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Rock salt caverns have been extensively used as reliable repositories for hazardous waste such as nuclear waste, oil or compressed gases. Undisturbed rock salt deposits in nature are usually impermeable and have very low porosity. However, rock salt formations under excavation stresses can develop crack networks, which increase their porosities; and in the case of a connected crack network within the media, rock salt may become permeable. Although the relationship between the permeability of rock salt and the applied stresses has been reported in the literature, a microscopic study that investigates the properties influencing this relationship, such as the evolution of texture and internal stresses, has yet to be conducted. This study employs in situ 3D synchrotron micro-computed tomography and 3D X-ray diffraction (3DXRD) on two small-scale polycrystalline rock salt specimens to investigate the evolution of the texture and internal stresses within the specimens. The 3DXRD technique measures the 3D crystal structure and lattice strains within rock salt grains. The specimens were prepared under 1D compression conditions and have shown an initial {111} preferred texture, a dominant {110}〈1 1 0〉 slip system and no fully connected crack network. The {111} preferred texture under the unconfined compression experiment became stronger, while the {111}〈1 1 0〉 slip system became more prominent. The specimens did not have a fully connected crack network until applied axial stresses reached about 30 MPa, at a point where the impermeability of the material becomes compromised due to the development of multiple major cracks. 

Abstract The tetrahedral geometry of organolead(IV) compounds can be readily transformed by using an organic ligand containing a dangling-arm oxygen functionality. The acidity of the Pb center results in so-called secondary bonding between O and Pb thereby pushing the geometry at Pb toward a trigonal bipyramidal (tbp) structure. Replacing a phenyl group by a chlorine atom dramatically enhances this phenomenon. Thus for (o-methoxybenzyl) triphenyllead (4), and (o-methoxybenzyl)diphenyllead chloride (5), the Pb–O internuclear distances are 3.362(4) and 2.845(3) Å, respectively; 83% (4) and 70% (5) of the sum of the van der Waals Pb and O radii. Within the group 14 element congeners the structural analysis of the (o-methoxybenzyl)triphenylE compounds, E = Si, Ge, Sn, and now Pb, demonstrates the relative acidities of E are Si < Ge < Sn < Pb. 

The syntheses of [2-(CH 3 ECH 2 )C 6 H 4 ]PbPh 3− n Cl n , ( n = 0, E = O (4), E = S (5); n = 1, E = O (6), E = S (7); n = 2, E = O (8), are described. NMR and single crystal data illustrate significant Pb⋯E interactions increasing as n progresses from 0 to 2. The Pb⋯E interactions stabilize the Pb–aryl bonding to the extent that the reactions of 4 and 5 with Me 2 SnCl 2 result in interchange of a Ph group and Cl to produce 6 and 7, respectively, together with Me 2 PhSnCl.