The influence of organophosphonic acid and conducting polymer on the adhesion and protection of epoxy coating on aluminium alloy

Abstract

In the present study we compared the beneficial effect on the incorporation of modified silane nanocoating and conducting polymer additive to the adhesion and protection of aluminium surface with epoxy coating. Results proved that the protection imparted by the silane coating, suitably modified with phosphonic groups, showed an excellent adhesion to the metallic substrate as well as good adherence with the epoxy outer layer, which result in an improved corrosion resistance. The incorporation of 1% of poly (3-methyl thiophene acetate) (P3TMA) also improved the adhesion force of the epoxy paint adhered to the aluminium surface. However, the adhesion force decreased with the increase of the immersion time in NaCl 3.5% solution. In conclusion, both bilayer systems [vinyltrimethoxysilane (VTMS)/tetraethylorthosilicate (TEOS) and VTMS/TEOS/ ethylenediaminetetra(methylene phosphonic acid) (EDTPO)] and also the employment of P3TMA in the epoxy coating showed better results in accelerated corrosion assays, i.e. very low blistering formation was observed, compared with control samples based in a monolayer coating directly adhered to the aluminium surface.

Recent Development in Phosphonic Acid-Based Organic Coatings on Aluminum

“…Surface morphology Scanning electron microscopy (SEM) [9,14,15] Atomic force microscopy (AFM) [8,15] Presence, composition and stability of layer X-ray photoelectron spectroscopy (XPS) [6][7][8]11,[16][17][18][19][20][21] Auger electron spectroscopy (AES) [22] Fourier-transform infrared spectroscopy (FTIR) [8,11,14,16,17,23,24] Time-of-flight secondary ion mass spectrometry (ToF-SIMS)…”

“…X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are both methods which determine the elemental composition in the first couple of nanometers of a surface and, hence, were often applied to verify the presence of phosphorus, indicating a successful organophosphorus coating chemically-bound to aluminum [6,8,11,16,17,[19][20][21][22]. As a general preparative step, the samples were usually rinsed/washed after the coating process to remove the residual chemicals and physically adsorbed organophosphorus compounds.…”

“…FTIR was applied to investigate the adsorption of the coating by detecting specific vibrational modes involving phosphorus bonds [8,11,14,16,17,23,24]. Table 3 contains a summary of frequencies of vibrational modes involving the phosphorus atom found in the literature for self-assembled organophosphorus monolayers on aluminum.…”

“…EDTPO, as a catalyst, was incorporated into VTMS/TEOS to form a sol-gel coating on the substrate surface and is believed to improve the formation of Al-O-P bonds which is beneficial for anticorrosive properties [17]. The concentration of EDTPO in the sol-gel deposition solution was 3.75 × 10 −5 mol·L −1 .…”

“…However, the adhesion of coating without EDTPO showed a reduction of 15%, and the adhesion of the coating without any sol-gel primer reduced to 40%. It was concluded that the EDTPO-modified silane coating (VTMS/TEOS) has excellent adhesion and anti-corrosion properties because of its barrier properties [17].…”