Eco-Friendly Sol-Gel Coatings with Organic Corrosion Inhibitors for Lightweight AZ61 Alloy.

The latest advances in technology and materials science have catalyzed a transformative shift towards the adoption of environmentally conscious and lightweight materials across key sectors such as aeronautics, biomedical, and automotive industries. Noteworthy among these innovations are the magnesium-aluminum (Mg-Al) alloys employed in aeronautical applications, contributing to the overall reduction in aircraft weight and subsequently diminishing fuel consumption and mitigating atmospheric emissions. The present work delves into a study of the anti-corrosive properties inherent in various sol-gel coatings, leveraging a range of environmentally friendly corrosion inhibitors, specifically tailored for samples of the AZ61 alloy. Methodologically, the work involves the synthesis and application of sol-gel coatings on AZ61 alloy containing eco-friendly inhibitors: L-cysteine, N-acetyl-cysteine, curcumin and methylene blue. Subsequently, an accelerated corrosion test in a simulated saline environment is performed. Through microstructural and compositional analyses, the best inhibitors responses are achieved with inhibitors containing S, N heteroatoms and conjugated double bonds in their structure, probably due to the creation of a continuous MgCl2 layer. This research contributes to the ongoing discourse on protective eco-coatings, aligning with the broader paradigm shift towards sustainable and lightweight materials in key industries.

Evaluation of Low-Toxic Hybrid Sol-Gel Coatings with Organic pH-Sensitive Inhibitors for Corrosion Protection of AA2024 Aluminium Alloy.

Today's environmental needs require the reduction of the weight of vehicles, thus reducing fuel consumption and associated emissions. For this reason, the use of light alloys is being studied, which, due to their reactivity, must be protected before use. In this work, the effectiveness of a hybrid sol-gel coating doped with various organic environmentally friendly corrosion inhibitors applied to an AA2024 lightweight aluminium alloy is evaluated. Some of the inhibitors tested are pH indicators, acting as both corrosion inhibitors and optical sensors for the surface of the alloy. Samples are subjected to a corrosion test in a simulated saline environment and characterised before and after the test. The experimental results regarding their best inhibitor performance for their potential application in the transport industry are evaluated.

Generation of Defective Few-Layered Graphene Mesostructures by High-Energy Ball Milling and Their Combination with FeSiCuNbB Microwires for Reinforcing Microwave Absorbing Properties.

Defective few-layered graphene mesostructures (DFLGMs) are produced from graphite flakes by high-energy milling processes. We obtain an accurate control of the generated mesostructures, as well as of the amount and classification of the structural defects formed, providing a functional material for microwave absorption purposes. Working under far-field conditions, competitive values of minimum reflection loss coefficient (RLmin) = -21.76 dB and EAB = 4.77 dB are achieved when DFLGMs are immersed in paints at a low volume fraction (1.95%). One step forward is developed by combining them with the excellent absorption behavior that offers amorphous Fe73.5Si13.5B9Cu1Nb microwires (MWs), varying their filling contents, which are below 3%. We obtain a RLmin improvement of 47% (-53.08 dB) and an EAB enhancement of 137% (4 dB) compared to those obtained by MW-based paints. Furthermore, a fmin tunability is demonstrated, maintaining similar RLmin and EAB values, irrespective of an ideal matching thickness. In this scenario, the Maxwell-Garnet standard model is valid, and dielectric losses mainly come from multiple reflections, interfacial and dielectric polarizations, which greatly boost the microwave attenuation of MWs. The present concept can remarkably enhance not only the MW attenuation but can also apply to other microwave absorption architectures of technological interest by adding low quantities of DFLGMs.

Hybrid Sol-Gel Coatings Doped with Non-Toxic Corrosion Inhibitors for Corrosion Protection on AZ61 Magnesium Alloy.

Physiological human fluid is a natural corrosive environment and can lead to serious corrosion and mechanical damages to light Mg-Al alloys used in prosthetics for biomedical applications. In this work, organic-inorganic hybrid coatings doped with various environmentally friendly and non-toxic corrosion inhibitors have been prepared by the sol-gel process for the corrosion protection of AZ61 magnesium alloys. Effectiveness has been evaluated by pH measurements, optical microscopy, and SEM during a standard corrosion test in a Hanks' Balanced Salt Solution. The results showed that the addition of an inhibitor to the sol-gel coating can improve significantly the corrosion performance, being an excellent barrier for the L-cysteine-doped hybrid sol-gel films. The incorporation of TiO2 nanoparticles, 2-Aminopyridine and quinine organic molecules slowed down the corrosion rate of the Mg-Al alloy. Graphene oxide seemed to have the same response to corrosion as the hybrid sol-gel coating without inhibitors.

Proton-transfer reaction dynamics within the human serum albumin protein.

We report on femto- to nanosecond studies of the excited state intermolecular proton transfer (ESPT) reaction of trisodium 8-hydroxypyrene-1,3,6-trisulfonate (pyranine, HPTS) with the human serum albumin (HSA) protein. The formed robust 1:1 complexes (K(eq) = (2.6 ± 0.1) × 10(6) M(-1)) show both photoacid (∼430 nm) and conjugated photobase (∼500 nm) emissions of the caged HPTS in its protonated structure. The proton-transfer reactions in these complexes proceed in a large time window, spanning from 150 fs to ∼1.2 ns. The ultrafast component reflects a direct H-bond breaking and making in the robust complexes, involving the carboxylate groups of the amino acids, while the slowest one is arising from the slow dynamics of the so-called biological water. Additional time constants of the caged photoacid to give the conjugated photobase are observed, assigned to the ESPT reaction within "loose" complexes (3 to tens of picoseconds), and 130 ps and 1.2 ns due to the slow dynamics of the water molecules around the protein residues and involved in the proton transfer. The fs-ns anisotropy measurements confirm the robustness of the HPTS:HSA complexes. Our results indicate that, even though robust 1:1 complexes between HPTS and the HSA are formed, the system is heterogeneous, due to different possible interactions of the dye with the inside/outside parts of the protein. Furthermore, we find lower values of the initial anisotropy (r(0)) in the protein (0.33) and in γ-CD (0.28) in comparison with buffered aqueous solution (0.385). We propose that caging HPTS by the HSA protein and by the cyclodextrin affects the electronic redistribution in a different degree of mixing between the (1)L(a) and (1)L(b) states in the formed deprotonated form, for which the interactions of the sulfonate groups with the surroundings should play a key role.

Single molecule photobehavior of a chromophore interacting with silica-based nanomaterials.

Single molecule studies of the free DY-630-MI and interacting with MCM-41 and (Al)MCM-41, show the conformational diversity of the molecule. The free dye is characterized by a single broad (fwhm = 0.7 ns) lifetime distribution histogram centered on 1.47 ns, which is also reflected in the broadness of the polarization value distribution histogram, covering almost the full range of values from -1 to 1. The fluorescence intensity traces of the free DY-630-MI show strong blinking behavior and weak photostability. Upon interaction with the mesoporous silica nanomaterials, MCM-41 and (Al)MCM-41, the dye molecule becomes more stable, with less blinking present in the fluorescence traces. The lifetime distribution histogram in the case of DY-630-MI/MCM-41 complexes is fitted by 3 Gaussians, indicating 3 distinct interaction sites. The Gaussian with the largest amplitude is centered on 2.19 ns, consistent with the confinement effect of MCM-41 and in agreement with the ensemble average studies. The polarization value distribution histogram becomes narrower in comparison with the free molecule and is more biased towards the positive limit. Replacing few Si(4+) ions with Al(3+) ones in the regular MCM-41 changes the local electrostatic field within the nanotube. This atomic substitution in the nanohosts results in a more selective orientation of the dye molecules, giving two populations with time constants 1.56 and 2.10 ns.