Simulation and modelling of medieval-type glasses deterioration in an urban atmosphere

Dans un environnement urbain pollué, les altérations qui affectent les verres du patrimoine dépendent de facteurs intrinsèques, extrinsèques et temporels. Afin de caractériser les altérations atmosphériques résultant des interactions entre ces différents facteurs une stratégie de recherche prenant en compte un environnement multiphasique, le matériau (composition et surface) et le temps a été mise en place. Pour ce faire une étude complémentaire est menée sur des verres de vitraux exposés plusieurs centaines d'année et de verres modèles exposés en site réel et altéré artificiellement en laboratoire. Une approche multi-instrumentale et multi-échelle a été mise en place. Elle a permis d'identifier des mécanismes d'évolution de la couche d'altération (CA) notamment par la formation de lamines concentriques de ~10 nm (anciens fronts d'altération probables). L'exploration de l'impact des eaux de ruissellement montre que l'évolution de l'épaisseur de CA est dépendante à la fois d'une cinétique de diffusion (√t) et de dissolution (t). Enfin l'influence indirecte des produits néoformés sur l'altération semble jouer un rôle majeur à la fois en condition de ruissellement, avec la présence de CaCO3 qui précipite le détachement des écailles, et en milieu abrité, où la présence de K2CO3 est mise en cause dans la dissolution du réseau vitreuxIn a polluted urban environment, alterations affecting heritage glasses depend on intrinsic and extrinsic factors as well as time. In order to characterize the atmospheric alteration resulting from the interactions occurring between these factors, a research strategy has been set up, taking into account the multi-phase environment, the material (composition and surface) and time. In order to do so, a complementary study was conducted on stained glasses displaying several hundred years of alterations and model-glasses exposed in-situ for a few years or artificially altered in the lab. A multi-instrument and multi-scale approach was used in this study. It allowed the identification of the mechanisms responsible for the evolution of the leached layer (LL), especially the presence of concentric 10nm thick laminae (probable traces of alteration front). The exploration of the run-off impact on alteration shows a dependency of LL thickness on both diffusion type kinetics (√t) and dissolution kinetics. Finally, the indirect impact of neoformed alteration products seems to take a major part both in run-off conditions, CaCO3 hastens the scaling, and in sheltered conditions, where K2CO3 can be cause for glass network dissolutio

Impact of realistic corrosion products (RCP) stemming from iron archaeological artefacts on the alteration of nuclear glass

International audienc

Impact of realistic corrosion products (RCP) stemming from iron archaeological artefacts on the alteration of nuclear glass

International audienc

Effect of natural and synthetic iron corrosion products on silicate glass alteration processes

International audienceGlass long term alteration in the context of high-level radioactive waste (HLW) storage is influenced by near-field materials and environmental context. As previous studies have shown, the extent of glass alteration is strongly related to the presence of iron in the system, mainly provided by the steel overpack around surrounding the HLW glass package. A key to understanding what will happen to the glass-borne elements in the geological disposal lies in the relationship between the iron-bearing phases and the glass alteration products formed. In this study, we focus on the influence of the formation conditions (synthetized or in-situ) and the age of different iron corrosion products on SON68 glass alteration. Corrosion products obtained from archaeological iron artifacts are considered here to be true analogues of the corrosion products in a waste disposal system due to the similarities in formation conditions and physical properties. These representative corrosion products (RCP) are used in the experiment along with synthetized iron anoxic corrosion products and pristine metallic iron. The model-cracks of SON68 glass were altered in cell reactors, with one of the different iron-sources inserted in the crack each time. The study was successful in reproducing most of the processes observed in the long term archaeological system. Between the different systems, alteration variations were noted both in nature and intensity, confirming the influence of the iron-source on glass alteration. Results seem to point to a lesser effect of long term iron corrosion products (RCP) on the glass alteration than that of the more recent products (SCP), both in terms of general glass alteration and of iron transport

Effect of secondary phases on the evolution of glass alteration

International audienceWhatever the environment (soils, water and atmosphere), glass of varying compositions undergo alteration process conditioned by exposure conditions and glass intrinsic chemical and physical properties. Modification varies from a simple loss of transparency to a severe material loss but always involve modifications of the structure and chemical composition at the interface between the glass and the environment (hydration, dealkalinisation, dissolution,…). In many cases, these alteration of the glass structure are associated to the conjointed precipitation of secondary phases outside of the glass network often in cracks and fractures or directly on the glass outer surface. On site and laboratory alteration were both carried out for two very different environent : atmospheric and burial conditions. In the case of atmospheric alteration analogues and original stained glasses were compared in order to study the early and long-term evolution of the glass weathering. The samples observed in the two types of site show comparable alteration patterns. The nature of the precipitates outlines the impact of specific environmental conditions but, in every exposure conditions, similarities can be drawn on the secondary phases retroactive impact on the glass alteration processes. Nano-scale chemical characterization of the various phases was carried out through SEM-EDX, TEM-EDX; mineralogical characterization through electron diffraction, and STXM (for the structural environment of Si and Fe). From those observation some comparison of the phases influence on the system evolution and glass alteration can be made. Often, the precipitations are located within cracks inside the glass object. In some cases the precipitates have a clogging effect and can even trap glass-borne elements released from further alteration, but more often than not, local dissolution/precipitation of these secondary minerals inside the network favours the widening of the fractures, which facilitate fluid circulation, hence triggering further glass dissolution (congruent and selective) and precipitation of other secondary phases

Effect of secondary phases on the evolution of glass alteration

International audienceWhatever the environment (soils, water and atmosphere), glass of varying compositions undergo alteration process conditioned by exposure conditions and glass intrinsic chemical and physical properties. Modification varies from a simple loss of transparency to a severe material loss but always involve modifications of the structure and chemical composition at the interface between the glass and the environment (hydration, dealkalinisation, dissolution,…). In many cases, these alteration of the glass structure are associated to the conjointed precipitation of secondary phases outside of the glass network often in cracks and fractures or directly on the glass outer surface. On site and laboratory alteration were both carried out for two very different environent : atmospheric and burial conditions. In the case of atmospheric alteration analogues and original stained glasses were compared in order to study the early and long-term evolution of the glass weathering. The samples observed in the two types of site show comparable alteration patterns. The nature of the precipitates outlines the impact of specific environmental conditions but, in every exposure conditions, similarities can be drawn on the secondary phases retroactive impact on the glass alteration processes. Nano-scale chemical characterization of the various phases was carried out through SEM-EDX, TEM-EDX; mineralogical characterization through electron diffraction, and STXM (for the structural environment of Si and Fe). From those observation some comparison of the phases influence on the system evolution and glass alteration can be made. Often, the precipitations are located within cracks inside the glass object. In some cases the precipitates have a clogging effect and can even trap glass-borne elements released from further alteration, but more often than not, local dissolution/precipitation of these secondary minerals inside the network favours the widening of the fractures, which facilitate fluid circulation, hence triggering further glass dissolution (congruent and selective) and precipitation of other secondary phases

Role of secondary phases in the scaling of stained glass windows exposed to rain

International audienceThe cyclic nature of atmospheric conditions triggers different weathering responses. Although studied in the past in solution, the complex alteration mechanisms were not adequately described. In the present work, atmospheric weathering of medieval SiO2-K2O-CaO glass was studied via field exposure of model-glasses and ancient stained glasses. Local dissolution and precipitation of secondary minerals, mainly calcite, create a fracture network, allowing water to move into the glass enhancing alteration processes and scaling of the surface. In fine, the renewal of glass surface by removal of altered scales helps accelerate the alteration rate and prevents the formation of a protective layer

Wet and dry atmospheric deposition on TiO2_2 coated glass

International audienceo prevent the soiling of glass window used in the built environment, the use TiO$_2$ coated products appears an important application matter. To test the cleaning efficiency and the sustainability of self-cleaning glass, a field experiment was conducted under real life condition, on a site representative of the background urban pollution. Samples of float glass, used as reference, and commercialized TiO$_2$ coated glasses were exposed to dry and wet atmospheric deposition during two years. The crossed optical, chemical and microscopic evaluations performed, after withdrawal, allowed highlighting a sensible difference between the reference and the self-cleaning substrate in terms of accumulation, nature, abundance and geometry of the deposit. This experiment conducted in real site emphasized on the efficacy of self-cleaning glass to reduce the maintenance cos

The Bayeux embroidery: a dust deposition assessment

Abstract Particulate matter in the showcase of the Bayeux embroidery was studied for 8 months in order to determine the conservation state of this precious and fragile work of art. Both the suspended and deposited particles were observed, analysed, and quantified. Microclimatic conditions were also monitored. This study presents different methods for the qualification (SEM–EDS and ion chromatography) and quantification (haze, surface coverage, deposition thickness, fibre concentration) of the deposition of particulate matter in such an environment. It allowed the evaluation of the hazard represented by particulate matter for the piece of art and the effectiveness of the measures taken to preserve it, namely air filtration in its over-pressured showcase. The results are very positive, since the PM concentration is very low (ISO 8 regarding the ISO 14644-1 norm) and dust deposition is still negligible after five and a half month