(13g) Examination of the Microstructure of Granules of Ultra-Fine Powders Using Xrct

Examination of the Microstructure of granules of  Ultra-Fine Powders using XRCT

Nathan B. Davis¹, James D. Litster^{1, 2}

1 Department of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, IN 47907, USA

2 Department of Industrial and Physical Pharmacy, Purdue University, West Lafayette, IN 47907, USA

Davis459@purdue.edu, jlitster@purdue.edu

Many granulated products used in consumer goods, agricultural chemicals, pigments, and specialty chemicals are made from ultrafine primary particles (0.1-10 µm). However, the granulation behaviour of ultra-fine powders is poorly understood.  These materials are known to naturally agglomerate, potentially leading to complicated microstructures which are strongly dependent on the history of the powders prior to granulation.  The material behaviour is also known to be highly dependent upon the particle size range.  In order to better predict granule behaviour, it is important to describe and quantify the likely granule structures.

In this work, the changes in the granular microstructure are quantified as a function of the powder handling history using X-Ray Computed Tomography (XRCT).  Single-droplet granules are formed in static powder beds from powders with varied stress-strain histories.  The formed granules exhibit a variety of structures which range from large, discrete macropores to a diffuse pore network, dependent upon the primary particle size.  The smallest primary particles show a strong dependence the method by which the powder bed is created.  The use of different sized sieves (1.4 mm, 710 µm, 500 µm) to sift the powder create different histories that produce natural agglomerates of varying sizes dependent upon the primary particle size.  Aluminium oxide powder in various size fractions are used as model powders with water and PVP/H2O solutions used as model liquids.  The XRCT analysis can quantify different types of structures.