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Epilithic bacteria play a fundamental role in the conservation of cultural heritage (CH) materials. On stones, bacterial communities cause both degradation and bioprotection actions. Bronze biocorrosion in non-burial conditions is rarely studied. Only few studies have examined the relationship between bacteria communities and the chemical composi- tion of patinas (surface degradation layers). A better comprehension of bacterial communities growing on our CH is fundamental not only to understand the related decay mechanisms but also to foresee possible shifts in their compo- sition due to climate change. The present study aims at (1) characterizing bacterial communities on bronze andmarble statues; (2) evaluating the differences in bacterial communities' composition and abundance occurring between differ- ent patina types on different statues; and (3) providing indications about a representative bacterial community which can be used in laboratory tests to better understand their influence on artefact decay. Chemical and biological charac- terization ofdifferent patinas were carried out by sampling bronze and marble statues in Bologna and Ravenna (Italy), using EDS/Raman spectroscopy and MinION-based 16SrRNA sequencing. Significant statistical differences were found in bacterial composition between marble and bronze statues, and among marble patinas in different statues and in the same statue. Marble surfaces showed high microbial diversity and were characterized mainly by Cyanobacteria, Proteobacteria and Deinococcus-Thermus. Bronze patinas showed low taxa diversity and were dominated by copper-resistant Proteobacteria. The copper biocidal effect is evident in greenish marble areas affected by the leaching of copper salts, where the bacterial community is absent. Here, Ca and Cu oxa- lates are present because of the biological reaction of living organisms to Cu ions, leading to metabolic product secre- tions, such as oxalic acid. Therefore, a better knowledge on the interaction between bacteria communities and patinas has been achieved.

In this work, Plasma Electrolytic Oxidation (PEO) coatings were produced on AZ91D Mg alloy, using as electrolyte an aqueous solution containing both silicates and phosphates. SiC particles, or borosilicate glass particles or a combination of them (SiC + borosilicate glass) were suspended into the electrolyte. The PEO-treated samples were characterized through Scanning Electron Microscope (SEM) (both on the surface and in cross section), X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) in order to study the morphology, thickness, adhesion, structure and composition of the coating as well as particle distribution. The corrosion behavior was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The wear resistance was evaluated by dry sliding tests vs. AISI 52100 bearing steel (block-on-ring contact geometry). The results showed that both SiC and borosilicate glass particles were incorporated into the PEO layers. Glass particles contributed to enhance corrosion resistance, whereas SiC particles decreased it. On the other hand, SiC particles improved the wear resistance (due to enhanced load support), leading to an increase of the friction coefficient (due to an increase of the abrasive component of friction). The best combination of properties was obtained with the addition of glass particles for 3 min treatment time. In this way, both the corrosion and wear resistance were increased, minimizing the detrimental effects of SiC particles on the corrosion properties and the friction coefficient.

International audience; A 3-mercapto-propyl-trimethoxysilane coating (PropS-SH) applied on Cu-Si-Mn bronze, patinated by “liver of sulphur”, was investigated as a non-toxic alternative to Incralac®, usually applied on outdoor artistic bronzes. Electrochemical testing was performed in synthetic acid rain. Exposure to temperature/UV cycles and accelerated corrosion test simulating unsheltered exposure to rainwater was also carried out. The exposed samples were characterised by FEG-SEM coupled with EDS on FIB cross-sections and XPS on free surfaces. The black patina without protective coating was scarcely protective against bronze corrosion and easily transformed into cuprous oxide. PropS-SH coating fully preserved the black patina microstructure and phase constituents (cuprous oxide and cuprous sulphide). The PropS-SH coating also resulted more protective than Incralac® when aged under run-off conditions. Selective dissolution of copper from the silicon bronze alloy was observed on both uncoated and Incralac®-coated bronze, leading to the formation of an internal Si-rich corrosion layer.

Recently, research gives emphasis to eco-friendly and sustainable approaches for the preservation of cultural heritage that could offer advantages in terms of compatibility, durability and safety. Hence, a biological treatment, based on a specific fungal strain of Beauveria bassiana, is exploited for the stabilization of soluble and/or active bronze corrosion products, converting them into copper oxalates. The chemical stability of the latter represents a real improvement for the long-term preservation of bronze, especially in case of exposure to acid rain. However, the corrosion behaviour of bronze differs from that of pure copper due to the presence of additional alloying elements. In natural environments, the selective dissolution of copper leads to a relative tin-enrichment within the corrosion layers, mostly in unsheltered areas exposed to rainwater runoff. To understand the influence of tin-enrichment on the formation of oxalates, pure tin and artificially tin-enriched bronze coupons were treated with this novel biological system and, in the case of bronze coupons, exposed to accelerated ageing. Tin enrichment and accelerated ageing were performed through runoff tests. Before and after treatment and ageing, the sample surface was characterized through Fourier transform infrared (FTIR) and Raman spectroscopies, scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS). Metals released in the ageing solutions were analysed through atomic absorption spectrometry (AAS). The analytical results allowed to better understand the response of unsheltered areas from outdoor bronze monuments to the biological treatment proposed.

International audience; When attempting to sufficiently protect outdoor bronze monuments from corrosion, searches for an effective solution are usually based on coating applications which have a high anticorrosive efficiency. In order to correctly assess the level of protection provided by such coatings, adherence (practical adhesion) measurements need to be performed for the proper evaluation of the deterioration of coating systems with aging. Although a coupled study of adherence with aging would be of great interest, very few such studies are available. In this work, a methodological approach is proposed for the evaluation of coatings applied to metallic cultural heritage monuments of, based on the use of a three-point bending test. Adherence characterization of different protective coatings has been performed both on bare and on traditionally black-patinated bronze coupons (Cu–Sn alloy with 5.9 wt% Sn), which were used as basic model substrates. The investigated coatings were Incralac®, silane, sol–gel oxysilane, and a silane-modified polymethacrylate (an adhesion promoter for fluoropolymer). The results of measurements which were obtained before and after accelerated aging in concentrated acid rain made it possible to more easily differentiate between the various adherence levels of different coating systems. Coupled with adherence measurements, the results of systematic optical and SEM observation of the different failure morphologies are also presented. In the case of the coated bare alloy, adhesive failures were mainly observed. The silane (PropS-SH) coating showed the best adherence. In the case of the patinated bronze test specimens, only cohesive failures occurred. Adherence is directly related to the cohesion of the black patina rather than that of the applied coating. It was observed that aging reduces the level of the adherence.

International audience; n this research, different Schiff bases were synthesized and tested as bronze corrosion inhibitors in concentrated synthetic acid rain at pH 3.3. Some of them showed good inhibiting effects, as detected by EIS and polarization curve recording. The most efficient inhibitor (2-(salicylideneimino) thiophenol, SITP) was also tested with ad-dition of sodium dihydrogen phosphate (P). P improved the surface film resistance against breakdown phe-nomena. XPS and SEM investigations showed that SITP and SITP + P significantly hinder decuprification. Moreover, SITP forms a protective layer on bronze, composed of both Cu(I)-SITP complexes and adsorbed in-hibitor molecules. Cu(II) phosphates were also detected with P addition.

Plasma Electrolytic Oxidation (PEO) was applied to extruded ZM21 Mg alloys to improve their corrosion resistance in a chloride-containing environment. PEO was carried out in DC mode and voltage control in a fluoride-free electrolyte. Potentiodynamic polarization tests in 3.5 wt.% NaCl aqueous solution and neutral salt spray (NSS) tests were carried out. Microstructural and profilometric characterization, as well as NSS tests were performed in different conditions: (i) bare ZM21, (ii) PEO-treated ZM21, (iii) powder-coated ZM21 (without PEO interlayer), and (iv) PEO-treated ZM21 with powder coating top layer (carboxyl-functionalized polyester resin). The PEO + powder coating double layer was identified as the best-performing corrosion protection.

This study detected and investigated the degradation effects and dynamics of the tin amalgam reflective layer of ancient mirrors. The experimental results have been obtained by different spectroscopic techniques: Light Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Microanalysis (SEM–EDS), Atomic Force Microscopy (AFM) and μ-Raman Spectroscopy. The latter two were applied for the first time to characterize the amalgam of ancient mirrors. Amalgam alteration products in form of concentric rings with alternate different compositions of tin oxides have been studied on both the amalgam reflective layer inner surface and on its cross-sections. For the first time SEM images of micro-cross-sections of different amalgam degradation products, such as amalgam “drops” and craters, have been obtained. The size of the nano-particles of tin oxides, as amalgam degradation products, was estimated around 3–8 nm by AFM and micro-Raman, as already previously detected through TEM. Micro-Raman showed the presence of both cassiterite and romarkite nano-crystals forming the concentric rings, as only previously hypothesized. This investigation allowed to obtain further experimental evidence and a more advanced comprehension about the structure and formation phases of the amalgam decay products, giving further support to some statements by previous authors and suggesting some assertions different from the ones of previous studies.

This paper reports on the diagnostic investigations on the bronze panel in the Church of San Moise in Venice (Italy), aiming at the identification of materials and causes of corrosion. Both the bulk metal and surface layers were investigated by a wide range of techniques: alloy composition and microstructure were determined by VP-SEM/EDS, the corrosion products by Raman spectroscopy and XRD. The organic compounds were analysed by pyrolysis gas chromatography mass spectrometry (Py-GC-MS). The adjacent mortars were analysed in terms of mineralogical composition and soluble salts content, in order to highlight their role in the degradation processes at the contact areas between the masonry and the bronze panel. The alloy is a quaternary bronze (Cu-Sn-Zn-Pb): high-relief figures were cast separately then mechanically joined to the panel. Traces of the clay core were detected in the back of the panel. The bronze surface was artificially patinated by potassium sulphide. The organic protective layer consisted of stearin and paraffinic wax. However, siccative oil was detected at the interface with the metal, likely corresponding to the original protective treatment. Also pine resin traces were detected. The corrosion products mainly consisted of basic copper chlorides (paratacamite, atacamite) and mixed copper/sodium carbonates (chalconatronite), deriving from the interaction with mortar.

This work aims at assessing the PEO (Plasma Electrolytic Oxidation) treatment conditions which may lead to an improved tribological behaviour for the Rare Earth-containing Mg alloy EV31A alloy, which is mainly used in aerospace, military and automotive applications. In particular, we investigated the influence of graphite nanoparticles addition and PEO treatment time (30–90 s) on microstructure, friction/wear and corrosion of layers obtained in phosphate/silicate electrolyte. The addition of graphite was investigated because it may limit the typical high friction of PEO/steel contacts. Since no hazardous additives (such as potassium fluoride) were added to this electrolyte, graphite was investigated also as a possible structure densifier. Dry sliding tests were carried out with a block-on-ring tribometer against AISI 52100 steel. The results showed that the addition of graphite decreased friction and wear, due to the formation of a compact, protective, low-shear transfer layer, consisting of iron oxides (due to mild tribo-oxidation of the countermaterial) and amorphous carbon (from the PEO layer). An intermediate treatment time of 60 s, combined with the addition of graphite, led to the growth of PEO layers with the best combination of thickness, compactness, roughness and microhardness, thus leading to the best tribological behaviour.

The effect of the addition of graphite nanoparticles into the electrolyte used to produce plasma electrolytic oxidation (PEO) coatings on AZ91 and AZ80 magnesium alloys was studied. The corrosion and wear resistances of the obtained coatings were investigated. A solution that contained both phosphates and silicates was used as electrolyte. Moreover, two different PEO treatment times were studied. The corrosion resistance was analyzed with potentiodynamic polarization and EIS tests; the wear resistance was investigated with a flat on ring tribometer. The results were related to the morphology, microstructure, elemental composition and thickness evaluated with SEM analysis. The presence of the graphite nanoparticles increased the thickness, produced a densification of the coating and sealed the pores on the surface, thus improving both the corrosion and wear resistance. The increase in the corrosion and wear resistances was more evident for AZ91 than for AZ80 due to the higher aluminum content.

To better understand corrosion behaviour of lead (Pb)-based alloys exposed to volatile organic compounds – specifically acetic and formic acid – a preliminary research has been carried out on laboratory-made samples replicating such alloys. Replicas have been manufactured by simulating specific types of Pb-based alloys, with antimony (Sb) and tin (Sn) as alloying elements, in order to characterise corrosion products and evaluate the influence of each alloying element. Replicas were cast in a refractory mould and later placed in size-specific desiccators and exposed to concentrated acetic and formic acid vapours for 15 days. Each specimen was also subjected to gravimetric measurements and periodically monitored in order to understand the corrosion behaviour. Micro Raman Spectroscopy (μRS) and Scanning Electron Microscopy together with energy Dispersive X-Ray Spectroscopy were used for the characterisation of Pb-based replicas. Results showed the presence of typical corrosion products – more or less hydrated forms of Pb and Sn acetates and formates – and also a sudden increase in the volume and brittleness of some Sb-rich specimens as well as the presence of seldom-detected metallic Sb peaks with μRS. In this perspective, the influence of Sb as an alloying element on the corrosion of Pb-based artefacts may generate serious problems when such objects have to be restored and particular attention should be given to conservation/stabilisation procedures. Copyright © 2014 John Wiley & Sons, Ltd.

AISI316L austenitic stainless steel is widely used in the food industry, usually in contact with aggressive environments. Low-temperature carburising (LTC) is a treatment increasingly applied to this steel in order to harden the surface without decreasing corrosion resistance. In the present work, electrochemical and immersion tests were carried out in acetic acid 3 vol.% (reference environment for metals in contact with acetic foodstuffs), so as to investigate the influence of LTC on metal release. The results showed that the LTC-treated steel is less passivable in this environment, producing higher alloying metal release than the untreated steel. (C) 2014 Elsevier Ltd. All rights reserved.

AISI 316L austenitic stainless steel is widely used in industrial applications, usually in contact with corrosive environments. Low temperature carburization (LTC) is a treatment increasingly applied to these steels in order to harden the surface without decreasing the corrosion resistance.In the present work, LTC techniques such as industrial and plasma-assisted treatments were applied to stainless steel and compared for their resistance to corrosion. The micro-chemical composition of hardened layer before and after corrosion treatments was studied on both the samples by surface-sensitive XPS and AES techniques. The results of plasma-assisted LTC treatment showed similar behavior of corrosion resistance as industrial LTC treatment. Hence, the plasma-assisted LTC treatment can be a suitable replacement for the industrial LTC treatment of stainless steels.

Low-Temperature Carburizing (LTC) is a thermochemical treatment that improves the wear resistance of austenitic stainless steels without decreasing their corrosion resistance. However, LTC does not contribute to the decrease in the coefficient of friction in steel-to-steel contacts, which take place in many tribological applications involving LTC-treated parts. Therefore, in this work the dry sliding behavior of a duplex system consisting of PA-CVD hydrogenated amorphous carbon (a-C:H) topcoat on LTC-treated AISI 316L, was investigated by a flat-on-cylinder tribometer, at room temperature and in laboratory air, so as to evaluate the influence of (i) the polishing procedure before a-C:H deposition, (ii) the LTC interlayer and (iii) the type of countermaterial (untreated or LTC-treated AISI 316L). The results showed that (i) the polishing step prior to a-C:H deposition to obtain low roughness and therefore low friction (and also low wear of the countermaterial) must be carried out before LTC, otherwise the thickness of the layer is modified uncontrollably. (ii) LTC improves the load bearing capacity of the substrate, thus leading to increased adhesion and longer coating life. (iii) Finally, the a-C:H topcoat proved to be effective in reducing both friction and wear compared to the uncoated LTC-treated steel (up to the transition load).

International audience; In order to bring the treatment of historical bronze monuments in line with proper engineering practice and cultural heritage regulations, the standardisation of artificially aged surfaces that are comparable with natural ones is still to take place. In this aim, this investigation reports a comparative study of corroded quaternary bronze samples produced by accelerated ageing tests, simulating the unsheltered and sheltered exposure conditions mainly affecting outdoor bronze monuments. The effects of run off in a dropping test (unsheltered simulation) and the exposure to stagnant acid rain in a wet & dry test (sheltered simulation) on a bronze surface were studied. A multi-analytical approach was performed including conventional analytical methods, such as a microscopy examination coupled with elemental and structural analyses of the surface. In addition, a focused ion beam (FIB) was used to produce cross sections in the size range up to a few tens of nanometres. It is evidenced that the corrosion layers, forming a nano-porous structure, are linked to a decuprification process marked by the preferential dissolution of Cu and Zn and the formation of a Sn-O species network within the barrier layer. A correlation between the tin content of the alloy and the corrosion amplitude is shown: the anodic areas are related to the lowest tin-content part of the alpha phase (in the centre of the dendrite), while the eutectoid areas (including the delta phase) are cathodic and therefore not attacked. The corroded samples artificially aged are well representative of natural corrosion structures observed on outdoor bronzes. (C) 2017 Elsevier B.V. All rights reserved.

An aluminum-cast statue, representing an open-armed Madonna, was positioned in 1938 on the memorial for the victims of World War I built in Lido di Venezia (Italy). Due to the severe exposure conditions (marine industrial atmosphere), the statue suffered extensive deterioration and fell down in summer 2003. In 2009, a restoration project started, with the aim of repairing and conserving the statue, at the time badly fragmented. In the present work, the results of investigations on (i) degradation factors and (ii) potential conservation strategies, are presented. In particular, in the first part of the study composition and microstructure of the cast alloy were determined, pointing out the influence of casting defects on the intrinsic brittleness of the statue. The corrosion products on the exposed surface were also identified and related to the exposure conditions, in order to identify the main corrosion factors. In the second part of the work, a cleaning procedure aimed at removing the active corrosive ions (namely chlorides), was setup and the Ion Chromatography (IC) method was used for monitoring its effectiveness. The results showed that water leaching requires a high number of rinsing cycles in order to obtain a significant decrease of Cl − concentration.

Cor-Ten steel is widely used in architecture, for its aesthetical and technological features (i.e. auto-protection from atmospheric corrosion). However, environmental conditions and exposure geometry strongly affect resistance to corrosion. This work focuses on the corrosion behaviour of Cor-Ten with different surface finish typically adopted in art/architecture (bare/pre-patinated/pre-patinated and waxed) in stagnant or runoff conditions. The evolution of the exposed surfaces and the metal release are followed as a function of exposure time. The results showed that pre-patination has no beneficial effects on corrosion and, in stagnant conditions, the high metal release suggests the need of field investigations to evaluate possible adverse effects on the environment.

The characterization of corrosion patinas on bronzes is preliminarily connected to the determination of proper conservation strategies. Moreover, it also provides an essential contribution to the comprehension of the mechanisms of formation of patinas. Concerning the last aspect, several studies highlighted that bronze corrosion behaviour cannot be assimilated to that of pure copper. In particular, decuprification and relative enrichment of tin in the corrosion layers were observed. Tin therefore, together with its insoluble salts, plays an important role in the mechanism of formation of bronze patinas. Thus, the characterization of Sn-based corrosion products becomes fundamental, although remaining quite problematic. This work reports several case studies where Sn-based corrosion products grown in bronzes have been identified, thanks to the hyphenated system scanning electron microscopy–energy dispersive spectrometry–Raman structural and chemical analyser. Combining the main characteristics of these techniques, different Sn-containing compounds, mainly crystalline and nano-sized tin dioxides, were detected in bronze patinas exposed to different environments (to the atmosphere, in both natural and accelerated ageing conditions, and to the soil). The main issues regarding the interpretation of Raman spectra of these compounds are presented and discussed. Copyright © 2012 John Wiley & Sons, Ltd.

The corrosion behaviour of a quaternary bronze UNS C83600 exposed to stagnant acid rain was examined through wet–dry tests. During the tests, parallel monitoring was performed to determine the evolution of both the bronze surface and the weathering solution composition. The results show that the kinetics of bronze oxidation is governed by diffusion through a two-layer patina: an inner Sn-rich layer and an external Cu and Pb-rich layer. The corrosion rate of the alloy decreases with time, but the dissolution of individual metals (Cu, Zn and Pb) in the environment increases with different trends, showing progressive patina destabilisation.

The effect of leaching rain on the corrosion behaviour of bronze UNSC83600 was investigated as to the influence of alloying elements (Cu, Sn, Zn, Pb) through dropping tests simulating a severe runoff condition with a solution reproducing natural acid rain. Corrosion was followed with time monitoring both samples and leaching solutions (up to 30 days) by SEM, EDS, Raman spectroscopy, XRD, AAS. The bronze patina behaves as a porous layer enriched in stable tin compounds allowing uniform dissolution of Cu, Zn and partly of Pb. Laboratory results are in good agreement with field studies of outdoor bronzes in unsheltered condition.

A comparative evaluation of the corrosion behaviour of a G85 bronze in acid rain solutions was performed. As weathering technique, a wet–dry device was used to simulate a cyclic exposure to stagnant rain. The weathering solutions were a collected natural rain and an artificial solution reproducing the natural rain. The solutions were periodically monitored as concerns pH and metallic ion concentrations. On the aged specimens, surface studies were performed through OM, SEM and Raman analyses. At the end of weathering tests (40 days), weight loss measurements were carried out. The aim of this work was to examine the reproducibility in laboratory of the corrosive conditions determined by a natural acid rain. The final goal of this research is to investigate the dissolution of a quaternary alloy exposed to acid rains. The results showed slightly different corrosion behaviours as a consequence of the exposure to natural or synthetic rain. Concerning the mechanism of corrosion of G85 bronze, the innovative approach adopted in this study allowed one to point out the contribution of each alloying element to the general corrosion. Actually, while Cu and Pb progressively form insoluble corrosion compounds, Zn continuously dissolves, without forming detectable insoluble products. The absence of dissolved tin is remarkable.

Surface and building runoff can significantly contribute to the total metal loading in urban runoff waters, with potential adverse effects on the receiving ecosystems. The present paper analyses the corrosion-induced metal dissolution (Fe, Mn, Cr, Ni, Cu) from weathering steel (Cor-Ten A) with or without artificial patinas, exposed for 3 years in unsheltered conditions at a marine urban site (Rimini, Italy). The influence of environmental parameters, atmospheric pollutants and surface finish on the release of dissolved metals in rain was evaluated, also by means of multivariate analysis (two-way and three-way Principal Component Analysis). In addition, surface and cross-section investigations were performed so as to monitor the patina evolution. The contribution provided by weathering steel runoff to the dissolved Fe, Mn and Ni loading at local level is not negligible and pre-patination treatments seem to worsen the performance of weathering steel in term of metal release. Metal dissolution is strongly affected by extreme events and shows seasonal variations, with different influence of seasonal parameters on the behaviour of bare or artificially patinated steel, suggesting that climate changes could significantly influence metal release from this alloy. Therefore, it is essential to perform a long-term monitoring of the performance, the durability and the environmental impact of weathering steel.

Fire-gilded bronze (replicating the materials of Lorenzo Ghiberti’s Paradise Door (Baptistery of Florence, 1452)) was aged in runoff/stagnant conditions by accelerated exposure tests in synthetic acid rain. After preliminary electrochemical investigations, a detailed characterization of gilded bronze samples before and after artificial ageing tests followed. Surface and cross-sections analyses were performed by FIB/FEG-SEM, SEM/EDS and micro-Raman spectroscopy. The protective efficiency of a coating based on 3-mercapto-propyl-trimethoxy-silane was also quantitatively assessed by GF-AAS through analysis of metal release, while the aesthetical appearance of coated and uncoated gilded bronze before and after ageing was evaluated by colour measurements.

The corrosion resistance of AISI 316 LN stainless steel was studied in contact with stagnant, oxygen-saturated liquid lead at 749 K for times up to 1200 h. The reaction products were analysed by means of optical and scanning electron microscopy, electron probe microanalysis, X-ray diffraction analysis and Mossbauer spectroscopy. Thin layers of largely variable thickness formed on the surface, mainly consisting of Fe3O4, with small amounts of FeO in the inner regions, Fe2O3 and an Fe-Pb-O ternary product in the outermost regions. The alloying elements Cr and Ni diffused to a different extent into Fe3O4. A mechanism is proposed to explain formation and growth of the reaction products.

The compatibility of steels with liquid lead and liquid lead–bismuth is a critical issue for the development of accelerator-driven system (ADS). In this work the results of a set of preliminary tests carried out in stagnant molten lead at 737 K and in lead–bismuth at 573, 673 and 749 K are summarised. The tests were conducted for 700, 1200, 1500 and 5000 h. Three steels were tested: two martensitic steels (mod. F82H and MANET II) and one austenitic steel (AISI 316L). The martensitic steels underwent oxidation phenomena at the higher testing temperature, due to oxygen dissolved in the melts. At a lower test temperature (573 K) and higher exposure time (5000 h) the oxidation rate of the martensitic steel seems to be lower and the developed oxide layer protective against liquid metal corrosion. The austenitic steel, in turn, exhibited an acceptable resistance to corrosion–oxidation under the test conditions.

Low temperature carburising (LTC) allows a significant hardness increase, with a consequent increase in wear resistance, without deteriorating corrosion behaviour. However, wear resistance strongly depends on contact conditions, therefore this work focuses on the dry sliding behaviour of LTC-treated AISI316L austenitic stainless steel against several countermaterials (AISI316L, LTC-treated AISI316L, hard chromium or plasma-sprayed Al2O3–TiO2). LTC produced a hardened surface layer (C-supersaturated expanded austenite), which improved corrosion resistance in NaCl 3.5% and increased wear resistance, to an extent which depends on both normal load and countermaterial. The best results were obtained when at least one of the contacting bodies was LTC-treated, because this condition led to mild tribo-oxidative wear. However, LTC did not improve the behaviour in terms of friction.

A copper-based armour, supposedly excavated in Eastern Georgia and tentatively dated to the I–II century AD, was investigated with the aim of checking its authenticity. The finding consisted of several pieces, mostly in a good state of conservation: helmet, lorica musculata (i.e. muscled cuirass), forearm guards, pterygies (covering the lower body and thighs), shin greaves and a spear tip. The combination of conventional metallography with in situ and non-destructive investigations (including Time of Flight Neutron Diffraction (ToF-ND)) on the front of the lorica , on one of the pterygies and on the spear tip showed that the composition and microstructure of the armour was not fully homogeneous. However, the results from the muscled cuirass are fairly coherent and raise suspicion about the authenticity of the piece, namely because of the (i) presence of metallic Al in the alloy, in solid solution with Cu, (ii) prevalence of an as-cast microstructure, which lead to a heavy weight as well to the need for a high amount of metal by comparison to hammered sheet and (iii) presence of an artificial patina, combined with earthy deposits which are not explainable if the original patina was removed before artificial patination for aesthetical reasons.

Corrosion inhibitors, associated or not with protective coatings, may be a good solution for planned conservation activities in the case of bronze and gilded bronze artworks. In this work, alternatives to BTA for the inhibition of bronzes and gilded bronze are investigated. The experimentation includes a screening of many organic substances as film-forming corrosion inhibitors for a copper alloy reproducing the composition and the microstructure of a Renaissance leaded bronze. The results, obtained after exposure to 3.5 wt.% NaCl solution or concentrated artificial rain, show that, if proper curing conditions are adopted, excellent protective properties are offered by 3-mercaptopropyl-trimetoxysilane.

Low temperature carburising (LTC) is a thermochemical treatment designed so as to achieve a good combination of wear and corrosion resistance in stainless and duplex steels. In this work, the influence of LTC on both corrosion and dry sliding behaviour of AISI 316L was investigated. LTC significantly enhanced surface hardness, due to the formation of the carbon-supersaturated S-phase. Consequently, the wear behaviour (evaluated against different countermaterials) improved, due to increased resistance to plastic deformation, as well as to decreased tendency towards adhesion. In order to evaluate the corrosion behaviour, electrochemical measurements were performed both in conventional environments and in reference conditions for the food industry. The results showed a significantly improved corrosion resistance in chloride environments, where the formation of a C-rich surface layer ennobles the treated steel, even though pitting corrosion was observed at very high anodic potentials. Conversely, the treated steel showed comparable (in acetic acid) or worse (in a sanitising solution) behaviour than the untreated one. In sulphuric acid the treated steel did not passivate, but it corroded at a limiting current density much lower that the critical current density for AISI 316L passivation.

The scanning electrochemical microscopy (SECM) was employed in the feedback mode for the visualisation of the local changes of morphology and reactivity, occurring on the surface of a quaternary copper-based alloy, due to exposure to environment. First, samples artificially aged by exposure to leaching acid rain were tested. The layer of corrosion products (“patina”) was investigated by performing SECM scans and approach curves, and the information provided by this electrochemical technique was compared with SEM–EDX–Raman characterisation. Successively, to highlight the early stages of localised corrosion processes, in situ examination of the surface exposed to an acidic environment was performed. The results show that SECM is a powerful characterisation tool of the deterioration process and is able to map the precursor sites of corrosion on the bronze surface.

Titanium alloys, due to their excellent combination of low density, high strength to weight ratio, high corrosion resistance and biocompatibility, are widely used in the aerospace, automotive, chemical and biomedical industries. However, a main limit to the use of Ti alloys is their poor tribological behaviour. For this reason, different surface treatments and coatings have been developed for improving surface properties of Ti alloys. Among the most recent surface modification techniques, plasma electrolytic oxidation (PEO) has been successfully applied to titanium alloys. The aim of the present study was to investigate the friction and wear behaviour of a PEO coating on the Ti6Al4V alloy. The tribological behaviour of the PEO treated Ti alloy was compared with that of thin PVD coatings, such as TiN, (Ti,Al)N and CrN/NbN superlattice deposited on the same substrate. The tests were carried out under dry sliding conditions (slider-on-cylinder geometry) against a plasma-spray Al 2 O 3 –TiO 2 coated steel. TiN gave the best tribological performance among the PVD coatings, up to 20 N. The PEO treatment significantly reduced both wear and friction of the Ti6Al4V alloy, even under higher applied loads, up to 35 N.

The corrosion of lead-rich pipes in historical organs in different parts of Europe has been investigated. The influence of the environment and the composition and microstructure of the pipe metal was studied. Pipe Corrosion was documented by visual inspection (boroscope). The corrosion attack and the composition and microstructure of the metal were characterized by OM, SEM, XRD, IC and FAAS. It is shown that the degree of corrosion of the pipes is correlated to the concentration of gaseous acetic and formic acid in the organ. The organic acids are emitted by the wood from which the wind system is built. It is also shown that pipe corrosion decreases with increasing tin content in the range 0-4% (wt). Possible conservation strategies are discussed. (c) 2008 Elsevier Ltd. All rights reserved.

Publisher Summary This chapter discusses influence of microstructure and composition on corrosion of lead-rich organ pipes. It reports the results of chemical and micro-structural investigations on samples from (1) the organ in the Basilica di Collemaggio (L'Aquila, Italy), selected as a reference organ affected by corrosion and (2) the organ in the Church of Madonna di Campagna (Ponte in Valtellina, Italy), selected as a reference for a healthy situation. The results of the characterization of the samples taken from corroded pipes indicate that lead carbonates are the main corrosion products that form on the inner surface of the foot of the pipes. Samples from reference organs with a high concentration of organic acids in the environment (e.g. L'Aquila) are extensively corroded. One of the key material factors in influencing the corrosion behavior of the pipes appears to be the tin content in the alloy and also copper traces seem to play a significant role. Further work is needed to evaluate the influence of tin and copper content on corrosion.

Tin-rich organ pipes are often affected by localised deterioration in the form of grey pustules, pinholes, cracks and exfoliations at the surface. Two main types of decay of tin-base materials that might have a similar appearance, i.e. the surface of the object covered with dark grey pustules, are known. The first is the allotropic transformation of white metallic tin into grey tin, the so-called “tin-pest”. The second form of decay is due to corrosion in the form of localised oxidation of tin. The identification of the causes of deterioration is of main concern because, whereas oxidised material can be treated, an object that suffers “tin pest” cannot be reconstituted. In the present paper the results of investigations on ancient tin-rich organ pipes affected by localised degradation are presented. The study of the composition and the microstructure of the pipes has been coupled with the results of analyses on the corrosion products. It was shown that oxidation clearly has a significant role in the deterioration of tin pipes, but it was not possible to establish if the allotropic transformation took place or not, because of the low probability of detecting the residual grey tin.

Architectural and artistic heritage exposed to environment undergoes spontaneous degradation. Thanks to its atmospheric corrosion resistance and pleasant aesthetical features, Cor-Ten (Weathering Steel) has been increasingly employed for outdoor applications. However, the exposure to aggressive atmosphere (e.g. marine or polluted sites) can significantly influence Cor-Ten performances. In this work, the behaviour of three kinds of commercial Cor-Ten (untreated, artificially patinated, artificially patinated and waxed) exposed to a coastal environment, in sheltered and unsheltered conditions, is examined. SEM/EDS and Raman investigations were performed on Cor-Ten surfaces and cross-sections to identify the main corrosion products and to study the evolution of the corrosion layer (patina). The corrosion-induced release of alloying metals (Cu, Cr, Fe, Ni, Mn) in runoff waters was also analysed. Chemometrical techniques were applied for the interpretation of experimental data in relation to the different surface finishes and to the environmental conditions. Results highlight the great influence the site and the geometry of exposure have on the composition of corrosion layer. Runoff process, on the other hand, result not related to rain amount but strongly affected by seasonal variations and atypical meteorological events.

To better understand corrosion behaviour of lead (Pb)-based alloys exposed to volatile organic compounds specifically acetic and formic acid a preliminary research has been carried out on laboratory-made samples replicating such alloys. Replicas have been manufactured by simulating specific types of Pb-based alloys, with antimony (Sb) and tin (Sn) as alloying elements, in order to characterise corrosion products and evaluate the influence of each alloying element. Replicas were cast in a refractory mould and later placed in size-specific desiccators and exposed to concentrated acetic and formic acid vapours for 15 days. Each specimen was also subjected to gravimetric measurements and periodically monitored in order to understand the corrosion behaviour. Micro Raman Spectroscopy (μRS) and Scanning Electron Microscopy together with energy Dispersive X-Ray Spectroscopy were used for the characterisation of Pb-based replicas. Results showed the presence of typical corrosion products more or less hydrated forms of Pb and Sn acetates and formates and also a sudden increase in the volume and brittleness of some Sb-rich specimens as well as the presence of seldom-detected metallic Sb peaks with μRS. In this perspective, the influence of Sb as an alloying element on the corrosion of Pb-based artefacts may generate serious problems when such objects have to be restored and particular attention should be given to conservation/stabilisation procedures.

This article aims to enhance the understanding of outdoor bronze alteration in light of a general model, take into account recent developments and according to exposure conditions (sheltered and unsheltered areas). The behaviour of the other alloying elements such as Sn, Zn and Pb is also mentioned. The importance of run-off effects inducing decuprification, the selective copper dissolution of bronze, is underlined on the basis of multi-scale investigation conducted both on natural patinas of outdoor monuments and on corrosion simulation performed in laboratory. A bronze disease affects outdoor bronze: in sheltered areas, bronze corrosion proceeds from a cyclic phenomenon linked to the repeated action of combined runoff and rainfall events.