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High temperature studies of sodalites

By Tabasum Fazal

Abstract

Aluminosilicate sodalites Na\(_8\)(Al\(_6\)Si\(_6\)O\(_2\)\(_4\))Br\(_2\), Na\(_8\)(Al\(_6\)Si\(_6\)O\(_2\)\(_4\)Cl\(_2\), and Na\(_8\)(Al\(_6\)Si\(_6\)O\(_2\)\(_4\))I\(_2\), were synthesised and subsequently loaded with various amounts of silver by aqueous ion exchange to produce Na\(_8\)-Ag\(_x\)(Al\(_6\)Si\(_6\)O\(_2\)\(_4\))Br\(2\) with x = 0, 2, 4, 6, 8, Naz\(_8\)-Al\(_6\)Si\(_6\)O\(_2\)\(_4\))I\(_2\). Characterisation by X-ray powder diffraction and Rietveld refinements showed that for the chloride and bromide systems the substitution of silver for sodium causes a contraction of the unit cell and M-X bonds in the MX4 tetrahedral units in the sodalite cages, with an expansion of the distance of the metal from the framework oxygen atoms. This can be attributed to the increased covalent bonding in an Ag-X bond vs. a Na-X bond. High temperature X-ray powder diffraction studies were then carried out on these systems and it was found that they all displayed positive thermal expansion from room temperature up to 822ºC. The coefficients of thermal expansion for the bromide system showed a clear trend of decreasing with silver doping, but no clear trends for the chloride system or in the thermal expansion of the M-X or M-O distances in either system were found

Topics: QD Chemistry
Year: 2011
OAI identifier: oai:etheses.bham.ac.uk:1488

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Citations

  1. (1999). Figure 1: Sodalite cage composed of eight six-rings and six four-rings (Johnson et al.,
  2. (2000). Figure 2b: The stacking sequence of 6-rings in the sodalite (ABCABC…), left. The derived pore structures (right). The red, blue and green represent the different positions of the vertically stacked layers (Weller,
  3. (1984). In ordered aluminosilicate sodalites, the lattice symmetry is P43n and has Td point symmetry (Zilli and Bagnato,
  4. (1970). In this study the sodium and silver forms of basic halosodalites have been studied. Sodalites occur as a number of natural minerals, and have been noted as being particularly good in the absorption and retention of halides (Barrer and Cole,
  5. (1999). Introduction The use of porous framework compounds to encapsulate nanoscale atomic clusters gives many possibilities to produce novel materials
  6. (2003). One interesting aspect of sodalites is their structural flexibility. The flexibility of cages is attributed to the change of bond angles rather than a change in bond distances. Due to this, the sodalite framework is termed partially collapsed (Acar et al.,
  7. (1976). Sodalites have received considerable attention during the last few decades. Studies have shown they have many useful properties, for example sodalite based materials are used as pigments (Volynets et al., 1984; Vakhidov
  8. (1985). Synthesis of Halosodalites Sodalites have been synthesised by various techniques, such as solid state reactions, hydrothermal growth, and transformation of zeolites (Suzuki et al.,
  9. (1984). The overall linkage of (Al, Si)O4 tetrahedra results in a cubo-octahedral cavity (Hassan and Grundy,
  10. (1984). These cages are ~ 6.5 Å in diameter and are accessible through six-membered rings of 2.2 Å diameter (Zilli and Bagnato,

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