•AA2198-T851 is a potential substitute for AA2524-T3 with higher pitting resistance.•AA7081-T73511 is more prone to pitting corrosion than the AA7050-T7451.•Cathodic Al7Cu2Fe particles promote ...dissolution of adjacent 7XXX matrix.
The 2XXX and 7XXX series aluminium alloys are commonly used in aircraft applications where high strength-to-weight ratios are required. The present study aims to compare the corrosion resistance of two novel alloys developed for aircraft industry (AA2198-T851 and 7081-T73511) to that presented by the alternative base alloys (AA2524-T3 and 7050-T7451, respectively). Results indicate that AA2198-T851 may show a superior corrosion performance compared to AA2524-T3, being a potential candidate for its replacement, due to best mechanical properties. In what concerns the 7081-T73511, its resistance to pitting corrosion may be lower than for the base line alloy 7050-T7451.
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Silica nanoparticles (SNPs) received more attention with the emergence of nanotechnology with the aim and promise of becoming innovative drug delivery systems. They have been ...fulfilling this objective with excellence and nowadays they play a central role in biomedical applications. New SNPs application routes are being explored such as the epidermal, dermal, and transdermal routes. With that, novel models of synthesis, functionalization, and applications constantly appear. However, it is essential that such innovations are accompanied by in-depth studies on permeation, biodistribution, metabolization, and elimination of the generated by-products. Such studies are still incipient, if not rare. This article reviews significant findings on SNPs and their skin interactions. An extensive literature review on SNPs synthesis and functionalization methodologies was performed, as well as on the skin characteristics, skin permeation mechanisms, and in vivo toxicity assessments. Furthermore, studies of the past 5 years on the main therapeutic and cosmetic products employing SNPs, with greater emphasis on in vivo and ex vivo studies were included.
The 5-alpha-reductase enzyme, present in pilosebaceous units, plays a crucial role in the appearance of cutaneous hyperandrogenism manifestations (hirsutism, acne, and androgenetic alopecia). Its ...inhibition is an excellent strategy to reverse these conditions. Given the limitations of existing treatments, with transient effects and delayed therapeutic response, as well as the possibility of causing undesirable side effects, this study sought to develop new drug delivery systems to overcome these limitations. In other words, innovative stimuli-responsive hybrid nanoparticles were synthesized using silica/natural polysaccharides, encapsulating 5-alpha-reductase enzyme inhibitors derived from the plant Stryphnodendron adstringens (Mart.) Coville (commonly known as 'Barbatimão'). Silica core was synthesized by the modified Stöber method. The pH responsive polysaccharides used to coat the porous silica cores were chitosan, and sodium alginate, this coating was carried out using the Layer-by-Layer technique. The hybrid nanoparticles were characterized at molecular and physical-chemical levels. Furthermore, encapsulation efficiency, pH-dependent release behavior, and cytotoxicity were evaluated. Amorphous mesoporous structure with adequate size for follicular delivery (between 300 and 600 nm) in addition to effective phytocompound loading capacity, above 80 % was obtained. Based on the release studies, it was possible to observe pH responsiveness. The ethyl acetate fraction (EAF) obtained from "Barbatimão" bark extract was released in a controlled and more efficient manner by the alginate-coated nanoparticle (SNP_EAF_SA) at pH 7.4, which corresponds to the pH at the deepest area of hair follicles. Furthermore, SNP_EAF_SA proved to be less cytotoxic compared to EAF and chitosan-coated hybrid nanoparticles (SNP_EAF_CH). Characterization, release, and cytotoxicity results indicate that SNP_EAF_SA is a promising system for on-demand follicular delivery of antiandrogenic actives contained in EAF.
•Carboxymethylcellulose microspheres containing BTA corrosion inhibitor were prepared by spray drying technique in one step.•The smart release of corrosion inhibitor (BTA) from the microspheres ...rendered active protection to carbon steel under aggressive conditions.•The corrosion inhibition properties imparted by the biopolymeric microspheres is associated with a high burst inhibitor release capacity.•An environmentally-friendly microcontainer was obtained and can be used in the development of smart anticorrosive coatings.
Biopolymeric microspheres containing corrosion inhibitor benzotriazole (BTA) were prepared by a spray-drying technique using carboxymethylcellulose (CMC-Na) as encapsulating material. The resulting microspheres were characterized by FTIR, TGA, SEM and TEM analysis. Microspheres containing BTA have an average diameter of 1.1 μm. FTIR analysis confirmed the presence of the core and encapsulating components. The release studies by UV−Vis spectrophotometry showed that the mechanism of inhibitor release from CMC-Na biopolymeric matrix is based on a hydrogel-swelling-driven mechanism triggered by water presence. Electrochemical impedance spectroscopy (EIS) measurements on bare carbon steel in NaCl solution revealed that the presence of CMC-Na does not affect the corrosion inhibition mechanism associated with BTA. Furthermore, the microcapsules were added to an epoxy coating and its active corrosion protection performance was also investigated by EIS. The results obtained indicate that capsules loaded with BTA do not affect negatively the barrier properties of the coating, and contribute for the enhancement of the corrosion protection of the metallic substrate. Therefore, this work shows the potential application of carboxymethylcellulose microspheres for development of new environmentally-friendly microcontainers for corrosion inhibitors.
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•Hybrid particles from silica and chitosan with benzotriazole, bearing different architectures were synthesized.•Silica/chitosan bio-hybrid capsules can potentially be used in ...corrosion inhibitor smart coatings.•According the chitosan location in capsule, the benzotriazole is delivered in a wide range of pH (from 3 to 9).
Chitosan-based organic-inorganic bio-hybrid nanocapsules, containing benzotriazole, a corrosion inhibitor, were prepared. In view of the versatile chemistry of silicon and the pH sensitivity of chitosan and benzotriazole, two synthesis approaches are presented. In both methods, tetraethoxysilane (TEOS) was used as the silicon source. Particles with different architectures, structural features and pH-dependent release behavior were obtained. The capsules prepared by the sol-emulsion-gel method demonstrated the highest release efficiency at pH 7.0 (∼90%) and pH 9.0 (∼65%) whilst the capsules prepared through layer-by-layer deposition technique showed the best efficiency at pH 3.0 (∼90%). Therefore, in combination, the particles delivered benzotriazole in a wide range of pH (from 3 to 9). The materials were fully characterized at the molecular, mesoscopic and nanometric length scales and the results suggest that they can successfully be applied in pH-sensitive smart coatings for corrosion inhibition.
This work aims to improve the corrosion properties of the 2198-T851 aluminium alloy by coating with a set of niobium oxide thin films, using the reactive sputtering technique. The structural and ...morphological properties of the niobium oxide thin films were characterized by using SEM/EDX, AFM, FTIR and Raman spectroscopy. Global electrochemical tests (OCP, PPc, CV, and EIS) were performed in 0.6 mol L−1 NaCl solution. The results demonstrated that the reactive sputtering technique was advantageous for producing thin films on the 2198-T851 aluminium surface. Raman spectroscopy results revealed a band near 650 cm−1 related to NbO single bonds, whilst the band centred at 868 cm−1 may be attributed to NbO double bonds. The PPc results indicated that the niobium oxide acts as a protective barrier, since a difference of about 210 mV was observed between Epitting and Ecorr. The coated specimens displayed a superior breakdown potential when compared to the base material (−0.387 vs − 0.505 V/SCE). The impedance modulus has increased more than one order of magnitude and the phase angle is closer to - 90°, demonstrating a capacitive thin film was deposited on the 2198-T851 aluminium alloy surface.
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•The reactive sputtering method was able to produce NbxOy film on the 2198-T851.•Coated material has increased the impedance modulus more than one order of magnitude.•A difference of about 210 mV between the corrosion and pitting potentials was obtained..•A higher resistance to localised corrosion was achieved when compared to the untreated alloy.
Sodium carboxymethylcellulose (CMC-Na) microparticles, containing corrosion inhibitor benzotriazole (BTA), were prepared using different spray drying processing parameters, with the purpose of future ...application in protective coatings for the delivery of corrosion inhibitors. The effects of the processing parameters, such as inlet temperature and spray flow rate, are discussed herein. The biopolymeric CMC-Na microparticles obtained were characterized morphologically by SEM and TEM, and their release profile studied by UV-Vis. The results show that the prepared microparticles (microspheres) were homogeneous, spherically shaped and of a matrix-type nature. Additionally, it was observed that the inlet temperature and spray flow rate significantly influenced the release profiles and process yields. From the different process parameters tested, it was found that the best conditions to achieve higher process yields, higher encapsulation efficiencies and better release properties, were an inlet temperature of 170 °C, a pump rate of 2.5 mL/min, and a drying air-flow rate of 440 L/h.
Modified supermartensitic stainless steel surfaces were investigated as protective means against deterioration in Cl−- and H+-rich media. Nitrogen plasma immersion ion implantation at the 300–400 °C ...range produced top nitride-rich layers (with mainly γ′-Fe4N and ε-Fe2-3N, but also with α′N, according to the treatment temperature) followed by underneath expanded martensite cases. The 400 °C nitrided sample presented the best performance in potentiodynamic polarization tests with NaCl electrolyte, featured by 4.3 times increase in the corrosion potential and the absence of pits, attributed to the thickest and continuous ε-phase containing nitride-rich layer. The hydrogen embrittlement was assessed through cathodic hydrogenation tests. Both reference and 400 °C nitrided surfaces disclosed the phenomenon of intensified plastic flow under normal and tangential loadings. A decrease in hardness, elastic modulus and scratch resistance featured a ductile-to-brittle transition on the nitrided surface, possibly due to improved hydrogen trapping by nitride species with subsequent effects in plasticity. In summary, while the nitride layer played an advantageous role in protecting SMSS from chlorine attack, it was susceptible against the hydrogen corrosion.
•N-PIII produced stratified layers with nitrides and expanded martensite on SMSS.•Corrosion resistance in Cl−-containing medium improved in all the nitrided surfaces.•Modified surfaces with ε-Fe2-3N provided 4.3 times increase in corrosion potential.•H-attack caused intensified surface plastic flow and ductile-to-brittle transition.•The layer's susceptibility against hydrogenation compromises the SMSS bulk protection.
Degenerative diseases, such as osteoarthritis, osteoporosis and accidents can cause hip problems and injuries leading to a necessary hip prosthetic replacement. Acetabular and femoral prosthesis ...parts, consisting of special alloys of steel and titanium, are fixed to the bones using orthopedic cement based on poly(methyl methacrylate) (PMMA). With aim of improving implant material properties in terms of compatibility with the human body, were evaluated the bioactive responses of ISO 5832-9 steel and Ti6Al4V alloy coated with electrospun PMMA nanofibers. The electrospinning technique is widely used due to the possibility of easily producing fibers within nano or micrometric scale using a low cost, simple experimental apparatus that allows large-scale production. In this work the metallic substrates were submitted to surface pretreatments with sanding alone or in combination with acid etching. After deposition by electrospinning, the surfaces were characterized morphologically, chemically, and for roughness. PMMA fibers were obtained, with nanometric diameter, forming a uniform and homogeneous layer over both metal sample surfaces without appreciable differences in adhesion. The sanded surface, being a one-step process, was chosen for the next step. Fibroblasts were grown on the sample surfaces, for seven days, to determine biocompatibility. Electrospinning Induced Surface Activation (EISA) was used to incorporate hydroxyl radicals into the PMMA chain to produce hydroxylated PMMA, that was later redissolved and electrospun into nanofibers. Both samples (PMMA and PMMA-OH nanofibers) resulted in good cell adhesion properties. However, a denser cell monolayer was observed on the hydroxyl-terminated sample, indicating better cell-material interaction. Hydroxyl (OH) functionalized molecules can regulate cell behavior acting as a linker capable of reacting with proteins, thus accelerating cell growth, migration, differentiation, synthesis of extracellular matrix components, and tissue morphogenesis. By a simple two-step methodology it was possible to obtain electrospun hydroxyl functionalized bioactive PMMA nanofibers deposited on metallic implant samples with an increased cell response.
•One step metal surface modification is adequate to nanofibers deposition.•Homogenously distributed PMMA nanofibers were produced by direct electrospinning.•PMMA nanofiber presented distribution homogeneity and good adhesion.•Hydroxylated PMMA nanofibers improved cell adhesion and proliferation.
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