Publications by authors named "Carsten Steiner"

4 Publications

  • Page 1 of 1

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film CeZrO by a Resonant Nanobalance Approach.

Materials (Basel) 2021 Feb 5;14(4). Epub 2021 Feb 5.

Institute of Energy Research and Physical Technologies, Clausthal University of Technology, 38640 Goslar, Germany.

Bulk ceria-zirconia solid solutions (CeZrO, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures O in the range of 10-0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO-ZrO as compared to CeO and ZrO were observed. A comparison of temperature- and O-dependences of the non-stoichiometry of thin films with literature data for bulk CeZrO shows enhanced reducibility in the former. The maximum conductivity was found for CeZrO, whereas CeZrO showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and O of 10 bar. The defect interactions in CeZrO are analyzed in the framework of defect models for ceria and zirconia.
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http://dx.doi.org/10.3390/ma14040748DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7915746PMC
February 2021

Determination of the Dielectric Properties of Storage Materials for Exhaust Gas Aftertreatment Using the Microwave Cavity Perturbation Method.

Sensors (Basel) 2020 Oct 23;20(21). Epub 2020 Oct 23.

Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95440 Bayreuth, Germany.

Recently, a laboratory setup for microwave-based characterization of powder samples at elevated temperatures and different gas atmospheres was presented. The setup is particularly interesting for investigations on typical materials for exhaust gas aftertreatment. By using the microwave cavity perturbation method, where the powder is placed inside a cavity resonator, the change of the resonant properties provides information about changes in the dielectric properties of the sample. However, determining the exact complex permittivity of the powder samples is not simple. Up to now, a simplified microwave cavity perturbation theory had been applied to estimate the bulk properties of the powders. In this study, an extended approach is presented which allows to determine the dielectric properties of the powder materials more correctly. It accounts for the electric field distribution in the resonator, the depolarization of the sample and the effect of the powder filling. The individual method combines findings from simulations and recognized analytical approaches and can be used for investigations on a wide range of materials and sample geometries. This work provides a more accurate evaluation of the dielectric powder properties and has the potential to enhance the understanding of the microwave behavior of storage materials for exhaust gas aftertreatment, especially with regard to the application of microwave-based catalyst state diagnosis.
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http://dx.doi.org/10.3390/s20216024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7660336PMC
October 2020

Catalyst State Diagnosis of Three-Way Catalytic Converters Using Different Resonance Parameters-A Microwave Cavity Perturbation Study.

Sensors (Basel) 2019 Aug 15;19(16). Epub 2019 Aug 15.

Bayreuth Engine Research Center (BERC), Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.

Recently, radio frequency (RF) technology was introduced as a tool to determine the oxygen storage level of a three-way catalyst (TWC) for gasoline vehicles. Previous studies on the investigation of commercial catalysts mostly use only the resonant frequency to describe the correlation of oxygen storage level and RF signal. For the first time this study presents a comparison under defined laboratory conditions considering both, resonance frequency and also the quality factor as measurands. Furthermore, various advantages over the sole use of the resonant frequency in the technical application are discussed. Experiments with Ø4.66'' catalysts and Ø1.66'' catalyst cores with alternating (rich/lean) gas compositions showed that the relative change in signal amplitude due to a change in oxygen storage is about 100 times higher for the inverse quality factor compared to the resonant frequency. In addition, the quality factor reacts more sensitively to the onset of the oxygen-storage ability, and delivers precise information about the necessary temperature, which is not possible when evaluating the resonant frequency due to the low signal amplitude. As investigations on aged catalysts confirm, the quality factor also provides a new approach to determine the ageing state of a TWC.
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http://dx.doi.org/10.3390/s19163559DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6719166PMC
August 2019

Planar Microstrip Ring Resonators for Microwave-Based Gas Sensing: Design Aspects and Initial Transducers for Humidity and Ammonia Sensing.

Sensors (Basel) 2017 Oct 24;17(10). Epub 2017 Oct 24.

Department of Functional Materials, University of Bayreuth, 95447 Bayreuth, Germany.

A planar microstrip ring resonator structure on alumina was developed using the commercial FEM software COMSOL. Design parameters were evaluated, eventually leading to an optimized design of a miniaturized microwave gas sensor. The sensor was covered with a zeolite film. The device was successfully operated at around 8.5 GHz at room temperature as a humidity sensor. In the next step, an additional planar heater will be included on the reverse side of the resonator structure to allow for testing of gas-sensitive materials under sensor conditions.
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http://dx.doi.org/10.3390/s17102422DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5677052PMC
October 2017