Dry Powder Particle Size Analyses for Dry Powder Processes (Restriction or Recommendation)

Abstract

It is generally known that the results of particle size analyses done in liquid suspension are more reliable than those in a dry system. This stems from the fact that most principles are based on sedimentation or electric conductivity changes in liquids. With the development of laser diffraction instruments for particle size distribution, the dry powder measurement became quite significant. Although we know the difficulties of dispersion of very fine particles in gases, we have to take into account the great importance of sample preparation procedures for the wet technique. This involves the influence of suitable liquid, the proper dispersant and the time of dispersion, The topic of this work is comparison of the results obtained by dry and wet techniques on laser diffraction instruments evaluated by mass balance for air classification processes with a cut size under 10 micrometers. The comparison was carried out with different materials. Wet analyses were made with well-known instruments. The results are supplemented also by other principles of measurement. The accordance of analyses and mass balance for fractions of coarse and fine products with input material is greatly influenced by instrument quality. The differences in the results obtained with the same instrument by wet and dry techniques are relatively small even in the range of the low limit of the instrument. So it wouldn't always be necessary to make use of the wet technique, rather, more attention should be given to the quality and performance of the instruments.