Academic literature on the topic 'Silica-alumina hybrid coatings'

The major responsibility of the marine industry includes the global transportation of goods, materials, and people. To cater the longstanding challenges like degradation of materials and biofouling, it has embraced nanotechnology solutions. Nano-technology offered numerous products such as nano-ZnO, nano alumina, and nano silica, etc. to deal with corrosion in a cost-effective manner. Similarly, to address the biofouling in the aquatic environment, hybrid nanocomposites of organic-inorganic materials, photocatalytic nanomaterials, metal and metal oxide nanomaterials (nanoparticles, nanowires, nanorods), etc. are employed as viable agents to create non-toxic or low-toxic antifouling coatings. On the other hand, membrane separation technology plays a significant role in various industries including water treatment plants, food, medicine, pharmacy, biotechnology, etc. in addition to the domestic arena for the purification of drinking water. Such a wonderful technology is being totally disturbed by a troublesome problem and a predominant barrier called membrane fouling, which drastically limits the commercialization of the membranes and the whole membrane industrial technology as well. Hence, this review exclusively throws light on the role of nanomaterials and nanotechnologies developed for the prevention of fouling that occurs on submerged structures and membranes as well and to give possible solutions with increased resilience against challenges to come.

Chromium pre-treatments of metal have been replaced by silane pre-treatments as more environmental friendly option. Nanoparticles can be added in the silane sol-gel network have been reported to improve corrosion resistance. In this work, the electrochemical corrosion resistance of low carbon steel coated with hybrid organic-inorganic sol-gel film filled with nanoparticles was evaluated. The sol-gel films have been synthesized from 3-glycidoxy-propyl-trimethoxy-silane (3-GPTMS) and tetra-ethyl-ortho-silicate (TEOS) precursors. These films have been impregnated with 300 ppm of silica or alumina nanoparticles. The electrochemical behavior of the coated steel was evaluated by means of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Equivalent circuit modeling, used for quantifying the EIS measurements showed that sol-gel films containing silica nanoparticles improved the barrier properties of the silane coating. The silica nanoparticle-containing films showed highest initial pore resistance over the five days of immersion in 0.05M NaCl.

Polymeric coatings reinforced with nanoparticles have recently occupied special focus by researchers and have been used in several industrial applications such as wind turbine manufacturing, oil and gas, aerospace and automotive industries. Yet, still more investigations are required to improve the tribological and mechanical properties of these coats and increase its service life. The effect of adding nano-silica/alumina to polyurethane coatings have been studied, however, their erosion resistance has not been investigated yet. The main purpose of this research is to investigate the erosion resistance of hybrid nano-silica/alumina polyurethane compositions with different weight fractions. To do this, erosion resistance experiments, scanning electron microscope and Zetasizer experiments to assess the agglomeration percentage were carried out. Results showed that the hybrid composition of nano-silica/alumina polyurethane significantly decreased the erosion rate and that the reduction in agglomeration was mirrored in much enhanced erosion resistance of the nanocomposites.

Les aciers inoxydables austénitiques sont très utilisés dans l’industrie. Reconnus pour leur résistance à la corrosion, ils le sont également pour leur forte susceptibilité à l’usure adhésive (grippage). Cela a pour conséquence une dégradation accélérée des matériaux, ce qui conduit à des pannes brutales, à des pertes de performances et à une augmentation des coûts d’exploitation. Le CETIM et le CIRIMAT explorent des solutions basées sur des revêtements protecteurs afin de diminuer le coefficient de frottement et le volume d’usure. Des sols chargés en carbone sont élaborés et déposés par trempage-retrait sur des substrats en acier inoxydable 304L. Après gélification et traitement thermique en atmosphère inerte, des revêtements carbone-céramique d’une épaisseur d’environ 2 à 7 μm sont obtenus. Deux matrices (alumine et alumine-silice) sont étudiées, ainsi que différentes charges carbonées: du graphite commercial et des nanotubes de carbone (NTC) dont le nombre de parois moyen est égal à 2, 8 ou 20. Des essais tribologiques rotatifs bille-plan réalisés selon la norme ASTM G99 (bille en acier, charge normale 2N, vitesse 10 cm/s, 250 m de glissement) ont montré que les revêtements graphite-alumine présentent un plus faible coefficient de frottement et une plus faible usure que les revêtements alumine et NTC-alumine. Nous montrons que la surface totale de carbone disponible dans l’échantillon est le paramètre pertinent et que l’exfoliation progressive du graphite en graphène oligocouche (2-5) pendant l’essai permet de générer in situ de nouvelles surfaces, tandis que les NTC ne subissent pas d’endommagement majeur. Nous mettons en évidence la formation d’un tribofilm lubrifiant au contact bille/revêtements composites. Nous nous sommes donc orientés vers la pré-exfoliation du graphite dans le sol par différentes méthodes. Nous mettons en évidence qu’une méthode impliquant de grandes contraintes de cisaillement permet la pré-exfoliation efficace du graphite, la surface de carbone étant alors 1300 fois plus grande qu’avec la dispersion par sonde à ultrasons. Nous montrons que ce sont les échantillons GBC-alumine qui présentent les plus faibles volumes d’usure (0,0023 mm3) et coefficient de frottement (0,14) de ce travail. Le dernier chapitre est consacré à l’étude de l’adhérence du revêtement au substrat et du comportement tribologique des revêtements lors d’un essai industriel sévère (ASTM G133). Il est notamment mis en évidence que les revêtements à matrice alumine-silice présentent une meilleure adhérence que ceux à matrice alumine
Austenitic stainless steels are widely used in industry. Recognized for their resistance to corrosion, they are also known for their high susceptibility to adhesive wear (seizure). This results in accelerated material degradation leading to sudden failures, loss of performance and increased operating costs. CETIM and CIRIMAT are actively exploring solutions based on protective coatings in order to reduce the friction coefficient and the wear volume. Carbon-loaded sols are prepared and deposited by dip-coating on 304L stainless steel substrates. After gelation and heat-treatment in an inert atmosphere, carbon-ceramic coatings about 2 to 7 μm thick are obtained. Two matrices (alumina and alumina-silica) are studied, as well as different carbonaceous fillers: commercial graphite and carbon nanotubes (CNT) with an average number of walls equal to 2, 8 or 20. Rotative friction tests performed according to the ASTM G99 standard (steel ball, normal load 2N, velocity 10 cm/s, distance 250 m) have shown that the graphite-alumina coatings show a lower friction coefficient and a lower wear than the alumina- and CNT-alumina coatings. We show that the total available carbon surface area in the sample is the relevant parameter and that the progressive exfoliation of graphite to flew-layered-graphene (2-5) during the test generates new surfaces in situ whereas the CNT do not sustain any major damage. We bring to light the formation of a lubricating tribofilm in the contact between the friction ball and the composite coating. Therefore, we have focused on the pre-exfoliation of graphite in the sol by different methods. We show that a method involving high shear stresses allows an efficient pre-exfoliation of graphite, the carbon surface area being 1300 times higher than when performing the dispersion using an ultrasonic probe. We show that the BLG-alumina samples have the lowest wear volumes (0.0023 mm3) and friction coefficient (0.14) reported in this work. The last chapter is devoted to the study of the adhesion of the coating to the substrate and to the tribological behavior of the coatings in a severe industrial test (ASTM G133). It is notably demonstrated that the alumina-silica matrix coatings show a better adhesion than the alumina-matrix ones

Aluminium metal is known for its high electrical conductivity, thermal conductivity and high reflectivity. Aluminium alloys of 2XXX series, particularly the 2024 alloy with the quaternary Al–Cu–Mg–Mn composition are widely used in aeronautical applications due to their high strength along with low density and good fracture toughness. It is the S-phase (Al2CuMg) precipitates which are responsible for strengthening the metal. Preferential dissolution of Al and Mg from the intermetallics and formation of copper-enriched particles have been proposed to be the major reasons for corrosion. Aluminium oxide film formed on the surface is stable only in neutral aqueous media (pH = 4–9) and hence does not protect the substrate under alkaline corrosive conditions. Therefore, aluminium components are often subjected to surface treatment to increase their durability and reduce maintenance needs. A typical aircraft coating system generally consists of three layers comprising a thin passivating base layer, an inhibitor containing primer layer, and a thick topcoat. The first layer generally referred to, as pre-treatment layer or conversion coating (∼2–3 μm) provides corrosion protection and improves adhesion of top layers with the substrate. Conventionally, chromate conversion coatings are used for this purpose. However, due to the toxicity and carcinogenic nature of hexavalent chromium, they are banned from usage and environmentally benign alternatives are being explored. In this direction, sol–gel based coatings are highly promising for corrosion protection of metals and alloys. The present thesis is directed towards the development of sol-gel coatings that exhibit improved corrosion protection properties and a low environmental impact. In particular, the present study aims to investigate the behaviour of the less-explored silica-alumina hybrid coating system as sol-gel pre-treatment layers for AA2024. Silica-alumina hybrid coatings in optimized precursor ratio possess good barrier property (Fig. 1). Coatings with different concentrations of cerium nitrate are assessed for corrosion inhibition property using electrochemical tests (Fig. 2). The coatings with 5 mM inhibitor act as good reservoirs for cerium (III) ions and provide enhanced protection to the substrate surface even after 336 h. of 3.5 % NaCl immersion. The protection offered is attributed to a combined effect of barrier property and the cathodic inhibition offered by Ce3+. XPS analysis provides strong evidence for the migration of cerium ions towards the corrosive sites. The observed corrosion protection is attributed to the synergistic effect of the stable barrier nature of the coating and the corrosion inhibiting nature of Ce3+ ions