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Title: Microporous titanosilicate AM-2: Rb-exchange and thermal behaviour

Abstract

Rb-exchange and thermal stability of the microporous titanosilicate AM-2 were analysed by powder X-ray diffraction, thermo-gravimetric analysis, and chemical analysis of the mother liquid after exchange. The dehydration and thermal stability of the exchanged structure were monitored with in situ high temperature powder X-ray diffraction. Crystal structures were refined with Rietveld methods at 25 and 400 deg. C. The AM-2 structure was found to incorporate Rb{sup +} by replacing K{sup +}. After four exchange cycles and 166 h reaction time at 90 deg. C, the chemical composition was refined to K{sub 0.18}Rb{sub 1.82}TiSi{sub 3}O{sub 9}.H{sub 2}O. Extrapolation suggests that higher exchange ratios may be obtained after further cycles. H{sub 2}O was expelled by heating, leading to a dehydrated structure at 360 deg. C. Dehydration was associated with a change of space group symmetry from orthorhombic P2{sub 1}2{sub 1}2{sub 1} to monoclinic P2{sub 1}, which proved to be reversible after rehydration. This change of symmetry leaves the AM-2 characteristic structural topology uninfluenced and causes only minor distortions. The monoclinic AM-2 structure breaks down above 600 deg. C to become X-ray amorphous, and at 750 deg. C a wadeite-type phase (K {sub x}Rb{sub 2-x}TiSi{sub 3}O{sub 9}) crystallises. This transformation is irreversible andmore » leads to immobilisation of Rb{sup +}.« less

Authors:
 [1];  [2]
  1. Laboratorium fuer chemische und mineralogische Kristallographie, Universitaet Bern, Freiestrasse 3, CH-3012 Bern (Switzerland). E-mail: nicola@doebelin.org
  2. Laboratorium fuer chemische und mineralogische Kristallographie, Universitaet Bern, Freiestrasse 3, CH-3012 Bern (Switzerland)
Publication Date:
OSTI Identifier:
20902499
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Research Bulletin; Journal Volume: 42; Journal Issue: 1; Other Information: DOI: 10.1016/j.materresbull.2006.05.006; PII: S0025-5408(06)00204-2; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHEMICAL PREPARATION; DEHYDRATION; EXTRAPOLATION; GRAVIMETRIC ANALYSIS; HEATING; MONOCLINIC LATTICES; ORTHORHOMBIC LATTICES; POTASSIUM IONS; POWDERS; RUBIDIUM IONS; SPACE GROUPS; STABILITY; SYMMETRY; X-RAY DIFFRACTION

Citation Formats

Doebelin, Nicola, and Armbruster, Thomas. Microporous titanosilicate AM-2: Rb-exchange and thermal behaviour. United States: N. p., 2007. Web. doi:10.1016/j.materresbull.2006.05.006.
Doebelin, Nicola, & Armbruster, Thomas. Microporous titanosilicate AM-2: Rb-exchange and thermal behaviour. United States. doi:10.1016/j.materresbull.2006.05.006.
Doebelin, Nicola, and Armbruster, Thomas. Thu . "Microporous titanosilicate AM-2: Rb-exchange and thermal behaviour". United States. doi:10.1016/j.materresbull.2006.05.006.
@article{osti_20902499,
title = {Microporous titanosilicate AM-2: Rb-exchange and thermal behaviour},
author = {Doebelin, Nicola and Armbruster, Thomas},
abstractNote = {Rb-exchange and thermal stability of the microporous titanosilicate AM-2 were analysed by powder X-ray diffraction, thermo-gravimetric analysis, and chemical analysis of the mother liquid after exchange. The dehydration and thermal stability of the exchanged structure were monitored with in situ high temperature powder X-ray diffraction. Crystal structures were refined with Rietveld methods at 25 and 400 deg. C. The AM-2 structure was found to incorporate Rb{sup +} by replacing K{sup +}. After four exchange cycles and 166 h reaction time at 90 deg. C, the chemical composition was refined to K{sub 0.18}Rb{sub 1.82}TiSi{sub 3}O{sub 9}.H{sub 2}O. Extrapolation suggests that higher exchange ratios may be obtained after further cycles. H{sub 2}O was expelled by heating, leading to a dehydrated structure at 360 deg. C. Dehydration was associated with a change of space group symmetry from orthorhombic P2{sub 1}2{sub 1}2{sub 1} to monoclinic P2{sub 1}, which proved to be reversible after rehydration. This change of symmetry leaves the AM-2 characteristic structural topology uninfluenced and causes only minor distortions. The monoclinic AM-2 structure breaks down above 600 deg. C to become X-ray amorphous, and at 750 deg. C a wadeite-type phase (K {sub x}Rb{sub 2-x}TiSi{sub 3}O{sub 9}) crystallises. This transformation is irreversible and leads to immobilisation of Rb{sup +}.},
doi = {10.1016/j.materresbull.2006.05.006},
journal = {Materials Research Bulletin},
number = 1,
volume = 42,
place = {United States},
year = {Thu Jan 18 00:00:00 EST 2007},
month = {Thu Jan 18 00:00:00 EST 2007}
}
  • The structure of EST-10, a member of synthetic microporous titanosilicates, was recently determined by an ingenious combination of experimental and simulational techniques. However, the locations of the alkali atoms in the framework remain elusive and its electronic structure is totally unknown. Based on first-principles local density calculations, the possible locations of the alkali atoms are identified and its electronic structure and bonding fully elucidated. ETS-10 is a semiconductor with a direct band gap of 2.33 eV. The Na atoms are likely to locate inside the seven-member ring pore adjacent to the one-dimensional Ti-O-Ti-O- chain. {copyright} {ital 1996 The American Physicalmore » Society.}« less
  • Titanosilicate ETS-10 crystals were prepared by hydrothermal synthesis varying Ti source (TiCl{sub 3} and commercial TiO{sub 2}-anatase), time in autoclave and seeding with previously prepared ETS-10 crystals. The crystalline powders were characterized by X-ray diffraction, N{sub 2} adsorption, thermogravimetric analysis, and scanning and transmission electron microscopies. Control of the particle size of ETS-10 crystals ranging from 0.32 {mu}m x 0.41 {mu}m to 16.4 {mu}m x 32.5 {mu}m was successfully achieved varying the seeding and synthesis conditions. In particular, it was found that the use of TiO{sub 2}-anatase alone or together with TiCl{sub 3} promotes heterogeneous primary nucleation. Transmission electron microscopymore » demonstrated that the largest crystals obtained here were twinned.« less
  • A new family of framework titanosilicates, A2TiSi6O15 (A=K, Rb, Cs) (space group Cc), has recently been synthesized using the hydrothermal method. This group of phases can potentially be utilized for storage of radioactive elements, particularly 137Cs, due to its high stability under electron radiation and chemical leaching. Here, we report the syntheses and structures of two intermediate members in the series: KRbTiSi6O15 and RbCsTiSi6O15. Rietveld analysis of powder synchrotron X-ray diffraction data reveals that they adopt the same framework topology as the end-members, with no apparent Rb/K or Rb/Cs ordering. To study energetics of the solid solution series, high-temperature drop-solutionmore » calorimetry using molten 2PbO{center_dot}B2O3 as the solvent at 975 K has been performed for the end-members and intermediate phases. As the size of the alkali cation increases, the measured enthalpies of formation from the constituent oxides ({Delta}H{sup 0}{sub f, ox}) and from the elements ({Delta}H{sup 0}{sub f, el}) become more exothermic, suggesting that this framework structure favors the cation in the sequence Cs+, Rb+, and K+. This trend is consistent with the higher melting temperatures of A2TiSi6O15 phases with increase in the alkali cation size.« less
  • The family of hydroxymonophosphates of generic formula AM{sup III}(PO{sub 3}(OH)){sub 2} has been revisited using hydrothermal techniques. Four new phases have been synthesized: CsIn(PO{sub 3}(OH)){sub 2}, RbFe(PO{sub 3}(OH)){sub 2}, RbGa(PO{sub 3}(OH)){sub 2} and RbAl(PO{sub 3}(OH)){sub 2}. Single crystal diffraction studies show that they exhibit two different structural types from previously observed other phases with A=H{sub 3}O, NH{sub 4}, Rb and M=Al, V, Fe. The ''Cs-In'' and ''Rb-Fe'' phosphates crystallize in the triclinic space group P1-bar, with the cell parameters a=7.4146(3)A, b=9.0915(3)A, c=9.7849(3)A, {alpha}=65.525(3){sup o}, {beta}=70.201(3){sup o}, {gamma}=69.556(3){sup o} and V=547.77(4)A{sup 3} (Z=3) for CsIn(PO{sub 3}(OH)){sub 2} and a=7.2025(4)A, b=8.8329(8)A, c=9.4540(8)A,more » {alpha}=65.149(8){sup o}, {beta}=70.045(6){sup o}, {gamma}=69.591(6){sup o} and V=497.44(8)A{sup 3} (Z=3) for {alpha}-RbFe(PO{sub 3}(OH)){sub 2}. The ''Rb-Al'' and ''Rb-Ga'' phosphates crystallize in the R3-bar c space group, with a=8.0581(18)A and c=51.081(12)A (V=2872.5(11)A{sup 3} and Z=18) for RbAl(PO{sub 3}(OH)){sub 2} and a=8.1188(15)A and c=51.943(4)A (V=2965(8)A and Z=18) for RbGa(PO{sub 3}(OH)){sub 2}. These two structural types are closely related. Both are built up from M{sup III}O6 octahedra sharing their apices with PO{sub 3}(OH) tetrahedra to form [M{sub 3}(PO{sub 3}OH){sub 6}] units, but the latter exhibits a different configuration of their tetrahedra. The three-dimensional host-lattices result from the connection of the [M{sub 3}(PO{sub 3}OH){sub 6}] units and they present numerous intersecting tunnels containing the monovalent cations.« less
  • A sodium titanosilicate of ideal composition Na{sub 2}Ti{sub 2}O{sub 3}SiO{sub 4}{center_dot}2H{sub 2}O was synthesized hydrothermally in highly alkaline media. Its crystal structure was solved from X-ray powder data by ab initio methods. The compound is tetragonal, a = 7.8082(2), c = 11.9735(4) {angstrom}, space group P4{sub 2}/mcm, Z = 4. The titanium atoms occur in clusters of four grouped about the 4{sub 2} axis and are octahedrally coordinated by oxygen atoms. The silicate groups serve to link the titanium clusters into groups of four arranged in a square of about 7.8 {angstrom} in length. These squares are linked to similarmore » ones in the c direction by sharing corners to form a framework which encloses a tunnel. Half the Na{sup +} ions are situated in the framework coordinated by silicate oxygen atoms and water molecules. The remaining sodiums are present in the cavity, but evidence indicates that some of them are replaced by protons. The composition is then closer to Na{sub 1.64}H{sub 0.36}Ti{sub 2}O{sub 3}SiO{sub 4}{center_dot}1.8H{sub 2}O. The sodium ions within the tunnels are exchangeable. Exhaustive exchange with CsNO{sub 3} yielded a Cs{sup +} phase of composition Na{sub 1.49}Cs{sub 0.2}H{sub 0.31}Ti{sub 2}O{sub 3}SiO{sub 4}{center_dot}H{sub 2}O whose structure was revealed from application of Rietveld methods to X-ray powder data. 19 refs., 7 figs., 5 tabs.« less