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Tucker, P. C. (2012). Synthesis of Cerium Rich Intermetallics Using Molten Metal Eutectics. Retrieved from http://purl.flvc.org/fsu/fd/FSU_migr_etd-5450
Metal eutectic fluxes are useful for exploratory synthesis of new intermetallic phases. In this work the use of cerium/transition metal eutectics such as: Ce/Co, Ce/Ni, and Ce/Fe have yielded many new synthetically and magnetically complex phases. Structural units that were previously observed in phases grown in La/Ni eutectic reactions have also been observed in new structures and analogs grown from cerium/transition metal eutectics. These structural units include a main group element coordinated by 9 rare-earth atoms (such as the Al@Ce9 clusters seen in Ce31.0(2)Fe11.8(5)Al6.5(6)B13C4), trigonal planar FeC3 units (also seen in Ce31.0(2)Fe11.8(5)Al6.5(6)B13C4), iron clusters capped by light elements (Fe46 frustrated tetrahedral in Ce21Fe8M7C14, and larger Fe clusters in Ce33Fe14B25C34). Variants of these building blocks were observed in Ce10Co2B7C16 with square Co units and chains of B and C connected to them, Fe2C8 units observed in Ce7Fe2C9, and FeC4 observed in Ce4FeGa0.85Al0.15C4 and Ce4FeAlC4. Two new phases were grown from Ce/Fe eutectic, Ce33Fe14B25C34 and Ce33Fe13B18C34 which exhibits very similar structures, but significantly different magnetic behavior. Structurally these two phases are similar. Both crystallize in the Im-3m space group, but differ by the centering of the Fe clusters. Ce33Fe14B25C34 contains Fe clusters centered by B atoms and Al doped on the Fe2 site. In Ce33Fe13B18C34 , the Fe cluster is a perfect cuboctahedron. Ce33Fe14B25C34 exhibits mixed valent behavior of cerium at 75K and no magnetic moment on iron, where-as Ce33Fe13B18C34 exhibits tetravalent cerium and its iron clusters undergo a ferromagnetic transition at 180K. Another borocarbide, Ce10Co2B7C16 was synthesized from Ce/Co eutectic flux. This structure features squares of Co surrounded by chains of C and B and a sea of cerium atoms. Temperature dependent magnetic susceptibility measurements at 1 Tesla were fit to a modified Curie-Weiss law and a moment per Ce was calculated to be 2.70µB. Field dependent data were collected at 200K and 2K. Paramagnetic behavior dominated at 200K and at 2K, ferromagnetic behavior was observed. XPS measurements were used to confirm that Ce is in the 3+ oxidation state. Intermetallics containing different Fe clusters (Y5Mg5Fe4AlSi, La6Fe10Al3Si, Ce21Fe8Al7-xSixC12, and Ce33Fe13.1Al1.1B24.8C34) were explored as potential catalysts for conversion of methane to Carbon Nanotubes (CNT). Different growth temperatures were explored. At 690ºC, Ce33Fe14B25C34 catalyzed the growth of single walled carbon nanotubes, Ce21Fe8Al7-xSixC12 multiwalled carbon nanotubes, and all other structures did not catalyze the growth of CNT.
A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Bibliography Note
Includes bibliographical references.
Advisory Committee
Susan Latturner, Professor Directing Dissertation; Naresh Dalal, Committee Member; Michael Shatruk, Committee Member.
Publisher
Florida State University
Identifier
FSU_migr_etd-5450
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Tucker, P. C. (2012). Synthesis of Cerium Rich Intermetallics Using Molten Metal Eutectics. Retrieved from http://purl.flvc.org/fsu/fd/FSU_migr_etd-5450
