Fabrication and investigations of thin films deposited by atmospheric pressure plasma jet using TEOS and argon for the corrosion protection of historic tintypes

Since tintype images carry artistic, aesthetic, cultural, and civilizational values, it is necessary to preserve them from damage that ultimately leads to their loss. This article addresses the primary support of tintype images, which is composed of iron. This work presents an innovative plasma-based approach for forming transparent, adherent, and hydrophobic SiOx films suitable for the conservation of metallic heritage objects (i.e., tintype supports), offering a non-invasive and effective protection method. An atmospheric pressure plasma jet was used with tetra-ethoxy orthosilicate (TEOS) precursor and argon as the carrier gas to deposit a thin, transparent protective layer of SiOx on the iron support of the tintype image at different deposition times: 5, 7, and 10 min. The deposited layers were characterized using various examination and analysis techniques, including a portable digital microscope, a scanning electron microscope equipped with an X-ray scattering unit (SEM-EDX), colorimetric measurements, an atomic force microscope (AFM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and contact angle measurements. Additionally, electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion protection performance of the plasma-deposited thin films. The results revealed that the sample deposited for five minutes exhibited RP = 104.45 Ω, IE = 97.99%, and a contact angle of 138.5°; while the sample subjected to a seven-minute deposition process showed the highest efficiency in protecting the surface from corrosion, with RP = 227.5 Ω, IE = 99.08%, and a contact angle of 129°. The sample subjected to a ten-minute deposition exhibited the most favorable initial characteristics, with RP = 8.49 Ω, IE = 75.38%, and a contact angle of 138°.