Improvement of the corrosion resistance of Ni-W coatings on steel using a mixed silane film

M.E. VELA; M.P. QUIROGA ARGAÑARAZ; GUILLERMO A. BENITEZ; ALDO ALBERTO RUBERT; EDUARDO D. PRIETO; LILIANA GASSA; ROBERTO C. SALVAREZZA; J.M. RAMALLO LÓPEZ

Saint Malo

Congreso; 17th Topical Meeting of the International Society of Electrochemistry; 2015

International Society of Electrochemistry

Self-assembly constitutes a simple method to modify surfaces that drastically changes properties like wettability and hydrophobicity, corrosion resistance and opens multiple strategies of postfunctionalization. In this presentation we show the surface characterization and the electrochemical behavior of Ni-W nanostructured coatings electrodeposited on carbon steel [1,2] that were post-functionalized with two types of silanes. In the first step a silica-rich layer was formed by the reaction of tetraethoxysilane (TEOS) solution in toluene with the surface oxides of the alloy. After this treatment the sample was immersed in an hexane solution of octadecyltrichlorosilane (OTS). The silanized surface was rinsed exhaustively with hexane. After this procedure the XPS analysis showed that the Ni and W signals almost disappeared and that the Si and C signals are the most significant in the spectra. The silanization procedure increases the contact angle from   70 for the bare Ni-W sample up to   110. The typical cauliflower topography of the nanostructured Ni-W coating was not altered by the functionalization indicating a conformal coverage of the TEOS and OTS self-assembled layers. The nanomechanical properties of the silanized samples were studied by AFM and a rigid behavior was observed in practically all the surface. In those force curves were the layer could be indented, a thickness of 2-20 nm was obtained which exceeded the expected monolayer value. The electrochemical behavior of the TEOS&OTS Ni-W coatings was studied in phosphate-borate buffer (0.1 M KH2PO4 + 0.05 M Na2B4O7) pH 8.00 with the addition of 1 M Na2SO4, an aggressive ion in neutral and alkaline solution, through cyclic voltammetry, following the temporal evolution of the open circuit potential and registering polarization curves at 2 mV/s. Our results showed that the two-step silanization procedure improves the corrosion resistance of Ni-W coated steel preserving their mechanical properties. [1] M.P. Quiroga Argañaraz, S.B. Ribotta, M.E. Folquer, L.M. Gassa, G. Benítez, M.E. Vela, R.C. Salvarezza, Electrochim. Acta, 56 (2011) 5898. [2] M.P. Quiroga Argañaraz, S.B. Ribotta, M.E. Folquer, E. Zelaya, C. Llorente, J.M. Ramallo-López, G. Benítez, A. Rubert, L.M. Gassa, M.E. Vela, R.C. Salvarezza, Electrochim. Acta, 72 (2012) 87