Influence of Thermodynamic, Material, and Bulk Properties on Electrical Resistivity of Particle Layers

Abstract

Although the influence of gas humidity and particle size distribution on dust resistivity is well known, the impact of thermic and electric balancing periods on the measurement of dust resistivity is less familiar. The dust resistivity of quartz glass (SiO2) and Al2O3 particle layers was measured and exhibits a non‐ohmic behavior as well as time dependence seen in a similar manner during electret formation. However, constant values of dust resistivity for the test dust were first measured after a rather long balancing period which cannot be explained in whole by adsorption and desorption kinetics of H2O into the particle layers. Rather, it could be presumed that the thermic and electric balancing periods overlap, whereas the electric balancing periods take a much longer time.

Preparation of Micron and Submicron Particles via Spray Drying and Electrostatic Precipitation

“…This phenomenon is known in the literature and named back‐corona. With increasing layer thickness at the collecting electrode, higher resistance is created – and thereby a higher potential drop in the particle layer 46, 48, 49. However, much higher drug contents were obtained compared to previous investigations 38.…”

“…The differences in drug content between the drug substances were attributed to varying charging performance. With materials like aluminum and silicium oxide [46], ashes [50], or organic compounds [51], it is due to varying electric properties [52]. Differences in the charging behavior of pharmaceutical, inhalable dosage forms were found, but the mechanism was not further analyzed [53,54].…”

“…Below this value, efficient particle precipitation is difficult due to reentrainment of particles from the deposited particle layer. A specific resistance above 10 11 Ωcm can cause back-corona effects due to the generation of a strong electric field within the particle layer [46,47]. To confirm the suitability of the chosen drug substances and the molten carrier (xylitol), the specific resistance was determined in accordance with Majid et al [41] (Tab.…”