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Molten metal fluxes are useful in materials synthesis. Dissolution in molten metal activates reactants at temperatures well below their melting point. Lower temperatures and the modified energetics in a flux increase the possibility of isolation of complex metastable or kinetically stabilized phases. In contrast to the powders often obtained by conventional solid state synthesis methods, the solution phase character of flux reactions promotes the growth of crystals, which are required for accurate structural and electronic characterization. Ca/Li flux solvates lightweight refractory elements such as carbon and boron. It also dissolves many ionic compounds such as CaH2, Ca3N2, and LiF. This allows for synthesis of phases ranging from strongly delocalized intermetallics to complex salts. In particular, dissolution of CaH2 makes Ca/Li flux a very promising medium for growth of new metal hydride phases. These hydride compounds may have great potential as hydrogen storage materials. The ionic products such as Zintl and complex salt phases have interesting electronic properties because these classes of compounds are usually semiconductors. Reactions of light main group elements (B, C, Si) and ionic compounds (CaH2, CaO, Li3N) have been carried out in Ca/Li flux. Several Zintl phase hydrides including LiCa2C3H and LiCa7Si3H3 have been produced. These compounds are of interest because of their new crystal structures and their release of H2 gas in decomposition reactions. Structures are discussed in detail to explain the different bonding environments in these compounds. Efforts to explore and eliminate the oxide and hydride contaminants in the reactive flux have also netted interesting results. A new boride carbide was found using distilled flux.
Flux Synthesis, Density of States, X-ray Diffraction, Hydrogen Storage Materials
Date of Defense
June 22, 2011.
A Thesis submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Susan Latturner, Professor Directing Thesis; Albert E. Stiegman, Committee Member; Oliver Steinbock, Committee Member.
Florida State University
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