The Role of Cu-Based Intermetallic on the Direct Growth of a ZnAl LDH Film on AA2024

The direct ZnAl layered double hydroxide growth on AA2024 is a fast-occurring reaction, yet is characterized by an inhomogeneous film thickness. It has been shown that at the periphery of Cu-rich intermetallic, the flakes tend to be larger and denser. A combination of in situ and ex situ measurements were used to monitor the changes in the layered double hydroxide film grown on the regions of intermetallics. Immediately after immersion, an activation of the intermetallic phases is observed due to the dealloying process with an almost immediate film growth. Dealloying is followed by trenching of the adjacent Al matrix leading to an excessive production of large and dense layered double hydroxide flakes at the periphery of the intermetallic. However, the scanning electron microscopy cross-section images revealed that the trenching process leads to defects in the area surrounding the intermetallic. This could weaken the corrosion resistance performance of the layered double hydroxide conversion coating and lead to adhesion failure of consecutive polymer coatings. Nevertheless, this work highlights a few advantages and drawbacks of the layered double hydroxide conversion coatings and pathways to its potential optimization and improvement

A critical review on the production and application of graphene and graphene-based materials in anti-corrosion coatings

Among the many potential applications of graphene and graphene-based materials, their use as protective films or as additives in coatings for corrosion protection has seen an increased level of interest in the last decade. Much of this interest is motivated by the need to implement additional functionalities, to enhance anti-corrosion performance and to ultimately extend the service life of metallic structures. Pristine graphene films, with their impermeable nature allied to flexibility and mechanical strength, appear as particularly attractive candidates for barrier films against corrosive agents, while graphene-based materials such as graphene oxide and reduced graphene oxide offer a wide range of opportunities for their dispersion in polymeric matrices for composite anti-corrosive coatings. Simultaneously, considerable progress in the development of scalable graphene and graphene-based materials production techniques has been made during the last several years. Currently, a broad range of graphene materials with different morphologies and properties is available, making the need for an adequate fit between the production method and the desired application even more evident. This review article aims to give the reader a general overview of the recent trends in both the production of graphene and graphene-based materials, and their implementation in different anti-corrosion solutions. Moreover, the present work provides a critical look on this subject, highlighting the areas in need of further exploration.publishe

As-cast and extruded MgZnCa systems for biodegradable implants: Characterization and corrosion behavior

The aim of the present study is to evaluate the effect of alloy processing and composition as well as the pH control and testing medium on the in vitro corrosion performance of MgZnCa systems for biodegradable implants. The grain size and secondary phases were analyzed by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Scanning kelvin probe force microscopy (SKPFM) was used to analyze the Volta potential values of the second phases. The corrosion performance of the three alloys was evaluated by electrochemical and hydrogen evolution methods in α-MEM with and without organic species (i.e. complete and inorganic α-MEM). Two strategies were followed to evaluate the influence of the pH on the corrosion behavior: daily solution replacement and CO2 flow based pH control. For all the materials, the organic medium accelerates the corrosion process. Constant pH maintained by CO2 flow through the medium results in considerably higher corrosion rates for all alloys. The impact of pH is lesser on the as-cast alloys due to the barrier effect of the secondary phases, particularly pronounced in the Mg1Zn1Ca alloy which showed the lowest corrosion rate. The wrought Mg0.5Zn0.2Ca alloy that lacks the refined secondary phase network and exhibits high number of twins undergoes accelerated uniform corrosion under constant pH conditions

One-step synthesis and growth mechanism of nitrate intercalated ZnAl LDH conversion coatings on zinc

An approach for the synthesis of ZnAl-NO3 LDH conversion coatings on zinc in an aqueous acidic Al(NO3)3/NaNO3 solution is demonstrated for the first time. The growth mechanism has been investigated using time resolved structural, microstructural and analytical methods. A LDH growth model involving both electrochemical and chemical processes is suggested.publishe

Atomic layer deposition of nanometric alumina for corrosion protection of heterogeneous metallic surfaces: the case of aeronautical grade aluminium alloy 2024-T3

Nanometric layers of Al2O3 were applied by atomic layer deposition (ALD) on 2024-T3 aluminium alloy. The ALD layers suppressed the corrosion of the alloy as confirmed by Scanning Kelvin Probe Force Microscopy (SKPFM), polarization curves and Electrochemical Impedance Spectroscopy (EIS). The protection provided by the ALD layers weakened with the time of immersion and this was attributed to the incorporation of hydroxyl species in the film during the deposition at low temperature (100 ◦C) making them vulnerable to water.publishe

Mistet på sjøen? En nyoppdaget fiskekrok fra steinalderen i Søgne, Vest-Agder.

The starting point for the present paper is a recent discovery of a well-preserved bone or antler fishhook, which turned up in a test pit during an underwater survey outside Tømmervigodden in Søgne, southernmost Norway. The hook is the third archaeological bone find from submarine context in Søgne. Tømmervigodden is located two kilometers away from Hummervikholmen, a submarine site known for revealing the oldest human remains from Norway, dated to the Middle Mesolithic (c. 8300-6300 cal. BC). Furthermore, a harpoon has been found in Lundeelva, approx. eight kilometers inland to the northeast. These finds demonstrate the extraordinary conditions for preservation of organic remains in the area. This article present the artefact and we discuss the issue of dating and deposition based on typology, context, and shoreline displacement curves. How old is the fishhook? How did it end up in the sea, and why is it so well preserved? The site is located in one of three areas along the Norwegian coast with potential for transgressed Mesolithic sites. The sea levels has fluctuated in Vest-Agder since the end of the Ice Age, and the sea has periodically been both higher and lower than today.The location close to Hummervikholmen and another Mesolithic site located on dry land at Tømmervigodden, initially suggested a Mesolithic date. However, the form of the fishhook, with a barb and elongated knob for attachment of the line, differs considerably from well-dated Mesolithic fishhooks in the region. The newly discovered fishhook has a distinct barb, an attribute previously considered a Neolithic trait. A precise dating would be crucial, but the closest typological parallels are undated stray-finds and C14-analysis would have destroyed the small object. Hence, dating of the hook requires a new assessment of the typology and chronology of the Stone Age fishhooks. Based on chronological and regional comparisons, we argue for a Middle Neolithic date of the fishhook from Søgne. Based on current knowledge of the local shoreline displacement curve and the formation processes influencing the seabed, we further suggest that the fishhook was lost at sea during fishing, when the sea level was at least five meters above present