Thermopower and conductivity of aerosol deposited BaFe1-xTaxO3-δ films

The thermopower, also known as Seebeck coefficient, is an important parameter to determine constants for defect chemical models of semiconductor materials since it is a measure for the charge carrier concentration. The Seebeck coefficient does not depend on the geometry of the material, like the often investigated conductivity. BaFe0.7Ta0.3O3-δ is known as a temperature independent conductometric oxygen sensor material with perovskite crystal structure. The present work considers the thermopower as well as the electrical conductivity of BaFe1-xTaxO3-δ for x in the range of 0.1 to 0.45 (BFTx). Seebeck coefficient and conductivity were measured simultaneously between 400 and 850°C under varying oxygen partial pressures from 10-2 to 1 bar. BFTx fine powders have been prepared by conventional mixed-oxide route and were calcined at 1350°C. Crystal structure and phase purity were investigated by X-ray diffraction. BFTx thick-films have been successfully deposited by the novel Aerosol Deposition Method (ADM) at room temperature on a special transducer. This well designed transducer includes four platinum electrodes and two gold-platinum thermocouples. Both, thermopower and electrical conductivity, of samples with tantalum contents between x=0.2-0.3 show almost no temperature dependency but depend strongly on the oxygen partial pressure in the temperature range from 700 to 850°C. Results are shown for sample BFT20 in figure 1 and figure 2. All samples have a positive Seebeck coefficient and no n-p-type transition was observed in the investigated oxygen partial pressure range. In contrast to the electrical conductivity, the Seebeck coefficient of all samples decreases with increasing oxygen partial pressure. An initial defect chemical model of BFTx will be presented in this study as well. Please click Additional Files below to see the full abstract

Comparative Study of Different Methods for Soot Sensing and Filter Monitoring in Diesel Exhausts

Due to increasingly tighter emission limits for diesel and gasoline engines, especially concerning particulate matter emissions, particulate filters are becoming indispensable devices for exhaust gas after treatment. Thereby, for an efficient engine and filter control strategy and a cost-efficient filter design, reliable technologies to determine the soot load of the filters and to measure particulate matter concentrations in the exhaust gas during vehicle operation are highly needed. In this study, different approaches for soot sensing are compared. Measurements were conducted on a dynamometer diesel engine test bench with a diesel particulate filter (DPF). The DPF was monitored by a relatively new microwave-based approach. Simultaneously, a resistive type soot sensor and a Pegasor soot sensing device as a reference system measured the soot concentration exhaust upstream of the DPF. By changing engine parameters, different engine out soot emission rates were set. It was found that the microwave-based signal may not only indicate directly the filter loading, but by a time derivative, the engine out soot emission rate can be deduced. Furthermore, by integrating the measured particulate mass in the exhaust, the soot load of the filter can be determined. In summary, all systems coincide well within certain boundaries and the filter itself can act as a soot sensor

Optische 3D-Messtechnik zur Schwingungsanalyse an Windkraftanlagen

Aus der Einleitung: "Der Anteil erneuerbaren Energien in der Energieversorgung soll auch in den kommenden Jahren weiter ausgebaut werden. Dadurch steigt der Bedarf an großen und effizienten Windkraftanlagen (WKA) mit immer höheren Anforderungen an Materialien und Strukturen. Die hohen Belastungen und limitierenden Faktoren in Bezug auf die Lebensdauer solcher Anlagen sind meist dynamisch und abhängig von Strukturschwingungen und Belastungsanregung. Hierzu werden vermehrt Simulationstechniken eingesetzt, die in der Praxis durch den Mangel an genauen Randbedingungen unpräzise sind bzw. als Modell durch Messungen validiert werden müssen. Während typischerweise zur Erfassung von Schwingwegen Beschleunigungsaufnehmer eingesetzt werden, gestaltet sich die Implementierung solcher Messtechnik in drehenden Strukturen meist komplex und aufwändig (Ozbek et al. 2010). Der Einsatz optischer Messtechnik ist im Vergleich einfacher und kann potentiell die Optimierung von Simulationsmodellen unterstützen (Ozbek et al. 2010, Schmidt-Paulsen et al. 2009, 2011).

Comparison of the electrical conductivity of bulk and film Ce1–xZrxO2–d in oxygen-depleted atmospheres at high temperatures

Featuring high levels of achievable oxygen non-stoichiometry d, Ce1-xZrxO2-d solid solutions (CZO) are crucial for application as oxygen storage materials in, for example, automotive three-way catalytic converters (TWC). The use of CZO in form of films combined with simple manufacturing methods is beneficial in view of device miniaturization and reducing of TWC manufacturing costs. In this study, a comparative microstructural and electrochemical characterization of film and conventional bulk CZO is performed using X-ray diffractometry, scanning electron microscopy, and impedance spectroscopy. The films were composed of grains with dimensions of 100 nm or less, and the bulk samples had about 1 lm large grains. The electrical behavior of nanostructured films and coarse-grained bulk CZO (x [ 0) was qualitatively similar at high temperatures and under reducing atmospheres. This is explained by dominating effect of Zr addition, which masks microstructural effects on electrical conductivity, enhances the reducibility, and favors strongly electronic conductivity of CZO at temperatures even 200 K lower than those for pure ceria. The nanostructured CeO 2 films had much higher electrical conductivity with different trends in dependence on temperature and reducing atmospheres than their bulk counterparts. For the latter, the conductivity was dominantly electronic, and microstructural effects were significant at T \ 700 °C. Nanostructural peculiarities of CeO 2 films are assumed to induce their more pronounced ionic conduction at medium oxygen partial pressures and relatively low temperatures. The defect interactions in bulk and film CZO under reducing conditions are discussed in the framework of conventional defect models for ceria

Modelling the Influence of Different Soot Types on the Radio-Frequency-Based Load Detection of Gasoline Particulate Filters

Gasoline particulate filters (GPFs) are an appropriate means to meet today’s emission standards. As for diesel applications, GPFs can be monitored via differential pressure sensors or using a radio-frequency approach (RF sensor). Due to largely differing soot properties and engine operating modes of gasoline compared to diesel engines (e.g., the possibility of incomplete regenerations), the behavior of both sensor systems must be investigated in detail. For this purpose, extensive measurements on engine test benches are usually required. To simplify the sensor development, a simulation model was developed using COMSOL Multiphysics® that not only allowed for calculating the loading and regeneration process of GPFs under different engine operating conditions but also determined the impact on both sensor systems. To simulate the regeneration behavior of gasoline soot accurately, an oxidation model was developed. To identify the influence of different engine operating points on the sensor behavior, various samples generated at an engine test bench were examined regarding their kinetic parameters using thermogravimetric analysis. Thus, this compared the accuracy of soot mass determination using the RF sensor with the differential pressure method. By simulating a typical driving condition with incomplete regenerations, the effects of the soot kinetics on sensor accuracy was demonstrated exemplarily. Thereby, the RF sensor showed an overall smaller mass determination error, as well as a lower dependence on the soot kinetics

Planar Zeolite Film-Based Potentiometric Gas Sensors Manufactured by a Combined Thick-Film and Electroplating Technique

Zeolites are promising materials in the field of gas sensors. In this technology-oriented paper, a planar setup for potentiometric hydrocarbon and hydrogen gas sensors using zeolites as ionic sodium conductors is presented, in which the Pt-loaded Na-ZSM-5 zeolite is applied using a thick-film technique between two interdigitated gold electrodes and one of them is selectively covered for the first time by an electroplated chromium oxide film. The influence of the sensor temperature, the type of hydrocarbons, the zeolite film thickness, and the chromium oxide film thickness is investigated. The influence of the zeolite on the sensor response is briefly discussed in the light of studies dealing with zeolites as selectivity-enhancing cover layers

Radio-Frequency-Controlled Urea Dosing for NH3-SCR Catalysts : NH3 Storage Influence to Catalyst Performance under Transient Conditions

Current developments in exhaust gas aftertreatment led to a huge mistrust in diesel driven passenger cars due to their NOx emissions being too high. The selective catalytic reduction (SCR) with ammonia (NH3) as reducing agent is the only approach today with the capability to meet upcoming emission limits. Therefore, the radio-frequency-based (RF) catalyst state determination to monitor the NH3 loading on SCR catalysts has a huge potential in emission reduction. Recent work on this topic proved the basic capability of this technique under realistic conditions on an engine test bench. In these studies, an RF system calibration for the serial type SCR catalyst Cu-SSZ-13 was developed and different approaches for a temperature dependent NH3 storage were determined. This paper continues this work and uses a fully calibrated RF-SCR system under transient conditions to compare different directly measured and controlled NH3 storage levels, and NH3 target curves. It could be clearly demonstrated that the right NH3 target curve, together with a direct control on the desired level by the RF system, is able to operate the SCR system with the maximum possible NOx conversion efficiency and without NH3 slip