a-ordm This work explains an efficient approach to improve corrosion performance of an epoxy-based coating with employing silane coupling agent treated ZrO2 nanoparticles. a-ordm Corrosion ...performance of zirconia nanocomposites coated on mild steel specimens was investigated utilizing EIS and electrochemical noise (ECN) techniques. a-ordm EIS and ECN results revealed, 2 or 3wt% additions of ZrO2 nanoparticles significantly improved the corrosion resistance of epoxy coating via increasing barrier properties and ionic resistances of the coatings. a-ordm The experimental results showed a good correlation between EIS and ECN findings. Clear epoxy coatings were modified by adding various levels of ZrO2 nanoparticles. In order to achieve proper dispersion of nanoparticles in the epoxy-based coating and making possible chemical interactions between nanoparticles and polymeric coating, the surface of the nanoparticles was treated with amino propyl trimethoxy silane (APS). Corrosion performance of mild steel coated specimens was investigated employing EIS, electrochemical noise (ECN) techniques and salt spray test. Coatings with 2-3wt% ZrO2 nanoparticles possessed the best corrosion performance among the coating specimens. Possible chemical interactions between polymeric matrix and treated nanoparticles in nanocomposites cause high barrier properties and ionic resistances.
•Various hybrids of clay and ZrO2 nanoparticles/epoxy nanocomposites are prepared.•EIS and ECN techniques are used to study corrosion performance of the coatings.•Simultaneous use of clay and ZrO2 ...nanoparticles reveal better corrosion protection.•Higher corrosion protection is due to barrier properties and ohmic resistance.•The results show a relatively correlation between EIS and ECN findings.
Epoxy-based nanocomposite coatings containing various amounts of nano-clay and aminopropyltrimethoxy silane (APS) treated zirconia nanoparticles were prepared via slurry method. Morphology and dispersion of nanoparticles within the nanocomposites were evaluated using XRD and TEM analyses. Corrosion performance of mild steel coated specimens was investigated using EIS and EN techniques. The results showed that the simultaneous addition of the spherical ZrO2 and layered clay nanoparticles promotes the exfoliation of the clay nanoparticles and in so doing improves the corrosion performance of nanocomposite coatings via enhancing the barrier properties and ohmic resistance.
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•Self-healing epoxy-based coating containing oil-filled microcapsules was prepared.•Effect of size and loading of microcapsules on performance of samples was studied.•Corrosion ...resistance of scratched samples was studied using different techniques.•A modified equivalent circuit model was proposed based on EIS measurement results.•Addition of microcapsules enhances the corrosion resistance of the samples.•Effect of capsule size was more significant than that of wt% on the performance.
Linseed oil filled urea-formaldehyde microcapsules with various sizes were prepared via in-situ polymerization. To understand the healing performance of linseed oil as a healing agent and the progression of corrosion processes beneath the healed area, long term corrosion performance of scratched epoxy-based coating samples containing microcapsules was evaluated using Electrochemical Impedance Spectroscopy (EIS) as well as salt spray testing over a period of 6-days. EIS results were fitted to various equivalent circuit models and a modified model for the justification of the observed corrosion behavior was proposed.
It was found that the addition of microcapsules enhances the corrosion resistance of the scratched samples, the extent of which depends on the microcapsule size and loading. At a given loading, corrosion resistance increased with increasing microcapsule size, however, the effect of microcapsule size was more significant than that of loading. Moreover, with increased exposure time to the salt solution, the corrosion behavior of scratched coated samples shifted from uniform corrosion to crevice corrosion.
EIS results showed that although linseed-oil can significantly improve the corrosion performance of the damaged coating in short term however it rapidly decreases with time and hence this should be taken into account in designing of microcapsule’s core composition.
Smart self-healing coatings have been attracting tremendous interest due to their capability for preventing crack propagation in the protective coatings by releasing active agents like isocyanate ...molecules from micro/nanocapsules. The quality of healed area and subsequent use of the healed coated module are directly related to the chemical composition of healing agent. Faster curing rate and more appropriate physical properties were anticipated for moisture curing of bulky isocyanate molecules than the low molecular weight monomeric analogous. For practical utilization of these advantages, encapsulation of such bulky isocyanate molecules was considered in this work. To this end, optimized preparation and characterization of novel single-layer polyurethane-type microcapsules, richly and efficiently loaded with bulky isocyanate molecules is described. This healing agent was prepared through the reaction of excess amount of isophorone diisocyanate (IPDI) with 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP). The healing agent was then encapsulated with a polyurethane shell via an oil-in-water (O/W) emulsion polymerization technique. The mixing rate and surfactant concentration were altered to optimize the size and shell thickness of the microcapsules. The prepared microcapsules were very stable after 10 months, and they just lost less than 7 wt% of their loaded isocyanate molecules. The microcapsules were loaded into an epoxy-based coating and the crack healing efficiency of incorporated healing agent was clearly recorded. Microcapsules containing monomeric IPDI were also prepared and crack healing efficiency of these two healing agents regarding crack healing was compared.
•Loading 8-HQ and Cerium acetate in microcapsules improves corrosion resistance.•A smart coating for covering the steel substrates was presented.•8-HQ can be released properly and sense corrosion at ...early stages.•The sample containing both types of inhibitors showed the best performance.
In this study, linseed oil-filled urea-formaldehyde-based microcapsules containing cerium acetate (Ce) and 8-Hydroxyquinoleine (8-HQ) were synthesized in an oil-in-water emulsion via in-situ polymerization method. The Field Emission Scanning Electron Microscopy (FE-SEM) and Optical Microscopy (OM) were used to study the shape and morphology of the prepared microcapsule. The results revealed the regular spherical capsules with 20–120 μm diameters. Prepared microcapsules were dispersed in the epoxy matrix in single (Ce and 8-HQ) and mixed (50 wt.% Ce +50 wt.% 8-HQ) forms. Electrochemical Impedance Spectroscopy (EIS) and standard salt spray test were conducted to study anti-corrosion properties of different epoxy-based samples on the mild steel substrate. The results revealed improved anti-corrosion and healing performance of microcapsule embedded coating samples compared with their blank counterparts during 28 days exposure to the salt spray test conditions. The sample containing mixed form microcapsules showed the best performance among all samples. After one-week immersion in 3.5 wt.% NaCl electrolyte, |Z| at low-frequency value (|Z|lf) for neat epoxy, 8-HQ, Ce and mixed forms samples decreased from 2.81 × 108, 2.70 × 109, 1.02 × 109 and 8.62 × 109 to 1.22 × 104, 2.69 × 108, 3.40 × 107 and 1.98 × 109 (ohm. cm2), respectively. Finally, fluorescence microscopic study showed that the 8-HQ compound was released at the damaged area on the coated substrate and detects the corrosion phenomenon at the early stage as a smart corrosion indicator.
In this study, TiO2/SiO2 nanocomposites were synthesized via a sol-gel route by adding tetraethylorthosilicate (TEOS) to a solution containing different molar ratios of Degussa P25 TiO2 ...nanoparticles. FTIR, TGA, EDAX and XRD techniques were used to characterize the modified nanoparticles. Photocatalytic activity of the nanoparticles in an aqueous solution and into the acrylic based coating was evaluated using colour coordinate data measurements, SEM analysis, gloss measurements and FTIR spectroscopy, in the presence of Rhodamine B (Rh.B) dyestuff, as a pollutant model, before and after exposure to the UVA (340nm) irradiation and compared to their unmodified counterparts. The results showed that silica grafting effectively reduced the photocatalytic activity of the TiO2 nanoparticles as evidenced by absorption spectra and colour changes of Rh.B aqueous solutions during the UVA irradiation. The results revealed the effectiveness of sol-gel route for preparation of TiO2/SiO2 nanocomposites. The optimum result was obtained with 1% molar ratio of TiO2:TEOS. Addition of TiO2/SiO2 nanocomposites into the acrylic based coating revealed reduction of photo-degradation of Rh.B compared to untreated nanoparticles. Finally, inclusion of TEOS treated TiO2 nanoparticles into the aqueous organic coatings, provides photocatalytic property and as a result, it can possibly be considered for self-cleaning coatings.
An epoxy based nanocomposite coating containing various combinations of treated-zirconia and clay nanoparticles were prepared. Morphology and dispersion of nanoparticles within the nanocomposites ...were evaluated using optical microscopy, XRD and TEM analyses. Mechanical, thermal properties and corrosion resistance of nanocomposites were studied using; tensile strength measurements, DMTA and DSC analyses and salt spray test.
The results showed that simultaneous use of spherical and plate-shape nanoparticles, have a positive effect on the clay exfoliation behavior in resulting nanocomposites.
Mechanical properties of nanocomposites containing nano-zirconia slightly increased compared with neat-epoxy coating. Mechanical properties of nanocomposites containing various wt.% of clay or ZrO2/clay nanoparticles slightly decreased; formation of physical barrier clay stacks, which leads to disturbing curing procedure and decreasing polymer cross-linking density, and development of nano-sized voids in the trapped regions by clay stacks. Corrosion performance of nanocomposites increased with addition of nanoparticles, due to improving barrier properties of the coating.
The influence of various blends of hexafluorozirconic-acid (Zr), polyacrylic-acid (PAA) and polyacrylamide (PAM) pretreatment on the performance of an epoxy coated aluminium substrate was ...investigated and compared to that of a so-called chromate/phosphate conversion coating (CPCC).
Adhesive-strength of epoxy coated substrates was evaluated using pull-off and tape tests. Salt spray, humidity chambers and EIS were employed to characterize corrosion performance of coated substrates with different initial surface pretreatments. Among the Zr-based formulations, PAA/Zr and PAA/PAM/Zr showed the best adhesion strength, while the later revealed a good corrosion performance as well. However, CPCC pretreated sample was still superior in these aspects.
Optical and SEM micrographs of linseed oil -filled urea-formaldehyde microcapsules, a) before and b) after APS-silane treatment at pH 7.5
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•Linseed oil filled polyurea-formaldehyde ...based microcapsules (PUF) were prepared.•The surface of PUF was treated with APS silane at various pH values and conditions.•Best chemically/physically adsorption for APS treatment was obtained at pH 7.5.•APS-treatment enhanced the tensile properties of the microcapsules-filled coatings.
In microcapsule-filled self-healing coatings, a good microcapsule/matrix interface improves repairing performance by directing the crack through the microcapsule and releasing the core material. In this study, the surface of the synthesized linseed oil filled polyurea-formaldehyde (PUF) based microcapsules was treated with 3-aminopropyltrimethoxy silane (APS, via a two-step sol-gel route), in order to improve its interface with an epoxy coating. The treated microcapsules were then characterized using various characterization techniques. The effect of silane treatment on the microcapsule/matrix interface and tensile properties of the coating was evaluated.
FTIR spectroscopy showed both physical and chemical interactions between APS and PUF microcapsules. SEM micrographs revealed an almost spherical morphology for both treated and un-treated microcapsules. TGA results showed that the maximum silane grafting occurs at pH 7.5. It was found that the addition of APS-treated microcapsules had a positive effect on the tensile properties of the coating due to improving microcapsule’s shell and polymer matrix compatibility. This was related to the reaction of hydroxyl groups on PUF microcapsules and silanol groups of the silane and the subsequent reaction of amine group of the silane with the epoxy group of the coating.
This work involves the optimized preparation and characterization of microcapsules which contain benzoyl peroxide (BPO) dispersed in dibutyl phthalate (DBP) with gelatin-gum arabic ...(Gel-GA)/polyurea-formaldehyde (PUF) shell. The microcapsules were prepared in two steps using complex coacervation and in situ polymerization techniques, respectively, at various mixing speeds and different core:shell ratios. The scanning electron microscopy (SEM), optical microscopy, and Fourier transform infrared (FTIR) spectroscopy were used for characterization of prepared microcapsules. The resultant microcapsules were spherical with average diameters about 120–200 μm, had no intercapsule bonding, and had thicknesses of 0.7–1.5 μm. The results revealed high core content loading, 82–89 wt % for microcapsules prepared at various mixing speeds. The differential scanning calorimetry analysis (DSC) indicated that the encapsulated BPO was not influenced by the encapsulation process and maintained its activity. Moreover, with a compact and double Gel-GA/PUF shell, the microcapsules were stable, and no leakage of core material in an acrylate-based resin and toluene as an organic solvent was recorded. The resultant microcapsules have the potential of usage in industries such as self-healing systems and structural adhesives where the impermeability of microcapsules is an important factor.
