Structural and chemical heterogeneity in ancient glass probed using gas overcondensation, X-ray tomography, and solid-state NMR

Rare ancient glasses have complex, multi-scale structures requiring more sophisticated and non-destructive pore characterisation techniques than usual. Homotattic patch models for nitrogen adsorption gave better fits to the isotherm data, more accurate void space descriptors, and also greater unders...

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Bibliographic Details
Published in:Materials characterization 2020-09, Vol.167, p.110467, Article 110467
Main Authors: Rigby, Sean P., Stevens, Lee, Meersmann, Thomas, Pavlovskaya, Galina E., Rees, Gregory J., Henderson, Julian, Bryant, Saffron J., Edler, Karen J., Fletcher, Robin S.
Format: Article
Language:English
Subjects:
Ancient glass
Computerized X-ray tomography
FEG SEM
Gas sorption
Heterogeneity
Modeling
Overcondensation
Pore network
Solid-state NMR
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Summary:Rare ancient glasses have complex, multi-scale structures requiring more sophisticated and non-destructive pore characterisation techniques than usual. Homotattic patch models for nitrogen adsorption gave better fits to the isotherm data, more accurate void space descriptors, and also greater understanding of the underlying physical factors affecting adsorption, than standard BET. These homotattic patch models revealed the critical role of iron impurities in determining adsorption behaviour. Non-destructive sodium-23 NMR relaxometry validated the homotattic patch model for some natron glasses, and, in turn, was validated using multiple quantum magic-angle spinning (MQMAS) 23Na NMR. X-ray tomography images of the glasses showed the presence of large macroporous bubbles, while FEG-SEM revealed nanopores within the glass matrix. A newly-developed, gas overcondensation technique, suitable for small amounts of low porosity material, assessed the inter-relationship between the disparate levels in this hierarchical porosity. This technique demonstrated that the nanoporosity did not form a ‘corona’ around the bubbles, due to leaching from the glass, as initially supposed from tomography data, but was completely disconnected, and, thus, is probably associated with glass alkalinity. Gas overcondensation is demonstrated as a non-destructive alternative to mercury porosimetry for probing multi-scale porosity in rare artefacts. [Display omitted] •New gas overcondensation characterisation technique for low surface area materials•Independent validation of gas sorption descriptors using solid-state NMR•Determination of impact of glass impurities on pore and matrix structure
ISSN:1044-5803
1873-4189
DOI:10.1016/j.matchar.2020.110467