Publikationsserver der RWTH Aachen University
Untersuchungen der elektrochemischen Eigenschaften pH-sensitiver Feststoffsensoren in unpolaren Flüssigkeiten
Abstract
dc:descriptionThe area of electrochemistry of non aqueous non-polar liquids has not been intensely studied. Coming from the issue of electrochemical sensors on non-polar liquids the analysis of lubrication oils in the engine of a motor vehicle was taken as an example. The investigation of electrode materials in these media appears interesting from a scientific as well as from a technical approach. An overview of the basics of oil chemistry emphases the importance of additives for the formulation of lubricating oils. These improve the characteristics of the carbon hydrates in important areas (viscosity, stability etc.), and make the quality of modern engine oils possible. With the introduction of a controlled aging process of the oils in combination with a classical wet chemical analysis the fabrication of oils with defined grades of degradation was possible. First, an overview of known technical concepts on oil condition measurement was given. This broad field of physical and electrochemical methods was enlarged by the first application of the SPME technique. With this method, polar substances were identified in the gas phase of the oil. Through gas and mass chromatography it was shown that these substances were mainly additives, their by-products and organic acids. The amount of these changes with ongoing aging of the oil and can thereby be used as an indicator for the oil condition. Only organic acids with seven carbon atoms or more were detected. These organic acids should be detected via a simple and robust sensor. Looking back at the known measurement concepts, potentiometry was identified and the electrochemical basics were shown. For the fabrication of the electrodes materials were used that are known to show a pH-sensitive behaviour: iridium(IV) oxide, ruthenium(IV) oxide and antimony electrodes were produced using screen printing, sputtering and galvanic deposition. The electrodes were then physically characterized. From the area of gas sensors it is known that often no rational parameters can be given for the tuning of the desired performance of the sensor. Small changes during fabrication or the microstructure of the sensor can have grave influence on the performance. This fact founded the area of combinatorial chemistry. In view of this area, concepts were developed to also use this approach in this work. A combinatorial screen printing technique was implemented and combined with a robotic based measurement of these substrates. The sensors were electrochemically characterized. First, their principal function in water was demonstrated. There, the sputtered sensors should a response closest to the theoretical Nernstian behaviour. As model media for non-polar fluids with low permittivity decane was chosen. Here, the screen printed iridium(IV) oxide sensor showed the best performance. A measurement in oil also showed a changing potential when the acid content was changed. This potential change though was going in the other direction as with water and decane. Finally, a qualitative model of the electrochemical reactions was developed. With some systems, the behaviour could be explained. The different course of the potential in oil can be explained by the adsorption of additive molecules to the surface of the electrode. Therefore, only secondary reactions can be seen there which are due to residual water on the surface and certain additives in the oil.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2009
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
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- Müller, Andreas
- Contributors dc:contributor
-
- Simon, Ulrich
Subjects
dc:subject × 10Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger