Corrosion evaluation and diagnostic: use of electrochemical techniques in metal conservation

Electrochemical techniques provide several methods to analyse corrosion mechanism and to measure values such as corrosion rate on metals and alloys. They are widely used in Materials Science as a tool to characterise metals corrosion and protection. In the last ten years several applications in the wide field of metal conservation have been developed, in order to characterise the corrosion mechanism in several environments, the corrosion products, and the conservation treatments (cleaning, protection treatments, etc.). A basic description will be provided for the more widely used techniques, namely: - basic principle - instrumentation - sample application to conservation studies Metallic objects of interest for Cultural Heritage preservation can extend over a wide range of size, shape, composition, and environment. Advantages and limits of the different techniques will be discussed in order to enlighten their field of applicability and to guess the usefulness of the different techniques according to the conservation issue to address. A special attention will be paid to the peculiar case of outdoor exposure of monuments

"Mi Fuma il Cervello" self-portrait series of Alighiero Boetti: Evaluation of a conservation and maintenance strategy based on sacrificial coatings

"Mi Fuma il Cervello" ("steaming brain") is the iconic self-portrait of Alighiero Boetti, in which the artist is represented standing up while a copper hose lets water flow on his head. A hidden electric resistance heats the sculpture's head so that the splashing water forms a dense vapour mist as it comes in contact with the hot metal surface. Such system is normally active only during museum exhibitions and determines critical conservation issues due to the inevitable formation of a thick and adherent calcareous deposit. Recently, the Fonderia Artistica Battaglia (Milan, Italy) conducted an extensive conservative intervention aimed at retrieving the original aesthetic features of the bronze surface and its artificial patina finishing. A conservation strategy was proposed based on the use of a superficial coating, to protect the surface and to ease the removal of the calcareous deposits in view of future cleaning operations. Three siliconic commercial paints were selected and preliminarily applied to specimens that simulate the actual alloy. The efficacy, compatibility and durability of the treatments were tested by accelerated ageing test based on combined thermal and wetting cycles, representative of the real working conditions. A multi-analytical diagnostic approach was followed for the evaluation of the coatings characteristics and performances before and after aging: stereomicroscopy, ESEM-EDX, VIS-Light spectrophotometry, micro-FTIR, electrochemical impedance spectroscopy (EIS). The research showed that from the aesthetic point of view all coatings induce only limited and rather comparable initial colour variations. The permanence of the treatments upon ageing, used as durability indicator, was assessed in all cases but the protective layers appeared damaged and no longer continuous over the metal surface. The best performing treatment was identified and further tested with respect to re-treatability. The results provide indications for the general conservation and maintenance protocol

Testing New Coatings for Outdoor Bronze Monuments: A Methodological Overview

Coatings to be used for cultural heritage protection face peculiar challenges. In the last few decades, several projects addressed the issue of new treatments in the field of copper alloy artworks. Nonetheless, no one has yet been recognised as a more acceptable solution with respect to traditional choices, with their known limits. The lack of standard methods to test new coatings that can be effectively applied to artworks make it more difficult to compare different studies and open the way to practical use in restoration. Over the years, several issues have gradually been better focused, even though they are not yet widely considered in new coatings efficacy evaluation for application on copper alloy artifacts. They are mainly linked to the quite complex surface of this category of heritage objects and the role it plays on coating effectiveness. An overview of the variety of relevant surface properties is provided (presence of corrosion products and old protective treatments, cleaning methods, surface unevenness, just to name a few) with a special focus on the role of coating performance. Some methodological choices are discussed for the selection of mock-ups, testing techniques and weathering procedures, with peculiar attention to comparison with real artworks

Species composition of carabid communities (Coleoptera Carabidae) in apple orchards and vineyards in Val d'Agri (Basilicata, Italy)

ABSTRACT An entomological investigation was carried out in an agricultural area, mainly apple orchards, of the Agri river plain, located in some municipalities of Basilicata, Italy. Between 2012 and 2014, species richness and composition of carabid assemblages were investigated on the ground surface of differently managed (abandoned, organic, commercial and IPM) apple orchards and vineyards. Ground beetles (Coleoptera Carabidae) were sampled by means of pitfall traps. 1288 individuals belonging to 40 species were collected, representing two-thirds of the carabid fauna of this area found in our and earlier studies. The species richness varied between 4 and 20 in the different orchards. The common species, occurring with high relative abundance in the individual orchards in decreasing order were: Pterostichus (Feronidius) melas (Creutzer, 1799), Pseudoophonus (Pseudoophonus) rufipes (De Geer, 1774), Brachinus crepitans (Linnaeus, 1758), Harpalus (Harpalus) dimidiatus (P. Rossi, 1790) and Poecilus (Poecilus) cupreus (Linnaeus, 1758). Most of the collected ground beetles were species with a wide distribution in the Paleartic region, eurytopic and common in European agroecosystems. The assemblages were dominated by small-medium, macropterous species, with summer larvae. No endemic species were found

Assessing protective treatment performance on outdoor sculptures:to be or not to be a representative model sample?

Protective treatments to be applied in the field of cultural heritage need to fulfil several constraints that have gradually been better outlined over the years. Along with the impact on aesthetic appearance and reversibility, it is nowadays well recognized that patinas and/or original historical coatings and finishings can play a relevant role in protective treatments’behavior[1,2]. Nonetheless, no standard characterization method has been drafted to test new coatings and their application on real artefacts

Attrazione Fatale - Metalli e ambiente: le trasformazioni dei materiali tra patina nobile e prodotti di corrosione

Would you like to get into the forge of the gods like Hephaestus? Discover how to extract the metals and get objects of fine workmanship? But beware: there is rust on the prowl! We go behind the scenes to explore the adventure of mankind in the art of producing lovely jewelry, melt the bells and monuments, getting mixed metal alloys of different colours. Let\u27s explore the irresistible attraction of metals and alloys with the environment: are you ready for a fast journey through transformations? What are the substances that ruin the features? How can we combat the degradation? With this practical workshop we want honour Giulio Natta in the fifty years anniversary of his Nobel Prize for Chemistry.Ti piacerebbe mettere piede nella fucina degli dei come Efesto? Scoprire come estrarre i metalli e ottenere oggetti di finissima fattura? Ma attenzione: c\u27? la ruggine in agguato! Andiamo dietro le quinte per esplorare l\u27avventura del genere umano nell\u27arte di produrre graziosi monili, fondere campane e monumenti, miscelare metalli ottenendo leghe di diversi colori. Esploriamo l\u27attrazione pi? o meno irresistibile di metalli e leghe con l\u27ambiente: sei pronto a un viaggio accelerato nelle trasformazioni? Quali sono le sostanze che ne rovinano le caratteristiche? Come possiamo combattere il degrado? Un laboratorio pratico per ricordare Giulio Natta a cinquanta anni dal suo Nobel per la chimica

Comparison of a bio-based corrosion inhibitor versus benzotriazole on corroded copper surfaces

This research aims to characterize and compare the protective behaviour of a bio-based treatment versus benzotriazole (BTA) for the preservation of copper-based artefacts affected by active corrosion induced by copper chlorides. For this, the treatments were applied on artificial copper hydroxychlorides produced on copper sample. Their inhibition performance was then investigated by Scanning Electron Microscopy, Infrared Spectroscopy and Electrochemical Impedance Spectroscopy. Results showed few BTA-Cu complexes formed and poor protectiveness of the BTA treatments. In contrast, the bio-based treatment resulted in the conversion of almost all copper hydroxychlorides into copper oxalates, providing a more efficient corrosion inhibition

Effetto di pulitura e biopassivazione su acciaio Corten

The increased sensitivity towards environmental issues has led to a growing research interest in sustainable approaches to heritage conservation. On the last ten years, a biopassivation treatment for corroded metal surfaces has been developed in Switzerland by exploiting the natural ability of some microorganisms to form metals oxalates [1-3]. In this work, different weathering steels belonging to the same family (Corten A), charaterized by different exposure histories, were first cleaned and then biopassivated with Beauveria bassiana fungal strain. The main aim was to produce a protective patina in a shorter time than natural exposure. The cleaning was intended to remove loose and/or powdery corrosion products and had a positive effect on the corrosion resistance, which improved slightly. regarding the biopassivation procedure, despite the strong surface heterogeneity after the treatment, some very promising results emerged form the comparison of the electrochemical measurements before and after the treatment.L'aumentata sensibilità verso le problematiche ambientali ha portato a un crescente interesse della ricerca per gli approcci sostenibili alla conservazione del patrimonio. Negli ultimi dieci anni è stato sviluppato in Svizzera un trattamento di biopassivazione per superfici metalliche corrose sfruttando la capacità naturale di alcuni microrganismi di formare ossalati metallici [1-3]. In questo lavoro sono stati prima puliti e poi biopassivati con ceppo fungino Beauveria bassiana diversi acciai patinabili appartenenti alla stessa famiglia (Corten A), caratterizzati da differenti storie di esposizione. Lo scopo principale era quello di favorire la formazione di una patina protettiva in tempi più brevi rispetto all'esposizione naturale. La blanda pulitura meccanica aveva lo scopo di rimuovere i prodotti di corrosione poco coesi e/o pulverulenti e ha avuto un effetto positivo sulla resistenza alla corrosione, che è leggermente migliorata. Per quanto riguarda la procedura di biopassivazione, nonostante sia stata osservata una forte eterogeneità della superficie dopo il trattamento, alcuni risultati molto promettenti sono emersi dal confronto delle misure elettrochimiche prima e dopo il trattament

Setup of Galvanic Sensors for the Monitoring of Gilded Bronzes

Traditional electrochemical techniques, such as linear polarization resistance (Rp), and electrochemical impedance spectroscopy (EIS), cannot be applied to gilded bronzes, as it may not be possible to interpret the results obtained due to the bimetallic nature of the studied material. The measurement of the macrocouple current generated by the gold/bronze galvanic couple can be used as an indicator of degradation processes. Nevertheless, this measurement cannot be performed directly on the original artifacts due to the systematic presence of short-circuits between the two metals. In the present work the use of galvanic sensors is proposed as a possible solution for the monitoring of gilded bronze artefacts. The sensors have been designed to simulate real gilded bronze surfaces in terms of composition and stratigraphy and have proved to be a reliable diagnostic tool for the in situ monitoring of the rates of deterioration of gilded bronze surfaces and to test new conservation treatments. Their set-up and application is reported and their performances discussed