Stress fractures are common injuries frequently overlooked on first radiographs, especially in the early course. The gold standard for accurate diagnosis is MRI and scintigraphy. We report six cases of stress fractures of the lower limb diagnosed with sonography and describe typical sonographic features.
Auxiliary power units (APUs) running on carbon-containing fuels provide solutions for high-efficient power supply and emission reduction. In order to ensure safe operation, unwanted degradation caused by carbon depositions should be avoided or controlled. Early detection allows trigerring of counteractions and avoids rapid deterioration of the cell performance as well as mechanical degradation of the cell microstructure and it is presented here. This study also shows that carbon does not only block the active catalyst sites and porous gas channels thus deteriorating the cell performance, but massive carbon depositions lead to destruction of the lattice YSZ-structure. In order to prolong the lifetime of the investigated cells, carbon-dioxide is tested as a possible agent for gasification of deposited carbon. Supplying with CO 2 gasifies carbon to carbon-monoxide, but experimental investigations show further degradation of the cell performance and a reduced methane conversion rate. A method, which represents a combination of CO 2 fed to the anode and an overvoltage applied to the cell, enabled complete performance regeneration in a cell-protecting manner. Solid oxide fuel cells are high-efficient devices, which convert the chemical energy of gaseous fuels directly into electrical energy without additional conversion steps. The heat losses occurring during the operation at temperatures between 600-1000• C can be used as a high-quality heat energy. SOFCs offer a great fuel flexibility and compared to other fuel cell types they can internally reform hydrocarbons. Internal conversion of carbon-containing fuels over nickel as the most widely used catalyst tends to promote carbonaceous deposits on the anode surface as well as inside the anode, causing deactivation of the fuel cells.1-3 The usage of other alternative materials such as Cu-, Gdand Sm-stabilized ceria-based materials or conducting oxides is possible to suppress carbon depositions, but Ni still offers a considerably better conductivity and electrocatalytic performance. 4-7Carbon deposition.-To date many researchers have investigated SOFC anode degradation. Khan et al.8 made a short review of Ni-YSZ degradation mechanisms, classifying these into four types: nickel coarsening, coking, redox instability and sulfur poisoning. A detailed analysis of challenges for nickel steam-reforming catalyst for industrial application can further be found in study from Sehestad.9 However, regarding operation of Ni-YSZ based SOFCs, if the cell is operated under expected conditions, which exclude sulfur in the fuel and the presence of oxygen on the anode side, redox instability and sulfur poisoning can be excluded as possible degradation phenomena. Nickel coarsening is a process where metal powder begins to sinter and small particles grow in size. It reduces the cell conductivity and worsens the cell performance. The sintering of nickel is also known to prone carbon formation, which requires prevention of this mechanism in order to reduce carbon build. 9 Coking can lead to an i...
High temperature electrolysis (HTE) of steam, CO2, and steam and CO2 for highly efficient generation of hydrogen, carbon monoxide as well as syngas was investigated for four solid oxide cell stacks, all supplied by different stack manufacturers. The SOCs employed within the stacks were planar, and electrolyte or electrode supported with an industrial size between 80 and 128 cm². A comprehensive electrochemical characterization of both stacks and individual cells within the stacks was conducted by means of electrochemical impedance spectroscopy and polarization curve measurement. Detailed performance analyses showed the highest efficiency when operating the stack under H2O electrolysis, followed by co-electrolysis and eventually CO2 electrolysis. Subsequently, the stacks were operated under reversible system-relevant steady-state conditions, thus varying the working temperatures, the current density and the gas inlet flow. For that purpose both the conversion rate and fuel utilization were set to be between 70% and 80%. All stacks were operated for long-term periods of >1,000 h, during which degradation monitoring was applied. The results obtained within the present study allow a better understanding of the electrochemical processes that occur during reversible operation and especially HTE, and provide a guideline for optimized operation of a fully autonomous rSOC system.
The greatest challenges of the solid oxide fuel cell (SOFC) technology are its reliability and durability, both of them considering a variety of possible fuels. To address those issues, understanding of the ongoing processes in SOFCs is of crucial importance. The ability to monitor electrochemical processes online and to identify fast alternating operating conditions offers a possibility to determine degradation-inducing processes at their preliminary stage. Thus, their early identification would provide timely counteractions and inhibit irreversible SOFC degradation. To guarantee the safe SOFC operation, the present study focuses on: (1) investigation of SOFC behavior during feeding with different fuels, (2) development and application of non-conventional tools for online-monitoring, and (3) identification of failure modes at the early stage.
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