Tarnish Testing of Copper-Based Alloys Coated with SiO2-Like Films by PECVD

The tarnishing test in the presence of hydrogen sulfide (H2S) vapors has been used to investigate the tarnish resistance capability of copper-based alloys coated with SiO2-like films by means of plasma-enhanced chemical vapor deposition (PECVD) fed with a tetraethoxysilane/oxygen mixture. The chemical and morphological properties of the films have been characterized by using infrared absorption spectroscopy (IR) and scanning electron microscopy (SEM) with energy disperse spectroscopy (EDS). The corrosion products of the samples after the tarnishing test have been identified by X-ray diffraction analysis (XRD). It has been found that SiO2-like films formed via PECVD with a high O-2 flow rate could protect copper-based alloys from H2S vapor tarnishing. The alloys coated at the O-2 flow rate of 20 seem remain uncorroded after 54 days of H2S 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.