Ralf Moos

P1GS.1 - Room Temperature UV-Enhanced NO2-Gas Sensing of Doped and Undoped Sol-Gel-Synthesized ZnO

ZnO is of interest for many applications, e.g. also for gas sensing. Here, sol-gel synthesized, nanosized ZnO is investigated with regard to its room temperature NO2 sensing behavior. It is shown that both doping and UV exposure shorten the response and the recovery times of the sensors. NO2 measurements were carried out with undoped, Sn-doped, and Al-doped ZnO sensors, respectively. The Al-doped samples provide the highest NO2-response. Furthermore, the effect of dry or humid atmosphere on the sensor response was investigated. The strong humidity influence on the sensor signal almost disappears with UV exposure. Hence, UV-light, nano-sized structure, and proper doping may be the key for room temperature NO2 sensing.

P1GS.21 - Dosimeter for Low-Level NOx Detection – Influence of the Deposition Method of the NOx Storage Film

The detection of low-level NOx concentrations and the dose of NOx for air-quality monitoring (AQM) is still a huge task and a widely discussed topic. Dosimeter-type NOx sensors detect directly the NOx dose and are advantageous considering mean value detection, linearity of sensor responses, and drift phenomena. The electrical properties of a NOx storage film, here potassium permanganate impregnated on alumina powder, depend linearly on the amount of sorbed NOx. The electrical resistance correlates very well with the amount of formed nitrate and nitrite species. The influence of the deposition method of the sensitive NOx storage material on the characteristic behavior of the dosimeter-type sensors is investigated. Aerosol-deposited dense films (ADM films) behave like porous thick-films, but typical sensor characteristics like detection limits and relative resistance changes seem to be different.

GS3.4 - Mixed-potential based direct catalyst conversion sensor: Independency of the sensor response from oxygen, electrode material, and from the type of analyte

On-board diagnostics (OBD), which ensures the functionality of exhaust gas aftertreatment systems of combustion engines, needs reliable gas sensors. Therefore, we investigate a sensor that is able to determine directly catalyst conversion (between 0 and 100%). A mixed-potential is formed at two similar electrodes connected to different gas atmosphere, e.g. upand downstream of a catalyst. Here, it is simulated by gas mixtures containing an analyte, e.g. a hydrocarbon. These mixtures can be adjusted so that different conversion of the catalyst is simulated. Identical analyte concentration indicate zero conversion and zero sensor response. The higher the catalyst activity is, the lower is the analyte concentration downstream of the catalyst and the mixed-potential at the second electrode increases. Theoretically, the sensor signal is only dependent on the conversion of the catalyst but on the analyte concentration of the feed gas. In this work, we verify these considerations for the first time also for the case of analyte mixtures, Au-electrodes, or varying oxygen contents.

A6.4 - Novel mixed potential sensor device to compare two gas compartments and to determine directly the conversion of an automotive catalyst

In this work, a novel sensor device is developed. It enables to compare two gas compartments electrochemically by applying the mixed potential sensing principle. Thereby, disadvantages that come along with the usually-used half-cell setups like indirect heating, complicated manufacturing and only destructive dismantling of sample and sealing are overcome. The device bases on an yttria-stabilized zirconia disc that is equipped with an integrated heater to provide a hot area in the center for sensing while at the same time it is cold enough at the outer radius for contacting with a polymer sealing (Oring). As an example for its functionality, the gas mixtures upand downstream of a catalyst were compared, while the sensor voltage correlates well with catalyst conversion.

Sensor stack for Tian-Calvet Calorimeter made in LTCC-Technology

Abstract The paper presents the construction and first tests of a new sensor stack for a Tian-Calvet Calorimeter made in LTCC Technology. In contrast to typical construction where wired thermocouples are directly connected, the here-presented solution replaces wired thermocouples by screen-printed thick-film thermocouples placed on a structured disc made of Low Temperature Co-fired Ceramics (LTCC). The advantage of screen-printed thermocouples is the ease of integration of them into thick-film hybrid structures, and to simplify the device setup. Moreover, using thermocouples integrated into a ceramic disc can increase the sensitivity of the system and simultaneously reduce the production costs. The paper shows the design and fabrication of the sensor stacks. It consists of several LTCC discs and ceramic spacers. On each LTCC disc, 34 Au/Pt thermocouples were deposited. The design of the disc was supported by FEM-modelling under consideration of device specific requirements. The very initial measurements, ...

Evaluation of screen-printable type S (Pt-PtRh) thermocouples on different ceramic substrates

Abstract The application of thermocouples as temperature sensors has been well known and has already been established for many years. However, for classical thick-film technology using screen-printing and firing, no standardized solutions exist. The here-presented newly developed PtRh thick-film compositions (90% Pt,10% Rh) allows to construct thick-film type S thermocouples (Pt/PtRh), following the IEC temperature characteristics. They can be fired in air, and therefore can be easily integrated into existing thick-film components and devices. In an earlier study, the new Pt-Rh composition was successfully tested on alumina substrates. Their electrical characteristics is equal with classical wire type S thermocouples. This study continues the investigations of thick-film thermocouples. We tested the newly developed pastes for high temperature applications on alumina substrates and evaluated the application of the new screen-printable type S thermocouples on LTCC ceramics. Three possible configurations wer...

3D-Shaping of Ceramic Tapes to Manufacture a High-Temperature Miniaturized Furnace

This contribution shows results of 3D-shaping experiments of ceramic tapes. The structures were made by wrapping structured tapes around a hexagonal alumina rod. After lamination, the rod was removed and the structure was finally fired, similarly as reported in [1]. One out of many possible applications of such structures is a miniaturized furnace for sintering of critical materials, which could contaminate expensive chamber furnaces, for tempering of single gas sensors, or for fast heating at controlled rate. While LTCC technology can be applied only up to 600–700 °C, application of HTCC tapes can extend temperature range to above 1000 °C. Therefore, 99.99% alumina tape (ESL 44007) was used. The here-shown miniaturized furnace has a hexagonal form. For a proper temperature distribution in the furnace chamber, the furnace was equipped with six platinum heaters that can be controlled independently. Finite Elements Analysis (FEM) supported the design process. The paper discusses manufacturing route, beginni...

P2.8.5 Sensing of NO, NO2, and NH3 with Zeolite-Based Impedimetric Gas Sensors

In this study, the suitability of zeolites for two different sensor principles is investigated. Zeolites can change their electrical properties with the sorption of gas molecules in their microporous network structure. Therefore, they are potential materials for impedimetric gas sensors. The screened zeolites H-ZSM-5, Fe-ZSM-5, Pt-loaded H-ZSM-5, and Pt-loaded Fe-ZSM-5 are tested for their sensitivity towards NO, NO2, and NH3 at varying temperatures. The two different sensor principles are considered: the integratingor accumulating-type sensing behavior at low temperatures and a conventional gas sensor behavior at high temperatures. At high temperatures, only the expected response towards NH3 occurs, whereas at low temperatures a cross effect towards NOx could be observed for H-ZSM-5 and Fe-ZSM-5. The sensor behavior seems to be an integrating one at 200 °C for NO and NO2. By inserting elementary platinum the sensitivity towards NO and NO2 was eliminated due to a higher catalytic activity of the Pt-loaded zeolite. At temperatures of 400 °C and 500 °C, the Ptloaded zeolites show no response even not towards NH3.