Carbon-containing titania on stainless steel by high voltage powder spray coating and its adhesion phenomena

Abstract

Nowadays, many studies involve coated materials on stainless steel prepared using various methods and many approaches have been taken to improve abrasion resistance of the coatings. Thus, this research introduces high voltage powder spray coating (HVPSC) as a new coating method to attach carbon/titania (C/TiO2) on stainless steel and evaluates its coating adhesion. Commercially available epoxy resin (Oxyplast PR12®) was used as the source of carbon and the transformation from epoxy resin to pyrolytic carbon was performed as the pyrolytic carbon has a higher surface energy compared to epoxy resin, hence possesses better adsorption properties. However, increasing the pyrolysis temperature caused the epoxy resin structure to change, thus making the adhesion on the stainless steel weaker. Therefore, it is hypothesized that the incorporation of inorganic particle will improve the adhesion properties through the reducing of the carbon shrinkage. C/TiO2 was prepared from the mixture of the epoxy resin (Oxyplast PR12®) and anatase TiO2 powder, followed by spraying the mixture onto stainless steel (AISI 304) surface using HVPSC. The sprayed powders on stainless steel underwent pyrolysis at several different temperatures in the range of 300– 700°С for an hour to determine the optimum temperature for a good adhesion. The physical properties of C/TiO2 coated samples were characterized using Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), electron dispersive X-ray spectroscopy (EDX), thermogravimetry analysis, X-ray diffraction spectroscopy, surface profiler meter and X-ray photoelectron spectroscopy. The FTIR analysis of C/TiO2 coating identified the appearance of sp3 C-H, C-O, C-O, and Ti-O peaks. The absorption band of sp3 C-H, C-O and C-O slowly disappeared as the pyrolysis temperature increased, indicating that the structure changed from epoxide to pyrolytic carbon. The FTIR results were in good agreement with the EDX data composition, detecting only C, O, and Ti elements. FESEM images showed that the TiO2 particles were fully covered with carbon layer and the thickness was in the range of 4.8–15.5 µm. The abrasive and peel adhesion tests were performed, and the results showed no detachment of coated material of C/TiO2 pyrolyzed at 300°С, suggesting that this temperature produces the best coating adhesion. The carbon-based coating adhesion phenomena were elucidated by XPS analysis of Fe2p, C1s and Ti2p element peaks. It was demonstrated that the presence of oxide layer on stainless steel, availability of functional groups and structure shrinkage were the factors that affected the adhesion of the carbonaceous coating. The shrinkage of the structure was minimized due to the presence of TiO2 which is associated with the strong coating adhesion. Moreover, it was also found that the carbonaceous structure produced from pyrolysis of epoxy resin had a good platform for the attachment of silver in antibacterial activity. The silver has been successfully attached to the surface of pyrolyzed C/TiO2 by a strong attachment and it was active in E. coli and B. cereus bacterial killing. This demonstrated that the carbonaceous coating produced by HVPSC formed a good adhesion in the presence of TiO2 and can also stand as a usable platform for further functionalization. Therefore, HVPSC with controlled temperature can be used as a promising method in C/TiO2 coating technique.