Text

theses

In ceramic powder processing, the correlations between the constituent particles and the product structure-property outcomes are well established. However, the influence of static powder properties on the dynamic bulk powder behavior in such advance powder processes remains elusive. A multi-scale evaluation is necessary to understand the full effects of the particle ensemble on the bulk powder behavior, ranging from the particle micro-scale to the bulk powder macro-scale. Fine powders, with particle size of 10 μm or less, often exhibit cohesive behavior. Cohesion in powders can cause poor flowability, affect agglomerate formation, as well as induce powder caking, all of which can be detrimental to the processing of the powders and/or final product structure-property outcomes. For this reason, it is critical to correlate the causal properties of the powders to this detrimental behavior. In this study, the bulk behavior of ceramic powders is observed under a simple powder process: harmonic, mechanical vibration. Four powder samples, two titania and two alumina powders, were studied. The main difference between the two powder variants of each material is particle size. The two alumina (Al2O3) powder samples had a primary particle size at 50% less than, or d50 of, 0.5 and 2.3 μm and the titania (TiO2) powder samples had a d50 particle size of 0.1 and 1 μm. Due to mechanical vibration, the titania powder variant with a primary particle size of 0.1 μm exhibited a clustering behavior known as auto-granulation. Auto-granulation is the growth of particle clusters within a dry, fine powder bed without the addition of any binder or liquid to the system. The amplitude and frequency of the mechanical vibration was varied to view the effect on the equilibrium granule size and density. Furthermore, imaging of cross-sections of the granules was conducted to provide insight into to the internal microstructure and measure the packing fraction of the constituent particles. As this auto-granulation behavior was unique to only one of the powder variants, an investigation was made into the differences in the powder fundamentals of the variants to identify the causal properties influencing the bulk dynamic behavior of all the powders in this study. The work performed in this thesis involved conducting extensive characterization of the properties of the powder samples. These properties ranged from micro-scale, discrete particle characteristics to viewing the bulk powder as a continuum material. The multi-scale linkages attained in this work provided an improved insight of cohesive behavior in powders to help guide improved structure-property outcomes in ceramic engineering.

ETD_6215

doi:10.7282/T3XP76ST

Ph.D.

Includes bibliographical references

by Nicholas Ku

ETD doctoral

The author owns the copyright to this work.