Basic Structure of Passive Layers of Cu-Sn Alloys Applied to Patinas of Archaeological Bronzes

International audienceThe passive bronze corrosion structures have been characterized on numerous single-phase archaeological bronzes from Late to Early Bronze Age period (1500-900 BC), from metallographical examinations of cross-sections of artifacts. This paper focuses on the microstructure and the elementary composition of the passive patinas by SEM and EDX analysis (ultrathin window). A basic structure of the protective patinas is first described, then, deviations to the standard model are given. This model of passive structure and its deviations well agree with observations of archaeological bronzes

Characterisation of passive layers of bronze patinas (Cu-Sn alloys) in relation with the tin content of the alloy

International audienceIn order to develop our knowledge of the relations between the high degree of protectiveness of passive layers and their composition, corroded archaeological bronzes of Bronze Age (1500-950 BC) have been characterised by different methods of analysis. Results reveal that the passive layers have a bilayer structure and are due to the selective dissolution of copper from the copper solid solution of the alloy to the electrolyte. For all of the objects, the ratio [(Sn/Cu)p / (Sn/ Cu)a], with p for the outermost passive layer and a the alloy, has about the same value. Sn concentration within outermost passive layers is discussed in relation with the theoretical implications of the Kirchheim model

Characterization of naturally grown oxide layers on copper with and without benzotriazole by electrochemical and photoelectrochemical measurements

Autorisation éditeur okInternational audienceThe active corrosion of ancient artefacts (bronze disease) is linked to the presence of copper chloride underneath Cu(I) oxide formed at the surface of bronze. The properties of the Cu(I) oxide determine the mechanism of formation of the corrosion layer and their knowledge would to develop efficient stabilization treatments. The aim of our work is to characterize the structure and the electronic properties of Cu(I) oxide layers formed in different conditions (atmospheric and aqueous electrolyte) under opencircuit potential, using electrochemical and photoelectrochemical methods and SEM. Photoelectrochemistry allows the characterization the semiconducting properties of the passive layer and leads to a better knowledge of the nature of the electrode/solution interface and of the electrochemical reactions occurring at the oxide surface. Atmospheric Cu(I) oxide shows mainly p-type behaviour, whereas Cu(I) oxide layers formed at open-circuit potential by immersion in a NaCl solution were shown to exhibit p-type behaviour during the first hours of immersion and simultaneous n-p behaviour for longer immersion times. In the presence of benzotriazole added to the sodium chloride solution, the photoelectrochemical measu-rements revealed modifications of the semi-conducting properties of the Cu2O layer (duplex p-n layer from short immersion times) and showed that BTA makes the oxide layer more insulating. Results will be discussed in regards to the Cu(I) oxide role on the bronze disease

RAMAN MICROPROBE SPECTROSCOPY OF CORROSION PRODUCTS FORMED ON ELECTRODES SUBJECTED TO CORONA DISCHARGES

Les produits de corrosion formés lors de l'interaction d'une décharge couronne avec les électrodes ont été déterminés grâce à la microsonde Raman associée aux techniques classiques d'analyse chimique.Corrosion products appearing under the interaction of a corona discharge with the electrodes have been identified by Raman microanalysis associated to classical rnethods of chemical analysis

Handbook of palladium-catalyzed organic reactions : synthetic aspects and catalytic cycles /

This handbook provides a synoptic description of the main types of reactions which are catalyzed by Palladium and the mechanism which causes the reactions. Each reaction is presented in graphical form and classified according to the type of transformation involved.Includes bibliographical references.Print version record.Front Cover; Handbook of Palladium-Catalyzed Organic Reactions: Synthetic Aspects and Catalytic Cycles; Copyright Page; Table of Contents; Foreword; Abbreviations; I- Introduction; II- Graphical abstracts of reaction numbers (RXN); III- Reactions catalysed by palladium complexes; RXN1 Cross-Coupling of Organometallics with RX Derivatives; RXN2 Cross-Coupling of Organometallics with RCOX Derivatives; RXN3 Cross-Coupling of Siloxycyclopropanes with RX and RCOX Derivatives; RXN4 Cross-Coupling of Terminal Alkynes with RX Derivatives; RXN5 Intermolecular HECK Reaction.This handbook provides a synoptic description of the main types of reactions which are catalyzed by Palladium and the mechanism which causes the reactions. Each reaction is presented in graphical form and classified according to the type of transformation involved.Elsevie

Alteration of lead silicate glasses due to leaching in heated acid solutions

Leaching processes were studied for lead glasses having a composition similar to that of certain archaeological materials (66 wt% PbO) to determine the mechanism of the structural evolution. The glasses were leached in two static acid media (HNO3 and CH3COOH, pH 2) at 90 °C for 35 days. Analyses were undertaken of the leaching solution (pH, inductive coupled plasma–atomic emission spectrometry) and of the bulk glass (scanning electron microscopy–energy dispersive X-ray spectrometry, Rutherford backscattering spectrometry, Raman). Results show that in both acids, up to 1 day a silicon-rich surface layer is formed via typical diffusion processes. This process continues up to 35 days in the case of acetic acid. In nitric acid, one observes a stabilisation of this layer and an increase in the metal content. In both cases, Raman data are used to interpret the structural evolutions which occur in the ‘gel' phase

Apport de la microbalance à quartz dans l'étude de l'influence des ions sulfate, chlorure et magnésium sur la cinétique d'entartrage

Dans le présent travail, nous avons fait appel à la microbalance à quartz électrochimique pour étudier l'influence des ions chlorure, sulfate et magnésium sur la cinétique d'entartrage de l'or au contact d'eaux synthétiques. Les résultats chronoélectrogravimétriques permettent l'évaluation des étapes de germination et de croissance cristalline. Des analyses infrarouge des dépôts formés permettent de lier la nature des espèces identifiées aux paramètres cinétiques, en particulier en présence d'ions SO$_{4}^{2-}$ ou Mg2+. Des effets de seuil sont mis en évidence pour chaque type d'ion étudié. Ils sont essentiellement attribués à des phénomènes d'accumulation d'espèces sur le métal ou sur les produits superficiels, comme l'indique l'étude de l'effet du potentiel d'électrode et de la concentration des espèces en solution