Investigation of airborne nanopowder agglomerate stability in an orifice under various differential pressure conditions

The stability of agglomerates is not only an important material parameter of powders but also of interest for estimating the particle size upon accidental release into the atmosphere. This is especially important when the size of primary particles is well below the agglomerate size, which is usually the case when the size of primary particles is below 100 nm. During production or airborne transportation in pipes, high particle concentrations lead to particle coagulation and the formation of agglomerates in a size range of up to some micrometers. Binding between the primary particles in the agglomerates is usually due to van der Waals forces. In the case of a leak in a pressurized vessel (e.g. reactor, transport pipe, etc.), these agglomerates can be emitted and shear forces within the leak can cause agglomerates to breakup. In order to simulate such shear forces and study their effect on agglomerate stability within the airborne state, a method was developed where agglomerate powders can be aerosolized and passed through an orifice under various differential pressure conditions. First results show that a higher differential pressure across the orifice causes a stronger fragmentation of the agglomerates, which furthermore seems to be material dependent.