A Comparative Study on Graphene Oxide and Carbon Nanotube Reinforcement of PMMA-Siloxane-Silica Anticorrosive Coatings.

Carbon nanotubes (CNTs) and graphene oxide (GO) have been used to reinforce PMMA-siloxane-silica nanocomposites considered to be promising candidates for environmentally compliant anticorrosive coatings. The organic-inorganic hybrids were prepared by benzoyl peroxide (BPO)-induced polymerization of methyl methacrylate (MMA) covalently bonded through 3-(trimethoxysilyl)propyl methacrylate (MPTS) to silica domains formed by hydrolytic condensation of tetraethoxysilane (TEOS). Single-walled carbon nanotubes and graphene oxide nanosheets were dispersed by surfactant addition and in a water/ethanol solution, respectively. These were added to PMMA-siloxane-silica hybrids at a carbon (CNT or GO) to silicon (TEOS and MPTS) molar ratio of 0.05% in two different matrices, both prepared at BPO/MMA molar ratios of 0.01 and 0.05. Atomic force microscopy and scanning electron microscopy showed very smooth, homogeneous, and defect-free surfaces of approximately 3-7 μm thick coatings deposited onto A1020 carbon steel by dip coating. Mechanical testing and thermogravimetric analysis confirmed that both additives CNT and GO improved the scratch resistance, adhesion, wear resistance, and thermal stability of PMMA-siloxane-silica coatings. Results of electrochemical impedance spectroscopy in 3.5% NaCl solution, discussed in terms of equivalent circuits, showed that the reinforced hybrid coatings act as a very efficient anticorrosive barrier with an impedance modulus up to 1 GΩ cm(2), approximately 5 orders of magnitude higher than that of bare carbon steel. In the case of GO addition, the high corrosion resistance was maintained for more than 6 months in saline medium. These results suggest that both carbon nanostructures can be used as structural reinforcement agents, improving the thermal and mechanical resistance of high performance anticorrosive PMMA-siloxane-silica coatings and thus extending their application range to abrasive environments.This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordination for the Improvement of Higher Education Personnel (CAPES), and São Paulo Research Foundation (FAPESP)This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/acsami.6b0478

Organic-Inorganic Hybrid Coatings for Corrosion Protection of Metallic Surfaces

A variety of organic-inorganic hybrids have been designed to act as anticorrosive coatings of metallic substrates. Among them, epoxy-silica and poly(methyl methacrylate) (PMMA)- silica hybrids, prepared by the sol-gel process and deposited onto steel or aluminum alloys, have demonstrated high anticorrosive efficiency combined with high thermal and mechanical resistance. Lignin, carbon nanotubes, and graphene oxide have been incorporated into PMMA-silica hybrids as reinforcement agents, and cerium (IV) as corrosion inhibitor. Both hybrids were characterized in terms of their structural and thermal characteristics using different pectroscopies, microscopies and thermogravimetric analysis. Both hybrids present homogeneous nanostructure composed of highly condensed silica nanodomains covalently bonded to the polymeric phase. The transparent coatings with a thickness of 2–7 μm have low surface roughness, high adhesion to metallic substrates, elevated thermal stability, and excellent barrier behavior. Electrochemical impedance spectroscopy showed for coated samples a high corrosion resistance of up to 50 GΩ cm2 and durability >18 months in saline solution. Further improvement of corrosion resistance, thermal and mechanical stability was achieved by incorporation of lignin, carbon nanotubes, and graphene oxide into PMMA-silica matrix, and a self-healing effect was observed after Ce(IV) addition. The results are compared and discussed with those recently reported for a variety of hybrid coatings

Protective Coatings Based on PMMA–Silica Nanocomposites Reinforced with Carbon Nanotubes

Polymethylmethacrylate–silica hybrids have been prepared using the sol–gel route by the radical polymerization of methyl methacrylate(MMA) using benzoyl peroxide (BPO) as a thermal initiator and 3-(trimethoxysilyl)propyl methacrylate(MPTS) as a coupling agent, followed by acid-catalyzed hydrolytic condensation of tetraethoxysilane (TEOS). Carbon nanotubes (CNTs) were first dispersed either by surfactant addition or by functionalization with carboxyl groups and then added at a carbon (CNT) to silicon (TEOS and MPTS) molar ratio (CCNT/SiHybrid) of 0.05% to two different hybrid matrices prepared at BPO/MMA molar ratios of 0.01 and 0.05. Films of 2–7 μm thickness deposited onto carbon steel by dip-coating were characterized in terms of their microstructure and their mechanical, thermal and anticorrosive behavior. Atomic force microscopy and optical microscopy confirmed that there was a homogeneous dispersion of CNTs in the nanocomposites and that the surfaces of the films were very smooth. X-ray photoelectron spectroscopy (XPS) confirmed the nominal composition of the films while nuclear magnetic resonance showed that the connectivity of the silica network was unaffected by CNT loading. Thermogravimetric analysis and mechanical measurements confirmed an increase of thermal stability, hardness, adhesion and scratch resistance of CNT-loaded coatings relative to those without CNTs. Electrochemical impedance spectroscopy measurements in 3.5% NaCl solution interpreted in terms of equivalent circuits showed that the reinforced hybrid coatings, prepared at the higher BPO/MMA molar ratio used in this work, act as a very efficient anticorrosive barrier, with an impedance modulus up to 109 Ω cm2

Construção de uma câmara para monitoramento in situ do processo de secagem de geis e sólidos porosos

The present work deals with the design and construction of an equipment for studying the drying process of gels and solids. The equipment was built using mainly a commercial oven and others peripherals for programmed control of temperature, humidity and data acquisition. The system allows the in situ monitoring of the gel drying, registering the weight loss, and the shrinkage of sample and the oven temperatures. This set of allowed parameters makes possible to establish the main steps involved in the drying of meso and nanostructured porous materials

On the structure of high performance anticorrosive PMMA–siloxane–silica hybrid coatings

Environmentally compliant organic–inorganic hybrid coatings for efficient corrosion protection of metallic surfaces are potential alternatives to the current method based on chromate passivation. In this context PMMA–siloxane–silica (PMMA–SS) hybrid films were prepared using the sol–gel process from the radical copolymerization of methyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate followed by acidic hydrolysis and polycondensation of tetraethoxysilane (TEOS), under variation of the ethanol to H2O ratio (0.0–1.0). The structural properties of about 2 μm thick coatings, deposited by dip-coating onto carbon steel, were related with their corrosion protection efficiency. The correlation of data obtained by X-ray photoelectron spectroscopy, nuclear magnetic resonance and small angle X-ray scattering has shown for intermediate ethanol to H2O ratios the highest connectivity (∼83%) of the inorganic phase, bonded covalently to organic moieties, yielding a dense and homogeneous nanocomposite structure with high thermal stability, very good adhesion to the metallic substrate and excellent barrier properties. The electrochemical impedance spectroscopy measurements have shown for coatings prepared at intermediate EtOH/H2O ratios a high corrosion resistance of almost 10 GΩ cm2, which remained unchanged for more than 6 months in contact with 3.5% NaCl solution and more than 3 months exposed to an acidic NaCl environment

Formation, stabilité et stucture des sols, gels et poudres obtenues par acidification de solutions aqueuses d'oxychlorure de zirconium

Le procédé sol-gel est couramment utilisé dans la préparation des matériaux céramiques pour contrôler la morphologie et la taille des particules.Nous avons étudié des oxydes de zirconium préparés par la méthode sol-gel à partir de solutions aqueuses de ZrOCl2.8H2O modifiées par HCL et H2SO4. Dans le diagramme ternaire Zr-S-Cl on distingue 3 régions différentes : i) une première région ,correspondant a une valeur de R=Zr/SO42,5, la formation de suspensions colloïdales est observée. Dans cette troisième région, pour 2,52.5, colloidal suspensions are formed, defining a third region. In this third region, we have observed that for 2.5<=R<5, suspensions present a thermoreversible sol-gel transition, uncommon for inorganic systems. In the region of precipitates formation, the samples are formed by a mixture of zirconium sulfate.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

SnO2:Eu nanocrystallites in SnO2 monolithic xerogels

By simple room temperature broad band time-resolved spectroscopy it was possible to discriminate different Eu3+ spectra in SnO2 monolithic gels obtained by a sol-gel synthetic route. Nanocrystalline domains of the cassiterite-like SnO2:Eu could be easily identified in the transparent medium. From X-ray diffraction profiles a mean particle radius of 2.2 nm was estimated. © 1992

Effect of lithium doping on the evolution of rheological and structural properties during gelation of siloxane-poly(oxypropylene) nanocomposites

The influence of lithium doping on the evolution of viscoelastic properties and structure during the gelation of siloxane-poly(oxypropylene) (PPO) nanocomposites has been studied. For several [O]/[Li] ratios (O being the oxygen of the ether-type), dynamic Rheological measurements allowed us to follow the evolution of storage and loss moduli, complex viscosity and phase angle during gelation of Li+-doped hybrid sols. All samples exhibit a Newtonian viscous character in the initial step of the process and are progressively transformed into viscoelastic gels. The evolution of the rheological properties of these systems allowed us to determine the aggregation mechanisms of silicon species present in hybrid sols, which lead to sol-gel transformation: mass fractal growth and nearly linear growth at the beginning of gelation, and percolation at the final stage of the process. The influence of doping on the aggregation mechanisms depends on the polymer molecular weight: while for hybrids containing long polymer chains (Mw = 4000 g mol-1) gelation occurs in the initial stages through diffusion-limited monomer-cluster aggregation (DLMCA) for all doping levels, this mechanism is only observed for hybrids containing short chains (Mw = 130 g mol-1) at low lithium concentration ([O]/[Li] = 80). For undoped and high doped siloxane-PPO130 composites ([O]/[Li] = 4), cluster-cluster aggregation is the predominant mechanism occurring at the initial gelation stages. The nature and the proportion of the different coordination sites for lithium cations in the hybrid sols, determined by 7Li NMR and infrared spectroscopy, affect the aggregation mechanisms during gelation and the condensation degree of the siloxane phase in the final dried materials. © The Royal Society of Chemistry 2005.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES