1,721,095 research outputs found
Ancient glass artefacts: from the conservator practice to a scientific inorganic chemical approach
No full textHistorical Glass Surfaces: an Inorganic Chemical Approach to Arrest Decay
No full textUnweathered inorganic glasses are smooth dense substances. Their surfaces are covered with layers of adsorbed water so that few materials will adhere satisfactorily to them.
Early painted glass, expecially of the XII and XIII centuries in central Europe, has the high potash, high lime composition which deteriorates with the formation of opaque crusts. As a consequence of this, most of medieval cathedrals with painted glass windows are rather dark inside.
To prevent this effect a chemical approach comes from the inorganic basin through an inorganic polymeric thin layer with properties of clarity, transparency, no discoloration with aging and an improved ability to adhere to glass and to polymerize in situ at room temperature with little or no shrinkage occurring. Its name is vitreous silica and it can be obtained through the sol-gel technique (polymerization of silicon alkoxide monomers).
We studied the chemical and morphological modifications induced on silica samples by the immersions in basic Ca(OH)2 solutions at different temperatures (room temperature, 60°C and 80°C) and for different time intervals (1 hour and 21 hours). Treatments with Ca(OH)2 solutions were carried out on two different kinds of pure silica: commercial fused-silica slides and silica films obtained via sol-gel process.
The experimental results show that calcium hydroxide can be chemisorbed by vitreous silica structure and that it can diffuse through the network forming a surface layer of calcium silicate, that is, a layer probably containing many Si-O-Ca-O-Si bridges. Furthermore it has been clearly noted a different behaviour of sol-gel films with respect to fused-silica slides after immersion, probably because of their different tridimensional structures: sol-gel coatings present a very low-density structure with holes and voids through which calcium ions can migrate and diffuse to the inner atomic layers. On the other hand, fused silica is able to keep a very little amount of calcium ions segregated to the few outermost atomic layers for its greater density; on more the SIMS analysis shows a leaching of the fused silica substrate
The development of growth rings on ancient glass surfaces: Description and simulation of the weathering
No full textThe present work investigates the weathering process of glass surfaces with the formation of corrosion growth rings investigated by
X-ray photoelectron spectroscopy, optical microscope, environmental scanning electron microscope and particle induced X-ray emission.
The analysed samples are both ancient and recent glasses. The first set of samples is constituted by Roman glass fragments originally
belonging to the load of the Iulia Felix ship, sunken in the Northern Adriatic sea (Grado, Italy) during II century AD. The samples
were already investigated in the past [F. Barbana, R. Bertoncello, L. Milanese, C. Sada, J. Non-Cryst. Solids 337 (2) (2004) 136; B. Dal
Bianco, R. Bertoncello, L. Milanese, S. Barison, J. Non-Cryst. Solids 343 (2004) 91; B. Dal Bianco, R. Bertoncello, L. Milanese, S. Barison,
Surface Eng. 21 (5–6) (2005) 393; B. Dal Bianco, R. Bertoncello, L. Milanese, S. Barison, Archaeometry 47 (2) (2005) 353], but their
production process is still unknown. The second set of samples belongs to the stained window of S. Giovanni church in Polegge (Vicenza,
Italy) and it is dated to 1930 ca. The glass production process is well known. In fact, every tessera is made of soda-lime glass. On one side
only, the glass is coated with a green pigment (low melting temperature glass) and then heated in oven in order to fix it on the glass. The
window is then mounted and fixed to the wall. Unfortunately, during this procedure, the window was positioned inside-out, so that the
painted surface was exposed to the direct action of the atmospheric conditions. This anomaly favoured the fast degradation of the tessera,
with the presence of concentric rings at the surface. Another set of samples was produced in order to simulate the effects of moisture
at the glass surface, using an industrial soda-lime glass and coating it with a painting originally used in 1930s. The comparisons between
the corrosion of the three sets of samples suggest that the Iulia Felix glasses could have been prepared with the same technique.
2007 Elsevier B.V. All rights reserved
Sol-gel silica coatings for the protection of cultural heritage glass
No full textTo slow down the phenomenon of weathering of ancient stained glass, the present work proposes the coating of glass. Several recipes
have been tested in the past. The coatings are made of sol–gel silica prepared with different catalysts like H+, Pb(II), Sn(IV) and without
catalyst. All the investigated samples show a good adhesion of the coating to the glasses used to simulate the behaviour of ancient artefacts
and a good resistance to ageing tests.
In the present work, some tests on Au and Ti surfaces coated with sol–gel silica were done, in order to investigate the adhesion of a H+
sol–gel coating to the surface of metals. In fact, in the case of glassy mosaics called ‘‘golden leaf tessera”, the adhesion of the glass to the
metal is a critical point, due to the fact that the weathering of such tesserae causes the detaching of the ‘‘cartellina” (small glass layer)
from the metal leaf. The main techniques adopted to investigate are optical microscopy (OM), X-ray photoelectron spectroscopy (XPS),
atomic force microscopy (AFM) and Rutherford backscattering spectroscopy (RBS)
- SINTESI DI FILM PROTETTIVI DI SILICE MEDIANTE PROCESSO SOL-GEL CATALIZZATO DA STAGNO –
No full textSilica thin-films from perhydropolysilazane for the protection of ancient glass
Full text linkSilica coatings from polysilazane precursors were prepared to protect ancient glass from weathering. Polysilazane can be converted to silica by simple exposition to air or basic vapours and the properties of the synthesized film make this precursor a valuable choice to obtain solid, crack-free, highly adhesive and protective coatings. The coating is prepared starting from a Perhydropolysilazane precursor (20% PHPS in n-butyl ether) that allows to achieve high-quality thin-films of silica at room temperature. The obtained films are uncoloured, even in absence of strong heat-treatment. Perhydropolysilazane (PHPS) is a polymer of [-SiH2-NH-SiH2-]n units. When deposited on a soda-lime microscope slide, it reacts with atmospheric moisture (Si-H and Si-NH bonds are hydrolysed to Si-O) and a silica film is produced. The conversion to silica is completed in about 2.5 hours, using vapours of a 10 mol L-1 ammonia solution. The reaction is promoted with the application of a weak heat-treatment (45-50 °C), achievable using as heater a common tungsten filament lamp. The reaction of PHPS with atmospheric moisture produces a migration phenomenon of the mobile ions from the soda-lime glass to the film (in particular sodium, calcium and magnesium). The characteristics of the migration process vary according to the concentration of the precursor solution and the thickness of the film. Laboratory samples have been investigated by optical microscopy and surface techniques: XPS and SIMS. Preliminary evidences, obtained through the laser scanning confocal microscope (LEXT), on the application of such coatings at the surface of ancient stained glass are also discussed
La grande vetrata di SS Giovanni e Paolo (Venezia): riflessioni sui restauri pregressi e proposte metodologiche d'intervento
No full textlibro da Congresso Scienza e Beni Culturali 24-27 giugno 2008 Bressanon
Synthesis of Silica Protective Films by Tin-Catalyzed Sol-gel Process
No full textI richiedenti hanno messo a punto una nuova metodologia per la preparazione di miscele dei precursori sol-gel che prevedono l’impiego di un catalizzatore dotato di proprietà acide di tipo Lewis, (SnCl4 in soluzione acquosa), aventi valori di pH variabili tra 4 e 7 a seconda della quantità di catalizzatore utilizzato.
Il fatto di poter variare il pH del mezzo, mantenendo comunque dei buoni tempi di gelificazione, permette di condurre la sintesi in modo tale da trovare la composizione della miscela che dia i risultati migliori per quanto riguarda il tempo di gelificazione e la morfologia dei depositi a seconda del materiale che si intende ricoprire.
I parametri operativi per la formazione e la deposizione del film di vetro sono controllati secondo quanto noto per la metodologia sol-gel classica come diffusamente discusso nel già citato “Sol-Gel Science – The Physics and Chemistry of Sol-Gel Processing” di C. J. Brinker e G. W. Scherrer, a parte i parametri di pH e temperatura.
Il film prodotto secondo la presente invenzione è costituito da silice vetrosa, il vetro più duraturo, meno facilmente attaccabile chimicamente e fisicamente e dotato quindi di buone caratteristiche di omogeneità, purezza, resistenza agli agenti atmosferici e trasparenza; inoltre, essendo composto da silicio e ossigeno, presenta una ottima compatibilità con substrati vetrosi.
Il presente metodo prevede:
- La deposizione del film in condizioni di pH neutro e non più in condizioni di pH acido, allo scopo di evitare fenomeni di degrado in manufatti sensibili all’acidità;
- la sostituzione del trattamento termico di densificazione con un processo di lenta asciugatura a temperatura ambiente, che evita danneggiamenti del substrato e l’inglobamento di impurezze nel film
Deposition of silica-based films for the protection of bronzes surfaces
No full textIn the present work, two different thin films of vitreous silica were tested to protect bronze surfaces from corrosion. A thin film of glass, less than 0.3 micrometer thick, presents excellent optical transparency and chemical inertia: it is particularly resistant to environmental corrosion, protecting the underlying material surface and its thinness guarantees elasticity. We compare the behavior of films obtained from two different chemical precursors and deposited on bronze samples of parallelepiped shape whose composition is similar to material present in Venice bronzes around 800 AD. The solutions of a silazanic precursor and a tetraethylorthosilicate (TEOS) based product have been employed to form the silica films by immersion of the bronze samples. The completely covered samples after the spectroscopic and morphological analyses were exposed to a corrosion test. In particular, the use of ammonia solution allows to observe at first sight if the colorless original solution turns to blue for the formation of copper-ammonia complex indicating the presence of corrosion phenomena.
The experimental results shows that the silica protective films starting from silazanic precursors provide coatings with protective, mechanical and optical properties better than the TEOS-based ones
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