Temperature independent resistive oxygen sensor for the control of combustion processes

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Oxygen sensors are required to control combustion processes of both fossil and renewable resources in order to ensure that their emissions comply with the strict limits. Long-term stable sensors that can withstand the very harsh exhaust gas conditions are required. In order to control combustion processes and exhaust aftertreatment systems to minimize pollutant emissions, combined gas sensors (also called multi-gas sensors, e.g. CO/O2, or NH3/O2 in SCR exhaust gas aftertreatment systems) would be of industrial interest. Multi-gas sensors can be realized in ceramic planar technology as miniaturized gas sensors by applying several functional films to the sensor substrate, whose resistance or impedance is measured as a function of the gases to be detected. Although the transfer project that is applied here will only deal with the implementation of the results achieved in the previous project on the temperature-independent resistive oxygen sensor, the long-term goal is to integrate several sensors into a single planar sensor component to form a multi-gas sensor. By combining the oxygen sensor with an oxygen cross-sensitive gas sensor, additional cross-sensitivities could be eliminated, thus increasing the accuracy of the detection of different gases. The industrial project partner, who has been working on an impedance-based nitrogen oxide sensor in planar technology for some time now, is also working in this direction. In the preceding DFG-funded project, BFATx = BaFe[(1-x)-0.01]Al0.01TaxO(3-y) was investigated as a functional material with a high dependence of the resistivity on the oxygen content but being temperature-independent between 700 and 800 °C. This behavior was also described in terms of defect chemistry. Towards the end of the project, a functional proof of principle was also provided for BFATx films for temperature-independent resistive oxygen detection manufactured using the novel powder aerosol deposition method (PADM). In this transfer project, on the one hand, complete sensor devices are to be built as demonstrators, and on the other hand, important questions of long-term stability and poisoning resistance are to be answered for the implementation. This is to be done comparatively for sensors whose BFATx functional films are manufactured using classical thick-film technology and are therefore porous, and for those sensors whose BFATx films are deposited using the novel PADM. The question should be answered whether oxygen sensor based on a BFATx functional films developed in the previous project are suitable for controlling combustion and exhaust gas aftertreatment processes. At the same time, however, these questions also address fundamentally interesting issues of long-term stability and poisoning of gas-sensitive layers, the findings of which may have an impact on the understanding of gas sensors in general.