Porous Wall Hollow Glass Microspheres (PWHGMs) were developed by the Savannah River National Laboratory. What makes these microspheres unique is the interconnected porosity spread throughout their wall allowing various materials to travel from the surface to the hollow interior. With their characteristic porosity, the PWHGMs are a great tool for encapsulating or filtrating different materials. Unfortunately, there is little information available on the mechanical properties of PWHGMs. The main goal of this research was to develop a method to crush individual microspheres and statistically analyze the results. One objective towards completing this goal was to measure the microsphere diameter distribution. Microsphere diameter is a major factor affecting strength as well as the Weibull parameters. Two different methods, microscopy counting and laser light scattering, used in the research yielded similar distributions. The main objective of this research was to analyze the crush strength of individual microspheres. Using nanoindentation, data were collected to analyze the crush strength of PWHGMs in uniaxial compression. Nanoindentation data were used to analyze how the strength of the PWHGMs changes through the different stages of production and at different diameter ranges. Data for 3M commercial microspheres were compared to ARC microspheres. Most data were analyzed using a statistical technique known as the two parameter Weibull analysis. The data indicated that the strength generally decreased as the microsphere diameter increased. Scattering in the data was nearly the same across all sample sets tested. Results indicated that the PWHGMs were weaker than the ARC hollow glass microspheres (HGMs). This is primarily due to the addition of wall porosity in the PWHGM.

It was hypothesized that bauxite digestion may be improved by using microwave heating as it has been shown in literature that some material processes have improved efficiency. To test this hypothesis, a set of digestion experiments were conducted using gibbsite, one of the major minerals in bauxite. Gibbsite was digested at various temperatures (50, 75, and 95°C) in either 1M or 6M sodium hydroxide solutions for 30 minutes using either a convection oven or a 2.45 GHz microwave applicator. Results show that microwave heating provided an increase of 5-7% in the digestion after 30 minutes and required around 1/10 th the time to heat the solutions compared to conventional heating. Electromagnetic simulations show that preferential heating occurs at the solution surface creating a temperature gradient within the solution. Although vigorous stirring of the solution was used to minimize the temperature gradient, it could still be responsible for the observed difference in digestion. Digestion of bauxite itself yielded similar results to the gibbsite.

There has been little research conducted on how ultrasonic cavitation may affect glass dissolution. The focus of this study was to examine how the mechanisms and kinetics of glass dissolution may change in a system that included ultrasonication. Experiments were conducted on lithium disilicate glass in deionized water at 50 °C between 1 and 7.5 h. Results showed that the erosion from ultrasonication affected the kinetics of glass dissolution. Samples with erosion had 2–3 × more dissolution compared to samples without erosion. The change in dissolution was thought to be partly caused by an increase in the surface area of the sample to volume of solution (SA/V) ratio due to the roughening of the surface and release of particulates and a reduction in the size of the depleted layer due to erosion. Stereoscopic 3D reconstruction of eroded samples was used to calculate the increase in surface area due to erosion. Type 2 surface areas (exfoliation mixed with normal leaching) were roughly 3–6% greater while Type 3 surface areas (heavy roughening of surface) were roughly 29–35% greater than the surfaces areas from Type 1 surfaces (normal leaching).

No abstract