Published: 2005
Total Pages: 204
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In this research study, polyaniline clay - polyimide (PACN - PI) hybrid nanocomposite coatings were cast onto AA 2024 to give corrosion resistant coatings. The PACN powders were prepared from different formulations containing varying concentrations of the dopant and clay. The powders were characterized by using various analytical techniques including the Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction technique (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis of X-rays (EDAX). The nanocomposite powders were dispersed in a polyamic acid solution and cast onto AA 2024 plate. After imidization at 250o C for 2.5 hours, a fully cured hybrid PACN - PI coating was obtained. For determining the composition and structure, the coatings were further analyzed by FTIR, XRD and for property evaluation, to determine the corrosion resistance Electrochemical Impedance Spectroscopy (EIS) was used. Two coating systems were processed; i) unfiltered coatings and ii) filtered coatings. Those which were cast without filtration of the PACN/DMAC solution were called the unfiltered coatings. When the PACN solution was filtered before the addition of polyamic acid, the system was called the filtered system. In this study the effect of filtration on corrosion properties of the coatings was determined. The effect of particle size distribution on PACN - PI nanocomposites was investigated. As the unfiltered system had a wider range of particle size, the coarse particles present in the coating introduced defects. Due to their large size, the electrolyte had easy passage into the coating and hence these coatings performed poorly. For the filtered coatings, due to filtration process all the coarse particles were removed and a very homogenous coating was obtained. Due to the excellent corrosion resistant properties of the filtered polyaniline - clay nanocomposites, a very good set of coatings was obtained even with very low concentrations of the PACN powder. To test the behavior of a different solvent on the properties of the coatings n-methyl-2-pyrrolidone (NMP) was used. Coating cast from NMP solution showed improved corrosion resistance. This was due to the higher solubility of the powder in this solvent. From this study, it was concluded that PACN powder even at low concentrations when homogenously dispersed in a polyimide matrix gave excellent corrosion resistant coatings.