13 research outputs found
Earthen plasters stabilized through sustainable additives: An experimental campaign
The earthen architecture widely spread in many countries of Europe, America, Asia, Africa, testifies to a particular material and immaterial culture. Nevertheless, it is a fragile heritage, which needs continuous maintenance. To encourage the preservation of such evidence of building techniques, an experimental campaign aimed at the development and evaluation of the performances of protective earthen plasters was undertaken. The durability of the plasters was improved through the addition of different additives, some of them traditional (such as lime and gypsum) and others innovative (geopolymers, enzymes), and resulting from industrial wastes (cement kiln dust). These additives have been selected considering low production costs and a reduced environmental impact, to improve the sustainability of the interventions. The performances of the earthen plasters in terms of efficacy (resistance to water erosion, water absorption, drilling, thermo-hygrometric cycles) and compatibility (changes in color and water vapor permeability) have been evaluated. Good performances were obtained by the different mixtures and, in particular, by those stabilized with gypsum. The results of this experimentation could find a useful application in the preservation of both ancient and new earthen built heritage
Spectroscopic, Morphological and Mechanistic Investigation of the Solvent.Promoted Aggregation of Porphyrins Modified in meso-positions by Glucosylated steroids
Solvent-driven aggregation
of a series of porphyrin derivatives was
studied by UV/Vis and circular dichroism
spectroscopy. The porphyrins are
characterised by the presence in the
meso positions of steroidal moieties
further conjugated with glucosyl
groups. The presence of these groups
makes the investigated macrocycles
amphiphilic and soluble in aqueous solvent,
namely, dimethyl acetamide/
water. Aggregation of the macrocycles
is triggered by a change in bulk solvent
composition leading to formation of
large architectures that express supramolecular
chirality, steered by the presence
of the stereogenic centres on the
periphery of the macrocycles. The aggregation
behaviour and chiroptical
features of the aggregates are strongly
dependent on the number of moieties
decorating the periphery of the porphyrin
framework. In particular, experimental
evidence indicates that the
structure of the steroid linker dictates
the overall chirality of the supramolecular
architectures. Moreover, the porphyrin
concentration strongly affects
the aggregation mechanism and the
CD intensities of the spectra. Notably,
AFM investigations reveal strong differences
in aggregate morphology that
are dependent on the nature of the appended
functional groups, and closely
in line with the changes in aggregation
mechanism. The suprastructures
formed at lower concentration show a
network of long fibrous structures
spanning over tens of micrometres,
whereas the aggregates formed at
higher concentration have smaller rodshaped
structures that can be recognised
as the result of coalescence of
smaller globular structures. The fully
steroid substituted derivative forms
globular structures over the whole concentration
range explored. Finally, a rationale
for the aggregation phenomena
was given by semiempirical calculations
at the PM6 level
Corrosion evaluation of artificially aged 6 wt-% tin bronze
This study concerns the corrosion behaviour of wrought 94 wt-%Cu-6 wt-%Sn (B6) bronze, whose composition is similar to materials used for outdoor bronze artefacts. In order to investigate the influence of the composition and microstructure on bronze corrosion processes, electrochemical ac and dc measurements in synthetic acid rain and chloride solutions were performed on the B6 binary alloy in comparison with an as cast bronze having a different degree of purity. Moreover, to perform thin layer activation (TLA) measurements of thickness loss, a suitable radio nuclide 65Zn (t1/2= 244 days) was produced on B6 specimens by a high energy proton beam. Artificial weathering experiments have been carried out by exposing activated and non-activated B6 specimens: To selected pollutants including NOx and SO2 at different concentrations to simulate urban and industrial atmospheres; in a cyclic salt spray cabinet to investigate the effects of marine environments; to basic (NH4)2SO4 solutions reproducing the aggressiveness of ammonia containing wet deposits. At the end of each test, the B6 corrosion rates obtained by weight loss determinations have been compared with those arising from the TLA method. Finally, the nature and microstructure of the surface oxidation products were investigated
Corrosion Monitoring of Different Steels by Thin Layer Activation.
Abstract not availableJRC.I-Institute for Health and Consumer Protection (Ispra
A corrosion study on artificially aged bronzes of artistic interest
The corrosion behaviour of wrought and as-cast Cu94-Sn6 (B6 and G6, respectively) bronze (whose composition is similar to bronzes for outdoor artefacts) has been investigated. Artificial weathering tests have been carried out by exposing bronze specimens to selected pollutants as NOx and SO2 at different concentrations to simulate urban and industrial environments. Furthermore, the effects of marine atmosphere and acid rains have been investigated by ASTM B117-64 tests carried out on a cyclic salt spray cabinet and by immersion tests. The aggressive action of ammonia containing depositions was investigatedby adopting (NH4)2SO4 solutions.
Dta obtained with conventional techniques have been compared with those arising from TLA technique
Supramolecular chirality in solvent-promoted aggregation of amphiphilic porphyrin derivatives: Kinetic studies and comparison between solution behavior and solid-state morphology by AFM topography
The solvent-promoted aggregation behavior of some amphiphilic porphyrin derivatives bearing chiral functionality in the form of a charged L-proline group has been investigated by UV/Vis, resonance light scattering, fluorescence and circular dichroism spectroscopy. The investigated macro- cycles give rise to aggregates featuring supramolecular chirality with high el- lipticity. Kinetic studies reveal peculiar differences in the fashion of aggregation, depending on the intimate nature of the chiral functionality, namely, cat- ionic (nitrogen-quaternized L-proline, 3H2) or anionic (carboxylate residue, 6H2) group. Formation of anionic 6H2 aggregates shows a diffusion-limited kinetic behavior. AFM topography studies show formation of tighter globular structures. On the other hand, the corresponding 3H2 aggregates are formed by a cooperative, fractal-type decay, and appear as long-fibrous, looser structures. In the templated aggregation of 3H2 over preformed 6H2 aggregates, AFM images show formation of globular structures with reduced sizes, as a likely consequence of shorter in- terchromophore distances, due to favorable Coulombic interactions. The results obtained show an interesting parallelism between the solution behavior and the solid-state aggregate structures, corroborating the sergeant- soldier effect observed in the templat- ed aggregation. The results presented give important insights for understanding the complex mechanisms involved in these issues, which are of key importance for the development of chiral supramolecular materials and stereose- lective sensors and devices. ©2010 Wiley-VCH Verlag GmbH & Co. KGaA
Solid state deposition of chiral amphiphilic porphyrin derivatives on glass surface
Herein, we present a straightforward method to achieve optically active films based on porphyrin derivatives. The introduction of an aminoacid functionality on the porphyrin platform confers to the macrocycle both the amphiphilic and chiral character exploited for its solvent-promoted self-aggregation leading to the formation of chiral supramolecular architectures. These ordered suprastructures have the propensity to spontaneously layer as solid films on glass surfaces. The deposited material has been characterized by means of UV-visible, fluorescence emission, circular dichroism spectroscopy and AFM. The reported studies show once more how the stereochemical information stored on a single porphyrin framework can induce the formation of supramolecular chiral architectures, in solution, as well as in solid state. Furthermore, slight modifications on the porphyrin skeleton can influence the aggregation process and the structural features of the final assemblies, leading to solid surfaces featuring different morphologies. These combined aspects can be of great importance for the achievement of solid state chemical sensors with stereoselective properties
Solid state deposition of chiral amphiphilic porphyrin derivatives on glass surface
Herein, we present a straightforward method to achieve optically active films based on porphyrin derivatives. The introduction of an aminoacid functionality on the porphyrin platform confers to the macrocycle both the amphiphilic and chiral character exploited for its solvent-promoted self-aggregation leading to the formation of chiral supramolecular architectures. These ordered suprastructures have the propensity to spontaneously layer as solid films on glass surfaces. The deposited material has been characterized by means of UV-visible, fluorescence emission, circular dichroism spectroscopy and AFM. The reported studies show once more how the stereochemical information stored on a single porphyrin framework can induce the formation of supramolecular chiral architectures, in solution, as well as in solid state. Furthermore, slight modifications on the porphyrin skeleton can influence the aggregation process and the structural features of the final assemblies, leading to solid surfaces featuring different morphologies. These combined aspects can be of great importance for the achievement of solid state chemical sensors with stereoselective properties