Susanne Kornely

Selective gas detection with high-temperature operated metal oxides using catalytic filters ☆

Metal oxide gas sensors in general, show high sensitivity but poor selectivity if pure sensor materials are used. The performance in terms of reproducibility may be enhanced by using very stable materials, which may be operated at quite high temperature but this does not help in the problem of selectivity. This paper discusses the use of gas pretreatment using filters operated at elevated temperatures to overcome this problem for special applications. Three different types of gas filters are discussed: a physical filter which is permeated by hydrogen only, a catalyst filter which removes disturbing solvent vapours by oxidation, and a gas conversion filter which ensures a defined NO/NO2 equilibrium. These filters relate to the applications of selective indoor CH4, H2, and automotive exhaust gas nitrogen oxide detection.

Thermal behaviour of WO3 and WO3/TiO2 materials

The knowledge of the interdependence between the structural, thermal and electric properties of oxide semiconductors contributes to widen their practical application. In this work the thermal behaviour of WO 3 and WO 3 /TiO 2 powders and thick films - studied by DSC...- is compared with the results of X-ray diffraction (XRD) investigation in the temperature range 25-500°C. The X-ray analyses show a reversible phase transition (from γ-WO 3 into β-WO 3 ) both in WO 3 and in WO 3 /TiO 2 . However, while in the WO 3 the transition takes place between 300 and 400°C, in the WO 3 /TiO 2 system it is not complete even at 400°C, during the measurement time. The phase transition in the WO 3 was identified between 320 and 360°C also by DSC, but in the bicomponent material no sharp transition could be detected. This may mean that titanium can thermally stabilize the WO 3 , influencing also its electric properties.

A self-organizing and fault-tolerant wired peer-to-peer sensor network for textile applications

Textiles are omnipresent in everyday life. Their combination with microelectronics will lead to completely new applications, thus achieving elements of ambient intelligence. The integration of sensor or actuator networks, using fabrics with conductive fibres as a textile motherboard enable the fabrication of large active areas. In this paper we propose a smart textile based on a wired peer-to-peer network of simple information processing elements with integrated sensors or actuators. A self-organizing and fault-tolerant architecture is accomplished which detects the physical shape of the network. Routing paths are formed for data transmission, automatically circumventing defective or missing areas. The network architecture allows the smart textiles to be produced by reel-to-reel processes, cut into arbitrary shapes subsequently and implemented in systems at low installation costs. The possible applications are manifold, ranging from alarm systems to intelligent guidance systems, passenger recognition in car seats, air conditioning control in interior lining and smart wallpaper with software-defined light switches.

Investigation of Al diffusion in different oxide thin-film layers by SNMS/HFM method

Depth profiles of Ga2O3/a-SiO2/Al2O3- substrate, Ga2O3/a-Si3N4/Al2O3- substrate, and Ga2O3/Al2O3 substrate thin layers were determined by the SNMS/HFM method. Al diffusion from the Al2O3 substrate was investigated after 50, and in some cases after 600 hours of heat treatment time at different temperatures (600 °C,850 °C,950 °C,1050 °C and 1150 °C). The diffusion coefficient of Al at 850 °C was found to be DAl=8.7 * 10−18 cm2/s in amorphous SiO2; DAl=1.5*10−17 cm2/s in amorphous Si3N4 and DAl=5.5* 10−16 cm2/s in Ga2O3 at 600 °C, respectively. The possible diffusion mechanism is explained in terms of the metal-oxygen bond-strengths. Although the studied materials have high resistivity at room temperature, the applied SNMS/HFM method has proven to be an efficient surface analytical tool even in these cases.

Causes of fast degradation of thin-film lambda probes in motor vehicle exhaust and initial measures to improve long-term stability

Abstract Oxygen sensors for cylinder-selective measurement of the lambda value in motor vehicle engines are exposed to extreme environmental conditions. At the mounting position close to the cylinder outlet valve, temperatures up to 1000 °C prevail, as well as vibrations > 50 g and powerful turbulent flows that are loaded with particles from the engine wear and with contaminants from engine oil and fuel. Thin-film oxygen sensors made from metal oxides, which function in a completely satisfactory and stable way in extensive laboratory experiments, already show significant signs of degradation during engine operation after a relatively short time (10 h). This paper discusses, for the first time in detail, experimental results on the degradation of thin-film oxygen sensors in motor vehicle engines and its concrete causes. For this purpose, comprehensive studies with surface and microanalysis methods (Auger electron spectroscopy, X-ray fluorescence analysis, X-ray photoemission spectroscopy, electron microprobe and optical microscopy) have been performed and correlated with changes in the sensor characteristics. The results show that both doping of the sensor material by contaminants from oil and fuel and deposition of particles from engine wear on the sensor surface give rise to changes in the sensor characteristic. An improved sensor housing reduces the particle deposition and thus contributes to a significant increase in the long-term stability of the fast lambda probe.