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- ATEX (1)
- Dispersion (1)
- Doped tin oxide (1)
- Ellipsometry (1)
- Explosionsschutz (1)
- Funktionale Sicherheit (1)
- Gas releases (1)
- Gas sensing (1)
- Gas sensor (1)
- Gaswarnsysteme (1)
- Heavy gas (1)
- Measurement (1)
- Messfunktion (1)
- Plasmonic absorption (1)
- SPR (1)
- Sensitive layer (1)
- Spectroscopic ellipsometry (1)
- Surface plasmon resonance (1)
- TiO2 (1)
- VDI guideline 3783 (1)
- ZrO2 (1)
- a-C:H (1)
In this study, thickness related changes of the optical properties of doped tin oxide were studied. Two different sets of samples were prepared. The first set was doped with iron or nickel on silicon substrate with thicknesses of 29–56 nm, the second was iron doped on gold/glass substrate with 1.6–6.3 nm. The optical constants were determined by using spectral ellipsometry (SE) followed by modelling of the dielectric function with an oscillator model using Gaussian peaks. The analysis of the optical constants shows a dependence of the refraction and the absorption on the thickness of the doped tin oxide coating. In addition to the tin oxide absorption in the UV, one additional absorption peak was found in the near-IR/red which is related to plasmonic effects due to the doping. This peak shifts from the near-IR to the red part of the visible spectrum and becomes stronger by reducing the thickness, probably due to the formation of metal nanoparticles in this layer. These results were found for two different sets of samples by using the same optical model. Afterwards the second sample set was tested in the Surface Plasmon Resonance Enhanced Ellipsometric (SPREE) gas measurement with CO gas. It was found that the thickness has significant influence on the sensitivity and thus the adsorption of the CO gas. By increasing the thickness from 1.6 nm to 5.1 nm, the sensing ability is enhanced due to a higher coverage of the surface with the over coating. This is explained by the high affinity of CO molecules to the incorporated Fe-nanoparticles in the tin oxide coating. By increasing the thickness further to 6.3 nm, the sensing ability drops because the layer disturbs the SPR sensing effect too much.
Heavy gases in large quantities are used worldwide in various industries. Past incidents, such as the liquefied gas disaster in Viareggio (2009) have shown that these materials are difficult to handle in a safe manner. According to the German Hazardous Incident Ordinance (StörfallVO 2000 - 12. BIMSchV), plant operators with extended responsibilities must produce a report in which they verify that , in the event of an unintentional gas release, the surrounding area will not be aversely affected. Essential elements of this report are calculations of both the released mass flow and the gas dispersion. Using models such as the VDI guideline 3783 (state of the art in Germany) plant operators are able to predict the characteristics of likely gas dispersions. The presented experimental investigations were carried out at the BAM better understand heavy gas dispersion with high gas concentrations in the air (≥ 1 Vol.-%), as well as concentrations with approximately neutral density characteristics (≤ 3000ppm) in order to test the accuracy of the VDI guideline. The starting point for experimental trials was the heavy gas releases resulting from pipeline, vessel or standard gas bottle leaks, with mass flows of between 20 and 100 g s-1. Investigations on the gas-phase release process focused on the unsteady mass flow associated with releases from standard gas bottles. The experimental results will be used as comparative parameters for future simulations. The goal of these simulations is to develop a model with which calculation of the unsteady mass flow, based on the material characteristics for any gas, is possible.
An ellipsometric gas sensor based on the surface Plasmon resonance (SPR) effect of ~ 43 nm thick gold layers was investigated. To protect the gold layer from contamination and to improve the detection limits, the gold layers were top-coated with 5–6 nm thick layers of organic a-C:H or with inorganic metal oxides TiO2 or ZrO2. The additional layers increased the long-term stability, whereas the metal oxide layers protect better than a-C:H. Furthermore, the additional layers decreased the detection limits by one order of magnitude in case of a-C:H and two orders of magnitude in case of the oxides. It could be shown that the detection limits also depend on the kind of preparation (sol–gel process or physical vapour deposition) of the additional layers.
Gaswarnsysteme, aber auch einfachere Gaswarngeräte und -anlagen, finden in der Industrie breite Anwendung zur Gefahrenabwehr in explosionsgefährdeten Bereichen im Sinne der Richtlinie 94/9/EG (ATEX 95). Hierfür werden meist Geräte zur Konzentrationsmessung von brennbaren Gasen mit einem Messbereich von 0 % bis 100 % der jeweiligen UEG eingesetzt. Ziel ist die rechtzeitige und zuverlässige Warnung vor unzulässig hohen Brenngaskonzentrationen unter Betriebsbedingungen. Sauerstoffmessgeräte, die bestimmungsgemäß für die Überwachung von Inertisierungsmaßnahmen verwendet werden, unterliegen ebenfalls den besonderen Anforderungen der ATEX-Richtlinie.