Company Germany
In many fields of application nanoparticles are employed to improve the properties of surfaces. Easy-to-clean coatings,
corrosion protection and fiber reinforcing are some examples. Unfortunately, particles in this size range are harmful to
health if inhaled and deposited in the respiratory tract.
For the resuspension of particles in gas flows, the ratio of the drag force to adhesion force is the determining criterion.
Larger particles easily detach from surfaces, but with decreasing particle size the decrease in drag force is larger than the
decrease in adhesion force. Furthermore even when using a turbulent airflow, there is a laminar sublayer at the surface,
reducing the effective drag force on the particles. Consequently, particles smaller than 10 µm are usually not removed
from a surface by air currents. For new nanoparticle-doted products this has to be proven by the manufacturer.
In the presented project, a test device that quantifies nanoparticle releases from surfaces has been developed. It focuses
on the particle reentrainment by drag force into an air flow. Furthermore it can be adapted to assess textile samples like
gas filters or clean room clothes with regard to particles released from the filter material.
The device consists of a nozzle and a sample carrier which can be moved in two directions. Through the nozzle, a
controlled side channel blower draws a flow rate of up to 20 l/min. The nozzle has a diameter of 5 mm. This narrow bore
hole is necessary to attain large shear stresses at low flow rates. Therefore, it becomes possible to avoid unacceptably
high dilution ratios. The examined sample can have a maximum area of 100 x 100 mm. It can be moved at a feed rate of
0 – 5 mm/s by a stepping motor. A controller enables the coverage of a selectable number of tracks. Consequently, a welldefined
scanning of a surface sample can be achieved.
The detection of the released particles is done by Condensation Particle Counter and a light scattering technique. Due to
the different detection limits of the particle detectors, a distinction between particles in the nanometer and the
submicron range at low concentrations is possible.
