Browsing by Author "Lee, Hyojin"

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    Conditions of Powder Flow and Fill
    (2020-05) Kotze, Samantha J.; Fowler, Ryan M.; Carty, William; Gaustad, Gabrielle; Lee, Hyojin
    Understanding the conditions that contribute to powder flow are essential to anticipate the segregation of particles in flow situations. Although various methods are used to quantify powder flow and powder fill in industry, these methods fail to properly capture observed behavior, particularly as the particle size decreases, thereby failing to accurately predict powder flow, fill, and packing outside of a specific process. It is unclear if there is a specific boundary below which particle flow will not occur. The hypothesis of this study is that there is a correlation between particle size, density and flow behavior, and there is a critical particle mass necessary for free flow. This study analyzes the flow behavior of a broad range materials, including glass sphere standards 1018a, 1017a, and NBS 1003. The flow of these powders was analyzed by inclining a roughened copper plate until particles began to tumble. The copper plate dissipated electrostatic charge. The angles of both the onset of flow, when the first observation of movement occurred, and critical flow, where all the powder flowed, were recorded. Although two flow angles were identified for some of the powders, this does not necessarily mean there are two different flow behaviors. Rather this study purposes that the first flow is agglomerate or large particle flow and critical flow is either true powder flow or the gravitational forces overcoming the interparticle forces. The samples were imaged by SEM to estimate particle size for initial and critical flow. It can be concluded that the powder flow data is not affected by density and is mass independent.
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    Constructing Ancient Korean Celadons for Modern Firing Cycles
    (2022-12) Dunham, Grace; Carty, William; Lee, Hyojin; Kelleher, Matt
    Ancient sherds and samples collected from Gangjin and Gimjae celadons (Koryŏ period, 918-1392 CE) were previously analyzed to determine the firing conditions and to evaluate the body and glaze chemistry. Those results show that ancient samples were fired with three- or four-day long soak time at temperatures between 1000°C – 1200°C. The firing conditions of ancient Korean celadons produce a deep glaze-body interaction zone that is responsible for the optical characteristics of the glaze. To mimic the optical effects of ancient Korean celadons in modern firing cycles, the depth of the glaze-body interaction can be obtained using a two-layer glaze system. A two-layer glaze system was created that mimics the microstructure observed in the glaze-body interaction zone of the ancient samples. Color analysis by spectrophotometry, as well as chemical content and distribution mapping via SEM/EDS were used to evaluate the two-layer glaze system. Analysis of these data indicate similar optical effects and chemistry as presented in ancient Korean celadon samples.
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    Development In-Situ Platelet Reinforced Alumina
    (2022-05) Jensen, David; Carty, William; Lee, Hyojin; McGowan, Garret
    It has been shown that alumina is a strong ceramic material, but it typically exhibits poor fracture toughness. Recently, studies have found that liquid-phase sintered alumina containing an invert glass (i.e., high calcium with low silica) can precipitate what appear to be high-aspect ratio needle-like crystals that have been determined to be calcium hexaluminate (CaO·6Al2O3, CA6). In this study, the chemistry and processing conditions used to create the first specimens were revisited and it was determined how the sintering conditions contributed to densification of the alumina matrix and the size and population of the CA6 precipitates. While keeping the ratio of CaO:SiO2 constant, it was observed that the number of CA6 precipitates appeared to increase in number and size with increased CaO and SiO2 level (that is, with more liquid phase). In addition, it appears that the precipitates are nont needles, but platelets. The sintering conditions had little contribution to the size and concentration of the precipitates but were found to aid in the densification of the alumina matrix. The ability to control the size and concentration of these grains may have the potential to affect the fracture toughness of alumina, but this is beyond the scope of this work.
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    Development of a Two-Parameter Model to Describe Particle Size Distributions
    (2021-05-10) Ciccarella, Mark A.; Carty, William; Lee, Hyojin; Keenan, Timothy J.
    Particle size distributions present a unique challenge for analysis and presentation and simply reporting the D50 value fails to capture any information that describes the width of the distribution. By fitting the particle size distribution to a statistical model, it is possible to describe a distribution with a two-parameter model, similar to that obtained from a Weibull analysis of mechanical testing data. In fact, as is demonstrated in this thesis, many native particle distributions actually fit a Weibull distribution, but when the distribution is scalped, as is common for industrial powders, the distribution is better described with a log-normal model. Both of these distribution types can be described by a mean and a modulus, and thus a two-parameter model. The two-parameter model can then be plotted on x-y coordinates to allow the tracking of particle size distributions for milling studies or for quality control purposes.
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    Evaluation of the Hardness of Alkaline Earth Aluminosilicate Glasses
    (New York State College of Ceramics at Alfred University. Inamori School of Engineering., 2021-12) Lee, Hyojin; Carty, William; LaCourse, William; Möncke, Doris; Keenan, Timothy
    The hardness of alkaline earth aluminosilicate glasses was evaluated focusing on the alumina level and atomic packing density of the system. To identify the compositional matrices, a comprehensive investigation was conducted to determine the glass formation region in ternary aluminosilicates (R2O∙RO∙Al2O3∙SiO2). Vickers hardness of the glasses were evaluated in steps: the calcium aluminosilicate system; a range of RO or R2O modifiers, including blended flux systems; and finally, the introduction of a high valency cation into the high hardness glasses to locally increase the density of the glass structure. The alumina edge of the glass formation boundary was similarly defined by a fixed molar ratio of 1.2 (±0.1) Al2O3 to R2O (Na2O or K2O), RO (MgO, CaO, etc.), or a mixture of fluxes (R2O+RO) over a broad range of silica levels and was shown to be independent of cooling rate. The alumina saturation level determined the experimental matrix to prepare samples for hardness measurement. The hardness results for CaO-Al2O3-SiO2 glasses demonstrated that hardness is strongly related to the alumina level and that the hardness of CAS glasses correlates with the melting behavior as predicted by the phase diagram. The hardness of CAS and MAS glasses were similar, ranging from 6.7 GPa to 7.2 GPa, and the replacement of CaO with MgO produced only a marginal increase in hardness. Conversely, the blending of CaO with SrO and BaO generally resulted in a decrease in hardness. The sensitivity to alumina and silica levels, however, was much greater ranging from ~4.5 to a maximum of ~8.2 GPa. Finally, high valency cations (Mo6+) were added to high hardness CAS glasses. High valency cations should have locally increased the compactness of the glass structure and thus enhanced the indentation hardness, but there was no increase in hardness. Mo serves as a heterogeneous nucleation site for crystallization resulting in anorthite precipitation. While there was a clear trend of increasing hardness with increasing Cation Field Strength (CFS), this trend did not extend to the introduction of high valency cations did not show further improvement in hardness. Overall, it was concluded that, in general, the hardness of aluminosilicate glasses correlates to melting behavior, and that within specific compositions, with the composite CFS of the modifier cations.
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    X-Ray Detection of Crystalline Particles in Amorphous Solids
    (2019-12-07) Rogers, Shannon R.; Carty, William M.; Lee, Hyojin; Stevens, Mackenzie
    It is relatively common to refer to glass samples as “completely amorphous” when the correct term should be “X-ray amorphous” meaning that crystalline particles are not detectable by X-ray diffraction. The threshold detection limit of crystalline material in a glass is dependent on several variables including the particle size, molecular weight of the glass, and the diffraction efficiency of the crystalline particle. Several powders, including Al2O3, ZrO2, ZrSiO4, quartz (SiO2), SiC, CeO2 and Si3N4, were mixed (via milling) with commercial glass frits ranging from 0.1 to 3.0 volume percent (v/o) and then measured with powder X-ray diffraction. The particle size and density of the crystalline powders was varied while keeping the volume fraction similar. The results show that the average atomic number of the glass frit contributes to X-ray scattering significantly increasing the detection threshold for crystalline particles.