TY - JOUR
T1 - Crystal chemistry and energetics of pharmacosiderite-related microporous phases in the K2O-Cs2O-SiO2- TiO2-H2O system
AU - Xu, Hongwu
AU - Navrotsky, Alexandra
AU - Nyman, May
AU - Nenoff, Tina M.
N1 - Funding Information:
We are grateful to D.E. Cox for assistance with the synchrotron X-ray experiments and to M.L. Balmer and Y. Su for helpful discussion. This work was supported by the US Department of Energy (DOE) Environmental Management Science Program (EMSP) (Grant No. FG07-97ER45674). Synchrotron X-ray diffraction was performed at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the DOE Division of Materials Sciences and Division of Chemical Sciences. Sample synthesis was conducted at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.
PY - 2004/7/8
Y1 - 2004/7/8
N2 - A complete series of solid solutions with compositions (K1-x Csx)3Ti4Si3O15( OH)· nH2O (n=4-6, 0≤x≤1) and having the pharmacosiderite structure (space group P 4̄3 m) has been synthesized using hydrothermal and ion-exchange methods. Rietveld analysis of synchrotron XRD data shows that the unit-cell parameter a increases linearly with increasing Cs+ content. In the structure, K+ is situated in the center of the eight-membered titanosilicate ring, whereas Cs+ is displaced from the ring center, and the displacement increases with higher K+/ (Cs+ + K+) ratio.The enthalpies of formation from the oxides and from the elements were determined by drop solution calorimetry into molten 2PbO · B2O3 solvent at 974 K. The formation enthalpies from oxides become more exothermic with increasing Cs+/(Cs+ + K+), suggesting a stabilizing effect of K+ → Cs+ on the pharmacosiderite structure. Calculation of the enthalpy of the K+ → Cs+ exchange reaction based on the measured formation enthalpies indicates that the Cs+ uptake in these phases is probably thermodynamically (rather than kinetically) driven.
AB - A complete series of solid solutions with compositions (K1-x Csx)3Ti4Si3O15( OH)· nH2O (n=4-6, 0≤x≤1) and having the pharmacosiderite structure (space group P 4̄3 m) has been synthesized using hydrothermal and ion-exchange methods. Rietveld analysis of synchrotron XRD data shows that the unit-cell parameter a increases linearly with increasing Cs+ content. In the structure, K+ is situated in the center of the eight-membered titanosilicate ring, whereas Cs+ is displaced from the ring center, and the displacement increases with higher K+/ (Cs+ + K+) ratio.The enthalpies of formation from the oxides and from the elements were determined by drop solution calorimetry into molten 2PbO · B2O3 solvent at 974 K. The formation enthalpies from oxides become more exothermic with increasing Cs+/(Cs+ + K+), suggesting a stabilizing effect of K+ → Cs+ on the pharmacosiderite structure. Calculation of the enthalpy of the K+ → Cs+ exchange reaction based on the measured formation enthalpies indicates that the Cs+ uptake in these phases is probably thermodynamically (rather than kinetically) driven.
KW - Crystal chemistry
KW - Enthalpy of formation
KW - Pharmacosiderite
KW - Thermodynamics
KW - Titanosilicate
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U2 - 10.1016/j.micromeso.2004.03.033
DO - 10.1016/j.micromeso.2004.03.033
M3 - Article
AN - SCOPUS:2942736813
VL - 72
SP - 209
EP - 218
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
SN - 1387-1811
IS - 1-3
ER -