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

Abstract

Sol-gel films were prepared using different ratios of two silica precursors, vinyltrimethoxysilane (VTMS) and tetraethylorthosilicate (TEOS), targeting the anticorrosion treatment of aluminum alloy 2024-T3. The electrochemical behavior of the alloy coated with such films, which was studied in a 0.05 mol L -1 NaCl solution, revealed that the VTMS/TEOS ratio drastically affects the anticorrosion performance. Electrochemical impedance spectroscopy (EIS) results provided evidences that the best anticorrosive response occurs with the films prepared from 50% v/v ethanol, 46% v/v water, 3% v/v VTMS and 1% v/v TEOS. Moreover, the effects of the addition of ethylenediamine tetra(methylene phosphonic acid) (EDTPO) to a hybrid sol-gel matrix were examined. The corrosion resistance was considerably improved when the concentration of added phosphonic acid was 3.7510 -5 mol·L -1 . Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses revealed that EDTPO-containing films provide a more uniform coverage. Results evidenced the formation of Si-O-Al linkages in the VTMS/TEOS and VTMS/TEOS/EDTPO systems and that the VTMS/TEOS/EDTPO system contained P-O-Al linkages. The P-O-Al bonds, combined with the silica network action, may be responsible for the good anticorrosive behavior of the VTMS/TEOS/EDTPO films.

Synergistic Effects of ppm Levels of Palladium on Natural Clinochlore for Reduction of Nitroarenes

“…In the Si region, two peaks at 102.9 and 103.6 eV are related to silanol (Si−OH) and silicone oxygen (Si−O) bonds, respectively (Figure S6 a) . The broad peak at 74.3 eV, which deconvoluted into two peaks at 74.2 and 74.6 eV, is related to Al III in Al−OH and Al 2 O 3 forms (Figure S6 b) . The peak at 1303.7 eV is attributed to the Mg 1s in MgO form (Figure S6 c) .…”

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

“…However, phosphorous was not detected at the silica surface in the 3VE5 network composition. According to our previous study [20], P 2p binding energy can be detected only after forty minutes of depth profiling, proving the hypothesis that organophosphonic groups actuate by formation of Al-O-P bonds, which promote a more compact layer in the interface metal/sol-gel film. The main binding energy of elements from silane coating and alloying metals from bare metal has been showed in the Figure 3.…”

“…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].…”

“…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.…”

Fourier Transform Infrared and Raman Characterization of Silica-Based Materials

“…Furthermore, silica is commonly used to protect or give special features to surfaces. In terms of protection, organosilanes are well known as corrosion protectors for metallic surfaces such as steel and aluminum alloys [18], where other metal such as cerium [19], metallic nanoparticles such as NiFe 2 O 4 [20] and other compounds such as phosphonic acid [21] can also be added to the coating to enhance the protection. The surface characteristics are another feature that are able to be tuned by the silica coatings.…”