Post-deposition modification

Studying aeolianites in terms of their mineralogy (indicating the provenance or source area of the sediments), bedding structures, palaeosol horizons and post-depositional modification, particularly at or near palaeo-surfaces, should potentially allow aeolianites to be used as aids in palaeoenvironmental reconstruction (see Curran and White, 1995). However, up until now, the overall usefulness of aeolianites in reconstructing former environments has been somewhat limited. 

Composition of the partings is a function of both the original materials and conditions, and the kind and extent of post-depositional modification. Therefore it is necessary to consider the primary composition (original) separately from the secondary composition (altered). 

Derome, D., Cathehneau, M., Lhomme, T, Crmey, M. (2003). Fluid inclusion evidence of the differential migration of H2 and O2 in the McArthur River unconformity-type uranium deposit (Saskatchewan, Canada). Possible role on post-ore modifications of the host rocks. Journal of Geochemical Exploration, 7B-79, 525-530. 

Pore size tailoring in traditional zeolitic molecular sieve materials has mainly focused on post-synthesis modification. Various organic and inorganic species have been reacted with zeolite surfaces or deposited into the internal pore system with the intent of increasing shape-selectivity and/or altering catalytic activity. Most of this work has focused on reducing the pore size of the molecular sieve. This area has been reviewed by Szostak [37]. 

The USTUR proposed modifications to the ICRP americium model, based on post-mortem americium measurements in human exposure cases (Kathren 1994). The major modifications are 1) the initial deposition fraction is assumed to be skeleton 45%, liver 25%, muscle 20%, other tissues 10% 2) the half-... 

The selectivity of the nickel(l 1 1) surface may thus be controlled by modification of the number of free step sites, and this notion was tested experimentally by blocking the steps with small amounts of silver (84). In other STM investigations it was found that when silver was deposited on nickelfl 1 1) at room temperature, the silver preferentially nucleated and grew as islands at the step edges. When this system was post-annealed to 800 K, the silver atoms were observed to become highly mobile and decorate all the step edges of nickelfl 1 1), as shown in Fig. 6b. 

MF1 type zeolites are known to show enhanced selectivity to p-substituted products in alkylation and isomerization of aromatic molecules [e.g. 1,2,3,4]. This shape selectivity is more pronounced with larger zeolite crystals and can be further enhanced by modification of the parent zeolites through post-synthesis treatments like impregnation with basic oxides, metal salts or the deposition of silica or coke [3,5,6,7]. The gain in selectivity is, however, usually accompanied with loss in catalytic activity and in some cases more rapid deactivation [8,9]. Despite the large number of patents and reports in open literature, the reasons for the enhancement of shape selectivity of MFI zeolites by post-synthesis treatment and the limits of the severity of this treatment are not unequivocally explained to date. 

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