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A study of freezing-melting hysteresis of water in different porous materials. Part I: Porous silica glasses
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.ORCID iD: 0000-0002-0231-3970
2011 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, Vol. 138, no 1-3, 221-227 p.Article in journal (Refereed) Published
Abstract [en]

The freezing and melting temperature hysteresis of water in Vycor porous glass and controlled pore glass (CPG) with the nominal pore diameters 7.0 and 7.5 nm, respectively, has been explored by NMR cryoporometry and NMR relaxometry techniques. The freezing branch of the hysteresis in Vycor was found to be much steeper than the melting one, presumably due to the pore blocking on freezing. This is not observed in CPG, which exhibits parallel freezing and melting branches. Sub-loops recorded starting from partially frozen states are self-similar with respect to the amount of unfrozen water, in both CPG and Vycor. On the other hand, sub-loops starting from partially molten states are self-similar only in CPG, while in Vycor, their shape does depend on the amount of unfrozen water. T-2 relaxation measurements undertaken along the freezing branch reveal in both glasses a slow (on an NMR timescale) exchange of water molecules between frozen and unfrozen pore domains, indicating a good segregation of those domains on freezing. On melting, however, the regime of slow exchange persists only for CPG, while in Vycor, a quasi-exponential T-2 relaxation is observed, characteristic of fast exchange. This suggests that frozen and molten regions in Vycor are well dispersed on melting, while in CPG they present extended domains. We explain such a difference assuming a worse interconnection of a Vycor's pore space as compared to CPG, taking into account its essentially lower porosity (0.28 versus 0.51 in CPG).

Place, publisher, year, edition, pages
2011. Vol. 138, no 1-3, 221-227 p.
Keyword [en]
Porous glass, Freezing-melting hysteresis, NMR cryoporometry, NMR relaxometry
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-28184DOI: 10.1016/j.micromeso.2010.08.012ISI: 000285168800029Scopus ID: 2-s2.0-78149410690OAI: oai:DiVA.org:kth-28184DiVA: diva2:385143
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20110111Available from: 2011-01-11 Created: 2011-01-10 Last updated: 2011-01-11Bibliographically approved

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Furó, Istvan

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