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Pressure-Induced Amorphization and Distinct Amorphous States of Clathrate Hydrates
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).ORCID-id: 0000-0003-2296-4911
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis summarizes a study on the pressure-induced amorphization (PIA) and structures of amorphous states of clathrate hydrates (CHs).

PIA involves the transition of a crystalline material into an amorphous solid in response of mechanical compression at temperatures well below the melting point. The first material observed to undergo PIA was hexagonal ice. More recently it was shown that compounds of water undergo the same phenomenon without decomposition, despite the presence of solutes. CHs, which are crystalline inclusion compounds consisting of water molecules encaging small guest species, undergo PIA at ca. 1–4 GPa below 145 K. The obtained amorphous CH phase can be further densified on isobaric heating at high pressure. This annealing step enables to retain an amorphous material on pressure release. There has been a significant amount of studies into the understanding of the nature of PIA and transformations between amorphous phases of pure ice. The aim of this thesis has been the understanding of the PIA in CHs and its relation to pure ice. New information on the nature of PIA and subsequent amorphous-amorphous transitions in CH systems were gained from structural studies and in situ neutron diffraction played pivotal role due to the sensitivity of neutrons to the light element hydrogen. Here a generalized understanding of the PIA in CHs and a clear image of amorphous CH structures are presented.

Abstract [sv]

Denna avhandling sammanfattar en studie om tryckinducerad amorfisering (TIA) av klatrathydrater (KH), samt strukturer av amorfa tillstånd där av.

TIA är övergången av ett kristallint material till ett amorft fast ämne som svar på mekanisk kompression vid temperaturer långt under smältpunkten. Det första materialet som observerades genomgå TIA var hexagonal is. Därefter har det visat sig att det finns strukturer av vatten som trots närvaron av lösta ämnen genomgår samma fenomen utan att strukturen bryts ned. KH:er är kristallina inneslutningskomplex som består av ett gitter av vattenmolekyler, vilka omsluter små gästmolekyler. Dessa strukturer genomgår TIA vid ca. 1–4 GPa vid temperaturer under 145 K. Den erhållna amorfa KH-fasen kan förtätas ytterligare vid isobarisk uppvärmning under högt tryck. Detta steg gör det möjligt att behålla ett amorft material vid tryckavlastning. Det har gjorts en betydande mängd studier av TIA:s natur och omvandlingar mellan amorfa faser av ren is. Syftet med denna avhandling har varit att förstå TIA i KH:er och dess relation till ren is. Ny information om karaktären hos TIA och efterföljande amorfa-amorfa övergångar i KH-system erhölls från strukturella studier, där in situ neutrondiffraktion spelade en avgörande roll tack vare neutronernas känslighet för det lätta elementet väte. Utifrån detta arbete presenteras här en generaliserad förståelse av TIA i KH samt en tydlig bild av amorfa KH-strukturer.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University , 2023. , s. 78
Nyckelord [en]
Clathrate Hydrates, Pressure-Induced Amorphization, Amorphous States, Glassy States, Ice, Neutron Diffraction
Nyckelord [sv]
Klatrathydrater, Tryckinducerad Amorfisering, Amorfa tillstånd, Glasartade tillstånd, Is, Neutrondiffraktion
Nationell ämneskategori
Den kondenserade materiens fysik Materialkemi
Forskningsämne
fysikalisk kemi
Identifikatorer
URN: urn:nbn:se:su:diva-214449ISBN: 978-91-8014-186-4 (tryckt)ISBN: 978-91-8014-187-1 (digital)OAI: oai:DiVA.org:su-214449DiVA, id: diva2:1733938
Disputation
2023-03-31, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2023-03-08 Skapad: 2023-02-03 Senast uppdaterad: 2023-03-01Bibliografiskt granskad
Delarbeten
1. Elucidating the guest disorder in structure II argon hydrate - A neutron diffraction isotopic substitution study
Öppna denna publikation i ny flik eller fönster >>Elucidating the guest disorder in structure II argon hydrate - A neutron diffraction isotopic substitution study
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2020 (Engelska)Ingår i: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 285, artikel-id 121220Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Clathrate hydrates with the cubic structure II (CS-II) form typically with large guest molecules, such as tetrahydrofuran, trimethylamine oxide, or propane. However, CS-II is also realized for argon hydrate despite the comparatively small van der Waals diameter of the guest (around 3.8 angstrom). Here, the structure of deuterated argon hydrate was studied at ambient pressure in the temperature range 20-95 K using neutron diffraction and comparing natural Ar with Ar-36, which scatters neutrons more than 13 times more efficiently. The procedure allowed to unambiguously establish the positional disorder within the large cages of CS-H, while simultaneously refining host and guest structures. These cages are singly occupied and off-centered argon atoms distribute on two tetrahedron-shaped split positions with a ratio 3:1. Molecular dynamics (MD) simulations revealed that the crystallographic positional disorder structure is due to mobile argon atoms even at 20 K. The MD potential energy distribution confirmed the diffraction model. It is noted that the unit cell volumes of argon hydrate in the investigated temperature range are virtually identical to N-2 hydrate, which has a similar composition at ambient pressure, indicating a very similar (slightly attractive) host-guest interaction.

Nyckelord
Clathrate hydrates, Disorder, Neutron diffraction
Nationell ämneskategori
Kemi
Identifikatorer
urn:nbn:se:su:diva-181309 (URN)10.1016/j.jssc.2020.121220 (DOI)000521107900003 ()
Tillgänglig från: 2020-05-24 Skapad: 2020-05-24 Senast uppdaterad: 2023-02-03Bibliografiskt granskad
2. Transitions in pressure-amorphized clathrate hydrates akin to those of amorphous ices
Öppna denna publikation i ny flik eller fönster >>Transitions in pressure-amorphized clathrate hydrates akin to those of amorphous ices
2019 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, nr 1, artikel-id 014502Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Type II clathrate hydrates (CHs) were studied by thermal and dielectric measurements. All CHs amorphize, or collapse, on pressurization to 1.3 GPa below 135 K. After heating to 160 K at 1 GPa, the stability of the amorphous states increases in a process similar to the gradual high density to very high density amorphous ice (HDA to VHDA) transition. On a subsequent pressure decrease, the amorphized CHs expand partly irreversibly similar to the gradual VHDA to expanded HDA ice transformation. After further heating at 1 GPa, weak transition features appear near the HDA to low density amorphous ice transition. The results suggest that CH nucleation sites vanish on heating to 160 K at 1 GPa and that a sluggish partial phase-separation process commences on further heating. The collapsed CHs show two glass transitions (GTs), GT1 and GT2. GT1 is weakly pressure-dependent, 12 K GPa(-1), with a relaxation time of 0.3 s at 140 K and 1 GPa; it is associated with a weak heat capacity increase of 3.7 J H2O-mol(-1) K-1 in a 18 K range and an activation energy of only 38 kJ mol(-1) at 1 GPa. The corresponding temperature of GT2 is 159 K at 0.4 GPa with a pressure dependence of 36 K GPa(-1); it shows 5.5 times larger heat capacity increase and 4 times higher activation energy than GT1. GT1 is observed also in HDA and VHDA, whereas GT2 occurs just above the crystallization temperature of expanded HDA and only within its similar to 0.2-0.7 GPa stable pressure range.

Nationell ämneskategori
Kemi Fysik
Identifikatorer
urn:nbn:se:su:diva-171762 (URN)10.1063/1.5096981 (DOI)000474214600007 ()31272168 (PubMedID)
Tillgänglig från: 2019-09-04 Skapad: 2019-09-04 Senast uppdaterad: 2023-02-03Bibliografiskt granskad
3. Elucidation of the pressure induced amorphization of tetrahydrofuran clathrate hydrate
Öppna denna publikation i ny flik eller fönster >>Elucidation of the pressure induced amorphization of tetrahydrofuran clathrate hydrate
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2019 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 20, artikel-id 204506Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The type II clathrate hydrate (CH) THF center dot 17 H2O (THF = tetrahydrofuran) is known to amorphize on pressurization to similar to 1.3 GPa in the temperature range 77-140 K. This seems to be related to the pressure induced amorphization (PIA) of hexagonal ice to high density amorphous (HDA) ice. Here, we probe the PIA of THF-d(8)center dot 17 D2O (TDF-CD) at 130 K by in situ thermal conductivity and neutron diffraction experiments. Both methods reveal amorphization of TDF-CD between 1.1 and 1.2 GPa and densification of the amorphous state on subsequent heating from 130 to 170 K. The densification is similar to the transition of HDA to very-high-density-amorphous ice. The first diffraction peak (FDP) of the neutron structure factor function, S(Q), of amorphous TDF-CD at 130 K appeared split. This feature is considered a general phenomenon of the crystalline to amorphous transition of CHs and reflects different length scales for D-D and D-O correlations in the water network and the cavity structure around the guest. The maximum corresponding to water-water correlations relates to the position of the FDP of HDA ice at similar to 1 GPa. Upon annealing, the different length scales for water-water and water-guest correlations equalize and the FDP in the S(Q) of the annealed amorph represents a single peak. The similarity of local water structures in amorphous CHs and amorphous ices at in situ conditions is confirmed from molecular dynamics simulations. In addition, these simulations show that THF guest molecules are immobilized and retain long-range correlations as in the crystal.

Nationell ämneskategori
Kemi Fysik
Identifikatorer
urn:nbn:se:su:diva-171157 (URN)10.1063/1.5083958 (DOI)000473301400044 ()31153163 (PubMedID)
Tillgänglig från: 2019-08-16 Skapad: 2019-08-16 Senast uppdaterad: 2023-02-03Bibliografiskt granskad
4. Pressure-induced amorphization of noble gas clathrate hydrates
Öppna denna publikation i ny flik eller fönster >>Pressure-induced amorphization of noble gas clathrate hydrates
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2021 (Engelska)Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, nr 6, artikel-id 064205Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The high-pressure structural behavior of the noble gas (Ng) clathrate hydrates Ar center dot 6.5 H2O and Xe center dot 7.2 H2O featuring cubic structures II and I, respectively, was investigated by neutron powder diffraction (using the deuterated analogues) at 95 K. Both hydrates undergo pressure-induced amorphization (PIA), indicated by the disappearance of Bragg diffraction peaks, but at rather different pressures, at 1.4 and above 4.0 GPa, respectively. Amorphous Ar hydrate can be recovered to ambient pressure when annealed at >1.5 GPa and 170 K and is thermally stable up to 120 K. In contrast, it was impossible to retain amorphous Xe hydrate at pressures below 3 GPa. Molecular dynamics (MD) simulations were used to obtain general insight into PIA of Ng hydrates, from Ne to Xe. Without a guest species, both cubic clathrate structures amorphize at 1.2 GPa, which is very similar to hexagonal ice. Filling of large-sized H cages does not provide stability toward amorphization for structure II, whereas filled small-sized dodecahedral D cages shift PIA successively to higher pressures with increasing size of the Ng guest. For structure I, filling of both kinds of cages, large-sized T and small-sized D, acts to stabilize in a cooperative fashion. Xe hydrate represents a special case. In MD, disordering of the guest hydration structure is already seen at around 2.5 GPa. However, the different coordination numbers of the two types of guests in the crystalline cage structure are preserved, and the state is shown to produce a Bragg diffraction pattern. The experimentally observed diffraction up to 4 GPa is attributed to this semicrystalline state.

Nyckelord
Elastic modulus, Pressure effects
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-192476 (URN)10.1103/PhysRevB.103.064205 (DOI)000619132400002 ()
Tillgänglig från: 2021-04-21 Skapad: 2021-04-21 Senast uppdaterad: 2023-02-03Bibliografiskt granskad
5. Exploring High-Pressure Transformations in Low-Z (H2, Ne) Hydrates at Low Temperatures
Öppna denna publikation i ny flik eller fönster >>Exploring High-Pressure Transformations in Low-Z (H2, Ne) Hydrates at Low Temperatures
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2022 (Engelska)Ingår i: Crystals, ISSN 2073-4352, Vol. 12, nr 1, artikel-id 9Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The high pressure structural behavior of H2 and Ne clathrate hydrates with approximate composition H2/Ne·~4H2O and featuring cubic structure II (CS-II) was investigated by neutron powder diffraction using the deuterated analogues at ~95 K. CS-II hydrogen hydrate transforms gradually to isocompositional C1 phase (filled ice II) at around 1.1 GPa but may be metastably retained up to 2.2 GPa. Above 3 GPa a gradual decomposition into C2 phase (H2·H2O, filled ice Ic) and ice VIII’ takes place. Upon heating to 200 K the CS-II to C1 transition completes instantly whereas C1 decomposition appears sluggish also at 200 K. C1 was observed metastably up to 8 GPa. At 95 K C1 and C2 hydrogen hydrate can be retained below 1 GPa and yield ice II and ice Ic, respectively, upon complete release of pressure. In contrast, CS-II neon hydrate undergoes pressure-induced amorphization at 1.9 GPa, thus following the general trend for noble gas clathrate hydrates. Upon heating to 200 K amorphous Ne hydrate crystallizes as a mixture of previously unreported C2 hydrate and ice VIII’.

Nyckelord
hydrogen hydrate, neon hydrate, pressure effects, neutron diffraction, molecular dynamics, clathrate hydrates
Nationell ämneskategori
Kemi
Identifikatorer
urn:nbn:se:su:diva-201882 (URN)10.3390/cryst12010009 (DOI)000749277100001 ()
Tillgänglig från: 2022-02-10 Skapad: 2022-02-10 Senast uppdaterad: 2023-02-03Bibliografiskt granskad
6. Structural investigation of three distinct amorphous forms of Ar hydrate
Öppna denna publikation i ny flik eller fönster >>Structural investigation of three distinct amorphous forms of Ar hydrate
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2021 (Engelska)Ingår i: RSC Advances, E-ISSN 2046-2069, Vol. 11, nr 49, s. 30744-30754Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Three amorphous forms of Ar hydrate were produced using the crystalline clathrate hydrate Ar·6.5H2O (structure II, Fdm, a ≈ 17.1 Å) as a precursor and structurally characterized by a combination of isotope substitution (36Ar) neutron diffraction and molecular dynamics (MD) simulations. The first form followed from the pressure-induced amorphization of the precursor at 1.5 GPa at 95 K and the second from isobaric annealing at 2 GPa and subsequent cooling back to 95 K. In analogy to amorphous ice, these amorphs are termed high-density amorphous (HDA) and very-high-density amorphous (VHDA), respectively. The third amorph (recovered amorphous, RA) was obtained when recovering VHDA to ambient pressure (at 95 K). The three amorphs have distinctly different structures. In HDA the distinction of the original two crystallographically different Ar guests is maintained as differently dense Ar–water hydration structures, which expresses itself in a split first diffraction peak in the neutron structure factor function. Relaxation of the local water structure during annealing produces a homogeneous hydration environment around Ar, which is accompanied with a densification by about 3%. Upon pressure release the homogeneous amorphous structure undergoes expansion by about 21%. Both VHDA and RA can be considered frozen solutions of immiscible Ar and water in which in average 15 and 11 water molecules, respectively, coordinate Ar out to 4 Å. The local water structures of HDA and VHDA Ar hydrates show some analogy to those of the corresponding amorphous ices, featuring H2O molecules in 5- and 6-fold coordination with neighboring molecules. However, they are considerably less dense. Most similarity is seen between RA and low density amorphous ice (LDA), which both feature strictly 4-coordinated H2O networks. It is inferred that, depending on the kind of clathrate structure and occupancy of cages, amorphous states produced from clathrate hydrates display variable local water structures.

Nationell ämneskategori
Kemi
Identifikatorer
urn:nbn:se:su:diva-199874 (URN)10.1039/d1ra05697b (DOI)000716016000001 ()
Tillgänglig från: 2022-01-10 Skapad: 2022-01-10 Senast uppdaterad: 2023-02-03Bibliografiskt granskad
7. Neutron scattering study of polyamorphic THF ∙ (H2O)17 – toward a generalized picture of amorphous states and structures derived from clathrate hydrates
Öppna denna publikation i ny flik eller fönster >>Neutron scattering study of polyamorphic THF ∙ (H2O)17 – toward a generalized picture of amorphous states and structures derived from clathrate hydrates
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

From crystalline tetrahydrofuran clathrate hydrate, THF-CH (THF ∙ 17H2O, cubic structure II), three distinct polyamorphs can be derived. First, THF-CH undergoes pressure-induced amorphization when pressurized to 1.3 GPa in the temperature range 77–140 K to a form which, in analogy to pure ice, may be called high-density amorphous (HDA). Second, HDA can be converted to a densified form, very-HDA (VHDA), upon heat-cycling at 1.8 GPa to 180 K. Decompression of VHDA to atmospheric pressure below 130 K produces the third, recovered amorphous (RA) form. Results from a compilation of neutron scattering experiments and molecular dynamics simulations provide a generalized picture of the structure of amorphous THF hydrates with respect to crystalline THF-CH and liquid THF ∙ 17H2O solution (~2.5 M). The calculated density of (only in situ observable) HDA and VHDA at 2 GPa and 130 K is 1.287 and 1.328 g/cm3, respectively, whereas that of RA (at 1 atm) is 1.081 g/cm3. Although fully amorphous, HDA is heterogeneous with two length scales for water-water correlations (less dense local water structure) and guest-water correlations (denser THF hydration structure). The hydration structure of THF is influenced by guest-host hydrogen bonding. THF molecules maintain a quasiregular array, reminiscent of the crystalline state, and their hydration structure (out to 5 Å) constitutes ~23 H2O. The local water structure in HDA is reminiscent of pure HDA-ice, featuring 5-coordinated H2O. In VHDA, this structure is maintained but the local water structure is densified to resemble pure VHDA-ice with 6-coordinated H2O. The hydration structure of THF in RA constitutes ~18 H2O and the water structure corresponds to a strictly 4-coordinated network, as in the liquid. Both VHDA and RA can be considered as homogeneous, solid solutions of THF and water. The local water structure of water-rich (1:17) amorphous CHs resembles most that of the corresponding amorphous water ices when compared to guest-rich CHs, e.g., Ar ∙ ~6H2O. The proposed significance of different contributions of water local environments presents a simple view to justify neutron structure factor features.

Nyckelord
Clathrate Hydrate, Amorphous, Neutron Diffraction
Nationell ämneskategori
Den kondenserade materiens fysik
Forskningsämne
fysikalisk kemi; materialkemi
Identifikatorer
urn:nbn:se:su:diva-214446 (URN)
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF)
Tillgänglig från: 2023-02-03 Skapad: 2023-02-03 Senast uppdaterad: 2023-02-06
8. Evidence suggesting kinetic unfreezing of water mobility in two distinct processes in pressure-amorphized clathrate hydrates
Öppna denna publikation i ny flik eller fönster >>Evidence suggesting kinetic unfreezing of water mobility in two distinct processes in pressure-amorphized clathrate hydrates
2022 (Engelska)Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 24, nr 34, s. 20064-20072Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Type II clathrate hydrates (CHs) with tetrahydrofuran (THF), cyclobutanone (CB) or 1,3-dioxolane (DXL) guest molecules collapse to an amorphous state near 1 GPa on pressurization below 140 K. On subsequent heating in the 0.2–0.7 GPa range, thermal conductivity and heat capacity results of the homogeneous amorphous solid show two glass transitions, first a thermally weak glass transition, GT1, near 130 K; thereafter a thermally strong glass transition, GT2, which implies a transformation to an ultraviscous liquid on heating. Here we compare the GTs of normal and deuterated samples and samples with different guest molecules. The results show that GT1 and GT2 are unaffected by deuteration of the THF guest and exchange of THF with CB or DXL, whereas the glass transition temperatures (Tgs) shift to higher temperatures on deuteration of water; Tg of GT2 increases by 2.5 K. These results imply that both GTs are associated with the water network. This is corroborated by the fact that GT2 is detected only in the state which is the amorphized CH's counterpart of expanded high density amorphous ice. The results suggest a rare transition sequence of an orientational glass transition followed by a glass to liquid transition, i.e., kinetic unfreezing of H2O reorientational and translational mobility in two distinct processes.

Nationell ämneskategori
Kemi
Identifikatorer
urn:nbn:se:su:diva-208218 (URN)10.1039/d2cp01993k (DOI)000827757400001 ()35856694 (PubMedID)2-s2.0-85134902758 (Scopus ID)
Tillgänglig från: 2022-08-25 Skapad: 2022-08-25 Senast uppdaterad: 2023-02-03Bibliografiskt granskad

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