Controlled formation of dielectric chain aggregates on material surfaces

This paper investigated the formation of chain aggregates from fine particles suspended in gas stream onto material surfaces under the action of electric field. The results showed that the shape of aggregate formed on material surface was greatly influenced by the field intensity and the surface condition of materials. In a weak electric field without corona discharge, particles tended to form clustered aggregates on a metal plate with smooth surface, but on a metal mesh and a porous alumina substrate, to form chain aggregate. On the other hand, in a corona discharge field, these surfaces were coated uniformly. Consequently, for forming chain aggregates on material surface, an electric field without corona discharge and a rough surface are necessary conditions. On rough surface, chain aggregates of dielectric particles or conductive particles grew from the protrusions of the surface and could form a rough and porous layer. When the external electric field was removed, the chain aggregates remained long time due to the Van der Waals forces. After sintered at proper temperature, the chain aggregates became fiber-like. The results indicate that the formation of chain aggregate can be controlled by electrostatic force, and sintering can be used as a method for increasing their mechanical strength. Introduction In the handling-processes of fine particles, the main problems are the adhesion of particles onto material surface, the agglomeration of particles, etc. As a method for controlling fine particles, electric field is widely used. Under the action of electric field, fine particles are agglomerated to large aggregates because of particle charging and dipole moment induced by the field, and collected on electrodes. Such aggregates can be classified into chain or cluster-like aggregates according to their shape. Frequently, the aggregates formed in electric field have very unpredictable shape, some more chain-like, some more clustered. In some cases, it is desirable to obtain a layer composed of chain aggregates on material surface, for example, fabricating catalytically active layer having large contact surface area. Thus, it is important to understand the relationship between electric field, the behavior of those aggregates, and the surface condition of materials. Furthermore, control the adhesion state of particles