Effect of Surface Finish on the Anti-Scaling of a Diamond-Like Carbon Coating

Abstract Diamond-like carbon (DLC) coatings have been used to combat chemical buildup (e.g., scales); however, their appropriate surface finish requirements are occasionally questioned. Surface preparation is critical for ensuring good physical and chemical substrate bonding. With respect to the deposition and adhesion of inorganic scales, there is a performance, practical, and economical need to clarify the role of surface preparation in the performance of thin DLC coatings, specifically coatings with an average roughness, Ra, between 4 μin (0.1 μm) and 250 μin (6.4 μm). This study specifically investigates the effect of surface finish on hydrophobicity (water contact angle) and carbonate scaling. Scale deposition was performed under flow using a rotating cage containing scaling fluids at ambient pressure and 70°C. All test materials were subjected to water contact angle measurements, visual examinations, mass change measurements and scale adhesion test measurements. This study showed that calcium carbonate deposition is strongly affected by surface finish and that the selected DLC coating lowered scale deposition, most noticeably, scale adhesion up to approximately Ra 32 μin (0.8 μm). To a secondary extent, the adhesion strength also highlighted the positive effects of the selected DLC coating, consistently less prone to deposition. Somewhat surprisingly, the lower water contact angles but greater scale reduction of the selected DLC coating infers that hydrophobicity may be overemphasized in solid mitigation coating specifications.