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.

Impact of γ-rays Irradiation on Hybrid TiO2-SiO2 Sol-Gel Films Doped with RHODAMINE 6G

In the present paper, we investigate how the optical and structural properties, in particular the observed photoluminescence (PL) of photocurable and organic-inorganic TiO2-SiO2 sol-gel films doped with Rhodamine 6G (R6G) are affected by γ-rays. For this, four luminescent films, firstly polymerized with UV photons (365 nm), were submitted to different accumulated doses of 50 kGy, 200 kGy, 500 kGy and 1 MGy while one sample was kept as a reference and unirradiated. The PL, recorded under excitations at 365 nm, 442 nm and 488 nm clearly evidences that a strong signal peaking at 564 nm is still largely present in the γ-irradiated samples. In addition, M-lines and Fourier-transform infrared (FTIR) spectroscopies are used to quantify the radiation induced refractive index variation and the chemical changes, respectively. Results show that a refractive index decrease of 7 × 10−3 at 633 nm is achieved at a 1 MGy accumulated dose while a photo-induced polymerization occurs, related to the consumption of CH=C, Si-OH and Si-O-CH3 groups to form Ti-O and Si-O bonds. All these results confirm that the host matrix (TiO2-SiO2) and R6G fluorophores successfully withstand the hard γ-ray exposure, opening the way to the use of this material for sensing applications in radiation-rich environments.

Self-Organized In-Depth Gradients in Highly Ti-Doped ZnO Films: Thermal Versus MW Plasma Annealing

Highly Ti-doped ZnO films have been produced by a spin-casting sol-gel process. The spin-casted films show high in plane homogeneity and optical quality. However, when inspected in depth, the surface composition is Ti rich. We show that two possible annealing processes can be considered depending on the properties to exploit. To promote in-depth homogenization, thermal annealing processes have been applied. Meanwhile, the gradients can be exacerbated, thanks to a non-negligible surface sputtering, by applying microwave (MW) plasma treatments with Ar discharges at different pressures. The microstructural properties of the differently processed films have been obtained prior to a study by grazing incidence X-ray fluorescence (GI-XRF) spectroscopy, which reveals the in-depth composition trends induced by the two alternative annealing procedures. The final wetting, electrical and optical properties of the films are described in accordance with the Ti distribution pattern revealed by GI-XRF. The study underlines for the first time how MW plasma annealing processes can be used to exacerbate self-induced atomic gradients in sol-gel films with potential implications in catalytic and biomedical applications.

Enhancing the Corrosion Protection of AA2024-T3 Alloy by Surface Treatments Based on Piperazine-Modified Hybrid Sol–Gel Films

The aim of this study was to develop new chrome-free surface pretreatments for AA2024-T3 aluminum alloy. These pretreatments were based on hybrid organic–inorganic sol–gel thin films prepared from mixtures of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethylorthosilicate (TMOS). Different MAPTMS/TMOS molar ratios were used for optimizing the physical–chemical characteristics of the sol–gel films. The formulation of a set of these sols was modified by incorporating piperazine (1,4-diazacyclohexane) as a corrosion inhibitor. The resulting sol–gel films were characterized by using Fourier transform infrared spectroscopy (FTIR), liquid-state 29Si nuclear magnetic resonance spectroscopy (29Si-NMR) and viscosity measurements. The corrosion performance of the sol–gel films was analyzed by using electrochemical impedance spectroscopy (EIS) and local electrochemical impedance mapping (LEIM). The characterization techniques indicated that piperazine behaved as a catalyst for the condensation reaction during the formation of the MAPTMS/TMOS organopolysiloxane network and produces an increase of the crosslinking degree of the sol–gel films. EIS and LEIM results showed that piperazine is an effective corrosion inhibitor, which can be used to enhance the active corrosion protection performance of sol–gel films.

Adsorption Behavior of GTMS on AA2024-T3 Aluminum Alloy and the Application on Surface Pretreatment

Basing on the study of adsorption behavior of glycidoxypropyl-trimethoxy-silane (GTMS), pretreatment method of AA2024-T3 aluminum alloy for sol-gel films was optimized. The morphology, composition and corrosion protective performance of alloy coated with the films were investigated by using FE-SEM, EDS, AFM and EIS. The results showed that the Al matrix exhibited better ability to adsorb GTMS molecules than the second phase particles, especially at lower concentration of GTMS. Further, the 5% GTMS films cover the whole surface, but the selective adsorption behaviors still exist. It was concluded that less second phase particles and smoother surface were benefit to the sol-gel films on aluminum alloy. Depending on this conclusion, the pretreatment method for sol-gel films was optimized. The optimized surface condition conducted with 50 g•L-1 sodium hydroxide and ultrasound at 60 oC for 30 s was obtained. These samples coated with the sol-gel films revealed good anti-corrosion performance. The coverage degree of the films was up to 97.95 %.