Characterization of four different bipolar charging devices for nanoparticle charge conditioning

Well-defined charge conditioning of nanoparticles is a prerequisite for a number of particle measuring techniques. We investigated two different soft X-ray devices (custom-built and TSI advanced aerosol neutralizer) an AC-corona discharge device (MSP electrical ionizer) and a radioactivity based Am-241 charger as a reference. Electrical mobility size distributions of positive and negative ions created in all devices were determined and their applicability for particle charging examined. The mobility spectra of the positive ions were found to be quite comparable for all chargers with a mean mobility of 1.50-1.60 cm(2) V-1 s(-1), whereas the spectra of the negative ions show differences in morphology leading to a broader range of mean mobilities (1.68-2.09 cm(2) V-1 s(-1)). However, results confirm that under the selected experimental conditions the charge equilibrium related to bipolar diffusion charging process was obtained in all charging devices.