Influence of carbon availability on dentrification in the central Baltic Sea

Denitrification was investigated in the Baltic proper at two stations with different conditions in the deep water. The Gotland Deep was examined as an example of a basin with anoxic, H2S‐containing deep water and station T was taken as an example of low‐oxygen (<0.2 ml liter−1), sulfide‐free deep water. Denitrification was measured by the acetylene blockage method; in addition, N2O reduction was followed in samples without acetylene. To shed light on the factors limiting denitrification, we compared in situ rates to denitrification after adding nitrate or electron donors. Denitrification was restricted to the layer of the oxic‐anoxic interface in the Gotland Deep and to the water layer near the sediment of station T. For both stations it could be shown that denitrification was not limited by nitrate availability. A lack of available organic C seemed to limit denitrification rates and growth of denitrifiers. As a result of C limitation in the water column, denitrification was restricted to energy‐rich interfaces. In the low‐oxygen water away from energy‐rich interfaces, the less C‐demanding nitrification‐denitrification coupling (NH4+ → N2O → N2) seemed to be favored. Denitrification in the water of the central Baltic seems to be subjected to strong variability due to changing C supply during the course of the year. However, limitation by C availability can be assumed for most of the year and should be taken into account in calculating the N budget of the Baltic

Thin Films as a Tool for Nanoscale Studies of Cement Systems and Building Materials

Many efforts have been made over the last decades to improve and develop new technologies for cement and chemical industries that can provide materials that are more durable and cost efficient, stronger and less environmentally harmful. Studies at small scale in cementitious materials usually require special sample preparation, which can damage the material and mislead the analysis. In nanoscale experiments, several techniques require samples to be extremely thin, while others need the samples to be very flat. The possibility of using thin films of clinker phases in cement research opens far-reaching opportunities for the development of this material and the materials associated to this. Testing different evaporation parameters, the deposition of films with a few tens of nanometers in thickness was achieved for all the clinker phases individually. This chapter will present the attempts for synthesizing thin films of all main clinker phases by the use of electron beam evaporation technique, as well as data on the hydration of the calcium silicate thin, flat and homogeneous samples. Changes are tracked chemically and mineralogically. This study redirects cement science to new perspectives of understanding the nanostructure of cement products. This leads to basis for developing stronger and more durable cement-based materials

Influence of an electric field on grain growth and sintering in strontium titanate

Within the last five years considerable efforts were done in investigating electric field assisted sintering (flash sintering). However the experiments are hard to control: shrinkage occurs within seconds and the local temperature is undefined due to joule heating. Therefore the present study removes these two parameters by investigating grain growth under electric field in the no-current-case for strontium titanate. The impact of an electric field on grain growth in strontium titanate is investigated between 1350°C and 1550°C for fields of up to 50V/mm. To prevent joule heating by a current flowing through the material insulating Al2O3 plates separate the electrodes from the samples. The seeded polycrystal technique is used, which allows evaluating the grain boundary mobility without an influence of the grain boundary energy. The growth direction of the single crystalline seeds is perpendicular to the electric field; hence electrostatic forces do not influence the growth. Below 1425°C the influence of the electric field is weak. However above 1425°C the field results in an increase of the grain boundary mobility at the negative electrode. The range of this increase is in the order of ~1mm. It is shown that abnormal grain growth can be triggered by the electric field. Based on the experimental findings a model is established based on a shift of charged defects. The enhancement of the grain boundary mobility on the negative electrode is explained by an accumulation of oxygen vacancies. This accumulation induces a reduction of the material. A reduction of strontium titanate by atmosphere also results in an increase of the grain boundary mobility, which accords well with the observed behavior under electric field

A Scanning Transmission X-ray Microscopy Study of Cubic and Orthorhombic C₃A and Their Hydration Products in the Presence of Gypsum.

This paper shows the microstructural differences and phase characterization of pure phases and hydrated products of the cubic and orthorhombic (Na-doped) polymorphs of tricalcium aluminate (C₃A), which are commonly found in traditional Portland cements. Pure, anhydrous samples were characterized using scanning transmission X-ray microscopy (STXM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and demonstrated differences in the chemical and mineralogical composition as well as the morphology on a micro/nano-scale. C₃A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C₃A ratio of 1.2, and the products obtained after three days were assessed using STXM. The hydration process and subsequent formation of calcium sulfate in the C₃A/gypsum systems were identified through the changes in the LIII edge fine structure for Calcium. The results also show greater Ca LII binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C₃A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments

Influence of ESP collector configuration on reduction of particulate emissions from biomass combustion facility

Development of compact electrostatic precipitators (ESPs) for reduction of particulate emissions from small scale biomass combustion is an actual task. Particle mass collection efficiency of an ESP depends from combustion conditions, geometry of precipitator ionizer, collector stage configuration and ESP operation parameters. The investigation of the influence of collector stage configuration on particle mass collection efficiency of a pilot space charge ESP was in the focus of the study. It was shown that the use of tube collector with integrated grounded plates enhanced particle mass collection efficiency. The loading of plates with aerosol provoked particle re-entrainment and decreased long-term ESP mass collection efficiency. The use of grounded brush electrodes ensured effective reduction of particle emissions but resulted in increase of pressure drop in the precipitator. The optimization of cleaning intervals of the ionizer and collector stages increased particle mass collection efficiency. It was shown, that the integration of automatic systems for ionizer and collector cleaning into the space charge ESP enhanced precipitator long-term operation stability and ensured effective reduction of particulate emissions form small scale biomass combustion