Penetration of Ultrafine Particles and Ion Clusters Through Wire Screens

Penetration of nanosized particles and ion clusters through a wire screen has been studied experimentally. Particles were generated by (1) evaporation- condensation or (2) corona discharge upon a vapor mixture of water and benzene. Ion clusters were produced by passing air containing organic vapors through an Am-241 ionizer. The theory of Cheng and Yeh predicts reasonably well the penetration of particles with sizes down to about 2 nm. For smaller particles, penetration attains a constant value seemingly dependent on the chemical nature of the material. Neither the constancy of this value nor its dependency on material properties can be explained by this theory. Inclusion of thermal rebound phenomena (sticking probability) in the model would probably explain the observed results. Although such a model currently exists, it is not possible to test its validity because the required mechanical and adhesion properties of the materials involved are not available at present.