An Inhibitor-Loaded LDH- and MOF-Based Bilayer Hybrid System for Active Corrosion Protection of Aluminum Alloys

A novel inhibitor-loaded bilayer hybrid system based on the LDH inner layer and MOF outer layer is designed on an aluminum alloy 2A12 surface to improve corrosion performance. The hybrid film system covers the inherent cavities and intercrystalline defects of the LDH film using the affinity between the LDH and the MOF compounds. The results demonstrate that the LDH-inhI precursor film is entirely covered by new Zn-based MOF microrods. The LDH-inhI precursor film is partially dissolved and recrystallized in favor of MOF crystal growth to strengthen the binding adhesion between LDH and MOF films. The LDH-inhI/MOF-inhII bilayer film shows significantly enhanced corrosion resistance through the synergistic action of LDH and MOF nanocontainers doped with different corrosion inhibitors (vanadates, 2,5-furandicarboxylic acid, and benzotriazoles). Due to the multiple loadings of the MOF film and the sustained-release of the LDH film, this method provides an effective approach to developing new anticorrosion systems and enhancing both the barrier ability and active corrosion protection performance of LDH-based conversion treatments.

Fluorinated Siloxane Modified Layered Double Hydroxide Sealing Film to Enhance the Corrosion Resistance of Anodic Oxide Film of Fricition Stir Welding Joint of Aluminum Alloys

Aluminum alloys and their welding structures have been widely used in aviation, aerospace, automobiles, ships, and other industrial fields. The non-uniform nature of welding structures of aluminum alloys causes intractable corrosion problems. Anodizing and subsequent sealing processes are common and effective methods to improve the corrosion resistance of welding structures. However, traditional sealing processes like hot water sealing and potassium dichromate sealing are criticized due to energy consumption or toxicity. In this work, a layered double hydroxide (LDH) sealing process with subsequent fluorinated siloxane modification is proposed to improve the corrosion resistance of the anodic oxide film of friction stir welding joints of typical aluminum alloys. The obtained sealing film with typical lamelliform structures of LDH grows well at the defects of oxidation film and also smoothens the sample surface. The hydrophobicity of the film can separate the corrosive medium from the sample surface and further enhance corrosion resistance. As a result, the corrosion current of the welded sample in 3.5 wt.% NaCl solution plummets about 3~4 orders of magnitude compared to the initial state without anodizing, indicating superior corrosion resistance brought by this method.

Corrosion Resistance of Li-Al LDHs Film Modified by Methionine for 6063 Al Alloy in 3.5 wt.% NaCl Solution

Methionine (Met) was introduced to modify the Li-Al layered double hydroxides (LDHs) film prepared on 6063 aluminum alloy by in situ method for the first time. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy, and X-ray diffraction confirmed the successful insertion of Met into LDHs film and revealed that the introduction of Met could make the LDHs film much denser. Electrochemical tests illustrated that the corrosion rate of the Met modified LDHs film was reduced by more than an order of magnitude compared with the bare Al alloy. Moreover, the corrosion rate of the modified LDHs film after immersion in 3.5 wt.% NaCl solution for 21 days was almost the same as that without immersion, which indicates that the modified film has good corrosion durability. The corrosion resistance of the scratched modified film could recover to the level without a scratch on the 14th day based on the scratch test results, meaning the modified film has a good self-healing property. Finally, the anti-corrosion mechanism of the Met was proved by molecular dynamic simulations and found that the enhanced corrosion resistance may be attributed to the addition of Met that slowed the diffusion of the corrosive medium Cl− and water molecules.

A Review on Anodizing of Aerospace Aluminum Alloys for Corrosion Protection

Aluminum alloys used for aerospace applications provide good strength to weight ratio at a reasonable cost but exhibit only limited corrosion resistance. Therefore, a durable and effective corrosion protection system is required to fulfil structural integrity. Typically, an aerospace corrosion protection system consists of a multi-layered scheme employing an anodic oxide with good barrier properties and a porous surface, a corrosion inhibited organic primer, and an organic topcoat. The present review covers published research on the anodic oxide protection layer principles and requirements for aerospace application, the effect of the anodizing process parameters, as well as the importance of process steps taking place before and after anodizing. Moreover, the challenges of chromic acid anodizing (CAA) substitution are discussed and tartaric-sulfuric acid anodizing (TSA) is especially highlighted among the environmentally friendly alternatives.

The Sealing Step in Aluminum Anodizing: A Focus on Sustainable Strategies for Enhancing Both Energy Efficiency and Corrosion Resistance

Increasing demands for environmental accountability and energy efficiency in industrial practice necessitates significant modification(s) of existing technologies and development of new ones to meet the stringent sustainability demands of the future. Generally, development of required new technologies and appropriate modifications of existing ones need to be premised on in-depth appreciation of existing technologies, their limitations, and desired ideal products or processes. In the light of these, published literature mostly in the past 30 years on the sealing process; the second highest energy consuming step in aluminum anodization and a step with significant environmental impacts has been critical reviewed in this systematic review. Emphasis have been placed on the need to reduce both the energy input in the anodization process and environmental implications. The implications of the nano-porous structure of the anodic oxide on mass transport and chemical reactivity of relevant species during the sealing process is highlighted with a focus on exploiting these peculiarities, in improving the quality of sealed products. In addition, perspective is provided on plausible approaches and important factors to be considered in developing sealing procedures that can minimize the energy input and environmental impact of the sealing step, and ensure a more sustainable aluminum anodization process/industry.

Layered Double Hydroxide Clusters as Precursors of Novel Multifunctional Layers: A Bottom-Up Approach

The specific microstructure of aluminum alloys is herein explored to grow spatially-resolved layered double hydroxide (SR-LDH) clusters on their surface. Upon chemical modification of LDHs via intercalation, adsorption and grafting with different functional molecules, novel surface-engineered surfaces were obtained. Crystal structure and phase composition were analyzed by X-ray diffraction (XRD) and surface morphology was observed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectrometry (GDOES) were used to correlate structural changes upon ion-exchange and interfacial modifications with chemical composition and surface profiles of the SR-LDH films, respectively. The protection conferred by these films against localized corrosion was investigated at microscale using the scanning vibrating electrode technique (SVET). LDH-NO3 phase was obtained by direct growth onto AA2024 surface, as evidenced by (003) and (006) XRD diffraction reflections. After anion exchange of nitrate with 2-mercaptobenzothiazole (MBT) there was a decrease in the SR-LDH thickness inferred from GDOES profiles. The subsequent surface functionalization with HTMS was confirmed by the presence of Si signal in XPS and GDOES analyses, leading to an increase in the water contact angle (c.a 144° ± 3°). SVET measurements of the SR-LDH films revealed exceptional corrosion resistance, whereas the bioluminescent bacteria assay proved the anti-microbial character of the obtained films. Overall the results obtained show an effective corrosion protection of the SR-LDHs when compared to the bare substrate and the potential of these films for biofouling applications as new Cr-free pre-treatments.

Synthesis of a New Nitrate-Fertilizer Form with a Controlled Release Behavior via an Incorporation Technique into a Clay Material

The current study shows an advanced synesthetic technique of a nitrate-fertilizer with a controlled release behavior into different soils (normal and acidic agriculture soils solutions) at different climate temperatures. The environmentally friendly and the biocompatible layered double hydroxide (LDH) clay material was used as a host to accommodate the nitrate anion into its interlayer gallery by applying a reconstruction-incorporation technique (the memory effect property of LDH that allows calcined LDH to memorize its original structure). The prepared materials were characterized by different spectroscopic techniques including; X-ray powder spectroscopy, IR, SEM, TEM, and TGA analyses. A remarkable loading ratio of the nitrate anion fertilizer was recorded into the LDH structure. Around 90 wt% of the intercalated nitrate anion was released in a sustained controlled behavior over around 24 days, while the same amount of nitrate was released over 10 days in the acidic soil. Accordingly, the present study offers a new passway for the formulation of controlled release fertilizers by using the hosting anionic clay LDH materials.

Corrosion Behavior of Welded Joint of Q690 with CMT Twin

Low alloy steel of Q690 was welded with the method of CMT Twin. The corrosion behavior of welded joint had been investigated using scanning vibrating electrode technique (SVET) in 3.5% NaCl solution. The research results showed that the appearance of the troostite increased the hardness of the heat affected zone. Furthermore, the corrosion products of different microstructure were identical, and the white products (Fe(OH)2) of welded joint turned into products of rufous (Fe(OH)3). The quantitative information provided by SVET was discussed, and the corrosion degree was measured by some parameters. In comparison with other areas, the corrosion rates of the overheated zone and the base metal were higher. Then, the corrosion resistance of the weld zone with CMT Twin was greatly improved, when compared with that of the base metal. Therefore, Ni has significant influence on corrosion resistance of weld zone. In summary, it can be discovered that the corrosion rates of various zones were related to the welding heat input.