MRI and PFG NMR studies of percolation effects in advanced melting during a cryoporometry characterisation of disordered mesoporous alumina

Himona, Eleni; Stevens, Lee; Williams, Huw; Rigby, Sean P.

Abstract

Cryoporometry (or thermoporometry) offers a way of pore structural characterisation for mesoporous materials that often needs little sample preparation, is relatively quick, and is statistically-representative for macroscopic samples. While it is well-known that freezing is controlled by pore-blocking, and is thus an invasion percolation process, the percolative nature of pore-to-pore co-operative advanced melting effects has been much less studied. In this work, PFG NMR studies, of diffusivity within the molten phase, have shown that the early melting process follows the scaling law, expected from percolation theory, below the percolation threshold. The percolation threshold thereby obtained was that for a 3D isotropic Poisson polyhedral lattice, consistent with the observation of patchwise macroscopic heterogeneities in the spatial distribution of local average pore size seen in MR relaxation time-weighted images. MRI has shown that once advanced melting effects kicked-in, around the percolation threshold, they occurred to different degrees in different slices along the length of the extrudate pellet. The macroscopic banding in pore-blocking, during freezing, and advanced melting effects, along the axis of the extrudate was consistent with anisotropic diffusional properties observed with MRI. Hence, it has been shown how the pore-pore co-operative effects can be utilised to improve structural characterisation of mesoporous solids.

Citation

Himona, E., Stevens, L., Williams, H., & Rigby, S. P. (2024). MRI and PFG NMR studies of percolation effects in advanced melting during a cryoporometry characterisation of disordered mesoporous alumina. Microporous and Mesoporous Materials, 377, Article 113202. https://doi.org/10.1016/j.micromeso.2024.113202

• Journal Article Type: Article
• Acceptance Date: Jun 3, 2024
• Online Publication Date: Jun 4, 2024
• Publication Date: Sep 1, 2024
• Deposit Date: Jun 6, 2024
• Publicly Available Date: Jun 20, 2024
• Journal: Microporous and Mesoporous Materials
• Print ISSN: 1387-1811
• Electronic ISSN: 1387-1811
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 377
• Article Number: 113202
• DOI: https://doi.org/10.1016/j.micromeso.2024.113202
• Keywords: NMR cryoporometry, MRI, alumina, pore network, advanced melting
• Public URL: https://nottingham-repository.worktribe.com/output/35730754
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S1387181124002245