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Home  > Raw materials & technologies  > Applications  > Protective & Marine coatings  > Protect carbon steel with siloxane sol films

Sunday, 15 September 2019
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Raw materials & technologies, Applications, Protective & Marine coatings

Protect carbon steel with siloxane sol films

Tuesday, 31 July 2012

Corrosion protection – especially on metals, the motor for new developments, is the target as well for this new development for carbon steel substrates by a hybrid dip coating.

A sol film avoids corrosion on carbon steel.

Source: Fotolia/Olga Lis

A sol film avoids corrosion on carbon steel.

Source: Fotolia/Olga Lis

Siloxane-polymethyl methacrylate films

Peter Hammer and his colleagues from the chemical Institut, UNESP in Brazil prepared a sol withacid-catalyzed hydrolytic co-polycondensation of tetraethoxysilane (TEOS) and 3-methacryloxy propyl-trimethoxysilane (MPTS), followed by radical polymerization of methyl methacrylate (MMA). This formed the Siloxane-polymethyl methacrylate hybrid films. The researchers deposited these films on carbon steel substrates by dip-coating.

Stability and adhesion on the substrate

The NMR and TGA results indicate a high degree of polycondensation (84 %) and elevated thermal stability of 410 °C for the hybrid film with a MMA/MPTS ratio of 8, exhibiting also and excellent adhesion to the substrate.

The XPS analysis confirmed the variation of the MMA phase in the hybrid, and showed that no corrosion-induced changes had occurred after 18 days immersion of the coated steel in 3.5 % NaCl solution.

Potentiodynamic polarization curves have shown that the hybrid coating prepared using a TEOS/MPTS ratio of 8 yielded the best anti-corrosion performance. It acts as a very efficient corrosion barrier, increasing the total impedance by almost 6 orders of magnitude and reducing the current densities by 4 orders of magnitude, compared to the bare electrode.

The structure analysed

Structural properties of the hybrids were studied using

  • 29Si and 13C nuclear magnetic resonance (NMR),
  • X-ray photoelectron spectroscopy (XPS) and
  • thermogravimetric analysis (TGA), as a function of the MMA/MPTS ratio, which ranged between 2 and 10.

The efficiency of the corrosion protection

The efficiency of corrosion protection of hybrid-coated carbon steel was investigated by

  • XPS,
  • potentiodynamic polarization curves and
  •  electrochemical impedance spectroscopy

    after immersion of the material in acidic and neutral saline aqueous solution.

The obtained results are discussed in the Journal of Sol-Gel Science and Technology, Volume 63, Number 2 (2012), 266-274, DOI: 10.1007/s10971-011-2672-8

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