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    High-Temperature Diffusion of Potassium in Silica
    (New York State College of Ceramics at Alfred University. Inamori School of Engineering., 2022-04) Schrock, Benjamin; LaCourse, William; Clare, Alexis; Möncke, Doris
    This work focuses on determining the diffusion coefficient of potassium in silica at high temperatures. Understanding this diffusion helps predict the final profile of optical fiber. This work also investigates several variables that may affect the potassium diffusion rate: viscous flow, oxygen diffusion, and water diffusion. The glass used in this experiment was HSQ300, a silica glass from Heraeus. The core of the glass cane was doped with ~1.2mol% potassium oxide. The cane underwent thermal cycling, then gradient index measurements were taken to trace the movement of potassium. Four thermal cycles were made on a glass-working lathe with a traversing set of hydrogen-oxygen burners that heated the cane for 31.5 minutes per cycle. The cane's surface was heated to 2256°C, and the equivalent temperature for diffusion in the core was calculated to be 1865°C. After four thermal cycles, the gradient index data showed a diffusion distance of 1.70mm. This resulted in a diffusion coefficient for potassium in silica D = (1.23 ± 0.54) x 10^-6 cm^2 /second. Further analysis indicated that potassium diffusion rate may have been influenced by water which diffused into the glass from the hydrogen-oxygen burner.
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    Synthesis of SiAlON Ceramics with Molecular Precursors as Additives
    (New York State College of Ceramics at Alfred University. Inamori School of Engineering., 2022-05) McGarrity, Kade A.; Shulman, Holly; Misture, Scott; Wang, Kun; Ding, Junjun
    Silicon nitride (Si3N4) and its related materials have been the subjects of research for 70 years and have garnered interest for applications ranging from cutting tools and bearings to turbine blades and spinal implants. The highly covalent nature of Si3N4 lends it exceptional structural properties such as high strength and hardness, but simultaneously renders it difficult to sinter. A few techniques are employed to ameliorate this challenge. The first is the generation of a solid solution of Al and O in the Si3N4 lattice, commonly through the use of Al2O3 powder, thereby reducing the covalency of the system and resulting in what is known as a SiAlON. The second is the incorporation of liquid phase sintering additives which enable a dissolution-reprecipitation sintering mechanism but which reside at the grain boundary after cooling as a relatively low-temperature glass. The present work investigates the incorporation of additives, including Al and O, via molecular-level precursors in order to tailor the sintering, microstructural evolution, and resultant structural properties of SiAlON ceramics. The first portion of this work demonstrates the incorporation of Al and O atoms with a very fine-scale homogeneous distribution via organometallic precursor aluminum tri sec-butoxide (ASB). A combination of chemical mapping, X-ray diffraction, thermogravimetric analysis, and differential thermal analysis was employed to investigate the pyrolytic decomposition of the organometallic precursor. Rietveld refinements were performed to assess the effectiveness of solid solution formation via the molecular precursor route to SiAlONs, in direct comparison to conventional Al2O3 powder-derived SiAlONs. Homogeneous distribution of Al which persists to at least 1000°C was achieved by the deposition of the organometallic precursor on starting Si3N4 powder surfaces, with no evidence of Al2O3 particle formation. Lattice refinements revealed that for various liquid phase concentrations and dwell times, the Al-organometallic more effectively facilitated the SiAlON solid solution than did Al2O3 powder. The second portion of this work investigates the incorporation of boron into the SiAlON system via precursor boric acid (H3BO3). Inspired by ultrahigh temperature polymer-derived ceramic SiBCN, this body of work aims to assess the roles of boron in a powder-route silicon-based ceramic system in the context of bonding, structural development, and ultimate structural properties. It was found through Raman spectroscopy and 11B SS MAS-NMR that boron exists in threefold coordination with nitrogen in the turbostratic boron nitride (t-BN) structure, similarly to in SiBCN. Increasing boron concentration in resultant SiAlONs results in a decrease in the population of both residual α-Si3N4 and second phases in the grain boundary, until a single phase β'-SiAlON was obtained at 3 wt% H3BO3. The grain size distributions of resultant SiAlONs were significantly narrowed by incorporating boron. Ultimately, fracture strength was increased from ~850 MPa to >1000 MPa by incorporating 3 wt% H3BO3. Subsequent in-depth fractographic analysis indicated that fracture origins of low-boron SiAlONs were predominantly inclusions consisting of either native material or foreign material from processing. However, boron-rich SiAlONs tended to fail from more elusive, less severe surface flaws such as machining cracks. It is proposed that the incorporation of boron reduces grain boundary diffusivity, mitigating abnormal grain growth or crystallization of second phases, effectively eliminating the worst flaw population in the present SiAlONs.
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    Development of Tests to Simulate Use Conditions and Fabrication of Additively Manufactured Ceramic Nozzles
    (New York State College of Ceramics at Alfred University. Inamori School of Engineering., 2022-04) Mahany, Timothy R.; Shulman, Holly; Sundaram, S.K.; Ding, Junjun
    Additive manufacturing (AM) allows for the rapid production of a desired shape, and enables the ability to modify the design before it is produced again. This can be a valuable tool in industry as a method for manufacturing prototypes, and larger runs of the same part, to an extent. There is a cost/benefit tipping point that is influenced by the complexity of the part, number of parts needed, frequency and value of design modifications, quality of parts produced, turnaround time, skill level of labor, infrastructure, profit margin for product, and other factors. AM of ceramics has lagged behind polymers and metals, as ceramic fabrication includes issues of shrinkage, distortion, and strength limiting process flaws. This AM alumina work was stimulated by a need in aerospace applications for a ceramic nozzle to replace a machined high temperature precious metal. This nozzles is an excellent test case for the rapid response of AM to develop a high value ceramic part. Technical ceramics can have superior characteristics, such as the ability to withstand high temperatures and high compressive forces, compared to other materials. Lithography-based Ceramic Manufacturing (LCM) is one of the current techniques that can be used for AM of ceramics. This work focused on producing nozzles out of Al2O3by means of LCM, and then subjecting the printed parts to internal pressure and thermal shock tests. To conduct pressure tests on the samples a custom apparatus had to be designed and produced to hold the sample while allowing the freedom to select the pressure that was applied. The testing jig was electronically controlled and allowed for a max pressure of 6.9 MPa (1,000 psi) to be tested. The printed Al2O3 parts were thermally shocked once to four different ΔT's; 300°C, 500°C, 700°C, 900°C. Each ΔT were then rapidly internally pressurized up to 205 times to two different pressures; 3.4 MPa (500psi), 6.9 MPa (1,000 psi). The ΔT's of 300°C and 500°C showed they could survive being thermally shocked and survive 6.9 MPa (1,000 psi). Whereas samples that had a ΔT of 700°C and 900°C received critical damage from being thermally shocked and could not handle any pressure.
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    Charge Storage in Defect Engineered Oxide Nanosheets
    (New York State College of Ceramics at Alfred University. Inamori School of Engineering., 2022-02) Flint, Madeleine N.; Misture, Scott; Pilgrim, Steven; Tidrow, Steven; Shulman, Holly
    Layered δ-MnO2 (birnessite) exhibits a unique response to the reduction of Mn4+ to Mn3+, where the reduced Mn3+ Jahn-Teller distorted octahedron creates a 'surface Frenkel defect.' The reduced Mn3+O6 octahedron migrates out of the the plane of the sheet and creates a vacancy within the sheet. The charged defect content may be controlled during flocculation of exfoliated nanosheets by equilibrating the nanosheet suspension in a pH regulated environment. It has been shown earlier that charged defects in δ-MnO2 improve electrochemical properties by increasing capacitance beyond 300 F/g, decreasing charge transfer resistance by a factor of 10, and improving life cycle stability. Building on earlier work, the present study aims to understand the synthesis of layered MnO2 and Mn-containing layered perovskites and their chemomechanical response during charge and discharge. X-ray total scattering, X-ray absorption spectroscopy, and Raman spectroscopy were employed to probe the chemomechanical response during electrochemical cycling of MnO2 electrodes in a custom-built electrochemical cell. While surface Frenkel defect content remained constant throughout electrochemical cycling, reversible reduction of Mn4+ to Mn3+ occurred, presumably within the sheet. MnO2 floccules equilibrated at a pH of 2 and 4 underwent 17% and 13% reduction from Mn4+ to Mn3+ upon K+ intercalation, respectively. Such reductions caused mechanical deformation of porous MnO2 electrodes and was found to be dependent on defect content and degree of restacking of the nanosheets. Floccules with a low degree of nanosheet restacking experienced lateral expansion upon K+ insertion of 0.7% and 0.5% for equilibration at a pH of 2 and 4, respectively, with no change in the interlayer (basal) direction spacing. However, MnO2 nanosheet floccules with a high degree of restacking experienced a 1.1% and 1.2% lateral expansion upon charging and a contraction in their basal direction of 1.7% and 0.7% for pH 2 and 4 samples, respectively. The interlayer contraction has been noted earlier, but largely eliminating the sheet-to-sheet stacking provides direct access to knowledge of the in-sheet chemomechanical response. Microstructures of air-dried and freeze-dried floccules as well as floccules with varying degrees of surface Frenkel defect content were similar. Surface Frenkel defect content remained constant across processing variations such as drying conditions and degree of restacking when equilibrated to the same pH.
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    Adhesion Studies with Ultra-Thin Glass
    (New York State College of Ceramics at Alfred University. Inamori School of Engineering., 2022-02) Fekety, Curtis; LaCourse, William; Sundaram, S.K.; Clare, Alexis
    A phenomenon was observed during work producing "ultra-thin glass" (<150μ thickness) where samples folded onto themselves displayed strong adhesion and served as a simple method to analyze contaminants in the process and packaging of resulting ware. Subsequent Contact Angle, Wedge Test, and T-Peel studies were performed to understand the baseline of Surface Free Energy (SFE) for this direct bonding and attempts were made to refresh aged and packaged samples through various cleaning steps to produce a similar effect. When results showed SFE change was minimal between aged, cleaned, and fresh glass and no treatments enabled similar direct bonding to fresh samples, 90° and 180° Peel Test with adhesive tapes and films were used as a surrogate to rank the effectiveness of attempted cleaning procedures. Such tests yielded widely ranging values inherent to known issues with peel testing, but provided useful data to calculate true adhesion values of just 2 - 2.5 N/m, which were 1 to 3 orders of magnitude less than the experimental values due to work absorbed by elastic/plastic effects when peeling the polymer adherend. Highly flexible glass samples do not experience plastic deformation, so studying direct bonded ultra-thin glass provides a unique perspective on adhesion studies by excluding plastic effects. It was also demonstrated that although the direct bonded samples had even lower peel strengths after initial separation, the bond strength was higher than strong tapes and even epoxy prior to edge-crack formation, showing the usefulness of direct bonding in optical materials and potential for future development.