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Structural investig...
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B. Brant Carvalho, Paulo H.Stockholms universitet,Institutionen för material- och miljökemi (MMK),Stockholm Univ, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden
(författare)
Structural investigation of three distinct amorphous forms of Ar hydrate
- Artikel/kapitelEngelska2021
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2021
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Royal Society of Chemistry,2021
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LIBRIS-ID:oai:DiVA.org:umu-189826
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https://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-189826URI
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https://doi.org/10.1039/d1ra05697bDOI
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https://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-199874URI
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Språk:engelska
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Sammanfattning på:engelska
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Three amorphous forms of Ar hydrate were produced using the crystalline clathrate hydrate Ar·6.5H2O (structure II, Fd3m, 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.
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Biuppslag (personer, institutioner, konferenser, titlar ...)
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Moraes, Pedro Ivo R.Department of Chemistry, Federal University of Juiz de Fora, MG, Juiz de Fora, Brazil
(författare)
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Leitão, Alexandre A.Department of Chemistry, Federal University of Juiz de Fora, MG, Juiz de Fora, Brazil
(författare)
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Andersson, OveUmeå universitet,Institutionen för fysik(Swepub:umu)ovan0001
(författare)
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Tulk, Chris A.Neutron Scattering Division, Oak Ridge National Laboratory, TN, Oak Ridge, United States
(författare)
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Molaison, JamieNeutron Scattering Division, Oak Ridge National Laboratory, TN, Oak Ridge, United States
(författare)
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Lyubartsev, Alexander P.Stockholms universitet,Institutionen för material- och miljökemi (MMK)(Swepub:su)lyuba
(författare)
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Häussermann, UlrichStockholms universitet,Institutionen för material- och miljökemi (MMK)(Swepub:su)ulrich
(författare)
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Stockholms universitetInstitutionen för material- och miljökemi (MMK)
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Sammanhörande titlar
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Ingår i:RSC Advances: Royal Society of Chemistry11:49, s. 30744-307542046-2069
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