Preparation of controlled particulate mixtures with glass beads of different sizes

摘要

A method of mixing/preparing binary and ternary mixtures of glass beads was developed using a viscous solution of glycerolin water. After mixing, the mixture was transferred to a prismatic vessel and glycerol was washed out. The different sized beadswere differently coloured and digital pictures taken from each face were automatically treated by image analysis to determine thecoloured fraction present in each face. Statistical analysis showed that no significant deviation existed in the colour distribution ofeach of the four faces.Achi-square test showed that a uniform distribution could be accepted for the beads, no segregation of beadsize nearby the edges was observed and that no wall effect was present. The two-dimensional picture obtained by image analysiswas converted to the corresponding three-dimensional distribution, from which the expected bed porositywas inferred. The porositypreviously estimatedwas compared with the experimental porosity determined by gravimetry directly on the bed.Nosignificantdeviations were found, thereby proving that the mixing method developed was reliable. Hundreds of experiments were doneshowing a very high reproducibility. The developed methodwas further used for studies on mixing of binary and ternary mixtures.In certain conditions (mixtures enriched with large size particles and having a significant difference in size) a segregation layeringeffect took place and the bottom layer presented a composition corresponding to the packing with the smallest porosity possible.