Dependence of the Intrinsic Conductivity Minimum of SrTiO3 Ceramics on the Sintering Atmosphere

A shift of the intrinsic conductivity minimum of strontium titanate ceramics, which depends on the oxygen partial pressure of the sintering atmospheres, was observed. Different hydrogen partial pressures (at constant oxygen partial pressures) did not affect the minimum position. A comparison of the results with defect chemical calculations may explain this behavior as an oxygen partial pressure dependent formation of strontium vacancies showing acceptor character.     

Hot model experiments of the metal bath spraying effect during the decarburization of Fe-C melts through oxygen top blowing

During recent years decarburization has been steadily gaining importance in converter steel metallurgy at the expense of refining reactions for other slag-forming companion elements. Because decarburization is currently a low-slag operation, the phase contact between gas and metal is critical. With the decrease in the amount of slag foam, more attention must be paid to the spraying of iron droplets during oxygen blowing. The experiments were carried out in a hot model reactor with a 50 kg capacity by oxygen top blowing upon Fe-C melts. The resulting spray of iron droplets was collected with the help of a special droplet sampler in the blowing converter. In the metal droplets a pronounced enhanced decarburization was found in comparison to the metal bath. The amount of metal spray was determined with respect to the oxygen blowing pressure, nozzle diameter, and distance between the lance and bath. Depending on the reactor contents, a high circulation rate of the droplets could be observed. At low blowing rates, FeO-slag is formed and sprayed along with the metal.     

Positive effects of wastewater ozonation displayed by in situ bioassays in the receiving stream

Tertiary treatment methods, like ozonation, are currently under discussion to improve removal efficiencies of micropollutants by municipal wastewater treatment plants (WWTPs). In order to assess the effects of a full-scale wastewater ozonation at WWTP Wu?eri, Switzerland, on the receiving stream, a total of seven in situ bioassays with Gammarus fossarum that lasted 7-days were conducted during an overall period of 33 months. Caged gammarids were exposed between 150 m up- and 400 m downstream of a WWTP effluent before, during and following the operation of the full-scale wastewater ozonation. During the release of nonozone treated wastewater, gammarid feeding was significantly reduced by up to 90% 50 and 150 m downstream of the WWTP effluent. In contrast, during the operation period of the ozonation, no significant alterations in feeding were observed downstream. The results of these bioassays were incorporated into a mathematical simulation of the release of nonozone treated wastewater in a Central European region, suggesting a 40% reduction in leaf litter breakdown and hence in energy provision for the remaining aquatic food web downstream of WWTP effluents, while the release of ozone treated wastewater did not affect this important ecosystem function.     

Latitudinal gradient of airborne polyfluorinated alkyl substances in the marine atmosphere between Germany and South Africa (53 degrees N-33 degrees S)

Neutral, volatile polyfluorinated alkyl substances (PFAS) were determined in high-volume air samples collected onboard the German research vessel Polarstern during cruise ANTXXIII-1 between Bremerhaven, Germany (53 degrees N) and Capetown, Republic of South Africa (33 degrees S) in fall 2005. An optimized and validated analytical protocol was used for the determination of several fluorotelomer alcohols (FTOHs) as well as N-alkylated fluorooctane sulfonamides and sulfonamidoethanols (FOSAs/FOSEs). Quantitative analyses were done by gas chromatography-mass spectrometry. This study provides the first concentration data of airborne PFAS from the Southern Hemisphere. Results indicate a strongly decreasing concentration gradient from the European continent toward less industrialized regions. The study confirms that airborne PFAS are mainly restricted to the Northern Hemisphere with a maximum concentration of 190 pg/m3 (8:2 FTOH) in the first sample collected in the channel between the European mainland and the UK. However, south of the equator, trace amounts of several FTOHs and FOSAs with a maximum of 14 pg/m3 (8:2 FTOH) could still be detected. Furthermore, a selection of ionic PFAS including perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) were determined in the particulate phase of high-volume air samples by liquid chromatography-mass spectrometry. Levels of ionic PFAS were almost 2 orders of magnitude lower than those of neutral PFAS, with maximum concentrations in the first sample of 2.5 pg/m3 (PFOS) and 2.0 pg/m3 (PFOA).     

Revisiting Basics of kLa Dependency on Aeration in Bubble Columns: a Is Surprisingly Stable

A comprehensive experimental characterization of a small-scale bubble column bioreactor (60 mL) is presented. Bubble size distribution (BSD), gas holdup, and k_La were determined for different types of liquids, relevant fermentation conditions and superficial gas velocities u_G. The specific interfacial area a and liquid mass transfer coefficient k_L have been identified independent of each other to unravel their individual impact on k_La. Results show that increasing u_G leads to larger bubbles and higher gas holdup. As both parameters influence a in opposite ways, no increase of a with u_G is found. Furthermore, k_L increases with increasing bubble size outlining that improved oxygen transfer is not the result of higher a but of risen k_L instead. The results build the foundation for further simulative investigations.     

Design of Plasma Surface‐Activated,Electrospun Polylactide Non‐Wovens with Improved Cell Acceptance

Electrospinning is a versatile technique to generate tissue engineering matrices possessing structural features similar to the extracellular matrix. Biodegradable polylactides are well suited for processing by this technique, but their innate hydrophobicity impairs initial protein adsorption and cell adhesion. In this work, therefore, electrospun poly(L ‐lactide‐co‐D,L ‐lactide) (70/30) non‐wovens are modified with an ultrathin plasma‐polymerized allylamine (PPAAm) coating. Using scanning electron microsocopy (SEM), it is shown that the fiber structure of the non‐woven is not affected by the plasma treatment. X‐ray photoelectron spectroscopy (XPS) and contact angle measurements of PPAAm‐coated non‐wovens confirm the presence of nitrogen and oxygen‐functional groups in the coating and a hydrophilic nature of the coated non‐woven surface. Cell experiments in vitro demonstrate that the PPAAm‐coated surface promotes occupancy of the non‐woven by human MG‐63 osteoblasts accompanied by improved initial cell spreading and filopodia formation along and between the electrospun polylactide fibers. Overall, plasma‐assisted incorporation of amino groups into electrospun polylactone non‐wovens represents a promising approach to tissue engineering scaffolds with improved cell–material interfaces.     

Strain in electroless copper films monitored by X-ray diffraction during and after deposition and its dependence on bath chemistry

X-ray diffraction based strain measurements have been carried out during the deposition and subsequent relaxation of electroless (autocatalytic) polycrystalline copper films. Thin polymer substrates were mounted on the surface of an electrolyte-filled plating cell, and the X-rays traversed the substrate to scatter of the growing Cu layer. The plating cell was rotated back and forth by up to 70° in order to find the strain of Cu crystallites within and perpendicular to the plane of the film (sin²ψ method). Three types of plating solutions were investigated. A Ni-free solution C leads to compressive strain during steady-state film growth, followed by an exponential relaxation of the film to a residual tensile strain. Electrolytes A and B contain Ni ions, and the resulting Cu(Ni) films have nearly constant strain with small counteracting strain variations during and after film growth. Cyanide-stabilized solution A yields films with a slight compressive strain, while solution B, stabilized by an aromatic nitrogen compound, yields films with tensile strain. Different and reproducible evolution patterns observed for these three electrolyte types establishes in situ X-ray diffraction strain monitoring as a method to evaluate chemical formulations for electroless deposition.     

In situ Raman cell for high pressure and temperature studies of metal and complex hydrides

A novel cell for in situ Raman studies at hydrogen pressures up to 200 bar and at temperatures as high as 400 °C is presented. This device permits in situ monitoring of the formation and decomposition of chemical structures under high pressure via Raman scattering. The performance of the cell under extreme conditions is stable as the design of this device compensates much of the thermal expansion during heating which avoids defocusing of the laser beam. Several complex and metal hydrides were analyzed to demonstrate the advantageous use of this in situ cell. Temperature calibration was performed by monitoring the structural phase transformation and melting point of LiBH(4). The feasibility of the cell in hydrogen atmosphere was confirmed by in situ studies of the decomposition of NaAlH(4) with added TiCl(3) at different hydrogen pressures and the decomposition and rehydrogenation of MgH(2) and LiNH(2).     

Experimental investigation of spray induced gas stratification break-up and mixing in two interconnected vessels

To analyze the effect of containment spray on gas mixing and depressurization, two experiments (ST3_1 and ST3_2) were performed with two interconnected vessels. These experiments were conducted in the frame of the OECD/SETH-2 project using the PANDA facility. The vessels were preconditioned such that a helium-rich layer is formed in the upper section of the first vessel, henceforth referred to as Vessel-1. In the case of the first experiment (ST3_1), the remaining volume of Vessel-1 and the entirety of the second vessel, Vessel-2, were filled with pure steam. For ST3_2, the second experiment presented here, pure steam was replaced with a steam-air mixture instead. Water was injected from the top of Vessel-1 with a spray nozzle projecting downwards. Transient behavior of system pressure, as well as global redistribution of gases is investigated. The results reveal that spray activation is very effective in containment system depressurization. Additionally it is found that the depressurization occurs at a higher rate for the systems containing more steam and less non-condensible gas. The depressurization rate gradually slows down, however, as the steam concentration decreases due to condensation, and non-condensible gases spread over the vessel system. It is also observed that the spray activation initiates the breakup of the helium-rich layer. The composition of the gas atmosphere plays a crucial role in determining the initiation time of the breakup; the presence of large amounts of non-condensible gas such as air delays the beginning of the helium layer breakup by approximately 200 s. The downward component of spray momentum causes the entrainment and the recirculation of the ambient gas atmosphere. Together with the entrainment and condensation effect, spray activation influences the gas mixture density in Vessel-1 and this generates a driving force for inter-compartment flow. As a result of this, an increase of helium-rich gas mixture is observed in the regions far away from the spray, i.e., in Vessel-2.