Anyone who works with metal recognizes the constant threat of corrosion, a problem that becomes especially profound for structures installed in the world’s oceans. In this complex chemical setting, the breakdown of metallic stability represents a leading safety hazard, which is why it sits uppermost in the mind of Faisal Khan, MCIC, who holds the Canada Research Chair in Offshore Safety and Risk Engineering at Memorial University of Newfoundland in St. John’s.

“In a marine environment, all actors are super-active,” he explains, pointing to the intricate mixture of organic and inorganic constituents that can interact with any piece built infrastructure. Through the university’s Centre for Risk, Integrity, and Safety Engineering Group, he has access to state-of-the-art laboratory equipment for modelling the harsh conditions of the North Atlantic.

Among the most effective ways of protecting metal from such conditions is electroplating. This venerable technique, with roots going back two centuries into the heart of the European industrial revolution, employs electro-chemical exchanges to form a thin coating of corrosion-resistant metals over the entire surface of a material immersed in a carefully balanced bath of critical constituents. Electroplating has traditionally prevented the tarnishing of elegant tableware, but Khan and his colleagues are more specifically interested in preventing the failure of steel superstructures at sea.

Cyanide and cadmium compounds were long used for this purpose, but the value of these toxic metals has been compromised by environmental and health concerns that have restricted their use. Zinc-nickel alloys subsequently emerged as the most effective coating for metal components, but until now there has been little formal investigation of the best way to apply that coating. Khan led a team that addressed this shortcoming, with results that appear in the latest edition of The Canadian Journal of Chemical Engineering.

According to Khan, a primary challenge around Zn-Ni electroplating is the consistency of coating. Any interruptions in this process will create weak points where corrosion can gain a foothold, which it will invariably do quickly and aggressively. He adds that the variables for optimizing deposition are found in the makeup of the bath. Various mixtures have been examined, including neutral saline and chlorine-urea solutions, but among the most promising have been citrate bath formulations.

Khan’s team identified five defining features of such a bath — molar concentration, temperature, current density, plating time, and the complexing agent — then electroplated standard steel samples in baths where each of these factors varied over different ranges. These samples were then submerged in tanks of ocean water under specific pH and temperature conditions to match those off shore.

The findings, which links the corrosion resistance of each sample with the qualities of its respective electroplating bath, reveal that citrate concentration, temperature, and plating time are the critical elements in obtaining the most desirable coating.

“For the electrodeposition to happen in the best possible way, it must provide a more stable deposition with no irregularities or breakages happening,” Khan concludes. “The key is maintaining a structured, stable morphology on the surface of the metal.”