Emma Paola Maria Virginia Angelini

Application of plasma deposited organosilicon thin films for the corrosion protection of metals

In this contribution it will be shown that plasma enhanced chemical vapor deposition (PECVD) of silicon containing organic compounds is a promising approach for the corrosion protection of metals (steel and magnesium alloys). When the deposition process is preceded by a suitable plasma treatment, which depends on the particular metal under study, a marked increase of the protective properties measured with electrochemical impedance spectroscopy (EIS) is detected. The highest impedance modulus obtained for Mg is 450 KΩ·cm2, 8000 times higher than for the bare metal. Highly protective coatings are obtained for inorganic films, free of sylanols. A marked decrease of the impedance modulus of coated substrates has been registered after immersion in electrolyte solution due to the presence of pinholes which represents defect points where localized corrosion starts.

Hydrogen evolution reaction on NiRE (RE=rare earth) crystalline alloys ☆

NiRE (RE=Y, Ce, Pr and Sm) crystalline alloys have been characterized by means of microstructural and electrochemical techniques in view of their possible application as electrocatalytic materials for the hydrogen evolution reaction (HER). The microstructure of the electrodes has been investigated by optical and electron microscopy. The electrocatalytic efficiency has been evaluated on the basis of electrochemical data obtained from Tafel curves and a.c. impedance measurements carried out in 1 M NaOH solution at 298 K. The microstructural features play a fundamental role in determining the electrocatalytic activity of the investigated alloys. The overall experimental data indicate that interesting electrocatalytic performances are obtained with Ni94Pr6 and Ni95Ce5 electrodes, which show the highest activities towards the HER.

Influence of the rare earth content on the electrochemical behaviour of Al-Mg-Er alloys

Abstract The electrochemical behaviour of a number of Al–Mg alloys with increasing content of erbium (rare earth metal) has been evaluated. To this end borate solutions with or without chloride have been used. The examined alloys show a complex microstructure, in which the Al solid solution coexists with such intermetallic compounds as Al3Mg2, Al66.7Mg23.3Er10 (τ) and Al3Er. In chloride-free solutions the alloys exhibit a good electrochemical behaviour independent of composition and microstructure. In chloride-containing solutions the intermetallic compounds have a strong influence due to the difference in electrochemical activity between these phases and the Al matrix; local galvanic cells form affecting the stability of the protective superficial oxide and lead to an accelerated localised corrosion attack. The presence of erbium is beneficial; the analysis of the anodic polarisation curves reveals a progressive increase in the passive range with increasing rare earth concentration.

Low-cost electrochemical impedance spectroscopy system for corrosion monitoring of metallic antiquities and works of art

Electrochemical impedance spectroscopy (EIS) is recognized to be a powerful and noninvasive technique to test the integrity of protective coatings on memorials, but commercial EIS systems are rather costly though versatile devices. This paper describes a low cost and portable EIS system that is based on a compact digital signal processor (DSP) board and embeds the potentiostatic function so that it can be used without requiring an external potentiostat. The software that runs on the DSP is designed to analyze the electrochemical impedance only in a reduced frequency range in order to produce a simple corrosion alert result. The device is equipped with a digital interface and can be connected to a personal computer to carry out a complete frequency analysis and perform a more complex data processing.

Corrosion under static and dynamic conditions of alloys used for magnetic retention in dentistry

In recent years magnetic retention has gained increasing popularity in dental practice. This investigation compared the corrosion resistance of the palladium-cobalt ferromagnetic alloy (constituent of the keeper cemented on the abutment teeth) coupled with the samarium-cobalt magnets embedded in the removable part of the denture. The behavior of three couples (cobalt-palladium, cobalt-palladium/titanium, and cobalt-palladium/palladium) has been studied. The magnets, because of their poor corrosion resistance, are encapsulated in various materials. To simulate clinical conditions, characterized by the continuous movement of the keeper with respect to the magnet, the experiments were conducted in artificial saliva under intermittent and continuous wear.

Ancient mercury-based plating methods: combined use of surface analytical techniques for the study of manufacturing process and degradation phenomena.

Fire gilding and silvering are age-old mercury-based processes used to coat thesurface of less precious substrates with thin layers of gold or silver. In ancient times, these methods were used to produce and decorate different types of artefacts, such as jewels, statues, amulets, and commonly-used objects. Gilders performed these processes not only to decorate objects but also to simulate the appearance of gold or silver, sometimes fraudulently. From a technological point of view, the aim of these workmen over 2000 years ago was to make the precious metal coatings as thin and adherent as possible. This was in order to save expensive metals and to improve the resistance to the wear caused by continued use and circulation. Without knowledge about the chemical-physical processes, the ancient crafts-men systematically manipulated these metals to create functional and decorative artistic objects. The mercury-based methods were also fraudulently used in ancient times to produce objects such as jewels and coins that looked like they were made of silver or gold but actually had a less precious core. These coins were minted by counterfeiters but also by the official issuing authorities. The latter was probably because of a lack of precious metals, reflecting periods of severe economic conditions. In this Account, we discuss some representative cases of gold- and silver-coatedobjects, focusing on unique and valuable Roman and Dark Ages period works of art, such as the St. Ambrogios altar (825 AD), and commonly used objects. We carried out the investigations using surface analytical methods, such as selected area X-ray photoelectron spectroscopy and scanning electron microscopy combined with energy-dispersive spectroscopy. We used these methods to investigate the surface and subsurface chemical features of these important examples of art and technology, interpreting some aspects of the manufacturing methods and of disclosing degradation agents and mechanisms. These findings may contribute to cultural heritage preservation, thus extending the applicability of the surface analytical techniques.

Corrosion and conservation of cultural heritage metallic artefacts

Introduction: Conservation versus laboratory investigation in the preservation of metallic heritage artefacts. Part 1 Conservation issues: Past, present, future: Conservation, corrosion science and evidence-based preservation strategies for metallic heritage artefacts Atmospheric corrosion of heritage metallic artefacts: Processes and prevention. Part 2 Analytical techniques for the study of cultural heritage corrosion: Analytical techniques for the study of corrosion of metallic heritage artefacts: From micrometer to nanometer scales The use of metallographic and metallurgical investigation methods in the preservation of metallic heritage artefacts Analysis of corroded metallic heritage artefacts using laser-induced breakdown spectroscopy (LIBS) Electrochemical measurements in the conservation of metallic heritage artefacts: An overview Electrochemical analysis of metallic heritage artefacts: Time-lapse spectroelectrochemical techniques Electrochemical analysis of metallic heritage artefacts: Voltammetry of microparticles (VMP). Part 3 Specific alteration processes: Artistic patinas on ancient bronze statues Ancient silver artefacts: Corrosion processes and preservation strategies Underwater corrosion of metallic heritage artefacts Long term anoxic corrosion of iron Reactivity studies of atmospheric corrosion of heritage iron artefacts Atmospheric corrosion of historic industrial structures. Part 4 On-site monitoring: Electrochemical impedance spectroscopy (EIS) for the in situ analysis of metallic heritage artefacts Oxygen monitoring in the corrosion and preservation of metallic heritage artefacts Issues in environmental monitoring of metallic heritage artefacts. Part 5 Protection mediums, methods and strategies: Alkaline desalination techniques for archaeological iron The use of subcritical fluids for the stabilisation of archaeological iron: An overview Monitoring, modelling and prediction of corrosion rates of historic iron shipwrecks The role of standards in conservation methods for metals in cultural heritage Coatings including carboxylates for the preservation of metallic heritage artefacts Sol-gel coatings for the preservation of metallic heritage artefacts Plasma treatments for the cleaning and preservation of metallic heritage artefacts Corrosion inhibitors for the preservation of metallic heritage artefacts.

Silver artefacts: plasma deposition of SiOx protective layers and tarnishing evolution assessment

Abstract Silver artifacts suffer tarnishing when exposed to a sulphur containg atmosphere. Plasma deposited SiOx thin films are proposed for the protection of silver artefacts, owing to their optical transparency and high barrier properties against vapours. The protective effectiveness of the SiOx films was assessed by means of electrochemical impedance measurements performed in an Na2S solution on a set of coated silver based alloy samples, and by submitting another set of samples to a tarnishing test in presence of H2S vapours. The experimental findings reveal that the SiOx deposition, performed in RF plasma fed with a tetraetoxysilane/oxygen/argon mixture, produces layers with excellent barrier effects against the aggressive agents. The protective effectiveness increases if the deposition is performed at increasing input powers and at decreasing tetraethoxysilane/oxygen ratios in the feeding gas. The tarnishing evolution onto the coated surface was assessed at the microscopical and macroscopical level by means of field emission scanning electron microscopy and by an easy to use diagnostic tool based on digital photography and image processing.

Structural characterisation and corrosion resistance of Ga-precious metal alloys formed by liquid–solid reaction at room temperature

Abstract An attempt to eliminate Hg from dental amalgams was made by substituting it with low melting Ga-based alloys, liquid at room temperature. However more information is needed on the influence of alloy composition and their questioned corrosion resistance. In this paper the reaction of some liquid Ga alloys and some solid precious metal alloys with different nobility was studied. Structural features, hardness and corrosion resistance of the obtained composite materials were investigated as a function of composition of the starting alloys, liquid/solid ratio and different mixing methods. Every combination of the solid precious metal powders and the liquid Ga-alloys gives rise to similar composite materials. The structure always consists of unreacted solid alloy particles embedded in a complex matrix composed of many reaction phases. The formation of some phases depends on the composition of the solid alloy, others originate all the time; however their topography and morphology may be different as well as their compositional range. The high porosity generally present in the composite materials markedly affects hardness values; nevertheless some prepared materials reach hardness comparable with the one of commercial amalgams. The nobility of the solid alloy and porosity percentage play a determinant role on the corrosion behaviour. In all cases the low corrosion resistance of the experimented materials may be attributed to a galvanic coupling between the reaction intermediate phases and the unreacted liquid alloy remained inside the pores.

Sensitization Phenomena on Aged SAF 2205 Duplex Stainless Steel and Their Control Using the Electrochemical Potentiokinetic Reactivation Test

Abstract Microstructural changes and resulting properties were studied for SAF 2205 (UNS S31803) austeno-ferritic stainless steel (SS) aged between 700°C and 900°C for up to 2 weeks and then water-...