on the pollutant concentrations by performing mobile measurements using a bicycle platform named as MOBAIR. In this investigation a bicycle was equipped with different measurement devices to measure air pollutants such as nitrogen oxides (NO and NO2), ozone (O3), Particulate Matter (PM), Ultrafine Particles (UFP) and Black Carbon (BC) as well as meteorological parameters such as air temperature, relative humidity, air pressure, wind speed, wind direction and solar radiation. A GPS device was used to relate the measured parameters to the location and a camera was installed to relate the measurement data to special events. The measurement route was around 12 km long covering a part of the city center with high traffic roads as well as side roads and a park in order to obtain a broader picture and to identify the contribution of traffic to the air quality in the measurement area. A total of around 120 trips of the 12 km route were performed in 14 measurement days in the months of February, June and July 2018 including each hour of the day and main seasons. In order to validate the measured results, the NO2 and NOX concentrations were measured at 16 different stationary locations along the bicycle route for a longer period using passive samplers.

Na-β”-alumina ceramics are applied as electrolytes in high-temperature Na/NiCl2 and Na/S batteries. Although featuring excellent sodium-ion conductivity in the order of 0.2 S cm−1 at 300 °C, the brittleness associated with ceramic materials makes Na-β”-alumina electrolytes vulnerable to mechanical stresses, e.g. during battery operation. In this study, the impact of grain size and density on the flexural strength of Na-β”-alumina ceramics is investigated. For constant composition but largely varying grain sizes, we report a constant flexural strength of 163 ± 10 MPa for sintering temperatures between 1560 °C and 1620 °C and dwell times ≤ 30 min. Addition of 5 vol % zirconia improves the flexural strength by 30 %, but reduces the conductivity by 15 %. Furthermore, we show that the addition of zirconia reduces the onset temperature of the liquid phase formation during sintering. These findings show promise for using lower sintering temperatures in the presence of zirconia, which is beneficial on an industrial level.

Note: Times Cited: 0 Reference EPFL-ARTICLE-206047doi:10.1016/j.jpowsour.2014.07.094View record in Web of Science URL: ://WOS:000342245400067 Record created on 2015-03-03, modified on 2017-05-12

We present a nanofabrication process for producing tungsten zone plates used in hard X-ray applications including a method of integrating a high-energy absorbing central stop with the optic. Tungsten zone plates are structured with electron-beam lithography and subsequent reactive ion etching. The central stop originates from a platinum wire. It is cut to dimension by focused ion beam etching, and afterwards attached to the zone plate center using ion beam induced deposition of platinum. A zone plate with integrated central stop will simplify alignment in hard X-ray scanning microscope arrangements where the 0th order light must be eliminated. The focusing performance of the zone plate device was investigated by scanning coherent diffraction imaging (ptychography) at 8 keV photon energy. We could demonstrate a diffraction-limited focus size of 53 nm diameter full-width-at-half-maximum. Tungsten zone plates with integrated central stops show promising results for use in hard X-ray microscopes at high-brightness facilities. QC 20140228

Titanium dioxide films were deposited on macroporous reticulated Al2O3 and alumina–mullite foams with pore sizes of 15 ppi (pores per inch). Coatings were prepared from suspensions of precursor powders of Aeroxide® P25 nanopowder and precipitated TiO2 by using a dip coating process. The TiO2 forms films with a thickness of ∼2–20 μm. The photocatalytic activity was characterized as the mineralization rate of an aqueous phenol solution under UVA irradiation by the TOC technique. Precipitated TiO2 films have nearly the same photocatalytic activity as a titania suspension, in which powder aggregates have a size comparable with the thickness of the films. Samples made of Aeroxide® P25 nanopowder, in which the size of aggregates is ∼0.1 μm show higher efficiency of photodecomposition in suspensions with films. The doping of precipitated anatase with Zr(IV) in the atomic ratio Zr/Ti = 0.008 significantly improves the photocatalytic activity of the foam supported titania. Zr doped anatase films show better performance as the films prepared only from Aeroxide® P25 nanopowder.

TiO 2 thick films deposited on macroporous reticulated Al 2 O 3 foams with pore size of 10 ppi and 15 ppi were prepared using dip coating from slurries of Aeroxide ® P25 nanopowder and precipitated titania. All prepared films have sufficiently good adhesion to the surface of the substrate also in case of strongly cracked films. No measurable release of deposited TiO 2 after repeated photocatalytic cycles was observed. The photocatalytic activity was characterized as the rate of mineralization of aqueous phenol solution under irradiation of UVA light by TOC technique. The best activity was obtained with Aeroxide ® P25 coated Al 2 O 3 foam with the pore size of 10 ppi, annealed at 600 °C. The optimal annealing temperature for preparation of films from precipitated titania could be determined at 700 °C. Films prepared by sol–gel deposition technique were considerably thinner compared to coatings made of suspensions and their photocatalytic activity was significantly smaller.

Environmental charcoals represent a poorly defined part of the black carbon (BC) combustion continuum and may differ widely in their chemical and physical properties, depending on combustion conditions and source material. The benzene polycarboxylic acid (BPCA) molecular marker method is well established to quantify the BC component in charcoal, soil and sediment, although observed variations between labs could stem from subtle differences in methods. The objectives of this study were to identify and improve potential sources of analytical uncertainty. The improved method was then used to qualitatively characterize wood charred at 200–1000 °C. One significant improvement of the BPCA method was to replace citric acid with phthalic acid as an internal standard, which is more stable in acidic solution and more similar to the target compounds. Also, including a soil reference material as a quality control in each analysis proved to be a robust tool to detect for variations in reproducibility. For the thermosequence, elemental O/C and H/C ratios typically decreased with temperature to ⩽0.03 at 1000 °C, whereas BPCA concentrations peaked at 700 °C. With temperature B6CA proportions increased consistently (6–98%), except for a plateau at 250–500 °C. Thus, relative contributions of B6CA reflected the pyrolysis temperature and probably also the degree of condensation of the charcoals we investigated. Future work will show if our results can be directly related to charcoal produced under oxygen limited conditions, including charcoal formed at wildfires or so called biochar for agricultural use.

Zone plates are high quality optics that have the potential to provide diffraction-limited nano-focusing of hard X-ray free electron laser radiation. The present publication investigates theoretically the temperature behavior of metal zone plates on a diamond substrate irradiated by 0.1 nm X-rays from the European X-ray Free Electron Laser. The heat transfer in the optic is simulated by solving the transient heat equation with the finite element method. Two different zone plate designs are considered, one small zone plate placed in the direct beam and one larger zone plate after the monochromator. The main result is that for all investigated cases the maximum temperature in the metal zone plate layer is at least a factor 2 below the melting point of the respective material, proving the efficiency of the proposed cooling scheme. However, zone plates in the direct beam experience large and rapid temperature fluctuations of several hundred Kelvin that might prove fatal to the optic. The situation is different for optics behind the monochromator with fluctuations in the 20 K range and maximum temperatures well below room temperature. The simulation results give valuable indications on the temperature behavior to be expected and are a basis for future experimental heat transfer and mechanical stability investigations of fabricated nanostructures.

High-temperature steam electrolysis by solid oxide electrolysis cells (SOEC) is a method with great potential for transforming clean and renewable energy from non-fossil sources to synthetic fuels such as hydrogen, methane or dimethyl ether, which have been identified as promising alternative energy carriers. With the same technology, fuel gas can be used in a very efficient way to reconvert chemically stored energy into electrical energy, since SOECs also work in the reverse mode, operating as solid oxide fuel cells (SOFC). As solid oxide cells (SOC) perform at high-temperatures (700–900 °C), material degradation and evaporation can occur, e.g., from the cell-sealing material, leading to poisoning effects and aging mechanisms that decrease the cell efficiency and long-term durability. To investigate such cell degradation processes, thorough examination of SOCs often requires a chemical and structural characterisation at a microscopic and nanoscopic level. The combination of different microscopic techniques such as conventional scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and the focused ion beam (FIB) preparation technique for transmission electron microscopy (TEM) allows for post-mortem analysis at a multi-scale level. These complementary techniques can be used to characterise structural and chemical changes over a large and representative sample area (micro-scale) as well as at the nano-scale level for selected sample details. This article presents a methodical approach for the structural and chemical characterisation of changes in aged cathode-supported electrolysis cells produced at Riso DTU, Denmark. Additionally, we present results from the characterisation of impurities at the electrolyte/hydrogen interface caused by evaporation of sealing material.

This paper contributes for the first time in Buenos Aires city to the temporal and horizontal distribution of the PM2.5 and PM10 concentrations. Their variations and relationships with relevant variables that characterize the air pollution potential of the urban air shed are also given. The measurements were carried out for one year from May 2006 to May 2007. During this period, particulate matter (PM) was continuously measured at one reference station and alternatively for shorter time periods at six different sites. The values and temporal variations on a daily and seasonal basis were consistent with the ventilation potential of the atmosphere. The cold season, which had the lowest values of the ventilation coefficient, indicated higher probabilities of poor air quality and this was confirmed by the higher concentrations of PM10 and PM2.5 measured. At the reference station, the daily EU limit value for PM10 was exceeded 36 times during one year while the Buenos Aires limit value was exceeded only once. The PM10 annual mean value was almost 70% of the Buenos Aires annual limit. The PM2.5 annual mean value (15 μg m-3) was same as the regulated one (15 μg m-3). The correlation between PM10 and PM2.5 concentrations and frequencies of wind directions showed that the highest concentrations were observed when the wind was from the city (land wind) and lowest concentrations when the wind was from Rio de La Plata (fluvial wind). The concentrations during land wind events exceeded the Buenos Aires PM2.5 annual limit value. The ratio of PM2.5 to PM10 was 0.44, which indicates the coarse particles (>2.5 μm) originated from road dust, soil re-suspension and abrasion processes are the dominated fractions of PM. Results of random PM measurements at 60 sites showed that PM2.5 was more homogeneously distributed over the city than PM10. Fil: Arkouli, Marcelina. Universität Stuttgart; Alemania Fil: Ulke, Ana Graciela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina Fil: Endlicher, Wilfried. Universität zu Berlin; Alemania Fil: Baumbach, Günter. Universität Stuttgart; Alemania Fil: Schultz, Eckart. Deutscher Wetterdienst; Alemania Fil: Vogt, Ulrich. Universität Stuttgart; Alemania Fil: Müller, Marlen. Universität zu Berlin; Alemania Fil: Dawidowski, Laura Elena. Comisión Nacional de Energía Atómica; Argentina Fil: Faggi, Ana Maria. Universidad de Flores; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Wolf Benning, Uta. Universität zu Berlin; Alemania Fil: Scheffknecht, Günter. Universität Stuttgart; Alemania

The redox behavior of iron during heating of a high-performance perovskite for ceramic oxygen separation membranes was studied by combined electron energy-loss (EELS, esp. ELNES) and Mossbauer spectroscopical in situ methods. At room temperature, the iron in ( Ba 0.5 Sr 0.5 ) ( Fe 0.8 Zn 0.2 ) O 3 - δ (BSFZ) is in a mixed valence state of 75% Fe 4 + in the high-spin state and 25% Fe 3 + predominantly in the low-spin state. When heated to 900 ∘ C , a slight reduction of iron is observed that increases the quantity of Fe 3 + species. However, the dominant occurrence is a gradual transition in the spin-state of trivalent iron from a mixed low-spin/high-spin to a pure high-spin configuration. In addition, a remarkable amount of hybridization is found in the Fe–O bonds that are highly polar rather than purely ionic. The coupled valence/spin-state transition correlates with anomalies in thermogravimetry and thermal expansion behavior observed by X-ray diffraction and dilatometry, respectively. Since the effective cationic radii depend not only on the valence but also on the spin-state, both have to be considered when estimating under which conditions a cubic perovskite will tolerate specific cations. It is concluded that an excellent phase stability of perovskite-based membrane materials demands a tailoring, which enables pure high-spin states under operational conditions, even if mixed valence states are present. The low spin-state transition temperature of BSFZ provides that all iron species are in a pure high-spin configuration already above ca. 500 ∘ C making this ceramic highly attractive for intermediate temperature applications ( 500 – 800 ∘ C ).

Perovskites of the composition La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} (x = 0.0, 0.1, 0.5, 0.9, 1.0) were prepared by the conventional solid state reaction route. The single phase behaviour was assessed by XRD analysis, the electronic properties were investigated by Fe K-edge X-ray absorption spectroscopy. The work is focused on the valence state of iron and the oxygen vacancies of the perovskites investigated. The XRD measurements revealed that the solid state reaction yields cubic perovskites for x = 1, 0.9, rhombohedral perovskites for x = 0.5, and orthorhombic perovskites for x = 0, 0.1. The X-ray absorption data are discussed in detail with respect to Fe K-edge shift, white-line intensity, pre-edge features, and the EXAFS data. The first peak in the Fourier transform of the Chi x k{sup 3} and Chi x k{sup 2} functions was simulated for a detailed analysis of scattering contributions from the first oxygen shell to evaluate the Fe-O bond length. The substitution of lanthanum by strontium leads to a corresponding increase of the iron valence state and thus to the formation of the Jahn-Teller Fe{sup 4+} ion. This is causing disorder in the first coordination shell and thus an increase of the Debye-Waller factor with increasingmore » x. The Fe-O bond length obtained from XRD and especially from X-ray absorption data are consistent with {delta}-values close to zero.« less

Polymethylsiloxane (PMS) was used as a binder to make self-supporting SiC preforms for pressurized aluminum melt infiltration. The SiC particles were coated with preceramic polymer by spray drying; this ensured a fine and homogeneous distribution coupled with a high yield of the binder. The conditioned SiC powder mixtures were processed into preforms by warm pressing, curing and pyrolysis. A polymer content of 1.25 wt.% conferred sufficient stability to the preforms to enable composite processing. Using this procedure, SiC preforms with various SiC particle size distributions were prepared. The resulting Al/SiC composites with SiC contents of about 60 vol.% obtained by squeeze casting infiltration exhibit a 4-point bending strength of ∼500 MPa and Young’s moduli of ∼200 GPa. These values are comparable to those of compositionally identical, but binder-free composites. It is thus shown that the PMS-derived binder confers the desired strength to the SiC preforms without impairing the mechanical properties of the resulting Al/SiC composites.

In this paper, we describe a numerical method of simulating two-dimensional images in a compact soft X-ray microscope using partially coherent illumination considerations. The work was motivated by recent test object images obtained by the latest generation in-house compact soft X-ray microscope, which showed diffraction-like artifacts not observed previously. The numerical model approximates the condenser zone plate as a secondary incoherent source represented by individually coherent but mutually incoherent source points, each giving rise to a separate image. A final image is obtained by adding up all the individual source point contributions. The results are compared with the microscope images and show qualitative agreement, indicating that the observed effects are caused by partially coherent illumination.

Differential interference contrast is a potentially powerful technique for contrast enhancement in soft X-ray microscopy. We describe the design and fabrication of single-element diffractive optica ...

Pre-ceramic polymer (MK-polymer)-based nitrogen-bounded silicon carbide (NBSiC) has been developed and the concept utilised to produce macroporous ceramic foam structures by a modified sponge replica technique. In order to increase the strut thickness and to fill up the hollow struts and thus increase the mechanical strength of the microporous structures, repeated re-infiltrations and pre-sintering steps are investigated. The double-ring bending strength could be increased with increasing polymer content and coating, respectively infiltration cycles up to a maximum value of 140 MPa for NBSiC discs, nitrided at 1400 °C. After a re-crystallisation process at 1850 °C, the influence of the polymer is negligible and the bending strength is only in the region of 50 MPa, as re-crystallised SiC (RSiC) is the dominant phase. The oxidation behaviour of NBSiC corresponds with the oxidation behaviour of commercial SiC. EDX analysis of samples nitrided at 1400 °C shows the composition containing grains of SiC, Si 3 N 4 and Si 2 N 2 O.

A new approach to manufacture short-fibre-reinforced ceramic matrix composites (CMC) by mixing carbon fibres, ceramic fillers and a viscous ceramic precursor by means of a plastic forming technique is introduced. To transform the composite from the polymer into a nitride ceramic state, a two-step process consisting of pyrolysis and nitridation is applied. Transformations of the polymer-modified RBSN (PMRBSN) during this process are examined in terms of dimensional changes, porosity and phase composition. The role of the precursor during the processing and nitridation sequence, aspects concerning fibre shortening and packing and the effects on the material properties as Young's modulus, strength, hardness, porosity, crack deflection and fibre pullout are discussed.

Thin film deposition by pulsed reactive crossed beam laser ablation has often advantages such as no need for annealing after deposition over conventional pulsed laser deposition. However, when depositing material from a target containing a low atomic mass component such as lithium, theresultingfilmsarefrequently sub-stoichiometricinthelightelements.Thisismostprobablydue toscatteringoftheplasmaplumeinthecrossed gas pulse, which creates a high local pressure. The light species are scattered more than the heavier elements, which leads to Li-deficiencies in the resulting film. Depositing lithium-spinels without the use of a crossed gas pulse is still strongly dependent on the applied background pressure. A background pressure below 10 Pa results also in lithium-deficient films. However, this is not due to scattering effects but very probably to the evaporation of lithium oxide from the growing film. These boundary conditions allow only a window of conditions for thegrowth of stoichiometric LiMn2O4 films that is useful as test electrodes for Li-batteries research. A strong influence of the experimental parameters was observed. The films deposited at different background pressures and different substrate/target distances showed very different behaviors in the electrochemical measurements. Extraction and insertion of lithium was only detected for films deposited at a distance between 3 and 4 cm and at a background pressure of 20 Pa, whereas films deposited at other conditions did not show this electrochemical activity. # 2005 Elsevier B.V. All rights reserved.

The consequences of air pollution scenarios caused by road traffic or the impact of exhaust gas reduction techniques are estimated by emission models. To ensure the quality of model results, it is necessary to evaluate the used emission factors under real-world conditions. Therefore, the Institut fur Meteorologie und Klimaforschung (IMK) of the Forschungszentrum Karlsruhe initiated the field campaign BAB II (BundesAutoBahn, Federal motorway). The campaign was conducted in May 2001 with the objective of measuring the traffic emissions at a motorway section and to compare them to modelled emissions. Based on experiences during a precursor campaign (BAB I, 1997), a symmetric experimental set-up was installed which allowed measurements up- and downwind of a motorway nearby Heidelberg, Germany. This paper focuses on the determination of source intensities and emission factors for CO and NOx, whereas other papers in this issue handle VOC and particulate matter. First the basic approach of BAB II measurements up- and downwind of a motorway was approved, showing that it is possible to detect the plume originating from traffic emissions. A case study during a traffic jam illustrates that driving patterns have a strong impact on the emissions and therefore a detailed traffic census is required to obtain reliable emission calculations. Two different strategies were used: (i) long-time measurements during the whole campaign to obtain vertical profiles each 30 min and (ii) measurements during eight special operation periods (SOP) in a higher temporal resolution of 5 min, using instrumentation in elevators. It could be shown that even at a distance of 60–80 m from the motorway the structure of the plume is still inhomogeneous, and concentration changes within short times. The inhomogeneity of the plume not only affects the temporal scale, the spatial scale is also influenced and frequently concentration maxima in higher altitudes are observed. Mean source intensities of 9.5 kg km−1 h−1 CO and 4.4 kg km−1 h−1 NOx on working days have been calculated. The ratio of CO/NOx was found to be 2.1 on working days and 4.5 on weekends and holidays. Emission factors of 2.62 g km−1 veh−1 CO and 1.08 g km−1 veh−1 NOx have been determined, which agrees well with results derived from similar studies.

In May 2001, the large-scale field project BAB II was performed at the highly frequented motorway BAB (Bundesautobahn) A656 with two traffic lanes in each direction between the German cities Heidelberg and Mannheim. Extensive measurements of air pollutants were carried out on both sides of the motorway. In a distance of 60 m (north side) and 84 m (south side) to the traffic lanes, two 52-m-high towers were installed, at which electrically powered elevators were fixed. In these elevators, two NOx analysers, an Electrical Low Pressure Impactor (ELPI; measurement of the particle number size distribution in the diameter range D between 30 nm and 10 μm) and a Diffusion Charger (DC; measuring the particle surface area concentration), were operated to record continuous vertical profiles from 5 to 50 m above the earth's surface. On the upwind side, particle number and surface area concentration as well as NOx values were constant over the entire height profile. On the downwind side, increased concentrations appeared in the near-ground range: in the forenoon, a monotonous decrease in pollutant concentrations with increasing height was found, while around noon the concentration maximum of the particles was slightly shifted to 10 m above ground. This height dependence was found for two different size ranges, i.e., for particles with D 300 nm (consisting of soot particles and nucleation mode particles formed by condensation as a result of cooling of the exhaust gas after emission), and for coarse particles ( D > 1 μ m , abrasion and resuspension products). In the size range between 300 and 700 nm, no height dependence was found, corroborating the fact that motor traffic emits only few particles in this size range. On the downwind side of the motorway, only background concentrations were measured above 25 m. The results of the profile measurements were confirmed by stationary measurements of particle size distributions with Scanning Mobility Particle Sizers (SMPS) at various heights. A good correlation between particle surface area and NOx concentration was observed. Vehicle emission factors were determined for the particle surface area, number and volume of several size ranges.

Non-methane hydrocarbons (NMHC) were measured vertically resolved up-wind and down-wind of the motorway BAB A656 Heidelberg–Mannheim, Germany, for 4 weeks in April and May 2001. The horizontal distribution of C2–C9 aliphatic and aromatic hydrocarbons was monitored by using two compact quasi on-line gas chromatography (GC) instruments. The vertical distribution of NMHC was determined by using adsorption tubes, which were analysed off-line by GC in the laboratory. More than 50 NMHC were detected and 26 of them were quantified. From the measured data, the emission source strength for a variety of NMHC were calculated and discussed.

The quality of an emission calculation model based on emission factors measured on roller test stands and statistical traffic data was evaluated using source strengths and emission factors calculated from real-world exhaust gas concentration differences measured upwind and downwind of a motorway in southwest Germany. Gaseous and particulate emissions were taken into account. Detailed traffic census data were taken during the measurements. The results were compared with findings of similar studies. The main conclusion is the underestimation of CO and NO x source strengths by the model. On the average, it amounts to 23% in case of CO and 17% for NO x . The latter underestimation results from an undervaluation by 22% of NO x emission factors of heavy-duty vehicles (HDVs). There are significant differences between source strengths on working days and weekends because of the different traffic split between light-duty vehicles (LDVs) and HDVs. The mean emission factors of all vehicles from measurements are 1.08 g km −1 veh −1 for NO x and 2.62 g km −1 veh −1 for CO. The model calculations give 0.92 g km −1 veh −1 for NO x and 2.14 g km −1 veh −1 for CO. The source strengths of 21 non-methane hydrocarbon (NMHC) compounds quantified are underestimated by the model. The ratio between the measured and model-calculated emissions ranges from 1.3 to 2.1 for BTX and up to 21 for 16 other NMHCs. The reason for the differences is the insufficient knowledge of NMHC emissions of road traffic. Particulate matter emissions are dominated by ultra-fine particles in the 10–40 nm range. As far as aerosols larger than 29 nm are concerned, 1.80×10 14 particles km −1 veh −1 are determined for all vehicles, 1.22×10 14 particles km −1 veh −1 and an aerosol volume of 0.03 cm 3 km −1 veh −1 are measured for LDVs, and for HDVs 7.79×10 14 particles km −1 veh −1 and 0.41 cm 3 km −1 veh −1 are calculated. Traffic-induced turbulence has been identified to have a decisive influence on exhaust gas dispersion near the source.

The main objective of the field project BAB II (Bundesautobahn—Federal motorway) was to calculate the emissions of a motorway from ambient air measurements upwind and downwind of the lanes. The project was accompanied by a series of quality assurance measures, because all results have to be comparable to each other. Consequently, NO/NOx, CO, and VOC analysers participated in an inter-calibration with calibration gases. Subsequent results of ambient air measurements with all analysers for all measured components—NO/NOx, CO, O3, VOCs, elemental carbon (EC), and particulate matter (mass and number concentration)—were compared to each other. The quality assurance program had two main objectives: On the one hand, the data were harmonised after the detection of systematic deviations between the readings of the different analysers by applying individual correction equations or correction factors. On the other hand, the harmonised data were used for the determination of measurement uncertainty. In general, the measurement uncertainties determined were about 3–9%, except for VOCs and the particle number concentration. For all components, the upwind–downwind concentration differences in the actual experiment were much higher than the measurement uncertainties determined, thus bending confidence to the concentration differences being due to the traffic emissions rather than to measurement uncertainties.

Preceramic polymers are enabling the development of a variety of advanced shaping methods which, in turn, make possible new and cost-effective approaches for the fabrication of composite materials. This opens new perspectives for the mass production of composites which might, for example, be used in cost-sensitive areas of application in the machine and automobile industries. In two examples it will be shown how preceramic polymers can be used to obtain both metal matrix composites (MMC) and ceramic matrix composites (CMC). Their properties will be discussed in particular with respect to the usage of a preceramic polymer. The first example shows an approach to manufacturing short-fibre-reinforced CMCs by means of a plastic forming technique which involves mixing of either carbon or SiC fibres, ceramic fillers and a viscous ceramic precursor. The precursor permits a fibre-reinforced ceramic with a low porosity to be obtained. The role of the precursor in the whole process and the resulting material properties will be discussed. The second example shows a method for fabricating porous SiC ceramic preforms which are subsequently infiltrated with aluminium to form a MMC. By using the precursor route, a machinable preform with tailored porosity can be produced. Correlations between precursor, preform and MMC properties will be drawn.

Al 2 O 3 –MoSi 2 composites with MoSi 2 volume fractions between 16 and 40% were fabricated from commercial ceramic Al 2 O 3 and intermetallic MoSi 2 powders by granulation, cold isostatic pressing and vacuum-sintering. The addition of MoSi 2 had only a slight influence on the densification of the composites, with sintered densities of 98% for samples with 16 vol.% MoSi 2 and 94% for samples with 40 vol.% MoSi 2 . Composites with MoSi 2 contents of 20 vol.% and higher were electroconductive due to the formation of a three-dimensional percolating network of the conductive MoSi 2 phase.

We describe the development of a table top soft X-ray source based on a laser produced plasma. The plasma is produced by a Nd:YLF pulse-train laser which delivers pulse trains of up to 400 pulses each of about 25 ps duration. Number and energy of the micropulses are fully computer controlled adjustable for an optimum interaction with a rotating solid target. Spectral, spatial and temporal characteristics of the X-ray emission from Mylar and copper targets have been studied. A calibrated back-illuminated CCD camera together with a slit grating spectrograph were utilized for the measurement of the absolute soft X-ray photon fluxes. The temporal measurements were performed using a streak camera while the plasma size was measured with a zone plate. An application of the system in a X-ray absorption experiment is shown. The advantages of the system in view of possible optical pump and soft X-ray probe experiments will be discussed.

Ceramic macroporous reticular alumina foams with a pore size of 15, 20 and 25 pores per inch (ppi) were prepared by the Schwartzwalder method and sintered at 1200 °C to preserve a high porosity. TiO 2 thick films were supported on the foam surface by a wash coating process, using Degussa P25 as a TiO 2 nanopowder source. After annealing at 600 °C, films with an adequate adhesion and with a thickness of 5–10 μm were obtained. An increasing pore size of the supported foams improves the specific photocatalytic activity of the TiO 2 coated scaffolds, the flow of solution through the highly active porous foam structure and the better access of light to the active TiO 2 surface.

Tethersonde and airship measurements were carried out in 1994 during two different seasons within the framework of the preparation of the Clean Air Plan of Freiburg. These investigations concerned the influence of the Freiburg mountain-valley wind system, the so-called Hollentaler, on Freiburg's air quality. Vertical and horizontal measurements carried out east of Freiburg in the Dreisam Valley revealed that when the mountain-valley wind system has developed during summer high-pressure weather conditions, Freiburg is supplied with low polluted air masses from the Black Forest at night up to the early morning hours. Conversely, it may occur that during stable weather conditions with low wind speeds, the polluted air masses which flow into the Black Forest during the day are transported back to Freiburg with the mountain wind, so that there is no fresh air supply.

We describe the fabrication and evaluation of platinum zone plates for 5-12kV X-ray imaging and focusing. These nano-scale circular periodic structures are fabricated by filling an e-beam generated mold with Pt in an electroplating process. The plating recipe is described. The resulting zone plates, having outer zone widths of 100 and 50nm, show good uniformity and high aspect ratio. Their diffraction efficiencies are 50-70% of the theoretical, as measured at the European Synchrotron Radiation Facility. Platinum shows promise to become an attractive alternative to present hard X-ray zone plate materials due to its nano-structuring properties and the potential for zone-plate operation at higher temperatures.