Tarnish Testing of Copper-Based Alloys Coated with SiO ₂ -Like Films by PECVD

The tarnishing test in the presence of hydrogen sulfide (H ₂ S) vapors has been used to investigate the tarnish resistance capability of copper-based alloys coated with SiO ₂ -like films by means of plasma-enhanced chemical vapor deposition (PECVD) fed with a tetraethoxysi- lane/oxygen mixture. The chemical and morphological properties of the films have been char- acterized by using infrared absorption spectroscopy (IR) and scanning electron microscopy (SEM) with energy disperse spectroscopy (EDS). The corrosion products of the samples after the tarnish- ing test have been identified by X-ray diffraction analysis (XRD). It has been found that SiO ₂ -like films formed via PECVD with a high O ₂ flow rate could protect copper-based alloys from H ₂ S vapor tarnishing. The alloys coated at the O ₂ flow rate of 20 sccm remain uncorroded after 54 days of H 2 S vapor tarnish testing. The corrosion products for the alloys deposited at a low O ₂ flow rate after 54 days of tarnish testing are mainly composed of brochantite.