Angewandte Physik
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- Gas storage areas (4)
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Gas cylinders made of composite materials receive growing popularity in light-weight applications. Current standards are mostly based on safety determination relying on minimum amounts of endured load cycles and a minimum burst pressure of a small number of specimens. This paper investigates the possibilities of a probabilistic strength assessment for safety improvements as well as cost and weight savings. The probabilistic assessment is based on destructive testing of small sized samples. The influence of sample size on uncertainty of the assessment is analysed. Furthermore, methods for the assessment of in-service ageing (degradation) are discussed and displayed in performance charts.
A permanent-magnet synchronous motor (PMSM) servo drive for lightweight robotic platforms that have a high torque demand at low rotational speeds has been developed. First, a current-independent torque controller is derived and cascaded with a speed and position controller, while merely an encoder is used as a sensor device in combination with a speed estimator. Finally, the speed estimator output is compared to gyroscope measurements and the overall functioning is verified on a real system.
The device performance of polycrystalline chalcogenide thin film solar cells is strongly influenced by different kinds of defects within the material. The presence of sodium or other alkali metals like potassium during the deposition process is well known to influence the electronic properties of the solar cell and thus to improve the efficiency of the final device. Structural analysis of neutron powder diffraction data collected at low temperatures and subsequent profile analysis by the LeBail and Rietveld method demonstrates the impact of sodium on the point defect characteristics in off stoichiometric CuInSe2. The analyzed materials are powder and thin film solar absorber material with addition of NaF and free of sodium. It is illustrated, the so called “sodium effect” cannot be reduced to one single origin. A range of effects, the reduction of InCu donors with a followed increase of VCu acceptors is possible. The main effect is an increased ordered character of the chalcopyrite crystal structure at off stoichiometric composition, when containing sodium.
Packages for intermediate level waste (ILW) often contain residual water besides the actual waste. The water either exists as obvious free water or it may be bound physically or chemically, e.g. as pore water. A water driven gas generation could occur by vaporisation and by radiolysis. Steam as the result of vaporisation causes an increasing pressure inside a package and can affect corrosion. Vaporisation and condensation processes itself change the thermal behavior of the content especially during strongly unsteady thermal situations like accident fire situations. Radiolysis changes the chemical composition of the content which could cause an unexpected interaction, e.g. hydrogen embrittlement. Besides the pressure build-up the radiolysis of water generates hydrogen and oxygen, which can be highly flammable respectively explosive. The gas generation caused by vaporisation and radiolysis must be taken into account during the design and the safety assessment of a package. Pressure build-up, a changed thermal behavior and content chemistry, and especially the risk of accumulation of combustible gases exceeding the limiting concentration for flammability has to be considered in the safety assessment. Approaches to ensure the transportability of stored packages due to radiolysis will be discussed.
CO2 streams captured from power stations or industrial plants may contain impurities that impact the consecutive steps of the CO2 capture and storage (CCS) chain. As the basis for an optimization of CO2 purity over the whole CCS chain, impacts of different impurities were investigated at key steps including studies on (i) corrosion of metallic materials in CO2 streams and brine, (ii) fluid and interfacial properties as a function of pressure, temperature and CO2 stream composition and their implications for CO2 transport, injection and geological storage, (iii) costs of different pipeline design options, (iv) geochemical alterations at typical reservoir conditions and their implications for geomechanical rock properties. Major findings are synthesized for two exemplary single source-single sink CCS chain scenarios involving CO2 stream compositions typical for pre-combustion capture and oxyfuel combustion. Recommendations for material selection for compression, transport and injection were derived for various CO2 stream compositions. To reliably control corrosion, a limitation of water contents to 50 ppmv is recommended for pipeline transportation of all CO2 streams. At geological storage conditions, the presence of either O2, NOx or SO2 only weakly affected fluid-mineral/rock interactions that still impacted geomechanical rock properties.
The paper presents the microstructure, chemical and phase composition of thin scale, obtained as a result of high temperature corrosion of X20Cr13 stainless steel. Samples were exposed to gas atmosphere of the following composition: 0.25 vol.% of SO2 and 99.75 vol.% of Ar at 600 °C for 5 h. As a consequence, thin compact scale was formed on steel surface.
This scale consisted of three different zones. An amorphous zone was formed close to steel surface. Then, nanocrystalline Zone could be observed. Finally, larger grains were formed during the corrosion process. The analysis of the chemical composition revealed higher concentration of chromium near steel surface. In contrast, to chromium, the content of iron, increased near the scale surface. It was found out that the (Cr, Mn, Fe)5O12 phase appeared in the thin scale.
A 400 m² soil test field with gas injection system was built up, which enables an experimental validation of linear gas sensors for specific applications and gases in an application-relevant scale. Several injection and soil watering experiments with carbon dioxide (CO2) at different days with varying boundary conditions were performed indicating the potential of the method for, e.g., rapid leakage detection with respect to Carbon Capture and Storage (CCS) issues.
Both chain scission and crosslinking reactions occur during ageing of EPDM rubber. However, with many conventional polymer analysis methods such as hardness and DMA, it is hardly possible to obtain information about the contribution of each reaction type to the measured data. For example, hardness and Tg both increase during ageing of EPDM, indicating crosslinking during ageing, but it is not clear whether this is partly counterbalanced by chain scission reactions which would lower hardness and Tg. An indication that chain scission reactions probably counteract the hardness or Tg increase by crosslinking is given by Compression Set (CS) measurements. CS exhibits a higher change than hardness or Tg, as CS increases additively through both chain scission and crosslinking reactions. In order to elucidate the share of chain scission reactions in the total degradation, a method testing relaxation and recovery behaviour using DMA equipment was applied. The method revealed the strong influence of chain scissions, leading to more pronounced relaxation and higher residual strain after compression.
We have studied the mechanism of hydrogen storage in the aluminium based metal–organic framework CAU-1 or [Al4(OH)2 OCH3)4(O2C-C6H3NH2-CO2)3] using a complementary multidisciplinary approach of volumetric gas sorption analysis, in situ neutron diffraction and spectroscopy and ab initio calculations. The structure of CAU-1 forms two different types of microporous cages: (i) an octahedral cage with a diameter of about 10 Å and (ii) a tetrahedral cage with a diameter of about 5 Å. Though all metal sites of CAU-1 are fully coordinated, the material exhibits relatively high storage capacities, reaching 4 wt% at a temperature of 70 K. Our results reveal that hydrogen sorption is dominantly driven by cooperative guest–guest interactions and interactions between guest hydrogen molecules and organic linkers. The adsorption of hydrogen on the organic linkers leads to the contraction of the host framework structure and as a result to changes in the electronic potential surface inside the pores. This, in turn, leads to cooperative rearrangement of the molecules inside the pores and to the formation of additionally occupied positions, increasing hydrogen uptake. At the final stage we observe the formation of solid amorphous hydrogen inside the pores.
We present a demodulation method that partially compensates for the nonlinear and random transfer function of fiber-optic direct detection coherent Rayleigh optical time-domain reflectometry (C-OTDR). Specifically, the proposed method is shown to improve the detection of small amplitude, high frequency dynamic optical fiber strain as it occurs in acoustic emission sensing. The method is applicable provided that the dynamic fiber strain to be sensed is known to affect a longer section of sensing fiber in a spatially homogeneous way. It is shown that this knowledge can be used to extract more quantitative information from the measured C-OTDR signal by averaging signal components from the affected fiber section in a suitable and efficient way. The theoretical basis of the method is developed and supporting experimental results are presented.