Rossella Arletti

Structural deformation mechanisms of zeolites under pressure

Abstract The HP behavior of the natural zeolite yugawaralite and of the synthetic zeolite Na-A was studied by in situ synchrotron X-ray powder diffraction, using a non-penetrating P-transmitting medium. The unit-cell parameters of yugawaralite were refined up to the pressure of 10 GPa, at which reductions were found of about 7, 2.4, 7, 1.3, and 15% for a, b, c, β, and V, respectively. Contractions of 6.5 and 18.4% were found for a and V, respectively, for zeolite Na-A in the range 10-4 to 6.8 GPa. Diffraction patterns collected during decompression show that the effects induced by high pressure on both samples are almost completely reversible. These results are compared with those obtained under similar experimental conditions for other natural zeolites, with the aim of rationalizing the deformation mechanisms of these porous materials and comparing their flexibility under high-pressure and high-temperature conditions.

The “template” effect of the extra-framework content on zeolite compression: The case of yugawaralite

Abstract The microscopic behavior of the Ca-zeolite yugawaralite has been studied by ab initio molecular dynamics simulations adopting experimental cell parameters obtained at pressures up to ~9 GPa. Pressure-induced volume contraction occurs via rotations of quasi-rigid TO4 tetrahedra that reduce the size of the channels in which the extra-framework species are located. Such rotations are governed by deformation of the coordination polyhedron of Ca, which is made up of water and framework O atoms. Contraction of the Ca-H2O distances is favored at moderate pressure; at higher pressure the shortening of Ca-framework O atom distances becomes prevalent. The hydrogen bond network plays a fundamental role in the overall response to pressure. Our results indicate that the high-P-induced deformation of the framework structure is strictly correlated to the extra-framework species that act as “templates” in the compression process.

Influence of dehydration kinetics on T-O-T bridge breaking in zeolites with framework type STI: the case of stellerite.

Abstract The thermally induced structural modifications of the natural zeolite stellerite [Ca8Al16Si56O144·58H2O, a = 13.5947(4), b = 18.1823(6), and c = 17.8335(6) Å, V = 4408.1(3) Å3, space group Fmmm, framework type STI] were studied in a temperature-resolved X-ray powder diffraction experiment, using synchrotron radiation, in the temperature range RT-976 K. In the initial stage of heating (below 430 K) Stellerite Phase A (space group Fmmm) is stable, and the cell volume decreases only 0.6% to this temperature. Between 430 and 490 K most of the water is released, the symmetry lowers, and a phase transition to the collapsed so-called Phase B (space group Amma) is observed. In this phase rotation of the 4254 Secondary Building Units causes cell volume contraction and deformation of the channel system. This new phase, at 530 K, shows the statistical breaking of T-O-T bridges in the four-rings and the migration of tetrahedral atoms to new .face-sharing. tetrahedra, which partially occlude both the channels parallel to [100] and to [001]. This framework deformation is interpreted as due to the strain induced by calcium atoms on the framework to achieve better coordination after the release of water. The new structure is stable up to 750 K and the total volume decrease is about 8%. The dehydration process causes a similar framework deformation and the transition to a collapsed phase characterized by the statistical breaking of T-O-T bridges in all zeolites with STI-type frameworks. However, comparing the results obtained with different thermal kinetics, it is possible to assume that the experimental conditions play a primary role in the mechanisms of dehydration and of framework bridge breaking.

Elastic behavior of MFI-type zeolites: Compressibility of H-ZSM-5 in penetrating and non-penetrating media

We report the results of an in situ synchrotron X-ray powder diffraction study on the elastic behavior of Na-ZSM-5, performed using both silicone oil (s.o.) and (16:3:1) methanol:ethanol:water (m.e.w.), as ‘‘non-penetrating’’ and ‘‘penetrating’’ pressure transmitting media, respectively. In the range from ambient pressure (Pamb) to 6.2 GPa, the reductions of a, b, c, and V observed in s.o. are: 6.4, 6.3, 6.9 and 18.5%, respectively. From Pamb to 7.4 GPa, a unit-cell volume reduction of about 14.6% is observed for Na-ZSM-5 compressed in m.e.w., and the corresponding reductions of a, b, and c cell parameters are 6.3, 4.6, and 4.5%, respectively. In both cases no phase transitions are observed and the unit cell parameters of ambient conditions are recovered upon decompression. The complete structural refinements relative to the experiments performed in m.e.w. up to 1.6 GPa reveal a strong increase in the extra-framework content – with the penetration of additional water/alcohols molecules in the partially occupied extra-framework sites of as-synthesized Na-ZSM-5. This P-induced penetration, which does not induce any cell volume expansion, is only partially reversible, since a fraction of the extra-molecules remains in the channels upon decompression. Our results show that Na-ZSM-5 is the softest microporous material among those so far compressed in s.o. Moreover, its compressibility is higher in s.o. than in m.e.w. (K0 = 18.2(6) GPa, K

Elastic behavior of zeolite boggsite in silicon oil and aqueous medium: A case of high-pressure-induced over-hydration

Abstract This paper reports the results of an in situ high-pressure synchrotron X-ray powder diffraction investigation on the natural zeolite boggsite [(K0.06Na0.36Sr0.01Ca7.00Mg1.20)(Al17.52Si78.62Fe0.05O192)·82.3 H2O]. The study was performed using both a (16:3:1) methanol:ethanol:water mixture (m.e.w.) as a nominally “penetrating” hydrostatic P-transmitting medium and silicon oil (s.o.) as a “non-penetrating” medium. The studied pressure ranges are: Pamb-7.6 and Pamb-5.9 GPa in m.e.w and s.o., respectively. No complete X-ray amorphization is observed up to the highest investigated pressures, and the original unit-cell parameters are almost completely recovered upon decompression in both media. The reductions of a, b, c, and V, within the pressure-ranges investigated, are 5.3, 4.2, 4.0, and 13.0% in s.o. and 4.1, 4.1, 3.8, and 11.5% in m.e.w. The Rietveld structural refinements of the powder patterns of the experiments in m.e.w. converged successfully up to 3.6 GPa and demonstrated the penetration of 13 additional water molecules between 0.3 and 2.9 GPa. This over-hydration occurs without any unit-cell volume expansion and can be explained by the fact that no new extraframework sites arise during compression and that water penetration is the only factor to increase the occupancy of already existing sites. Boggsite compressibility is higher in s.o. than in m.e.w. In particular, compressibility in m.e.w. is lower below 3 GPa, whereas above this pressure, the P-V trend becomes similar in the two media. This can be ascribed to the fact that, during water molecule penetration (0.3 < P < 3 GPa), the effect of the P-transmitting medium is directed to compress the system as well as to penetrate the channels.

Archaeometric analyses of game counters from Pompeii

Abstract Among the glass finds of the Pompeii excavations, numerous objects of opaque and transparent glassy material of different colours were recovered and classified as game counters. The main aims of this work were to characterize these samples so as to identify the materials used as colorants and opacifying agents, and subsequently to deduce the technology used for their production. The results of the chemical and mineralogical analyses obtained for game counters were also compared with those obtained for transparent and opaque glass artefacts. The chemical analyses were carried out, using only 300 mg of sample, by both wavelength-dispersive electron microprobe and X-ray fluorescence analysis. The crystalline phases present in the opaque glass were identified using both an automatic X-ray powder diffractometer and a Gandolfi camera. Secondary and backscattered electron images were obtained to study the distribution and morphology of the opacifier particles, and qualitative chemical analyses were obtained with an energy-dispersive system. All the game counters analysed can be classified as silica-soda-lime glass. Two calcium antimonates (CaSb2O6 and Ca2Sb2O7) were identified in the opaque white, green and blue glass, and Pb2Sb2O7 particles were detected in the opaque yellow glass. Particles of metallic copper were detected by both energy-dispersive system and X-ray powder diffraction. These results support the hypothesis that transparent game counters were obtained by remelting of fragments of common transparent artefacts. In contrast, opaque finds were probably produced using the glassy paste employed in the production of mosaic tesserae.

High-pressure-induced structural changes, amorphization and molecule penetration in MFI microporous materials: a review

This is a comparative study on the high-pressure behavior of microporous materials with an MFI framework type (i.e. natural mutinaite, ZSM-5 and the all-silica phase silicalite-1), based on in-situ experiments in which penetrating and non-penetrating pressure-transmitting media were used. Different pressure-induced phenomena and deformation mechanisms (e.g. pressure-induced over-hydration, pressure-induced amorphization) are discussed. The influence of framework and extra-framework composition and of the presence of silanol defects on the response to the high pressure of MFI-type zeolites is discussed.

Glass beads from Villanovian excavations in Bologna (Italy): an archaeometrical investigation

Excavations performed in the 1970s in the present-day trade fair zone of Bologna brought to light remains of civilisations of the 8–7th century B.C. Archaeological studies identified a large number of objects which clearly indicated the existence of an extensive Villanovian village. Fifteen blue, turquoise, and dark green glass beads were selected and analysed in the present study. Chemical analyses of major and minor elements were obtained by EMPA, whereas trace elements were determined on selected samples by LA-ICP-MS. The occurrence of eventual opacifying agents dispersed in the matrix was attested by SEM observations. The chemical data allow identification of a group of four beads characterised by a mixed alkali composition, typical of Frattesina Final Bronze Age production. All the other samples have low levels of K 2 O ( 2 O (>15 wt%). Among these last samples, which can be classified as natron-based glass, a number of blue beads show a high quantity of MgO (about 3 wt%), in combination with a low K 2 O amount. These low-K, high-Mg glasses also exhibit extremely high amounts of Al 2 O 3 , possibly due to the use of Co-bearing alum as colouring compound. Also the trace-element data confirm the division of the natron-based samples into two different sub-groups on the basis of the concentration of V, Cr, Ti and Zr. This suggests that the glass found at this site derives from three different melts. Regarding the opacity of the samples, in most of the cases this effect is due to the dark colour of the glass ( i.e., blue, dark green) which hinders the transmission of light. Crystalline particles of calcium antimonate were found only in the turquoise-colour samples.

Irreversible Conversion of a Water–Ethanol Solution into an Organized Two-Dimensional Network of Alternating Supramolecular Units in a Hydrophobic Zeolite under Pressure.

Turning disorder into organization is a key issue in science. By making use of X-ray powder diffraction and modeling studies, we show herein that high pressures in combination with the shape and space constraints of the hydrophobic all-silica zeolite ferrierite separate an ethanol-water liquid mixture into ethanol dimer wires and water tetramer squares. The confined supramolecular blocks alternate in a binary two-dimensional (2D) architecture that remains stable upon complete pressure release. These results support the combined use of high pressures and porous networks as a viable strategy for driving the organization of molecules or nano-objects towards complex, pre-defined patterns relevant for the realization of novel functional nanocomposites.

A new framework topology in the dehydrated form of zeolite levyne

Abstract The thermoelastic behavior and structural evolution of a natural levyne-Ca [(Ca7.8 Na2.2K1.1)Σ11.1 Al20.0Si34.2O108⋅51.5H2O; R3m; a = 13.377(4) Å, c = 22.870(1) Å, V = 3544.1(3) Å3] were studied by both T-resolved synchrotron X‑ray powder diffraction (SR-XRPD) between room temperature and 800 °C, and by conventional-source high-temperature single-crystal X‑ray diffraction (SC-XRD). Above 230 °C, water loss and reallocation of extraframework cations induce the straining and consequent breaking of T-O-T bridges in the D6R, with resulting migration of tetrahedral cations to new tetrahedral sites. The new tetrahedra share an edge with the previously occupied tetrahedra. This phenomenon gives rise to a new topology, which coexists to about 40%, with the original one. The new framework consists of a sequence of a novel zeolitic cage (described as a 20-hedron formed by fourteen 6mR and six 4mR) and two consecutive cancrinite cages along [0001]. This topology, which is reported in the database of the hypothetical zeolite structures as 166_2_293, belongs to the ABC-6 family and can be described by the following sequence of 6-rings: ABCBCACAB, to be compared with that of levyne AABCCABBC. In the new topology the extraframework cations are distributed over 3 new sites: one at the center of the 6mR ⊥ [0001] shared by the two cancrinite cages, one near the center of the 6mR ⊥ [0001] at the base of the new cage, and a last one in a 6mR window of the new cage. The 8mR bidimensional channel system originally present in levyne is therefore absent in the new topology and hence molecular diffusion is likely to be partially hindered in the dehydrated form. The phase transition is not completely reversible, at least in the short term, as only partial rehydration was demonstrated