Formation of Hollow Granules from Hydrophobic Powders
Granulation of poorly wetting powders is a common problem in the pharmaceutical, minerals and fertilizer industries. It is usually assumed that good wetting is a prerequisite for good nucleation. Although this is generally true, robust granulations with poor wetting powders are possible. Recent investigation confirmed that nucleation can occur by spreading of hydrophobic sub-micron particles around the droplet, termed “solid spreading nucleation”. Moreover, nuclei formed consist of a consolidated powder shell and an empty core, and have extremely high porosity with adequate strength.
In this study, single drop solid-spreading nucleation experiments were performed, where single drops of water and glycerin were produced using a microlitre syringe and placed on to loosely packed powder beds. Several powders including salicylic acid, 2-Ethoxybanzamide and three size grades of hydrophobic glass ballotini were used. Nucleus formation was observed via high speed video camera and a microscope. This paper will present the experimental results of particle motion and solid shell formation as a function of powder and liquid variables.