Oxidation resistant TiO2–SiO2 coatings on mild steel by Sol–Gel

Single and multilayer titania–silica (TiO2–SiO2) oxidation resistant dry gel thin film was applied on mild steel (MS) through sol–gel based dip coating. The coated samples were fired at 410 °C for 30 min and the coating film thickness was found to be 200–400 nm using spectroscopic ellipsometry. The structural and chemical analysis of the films was carried out by XRD, SEM–EDS and TG–DTA. The oxidation resistance of coatings was evaluated by weight gain per unit area after exposing to 400 °C for 20 h in air. Uncoated specimens exhibited a weight gain of 0.72 mg/cm2. However, the weight gain was less by 6 times for single layer and 16 times for 3 layers of coatings (deposition). Further, oxidation kinetics study revealed a reduction of parabolic oxidization rate constant by 43 times (0.026 mg2 cm−4.h−1) for single layer and 325 times (8 × 10−5 mg2 cm−4.h−1) for 3 layer coatings, compared to bare MS exposed to identical conditions. Such a high reduction in oxidation with multilayer deposition is probably due to the effective coverage of micro–cracks, which may be induced due to the thermal mismatch between the coatings and MS. An improvement in adherence of coating was confirmed due to the formation of (Fe0. 927Ti0.073)2.O3 at the interface using XRD. The addition of SiO2 to TiO2 was found to minimise the coating defects associated with sol–gel and also inhibit the formation of anatase. Thus, the present work demonstrated the application of TiO2–SiO2 thin film coating on MS through sol–gel technique to form an impervious layer to substantially enhance the oxidation resistance at elevated temperatures. [Display omitted] •400 nm amorphous dense TiO2–SiO2 thin films were synthesized on mild steel.•Formation of (Fe0.927 Ti0.073)2O3 interface prevents the delamination.•TiO2–SiO2 and (Fe0.927 Ti0.073)2O3 protects the mild steel from high temperature oxidization.•Parabolic rate constant (PRC) of bare MS at 400 °C is 0.026 mg2 cm−4.h−1.•The coated MS shows 8 × 10−5 mg2 cm−4.h−1, which is 320 times less compared to uncoated one.