AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Estimating the Primary Particle Size of an Agglomerate Using APM and SMPS
MIKA IHALAINEN, Terttaliisa Lind, Jorma Jokiniemi, Paul Scherrer Institut, Switzerland
Abstract Number: 746 Working Group: Instrumentation and Methods
Abstract Evaluating the size of the primary particle in an agglomerate traditionally requires the use of the microscopy methods. Being able to measure the primary particle size online would make the analysis not only much faster but also cheaper. One possible approach to tackle the problem could be the measurement of size dependent effective density of the agglomerates and utilising it in addition to the bulk density of the agglomerate material to estimate the primary particle size.
The method to estimate the primary particle size was the following. An aerosol particle mass (APM) analyzer combined with a scanning mobility particle sizer (SMPS) was used to calculate the size dependent effective density of the agglomerates. The relation between the electrical mobility diameter and the effective density could be described with a power law. An asymptotic extrapolation was then made to see at which electrical mobility particle size the effective density would reach the bulk density of the material and, thus, revealing the primary particle size. The method assumes that the power law relation between the electrical mobility and effective density holds over the size range from the size of the primary particle to the agglomerate size and that the size distribution of the primary particles is monodisperse.
TiO2 agglomerates of different primary particle diameter were generated through chemical vapor synthesis to test the described method. Transmission electron microscopy (TEM) was used as a reference method to measure the primary particle sizes. The preliminary results show that for the primary particle sizes 37, 26, 22 and 10 nm measured with the TEM while the APM-SMPS system gave 43, 27, 23 and 5 nm, respectively. The results show that while there were variations in the primary particle size results measured with the APM-SMPS system compared to the TEM method, it still gave reasonably good estimations of the primary particle size.