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Browsing by Author "Dillinger, Benjamin Eugene"

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    Crush Strength Analysis of Hollow Glass Microspheres
    Dillinger, Benjamin Eugene (Virginia Tech, 2016-09-21)
    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.
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    A Parametric Study on the Effects of External Stimuli on the Aqueous Dissolution of Lithium Disilicate Glass
    Dillinger, Benjamin Eugene (Virginia Tech, 2021-06-11)
    The chemical resistance of glass is an important property for many applications. This property has been extensively studied for many types of glass under static conditions (no liquid is removed during the experiment). There has been little research conducted on the effects of additional stimuli on the dissolution of glass. For this research lithium disilicate was leached in deionized water at multiple temperatures while microwave radiation, ultrasonication or flow conditions were also applied to the system. These results were then compared to static baseline to determine if these stimuli would cause any change to the mechanisms and kinetics of the reaction. It was determined that for the experimental conditions used there was little to no change in dissolution when 2.45 GHz microwave radiation instead of conventional methods was used to heat the reaction. Results from ultrasonication found that samples that experienced erosion showed an increase in dissolution with an increase in dissolution following heavier erosion. This was thought to be due to both an increase in the surface area of the sample to volume of solution (SA/V) ratio (erosion would modify the surface area and release small particulates) and the accelerated removal of the depleted layer due to erosion. Stereoscopic reconstruction was used to semi-quantitatively measure the change in surface area. Regions that experienced minor erosion showed a 3-6% increase in surface area while those that experienced heavy erosion showed a 29-35% increase in surface area. Due to inconsistencies in the size of the eroded area it was not possible to determine the effects of power intensity with this research. Flow dissolution showed similar trends in concentration and different trends for the total normalized mass loss (TNL) to previously published research on more complex glasses. The elemental concentration initially increased before reaching a peak and decreasing to steady state. This peak was thought to be caused by the combination of flow, increasing thickness in the depleted layer, and an initial fluctuation in the forward reaction rate due to changes in pH. For the lithium disilicate glass used in this research both the elemental concentration and the TNL increased with increasing temperature and decreasing flow rate (silica dissolution was an exception as it did not show any change in TNL due to flow). All experimental conditions were shown to achieve steady state (dC/dt~0) by the seventh day of leaching. The contrast in the observed TNL trends between lithium disilicate and more complex glasses was thought to be due to differences in reaction rates and the presence of an additional surface layer in the complex glasses due to precipitation. Microscopy of the leached glass showed that surface features introduced during grinding (scratch lines and microcracks) were preferentially leached and grew in size and number visible during dissolution. A semi-quantitative model was created using stereoscopic reconstruction to describe the preferential leaching of the microcracks as there was little available discussion found in literature outside of associating the growth of these features with localized network dissolution. In this model the microcracks experience preferential dissolution leading to a change in size and shape. The SA/V ratio inside the crack would be much larger than the bulk system (calculated to initially be ~768,000cm-1 compared to the bulk's 0.1cm-1). This would cause massive acceleration in the initial ion exchange, raising the pH of the solution which would in turn cause network dissolution to occur much faster inside the crack. Based on static experiments on lithium disilicate frit (SA/V of 1,010cm-1) the pH inside the crack would jump to above 11 in minutes. As the crack grows, the SA/V ratio inside it would decrease (largest cracks were found to have a ratio ~100,000cm-1). The accelerated leaching caused by these features could have a noticeable effect on the dissolution results. In addition to the accelerated leaching inside a crack, the size of the depleted layer under the crack would be different from the bulk glass.