1,720,992 research outputs found
Effect of solvents and pH on in situ formation of hydroxyapatite for stone conservation
No full textIn situ formation of hydroxyapatite (HAP) inside the cracks and on the surface of calcareous substrates (e.g. marble and limestone) has been proposed for consolidation and protection of cultural heritage. HAP can be formed in situ by reacting the substrate with an aqueous solution of diammonium hydrogen phosphate (DAP). Taking inspiration from literature on bioceramics and from recent computational results, in the present study different strategies were explored to improve the consolidating efficacy of the DAP solution, namely by increasing pH or by adding organic solvents. A 1 M DAP +1 mM CaCl2 solution was taken as a reference and compared to 10-fold more diluted solutions (0.1 M DAP + 0.1 mM CaCl2) at pH 8, 10 or 12 and with addition of 20 wt% ethanol, isopropanol, or acetone. The solutions were applied onto weathered marble specimens and the formation of the new phases was characterized by FEG-SEM and XRD, while the strengthening ability was assessed in terms of bulk mechanical properties and surface properties. The results of this study indicate that apatite phases (mostly likely carbonate HAP with possible stoichiometric HAP) were formed as the result of all treatments, except at pH 12 when undesired ammonium calcium phosphate hydrate was formed. In terms of strengthening efficacy, when in-depth consolidation is needed, the more concentrated DAP solutions are able to provide higher strengthening ability. When consolidation of the most superficial layer is desired, less concentrated solutions are able to provide satisfactory results, allowing for a substantial reduction in the use of DAP with economic and environmental advantages
Nanolime, nanosilica or ammonium phosphate? Laboratory and field study on consolidation of a byzantine marble sarcophagus
Full text linkThe present paper aims at comparing commercial nanolime and nanosilica dispersions with an aqueous solution of diammonium hydrogen phosphate (DAP) for consolidation of marble. The consolidants were first tested in the laboratory on artificially and naturally weathered marble specimens. The DAP-treatment applied by poulticing outperformed nanolime and nanosilica in terms of consolidating effectiveness, while showing good compatibility with the substrate. After preliminary testing of all the three consolidants on small areas of a byzantine marble sarcophagus, the DAP-treatment applied by poulticing was finally selected for application onto the whole sarcophagus. Field results confirmed the promising performance of the DAP-treatment
Durability of Lime Mortars Treated with Ammonium Phosphate
No full textThe present paper aims at comparing diammonium hydrogen phosphate (DAP) and nanolimes (NL) as consolidants for the preservation of lime mortars. The durability of the two consolidants was evaluated in terms of resistance to freezing thawing and salt crystallization cycles. The results of the study point out that, compared to the untreated reference and NL-treated samples, DAP-treated mortars showed much improved resistance to freezing-thawing cycles. A lower benefit was found in the case of salt crystallization cycles, as DAP-treated samples exhibited a behavior substantially similar to untreated and NL-treated ones. The different improvement in durability observed for the two weathering processes could be ascribed, on the one hand, to the slight modification of the pore size distribution after treatment (which may lead to increased crystallization pressure) and, on the other hand, to the severity of the salt weathering test (involving the use of a saturated Na2SO4·10H2O solution). All things considered, the potential of the DAP treatment for the conservation of lime-based mortars is confirmed
Adsorption of water and organic solvents on the calcite [101 ̄4] surface: Implications for marble conservation treatments
Full text linkWhen exposed outdoors, marble artefacts are subject to degradation caused by dissolution in rain. To improve acid-resistance of marble, surface treatments involving the in situ formation of a passivating calcium phosphate (CaP) layer have been developed. Adding alcohol to the treatment improves CaP coverage but the reason is still unclear. Here, we use computational and experimental studies to ascertain whether the interaction of the organic additives with the marble surface plays a role in determining the treatment outcome. Density functional theory calculations are employed to determine the binding energy of additives on the calcite [101 ̄4] surface and identify acetone as a promising new additive due to its weak adsorption. Molecular dynamics calculations show that ethanol and isopropanol displace water from the calcite [101 ̄4] surface forming an immobile, ordered, and hydrophobic layer, while acetone and water form a mixed, dynamic environment. In experimental trials, a continuous (yet cracked) layer of carbonate hydroxyapatite is formed after 24 h, with all organic additives improving the final coating. This result suggests that the interaction of the additive with the marble surface does not play a major role in determining treatment outcomes and other factors should be investigated for the design of improved treatments
Influence of salt contamination on consolidation of slaked lime mortar by ammonium phosphate and nanolimes
Full text linkThis study aimed at evaluating the influence of salt contamination on the performance of two consolidants (diammonium hydrogen phosphate, DAP, and nanolimes, NL), applied onto slaked lime-based mortars contaminated with sodium sulfate before and/or after consolidation. The strengthening ability of the two treatments was assessed in terms of dynamic elastic modulus and compressive strength by double punch test, while the alterations in the pore system were evaluated by MIP and the features of the new consolidating phases were assessed by XRD and FEG-SEM. To test the durability of the consolidated mortars, salt weathering cycles were performed by alternating immersion into a 14 wt% aqueous solution of Na2SO4·10H2O and drying in oven, as recommended by the European Standard EN 12370. The effects of the salt weathering cycles were assessed by measuring the changes in weight and dynamic elastic modulus after each cycle and the residual compressive strength after 10 cycles and desalination. The results of the study show that, right after the consolidant application, with or without salts initially present in the mortar, the strengthening ability of DAP was higher than that of NL. The DAP treatment induced formation of carbonate hydroxyapatite, as assessed by XRD, and notably the initial presence of salt inside the mortar pores did not negatively affect the outcome of the treatment. However, the formation of carbonate hydroxyapatite was responsible for a shift of the pore size distribution towards smaller pores, which may increase the stress generated by salt crystallization. When the consolidated mortar specimens were subjected to salt weathering cycles, both consolidants provided some benefit against salt weathering, but the high aggressiveness of the salt weathering test might have reduced the performance of the consolidants
Resistance of consolidated lime mortars to freeze-thaw and salt crystallization cycles by different accelerated durability tests
Full text linkThe present study aimed at evaluating the performance of untreated and consolidated lime mortars, in terms of durability and possible "delayed incompatibility" of the consolidants. Lime mortars samples were treated by an aqueous solution of diammonium hydrogen phosphate (DAP treatment) and a dispersion of nanolimes (NL treatment). The samples were then subjected to accelerated ageing by different methods: (1) freeze-thaw cycles; (2) salt crystallization cycles based on the European standard EN 12370 (often considered as highly aggressive); (3) salt crystallization cycles according to a new recommendation proposed by the RILEM TC 271-ASC (designed to provide less aggressive and more reliable ageing). The results of the study showed that the DAP-based treatment was able to significantly reduce damage caused by freeze-thaw cycles and salt weathering cycles by the RILEM procedure. In the case of salt weathering by the EN procedure, some risk of "delayed incompatibility" was highlighted for DAP, which can be considered an outcome of the combination between the salt weathering procedure itself and the consolidating treatment. For both freeze-thaw and salt weathering by either procedure, the residual mechanical properties of DAP samples at the end of the cycles were significantly higher than those of the untreated references and of the NL samples, for which the effects of the NL treatment were very modest
“La biopsia del linfonodo sentinella nel carcinoma a cellule squamose della cavità orale e dell’orofaringe: risultati preliminari”.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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