2. Experimental
2.1. Materials and sample preparation
Different concentrations of Al2O3 nanoparticles were added to the epoxy-polyamide coating formulation. For this purpose,the pre-dispersed nano-Al2O3(BYK-3610) particles (dispersed in methoxy propyl acetate solvent) with a mean particle size of 20 nm was prepared from BYK Co. Epoxy resin of Araldite GZ7 7071X75(based on bisphenol-A in a xylene solution) was prepared from SabaShimi Co. The solid content, epoxy value and density of the resin were 74.76%, 0.1492.0.1666 Eq/100 g, and 1.08 g cm.3, respectively. To prepare the nano composites, different weight contents of nanoparticles (1, 2.5 and 3.5 wt%) were added to the epoxy resin. Nanoparticles were dispersed in the resin by a high shear mixer (2000 rpm). Then, stoichiometric values of polyamide curing agent (having solid content of 50 wt%) were added to the epoxy nanocomposites (epoxy:polyamide ratio of 70:40 w/w). Moreover,to improve the film formation properties, additives like levelling agent (BYK-306) and defoamer (Efka-2025) were added to the coating formulation. Aluminium alloy 1050 samples with dimensions of8 cm ~ 10 cm ~ 2 cm were prepared from Arak Al Co. The chemical composition of the aluminium alloy 1050 is presented in Table 1.Table 1 Preliminary surface cleaning of the aluminium samples was done by immersion in a 5% (w/w) solution of NaOH for 3 min at 50.C followed by washing with distilled water. The specimens were then placed in 50% (v/v) solution of nitric acid in water for 1 min. Finally, the cleaned specimens were washed with distilled water. Nanocomposites were applied on the cleaned Al samples by film applicator (at wet thickness of 120 m). Samples were then baked at curing temperature of 120.C for 30 min. Nanocomposites were also applied on the glass sheets followed by curing at 120.C for 30 min. The free films of each nanocomposites were prepared from the glass sheets.
2.2. Characterization
2.2.1. Nanoparticles dispersion studied
A Cary 100 Scan type UV. vis spectrophotometer was utilized in order to investigate the optical properties of the nanocomposites.The dispersion of the nanoparticle in the epoxy coating matrix was studied by field emission scanning electron microscopy (FE-SEM,Mira).
2.2.2. Anticorrosion properties of the nanocomposites
The anticorrosion performance of the nanocomposites was studied by salt spray and electrochemical impedance spectroscopy(EIS). The salt spray test was performed according to ASTM B117.In this test, the coated panels were exposed to NaCl 5% (w/w) solu-tion at 35.C for 1000 h. Moreover, an electrochemical impedance spectroscopy (EIS) was utilized in order to investigate the corrosion resistance of the nanocomposites. The test was carried out by an AUTOLAB G1 at frequency range and perturbation of 10 kHz to10 mHz and }10 mV, respectively. Moreover, the measurements were done in 3.5 wt% NaCl solution at open circuit potential (OCP)on 1 cm2 areas of the coatings. The rest of the coating was masked by a waterproof mixture of 3:1 of beeswax-colophony. The test wasdone in a standard electrochemical cell including coated sample(working electrode), Ag/AgCl (3 M KCl) (reference electrode) and platinum (auxiliary electrode). EIS was carried out on three replications of each sample in order to evaluate the standard deviation of the measurements.
2.2.3. Coating degradation
The surface morphology of the coatings was studied after salt spray test by optical microscope (Leica DMRX) and digital camera images. FTIR in transmission mode (model Perkin-Elmer Spectrum One) was also utilized in order to evaluate coating degradation. To this end, the surface of the coatings was scraped and mixed with KBr to prepare pellets.
2. ทดลอง2.1. วัสดุและการเตรียมตัวอย่างDifferent concentrations of Al2O3 nanoparticles were added to the epoxy-polyamide coating formulation. For this purpose,the pre-dispersed nano-Al2O3(BYK-3610) particles (dispersed in methoxy propyl acetate solvent) with a mean particle size of 20 nm was prepared from BYK Co. Epoxy resin of Araldite GZ7 7071X75(based on bisphenol-A in a xylene solution) was prepared from SabaShimi Co. The solid content, epoxy value and density of the resin were 74.76%, 0.1492.0.1666 Eq/100 g, and 1.08 g cm.3, respectively. To prepare the nano composites, different weight contents of nanoparticles (1, 2.5 and 3.5 wt%) were added to the epoxy resin. Nanoparticles were dispersed in the resin by a high shear mixer (2000 rpm). Then, stoichiometric values of polyamide curing agent (having solid content of 50 wt%) were added to the epoxy nanocomposites (epoxy:polyamide ratio of 70:40 w/w). Moreover,to improve the film formation properties, additives like levelling agent (BYK-306) and defoamer (Efka-2025) were added to the coating formulation. Aluminium alloy 1050 samples with dimensions of8 cm ~ 10 cm ~ 2 cm were prepared from Arak Al Co. The chemical composition of the aluminium alloy 1050 is presented in Table 1.Table 1 Preliminary surface cleaning of the aluminium samples was done by immersion in a 5% (w/w) solution of NaOH for 3 min at 50.C followed by washing with distilled water. The specimens were then placed in 50% (v/v) solution of nitric acid in water for 1 min. Finally, the cleaned specimens were washed with distilled water. Nanocomposites were applied on the cleaned Al samples by film applicator (at wet thickness of 120 m). Samples were then baked at curing temperature of 120.C for 30 min. Nanocomposites were also applied on the glass sheets followed by curing at 120.C for 30 min. The free films of each nanocomposites were prepared from the glass sheets.2.2. Characterization2.2.1. Nanoparticles dispersion studied A Cary 100 Scan type UV. vis spectrophotometer was utilized in order to investigate the optical properties of the nanocomposites.The dispersion of the nanoparticle in the epoxy coating matrix was studied by field emission scanning electron microscopy (FE-SEM,Mira).2.2.2. Anticorrosion properties of the nanocompositesThe anticorrosion performance of the nanocomposites was studied by salt spray and electrochemical impedance spectroscopy(EIS). The salt spray test was performed according to ASTM B117.In this test, the coated panels were exposed to NaCl 5% (w/w) solu-tion at 35.C for 1000 h. Moreover, an electrochemical impedance spectroscopy (EIS) was utilized in order to investigate the corrosion resistance of the nanocomposites. The test was carried out by an AUTOLAB G1 at frequency range and perturbation of 10 kHz to10 mHz and }10 mV, respectively. Moreover, the measurements were done in 3.5 wt% NaCl solution at open circuit potential (OCP)on 1 cm2 areas of the coatings. The rest of the coating was masked by a waterproof mixture of 3:1 of beeswax-colophony. The test wasdone in a standard electrochemical cell including coated sample(working electrode), Ag/AgCl (3 M KCl) (reference electrode) and platinum (auxiliary electrode). EIS was carried out on three replications of each sample in order to evaluate the standard deviation of the measurements.2.2.3. Coating degradation
The surface morphology of the coatings was studied after salt spray test by optical microscope (Leica DMRX) and digital camera images. FTIR in transmission mode (model Perkin-Elmer Spectrum One) was also utilized in order to evaluate coating degradation. To this end, the surface of the coatings was scraped and mixed with KBr to prepare pellets.
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