Phosphonic acid/silica-based films: A potential treatment for corrosion protection

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

“…In our previous work we verified that the silica precursors, vinyltrimethoxysilane (VTMS)/tetraethylorthosilicate (TEOS), when mixed in adequate ratio (3/1) propitiate the suitable balance between hydrophobicity and porosity to be used as anticorrosive barrier and adhesion promoter [20]. We also verified that the incorporation of a catalytic amount of phosphonic acid, ethylenediaminetetra(methylene phosphonic acid) (EDTPO), to silica network promoted the formation of Al-O-P bonds, resulting in a great benefit for silane adhesion and corrosion protection [21][22][23][24][25].…”

“…Both sol-gel films, without (3V) and with EDTPO (3VE5) presents higher phase angle and log |Z| than the uncoated metal surface. This behaviour is attributed to silica barrier network and to the interface between silica and metal composed by metalosiloxane covalent bonds and oxide layer, being detected as two relaxation process at high and medium frequency [13,29,21,24], respectively (Figure 4a). Nevertheless, the protective response of 3V and 3VE5 films decreases after 7 days of exposition to 3.5 % NaCl (Figure 4b).…”

“…Surprisingly, the adhesion reduction was 0% for the system that contains organophosphonic molecules (3VE5/epoxy). It is only possible if these molecules are actuating as an adhesion promoter [19][20][21][22][23][24]. Thus, phosphonic acid has a positive effect on the adhesion of silane coating to the aluminium surface.…”

Improving the corrosion performance of hybrid sol–gel matrix by modification with phosphonic acid

“…FTIR spectroscopy is a powerful technique for monitoring the evolution of hydrolysis and condensation reactions during the sol-gel process [23,24] and the formation of the silica network [11,25,26]. Figure 1 shows the FTIR spectra for the films formed on AA2024 substrates with different VTMS/TEOS ratios.…”

“…Previous studies were devoted to investigate the addition of phosphonic acid onto TEOS, evidencing a remarkable improvement of the corrosion performance for the AA2024 alloy coated with films of such combined system [22,23]. However, the silica network produced by TEOS exhibited hydrophilic characteristics, which resulted in poor corrosion protection [22].…”