CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 3
In the present investigation magnetron sputtering was used to deposit thin films of
titanium (Ti), titanium dioxide (TiO 2 ) and duplex Ti-TiO 2 coating on 304L SS to investigate the
effect of top-surface coating on the passive film stability and corrosion resistance in 1 M and 8 M
nitric acid medium compared to uncoated specimens. The coatings were deposited by RF
magnetron sputtering (Excel Instruments, India) in a custom designed 12 inch diameter chamber.
Titanium (Ti) coating was deposited over 304L SS (1 cm×1 cm×1.5 cm) by sputtering titanium
with 99.99 % purity at temperature of 400 °C and pressure 1×10 -1 Pa after pre-sputtering for 10
min. Titanium dioxide (TiO 2 ) coating was deposited on the polished specimens of 304L SS by
reactive magnetron sputtering of titanium of 99.99 % purity using Ar + and adding oxygen in the
ratio of 80 sccm and 20 sccm, respectively. Prior to introduction of sputtering gas, the base
pressure was 5×10 -4 Pa, and then pre-sputtering was performed for 10 min at pressure of 1×10 -1 Pa
to remove the carbon contamination and hydrated layers present on the surface of target. The
magnetron power used was 100 W and bias voltage applied to the target was 200 V. The distance
between substrate and target was 10 cm and the substrate temperature was maintained around 200
°C during deposition. Thickness of Ti and TiO 2 coating was maintained at 1 µ, respectively.
Similarly, duplex Ti-TiO 2 coated specimens were prepared by first depositing Ti followed by TiO 2
as explained above. The thickness of the Ti interlayer was maintained at 100 nm and the total
thickness of the duplex Ti-TiO 2 coating was 1.2 µ.
3.1.3 Morphological study
3.1.3.1 Optical microscopy
Optical microscope is the oldest and most common instrument for characterization of
materials. Over the past decade enormous growth in the application of optical microscope has
been witnessed in wide variety of material characterization from micron to sub-micron level.
Moreover, with continued development of specialized techniques such as new light source,