Q-Carbon as a Corrosion-Resistant Coating.

A newly discovered quenched form of carbon, widely known as Q-carbon, thin films are synthesized by the direct conversion of the amorphous carbon layer using the nanosecond pulsed laser annealing technique, and its corrosion-resistant properties, that is, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy technique, are investigated. The unique microstructure and the existence of defects (sp 2 content) in sp 3 -rich Q-carbon are highly desirable for efficient corrosion-resistant performance. The sp 3 percentage of the as-grown Q-carbon is measured to be ∼80.5% from the D and G peaks of the Raman and C-1S X-ray photoelectron spectrum. The anti-corrosion properties with inhibition durability of Q-carbon thin films are systematically investigated in various concentrations of Na 2 SO 4 solutions, and the corrosion potential, corrosion current, and corrosion rate of Q-carbon are determined to be -253 V, 30.1 × 10 -5 A/cm 2 , and 0.00528, respectively, for 1 M Na 2 SO 4 solution. Both series and contact resistance decrease from 5498.6 and 821.1 Ω to 698.8 and 124.3 Ω with an increase of Na 2 SO 4 concentration from 0.1 to 1 M, respectively. The small shift of PDP curves toward more negative potential, the shrinkage of the radius of semicircular arcs in the Nyquist plot ( Z″ vs Z' ), and negligible loss in corrosion resistance (∼78%) are observed for Q-carbon thin film at the immersion time up to 48 h. The unique sp 2 -sp 3 ratio, shorter bond length, compact atomic arrangement, and minimum porosity, along with the high adhesion strength, due to the ultrafast solid-liquid-solid growth route, of Q-carbon thin film on the substrate signify it as a better alternative compared to the existing corrosion-resistant materials.