Synthesis and structure of hybrid sol-gel ZrO2-SiO2 coatings

Corrosion resistance of stainless steel can be enhanced through the application of SiO2 coatings. However, these coatings are sensitive to alkaline attack, that produces the partial dissolution of the SiO2 network. An homogeneous structure incorporating ZrO2 to the SiO2 coatings would increase their resistance in basic media. In this work, hybrid ZrO2/SiO2 coatings were prepared and the effect of processing conditions was analysed, including the variation of sol synthesis, coating deposition and sintering treatments. Sols were prepared by hydrolysis and polycondensation of complexed zirconium tetrabuthoxide and pre-hydrolysed methyltriethoxisilane (MTES). For the higher MTES content, critical thickness around 0.5mum were measured. High concentrations of Si-O-Zr bonds were revealed for sintering temperatures lower than 700degreesC from FT-IR and DRX studies, and crystallisation of ZrO2(t) from T=700degreesC. The electrochemical resistance and coating stability were evaluated from cyclic polarisation tests, performed oil coated AISI304 stainless steel. The coatings revealed a high resistance against alkaline media preserving an excellent electrochemical behaviour in Cl- rich solutions.