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Browsing Research and Scholarship by Author "Amoroso, Jake"

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    Durable Cr-substituted (Ba,Cs)1.33(Cr,Ti)8O16 hollandite waste forms with high Cs loading
    (Wiley, 2022-02) Misture, Scott; Zhao, Mingyang; Birkner, Nancy; Schaeperkoetter, Joseph; Koch, Robert; Russell, Patrick; Besmann, Theodore; Amoroso, Jake; Brinkman, Kyle
    A series of Cr-substituted hollandite solid solution BaxCsyCr2x+yTi8−2x−yO16 over a broad range of Cs content (x + y = 1.33, 0 ≤ x and y ≤ 1.33) were systematically investigated. A monoclinic-to-tetragonal phase transition was induced by increasing Cs content in the tunnel sites of the hollandite structure, and all members of the series show structure modulations related to the ordering of the Ba/Cs and vacancies along the tunnels. The thermodynamic stability of the Cr-substituted hollandite samples was measured via high-temperature oxide melt solution calorimetry, which included making the first measurements of the enthalpies of drop solution for Cs2O and BaO in sodium molybdate solvent at 800°C. Thermodynamic stability increased with increasing Cs content for the series of Cr-substituted hollandite, which also exhibited a greater thermodynamic stability compared to other substituted hollandite analogs including Zn, Ga, Fe, and Al variants. The leaching performance, also known as aqueous durability, demonstrated that the fractional Cs release in the Cr hollandite samples is much lower than in other hollandite systems. After 7 days of leaching at 90°C, the lowest Cs release was observed in the sample with the highest Cs content, approximately 22 wt.% Cs. The Cs release could be further suppressed, by approximately 3× if the sample was further densified and sintered. The Cs release results correlated inversely to the thermodynamic stability, suggesting that the thermodynamic stability may be used in future materials design for nuclear waste immobilization.
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    Synthesis, Characterization and Electrical Properties of the Sodium Conductor NaxGa4+xTi1-xO8 (X~0.7) and its Analogs
    (New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering., 2010-02) Amoroso, Jake; Edwards, Doreen
    The material NaxGa4+xTi1-xO8 (x~0.7) (NGTO) is believed to be a 1-dimensional conductor of sodium and, as such, has potential technological importance. Furthermore, the structure of NGTO is such that it possesses single dimensional tunnels (or channels) along which conduction is presumed to occur, which are large enough in size to accommodate a variety of alkali ions in addition to sodium. The focus of this work was two-fold: 1) prepare and characterize single crystal and polycrystalline NGTO samples and 2) replace the sodium in the NGTO with other ions (K+, Li+, Ag+) through a variety of methods and subsequently characterize these analogs. Initially, the synthesis of polycrystalline NGTO was explored and improved through the examination of batch components and processing methods. Attempts were then made to synthesize various alkali analogs. The thermal, electrical, physical, and chemical properties were studied using a multitude of characterization techniques. For polycrystalline NGTO, the total electrolyte conductivity varied among samples from approximately 10-7 – 10-5 (Ω-cm)-1 at 400°C to approximately 10-3 – 10-2 (Ω-cm)-1 at 1000°C. The activation energy was calculated to be between 0.86 – 1.08 eV. A bulk conductivity of ~10-2(Ω-cm)-1 at 550°C with an activation energy ~0.28eV was calculated for single crystal NGTO. For NGTO exposed to ion-exchange treatments, the measured conductivity decreased with increasing ion size for potassium and silver exchanged samples. However, samples exposed to lithium exchange treatments exhibited a lower conductivity than any of the other samples.