Non-penetrating Media Research Articles

The evolution of yugawaralite structure at high pressure: A single-crystal X-ray diffraction study

The structural evolution of yugawaralite |Ca1.93Na0.08(H2O)8.1|[Al3.94Si12.06O32], space group Pc, a = 6.72309(15), b = 13.9990(2), c = 10.0477(2) Å, β = 111.164(2)°, V = 881.87(3) Å3, compressed in penetrating (ethanol:water 4:1) and non-penetrating (paraffin oil) media, was studied up to 3.2 GPa. Under the compression in a penetrating medium, yugawaralite experiences pressure-induced hydration. Additional H2O molecules occupy two positions which do not enter the coordination of the extra-framework cations: one of them is partially filled under ambient conditions, and the second is initially vacant. At around 2 GPa, yugawaralite experiences a phase transition with doubling of the a- and b-parameters of the unit cell. At high pressure the diffraction frames contain sharply broadened low-intensity diffuse reflections corresponding to a multiple increase of the unit cell metric. The structure of the high-pressure phase solved in the sub-cell, corresponding to the initial metric, is characterized by the disordering of the framework sub-chains in which the SiO4-tetrahedra become alternatively oriented. The pressure-induced structural changes are completely reversible. The compression of yugawaralite in a non-penetrating medium does not lead to radical structural changes. The structure symmetry is preserved; there are no signs of diffuse scattering or the splitting of atomic positions.

Synthesis and Properties of the Helium Clathrate and Defect Perovskite [He2-x □ x ][CaNb]F6.

The defect double perovskite [He2-x □ x ][CaNb]F6, with helium on its A-site, can be prepared by the insertion of helium into ReO3-type CaNbF6 at high pressure. Upon cooling from 300 to 100 K under 0.4 GPa helium, ∼60% of the A-sites become occupied. Helium uptake was quantified by both neutron powder diffraction and gas insertion and release measurements. After the conversion of gauge pressure to fugacity, the uptake of helium by CaNbF6 can be described by a Langmuir isotherm. The enthalpy of absorption for helium in [He2-x □ x ][CaNb]F6 is estimated to be ∼+3(1) kJ mol-1, implying that its formation is entropically favored. Helium is able to diffuse through the material on a time scale of minutes at temperatures down to ∼150 K but is trapped at 100 K and below. The insertion of helium into CaNbF6 reduces the magnitude of its negative thermal expansion, increases the bulk modulus, and modifies its phase behavior. On compressing pristine CaNbF6, at 50 and 100 K, a cubic (Fm3̅m) to rhombohedral (R3̅) phase transition was observed at <0.20 GPa. However, a helium-containing sample remained cubic at 0.4 GPa and 50 K. CaNbF6, compressed in helium at room temperature, remained cubic to >3.7 GPa, the limit of our X-ray diffraction measurements, in contrast to prior reports that upon compression in a nonpenetrating medium, a phase transition is detected at ∼0.4 GPa.

Comparative study of the HP‐HTbehavior of a layered silicate apophyllite in water and paraffin oil

AbstractThe interaction of porous minerals with liquids, especially water, is involved in many technological and geochemical processes. Apophyllite (K,Na)Ca4[Si8O20](F,OH).8H2O, exhibiting mixed properties of layered and framework microporous silicates, is a promising object to model the interaction of a fluid with porous material. It was studied by the in situ Raman spectroscopy at simultaneously high pressure (HP) and high temperature (HT) up to 225°C and 9 GPa in order to clarify the effect of the composition of the pressure medium and the temperature on its HPbehavior. Penetrating (water) and nonpenetrating (paraffin oil) media were used. Independently of the compressing medium, at HT, the lattice vibrational modes of apophyllite demonstrate regular pressure shifts. Almost uniform shift rates imply little differentiation between the compression of silicate layers and interlayer ion‐molecular assemblage. Similar HPbehavior of apophyllite in penetrating and nonpenetrating media indicates no pressure‐induced overhydration within 1–9 GPa. Thereby, the significance of such structural factors, as a limited H2O mobility and relatively strong contacts between silicate layers, determining low structure tolerance towards the penetration of additional molecules, is emphasized. The elevated temperature does not affect the mobility of the interlayer H2O molecules to allow the pressure‐induced intercalation in apophyllite.

Stability of zeolitic imidazolate frameworks (ZIF-7) under high pressures and its implications on storage applications of ZIFs

We report the chemical stability of ZIF-7 under pressure using Raman spectroscopy. Our results show a reversible pressure response of ZIF-7 in non-penetrating media up to 8 ​GPa. Increasing pressures above 12 ​GPa leads to an irreversible ring-opening polymerization to a disordered phase. The lower chemical stability of ZIF-7 over prototypic ZIF-8 is explained to be due to hydrogen bonding C–H-π interaction. This study highlights the role of various substituents in the imidazole linkers in ZIFs for their gas storage applications under pressure.

Compressibility, Phase Transition, and Argon Insertion in the Siliceous Zeolite Mobil-Twelve at High Pressure

The siliceous zeolite Socony Mobil-twelve (ZSM-12) or MTW (Mobil-TWelve) with a one-dimensional pore system was studied at high pressure by synchrotron X-ray powder diffraction in nonpenetrating DAPHNE7474 oil and in a penetrating argon pressure medium. A phase transition from the space group C2/c to P2/n is observed in the nonpenetrating medium at close to 1.5 GPa with a 4% volume decrease and a strong increase in compressibility in the ac plane corresponding to partial collapse of the pores. Strong decreases in diffracted intensity are observed with further compression, and the diffraction pattern contains broad features characteristic of an amorphous material above 10 GPa. Distinct behavior is observed when this material is pressurized in argon. Argon fills the pores with 9 ± 1 Ar atoms per unit cell. In this medium-pore zeolite, the quantity of inserted argon was not found to vary with pressure. Argon-filled MTW is 35% less compressible than the corresponding empty form.

Structure of K,Na-Exchanged Stellerite Zeolite and its Evolution under High Pressures

K,Na-exchanged stellerite |K6.35Na1.53(H2O)25|[Al7.89Si28.11O72], space group F2/m, a = 13.6212(5) A, b = 18.1589(7) A, c = 17.8495(5) A, β = 90.202(3)°, V = 4415.0(3) A3, Z = 2, is studied by single-crystal X-ray diffraction under ambient conditions and upon compression to 3.5 GPa in water-containing penetrating and non-penetrating (paraffin) media. A specific property of the structure of the K,Na-exchanged form is a vacancy at the site that is occupied by Ca2+ cations in initial stellerite. The cations are distributed over six main positions with a local coordination 7–10 for K+ and 5 for Na+. The compression of K,Na-exchanged stellerite in the 4:1 ethanol:water mixture causes its additional hydration: initially, due to the occupation of partially vacant H2O sites and then, upon further compression, due to the occupation of initially vacant positions. The environment of the cations in other positions is not changed substantially in the course of overhydration. The differences in the degree of hydration of the K,Na-exchanged form under compression in penetrating and non-penetrating media are manifested in the characteristics of the compound’s compressibility.

Structure of K-Substituted Zeolite Clinoptillolite and Its Behavior Upon Compression in Penetrating and Non-Penetrating Media

K6.16Na0.16Ca0.07Mg0.03(H2O)19.2|[Al6.45Si29.55O72] (space group C2/m, a = 17.6490(3) A, b = 17.9982(2) A, c = 7.39329(12) A, β = 116.0655(19)°, V = 2109.63(5) A3, Z = 1) is studied by the single crystal X-ray diffraction analysis under ambient conditions and also upon compression to 4 GPa in penetrating (water-containing) and non-penetrating (paraffin) media. Compression of Ksubstituted clinoptillolite in a water:ethanol (1:1) mixture results in its additional hydration: inclusion of 2.2 additional H2O molecules into the structure at the initial stage. Upon further compression the H2O concentration increases by two molecules. This is caused by additional occupancy of partially vacant H2O sites. The cation environment practically does not change during overhydration. Changes in the coordination polyhedra of cations during compression in paraffin are reduced to a small (0.02-0.1 A) decrease in bond lengths. Distinctions in the degree of hydration of the K-form upon compression in penetrating and non-penetrating media are manifested in the features of the compressibility of the compound.

Структура K-замещенного цеолита клиноптилолита и его поведение при сжатии в проникающей и непроникающей средах

Структура K-замещенного цеолита клиноптилолита и его поведение при сжатии в проникающей и непроникающей средах

The deformation mechanism of a pressure-induced phase transition in dehydrated analcime

AbstractThe elastic and structural behaviour of dehydrated analcime in compression in a non-penetrating medium up to 3 GPa was studied in a diamond anvil cell usingin situsynchrotron powder diffraction. A first-order phase transition at 0.4–0.7 GPa is accompanied by a symmetry change from monoclinic (I2/a) to pseudo-rhombohedral (R3) due to trigonalization of the aluminosilicate framework. This is due to the migration of cations to new positions close to the 6-membered rings forming the channels. The reduction of the mean aperture of the structure-forming 6- and 8-membered rings, as a result of tetrahedral tilting, leads to a 7.5% reduction in volume at the phase transition. The bulk modulus values are 38(2) GPa for the low pressure (LP) phase [fitted with a Murnaghan equation of state,K' = 4 (fixed)] and 11(4) GPa for the high pressure (HP) phase [fitted with a third-order Birch–Murnaghan equation of state,K' = 9(1)]. The elastic behaviour of the LPphase is anisotropic, with compressibilities βa:βb:βcin the ratio 1:4:2; the most compressible directionbcoinciding with the orientation of empty 8-membered rings. The compressibility of the HP phase is isotropic. Trigonalization appears to be the most effective (and probably unique) mechanism of radical volume contraction for the ANA structure type.

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

The elastic behavior of H-ZSM-5 was investigated by in-situ synchrotron X-ray powder diffraction, 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. From P amb to 6.2 GPa the volume reduction observed in s.o. is 16.6%. This testifies that H-ZSM-5 is one of the most flexible microporous materials up to now compressed in s.o. Volume reduction observed in m.e.w. up to 7.6 GPa is 14.6%. A strong increase in the total electron number of the extraframework system, due to the penetration of water/alcohol molecules in the pores, is observed in m.e.w. This effect is the largest up to now observed in zeolites undergoing this phenomenon without cell volume expansion. The higher compressibility in s.o. than in m.e.w. can be ascribed to the penetration of the extra-water/alcohol molecules, which stiffen the structure and contrast the channel deformations.

Elastic behavior of MFI-type zeolites: 1-Compressibility of Na-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 ( P amb) 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 P amb 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. ( K 0 = 18.2(6) GPa, K′ = 4 (fixed) and 28.9(5) GPa, K′ = 4 (fixed), respectively). This can be ascribed to the penetration of the extra-water/alcohol molecules, which contribute to stiffen the structure and to contrast the channel deformations.

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

This paper reports the results of an in situ high-pressure synchrotron X-ray powder diffraction investigation on the natural zeolite boggsite [(K 0.06 Na 0.36 Sr 0.01 Ca 7.00 Mg 1.20 )(Al 17.52 Si 78.62 Fe 0.05 O 192 )·82.3 H 2 O]. 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: P amb -7.6 and P amb -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.

Pressure-induced over-hydration of thomsonite: A synchrotron powder diffraction study

The structural behavior of thomsonite compressed in aqueous medium up to 3 GPa was studied by means of in situ synchrotron powder diffraction with a diamond anvil cell. In the range between 0.0001 and 2 GPa, the compressibility of thomsonite is markedly lower than that reported previously, where a non-penetrating medium (with only 6% H 2 O) was used. This indicates a pressure-induced hydration (PIH), which results in the transition to an over-hydrated phase observed at 2 GPa. The structure of over-hydrated thomsonite contains one additional, half-occupied H 2 O position, coordinated by the calcium at the Ca2 site, with a scolecite-like coordination [CaO 4 (H 2 O) 3 ]. The appearance of new H 2 O position causes a 4.5% volume expansion through the cooperative rotation of [T 2 O 5 ] ∞ chains, leading to the enlargement of the cross-section of the main channels parallel to c axis. The observed deformation mechanism is similar to that found in high-hydrated and super-hydrated natrolite, although only a half of the channels are affected by PIH. The present data indicate that the over-hydration effect in fibrous zeolites strongly depends on the partial water pressure in compressing medium.

Amorphization of natrolite and edingtonite at high pressure

Amorphization of natrolite Na 2 [Al 2 Si 3 O 10 ]2H 2 O (Khibiny, Kola Peninsula, Russia) and edingtonite Ba[Al 2 Si 3 O 10 ]4H 2 O (Bohlet, Sweden) was investigated at high pressures up to 11 GPa, using Raman spectroscopy. Natrolite compressed in a non-penetrating medium of methanol-ethanol shows one apparent crystal-to-crystal transition at approximately 3.7 GPa before amorphization. Amorphization, reflected by decrease of Raman spectrum intensity, starts in the pressure range of 6–7 GPa and is completed by ~9 GPa. Amorphized Na 2 [Al 2 Si 3 O 10 ]2H 2 O exhibits partial reversibility to crystalline natrolite after amorphization at ~7-8 GPa and partially recovers its Raman spectrum after release of pressure. It was shown that amorphization of natrolite begins in soft structural units (water sublattice) and finishes in rigid units (T-O bonds). Comparison of natrolite and edingtonite behaviour at high pressures shows that amorphization of both zeolites begins at similar pressures but differ in their crystalline phase transitions. Edingtonite compressed in methanol-ethanol has no crystalline transition at high pressure. Ba[Al 2 Si 3 O 10 ]4H 2 O amorphized after compression up to higher pressure of ~11 GPa also exhibits partial reversibility to edingtonite crystal structure on release of pressure.

Raman spectra and lattice-dynamical calculations of natrolite

Polarized single-crystal Raman scattering and powder infrared absorption spectra of Fdd2 orthorhombic natural natrolite (Na1.88 K0.02 Ca0.04 )(Al1.96 Si3.03 O10)⋅2.03 H2O from Khibiny, Kola peninsula, were measured. Using short-range models, lattice-dynamical calculations were performed for an idealized natrolite structure Na4(Al4Si6O20)4H2O containing 46 atoms in the primitive unit cell (Z = 2). By varying the valence force constants, the calculated frequencies in the Raman and IR spectra were fitted to the observed frequencies. On considering their calculated intensities as well, nearly all the observed bands (especially those corresponding to the A1 modes) could be unambiguously assigned and interpreted. The external vibrations of H2O could be correctly assigned using deuter- ated samples. The strongest Raman band at 534 cm-1 corresponds to a breathing mode of the four-membered alumi- nosilicate ring. The calculated bulk modulus (52.7 GPa at zero pressure) is close to the experimental value of 47 ± 6 GPa. The natrolite structure has some advantages upon other zeolites to understand the amorphization mechanism, because samples of this mineral surrounded by a non-penetrating medium show no crystal phase transitions with increasing pressure. Lattice energy minimization calculated with variable unit-cell dimensions shows the crystal structure to become unstable at about 5.5 GPa, thereby apparently explaining the amorphization process at 4-7 GPa. This instability is connected with shear acoustic modes coupled with soft internal framework vibrations.

Structural transformations in natrolite and edingtonite

Results of structural transformation studies in the natural fibrous zeolites natrolite and edingtonite are presented. The minerals were studied in situ in a wide range of temperatures, pressures and compositions by differential scanning microcalorimetry, thermogravimetry, dilatometry, X-ray diffractometry, nuclear magnetic resonance (NMR)and Raman-spectroscopy. The high-pressure experiments were done in diamond anvil cell and Be-bronze bomb for NMR using liquids with various dimensions of molecules as pressure-transmitting media. A number of structural transformations in natrolites and edingtonite have been found with constant or changing water content during transformation. Under high water pressures, some additional H2O molecules entered the framework channels causing a framework deformation and an anisotropic “swelling” of the crystal. Under compression in nonpenetrating liquids no transformations were detected and above 70 kbar amorphization of the minerals was observed. The same displacive-tilt transformations were observed in zeolites at elevated temperatures as a result of the dehydration, e.g. natrolite ⇌ α-metanatrolite at 280° C. Fully reversible phase transitions at constant H2O content were observed in natrolites and edingtonite at low temperatures (down to -120° C). These are connected with a variation in the mobility and position of exchange cations and water molecules within the framework channels and are followed by significant volume and thermal effects. In dehydrated zeolites, the transformations were found to be similar to the α ⇌ β transition in quartz (α-metanatrolite ⇌ β-metanatrolite). Heating of fibrous zeolites above 500 ÷ 700° C causes their amorphization and formation of porous quasiglass. The principal difference in structural behaviour of microporous crystals under compression in penetrating and nonpenetrating media has essential geochemical implications. Structural transformations of zeolites in P-T-X space demonstrate crystal chemical analogy of these parameters. Some deviations from this analogy depend on complex interactions between channel “filling”, H2O and cations, and the [(Al,Si)-O4/2] framework.