AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Comparison of the Ion Mobility Spectra of Four Different Bipolar Chargers
PETER KALLINGER, Gerhard Steiner, Wladyslaw Szymanski, University of Vienna
Abstract Number: 106 Working Group: Instrumentation and Methods
Abstract Well-defined charge conditioning of nanoparticles is a prerequisite for a number of particle measuring techniques. We investigated two different soft X-ray devices (TSI Advanced Aerosol Neutralizer and a custom-built unit), an AC-corona discharge device (MSP Corp. Electrical Ionizer), and a radioactivity based Am-241 charger as a reference. Electrical mobility size distributions of negative and positive ions produced in chargers due to different processes in a particle-free dry (below 2 % RH) air were measured with a high resolution DMA (Vienna Ultra-DMA operated at about 6.5 lpm aerosol flow and 550 lpm sheath air flow). The mobility spectra of the positive ions were found to be quite comparable for all chargers with a dominant peak at about 1.1 nm in terms of the equivalent electrical mobility diameter, whereas the spectra of the negative ions show a rather complex morphology. We did find that under certain conditions the commercial chargers need a warm up period of about 20 minutes to reach a stable negative ion mobility distribution. Nevertheless, the experimental results of nanoparticle charging show that charge conditioning by means of the AC-corona and soft X-ray created ions is very comparable to the charging results by radioactivity caused ions allowing the postulation that in all cases the Boltzmann-Fuchs charge equilibrium was obtained. Consequently both charger types can be used for charge conditioning of nanoparticles as an alternative to the radioactivity based nanoparticle charging devices.