Untersuchungen zum Anwendungsbereich und zur Steigerung der Nachweisempfindlichkeit eines Partikelmassenspektrometers (PMS)

In the present work the applicability and the improvement of the detection sensitivity of a particle mass spectrometer (PMS) were studied. The PMS was originally used by Hospital and Roth for the investigation of the growth of soot-particles produced in combustion processes. It consists of a molecular beam sampling system and a high vacuum chamber which contains the necessary measurement instrumentation for the in-situ particle sizing.

Three reactors were employed to investigate the applicability: a low-pressure flame reactor, a microwave reactor and a spark reactor. The reactors are different in respect of the energy transfer into the reactive gases and the bulk material respectively. The flame reactor was used to produce well-known soot particles as reference particles for the experiments related to the improvement of the detection sensitivity of the PMS. Soot-, Silver-, Carbon-, Siliconoxide-, Tinoxide and Nickel- Nanoparticles were produced. The results have shown that the applicability of the PMS could be extended and be applied to particles generated in the microwave reactor as well as in the spark reactor.

Neutral charged Soot- and Tinoxid-Nanoparticles which were produced in the flame reactor were charged by electron impact ionisation in the high vacuum chamber of the PMS. The charging effect increases with decreasing amount of charged particles in the aerosol. Thus, in the case of neutral or weakly charged aerosols the particles could be characterised with the PMS leading to a further extension of the application range.

A new detector was developed to improve the detection sensitivity of the PMS. The detector consists of a secondary electron multiplier (SEM) and an external conversion dynode. The dynode was set to a high electrical potential. Thus, the particles were accelerated to a velocity which is sufficient to release secondary electrons or ions from the dynode after the impaction of the particles with the surface of the dynode. Afterwards these secondary electrons and ions respectively were amplified by the SEM. In comparison with the conventional detector, a Faraday-Cup, an increase of the signals of about 105 was achieved with this new detector.


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