Plasma deposited organosilicon multistacks for high-performance low-carbon steel protection

The alternated deposition of silicon oxide and organosilicon layers, yielding to ultra-barrier films against the transmission of vapors and gases through plastic substrates, has been demonstrated to be also an effective tool for the deposition of highly corrosion protective coatings on low-carbon steel substrate. PECVD is really efficient for the deposition of multilayered stacks since it allows the deposition of the organosilicon and silicon oxide layers in the same process chamber and using the same precursor, the tetraethoxysilane. The multilayer approach leads to 600-nm-thick coatings with high corrosion resistance (1.1×10⁷ω²), while a layer of SiO_x has the same protective effectiveness only for thickness greater than 1μm. The use of modulated discharges for the multilayer deposition exhibits an improved resistance to corrosion by two orders of magnitude with respect to continuous mode. Multilayer architectures, made of alternated organosilicon and silicon oxide layers, were tested for the deposition of corrosion resistant coatings on metal substrates. Such coatings reached the same protective effectiveness of a single silicon oxide layer but with halved thickness. Multilayer deposited through modulated discharge showed a further two-orders-of-magnitude-improvement. FT-IR of the gas phase was correlated to the FT-IR film characterization.