Data di Pubblicazione:
2014
Citazione:
Compressional behaviour of paulingite -A sub-nanosponge? / G.D. Gatta, T. Pippinger, R. Miletich, R. Skala, Y. Lee. ((Intervento presentato al 9. convegno Zeolite 2014 - 9th International Conference on the Occurrence, Properties and Utilizatian of Natural Zeolites tenutosi a Belgrade, Serbia nel 2014.
Abstract:
Introduction
Paulingite is a rare zeolite, found in vesicles in basalt flows, with ideal chemical formula: (K,Na,Ca0.5,Ba0.5,)10(Al10Si32O84)30H2O (Z = 16). Its crystal structure was solved and refined by Gordon et al. (1966) in the space group Im3m, showing the complex framework topology of this zeolite designated with the IZA-code “PAU”. A structural re-investigation was carried out later by Lengauer et al. (1997). The tetrahedral framework topology of paulingite is characterized by a connecting double 8-ring (D8R), which links alternatively the -cage (truncated cuboctahedron) and the -cage (gmelinite-type cage). The D8R, the -cage and the -cage represent the building-block units of the PAU framework. The main voids systems of the PAU framework are represented by two parallel (and independent) sets of a three-dimensional channel systems oriented along the principal axes and shifted ½, ½, ½ against each other. Along the threefold axis of the PAU framework, a second type of a channel system exists, which is built up by the -cage and a modified form of the levyne-cage only observed in the paulingite topology (i.e., -cage) (Lengauer et al. 1997). The PAU framework type is considered as one of the most complex in the mineral world. In all the structure refinements so far reported, the Si/Al-distribution was modelled as completely disordered. A series of extra-framework sites were located. The long “free diameters” of the channel systems make this zeolite a good candidate to explore the P-induced penetration of external molecular species in response to hydrostatic compression (e.g., Gatta 2008, 2010).
Experimental Methods
A sample of paulingite from Vinařická hora Hill near Kladno (Czech Republic) was used for our experiments. A sample from the same locality was previously used by Lengauer et al. (1997) for their chemical and crystallographic study. Electron microprobe analysis (in wavelength dispersive mode) along with thermo-gravimetric data yielded the following chemical formula: (Ca2.57K2.28Ba1.39Na0.38)(Alll.55Si30.59O84)x 27H2O (Lengauer et al. 1997).
A single-crystal of paulingite, free of defects under polarized microscope, was selected for the in-situ diffraction experiment with a diamond anvil cell (DAC). Intensity diffraction data were first collected at room-conditions with a Stoe StadiVari diffractometer with an high-brilliance Incoatec Mo Iµs X-ray-source and a Dectris Pilatus 300K pixel detector. The structure refinement was performed in the space group Im3m using the structural model of Lengauer et al. (1997) to a R1 = 0.0802 for 2477 Fo > 4(Fo) and 255 refined parameters. The same crystal was used for the high-pressure (HP) experiment performed using an ETH-type DAC. The experiment was conducted using a mixture of methanol:ethanol = 4:1 as hydrostatic P-transmitting medium, along with a few ruby chips serving as P-calibrant. Unit-cell parameters were measured between 0.0001 (crystal in the DAC with no pressure medium) and 3.3(1) GPa.
Two further in-situ HP synchrotron X-ray powder diffraction experiments were performed at the X7A beamline at the national synchrotron light source (NSLS) at Brookhaven National Laboratory (BNL). A gas-proportional position-sensitive detector was used. The wavelength of the incident beam was 0.60046(1) Å as determined from a CeO2 standard. A modified Merrill–Bassett DAC was used to generate HP-conditions. Two compression experiments with two different P-fluids were performed, i.e., with silicon-oil and a mix of methanol:ethanol:water = 16:3:1. The evolution of the cell parameters with P for all three pressure-transmitting media is shown in Fig. 1.
Results and Discussion
The evolution of the unit-cell parameters of paulingite with P based
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Elenco autori:
G.D. Gatta, T. Pippinger, R. Miletich, R. Skala, Y. Lee
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