Where Corrosion Science and Cathodic Protection Commenced

Not far from Piccadilly Circus in London's West End, stands the impressive Royal Institution building, opened in 1799 for the advancement of science. In this building, two of the most eminent scientists of the nineteenth century made significant contributions to corrosion science and technology, including work on the fundamentals of galvanic corrosion, discovery of cathodic protection (CP), and creation of the terminology for corrosion reactions still in use today.

Right from the start, the Royal Institution considered it important to reach out to the general public to show the importance of science in all works of life. It employed the young chemist Humphry Davy (1778-1829) in 1801 to stage entertaining and spectacular demonstrations of science in public lectures. These became one of the most popular events in London, and Albemarle Street became its first one-way street. Davy also established a laboratory for scientific research and received a knighthood for his invention of the miner's safety lamp. But less well known were his researches into electrochemistry. Following Volta's discovery of the electric battery in Italy in the late 1790s, Davy set about building the largest battery in the world at that time with 2,000 pairs of plates. Using this, he managed to isolate elements such as sodium, potassium, calcium, and other reactive elements for the first time. He showed there was a relationship between chemical reactivity and electricity, and produced what is probably the first Galvanic Series, which he described as "the different substances are arranged according to the order of their known galvanic powers, [and] will shew [sic] how intimately chemical agencies are related to the production of galvanism."

Davy recognized the importance of dissimilar metals in corrosion behavior: "Iron nails soon wear out when used to attach copper sheeting to ships and iron pins employed to attach lead to roofs of buildings rust with great rapidity, which is owing to chemical operations being increased by the electrical energy of contact." He was asked to look at the corrosion of copper cladding used to prevent worms attacking the hulls of wooden naval ships. In 1824, Davy found that attaching iron or zinc "protectors" prevented copper corrosion, pioneering CP. Unfortunately, this major discovery was a practical failure because copper needs to corrode to prevent formation of marine growth. But Davy can be considered as the father of CP, and an important pioneer in understanding of corrosion.

Davy's successor at the Royal Institution became an even more famous scientist. Michael Faraday (1791-1868) is rightly remembered for his discoveries in electromagnetism leading to development of the electric motor and electric generator. But Faraday also carried out work in electrochemistry, initially as assistant to Sir Humphry Davy. His most important discovery in this area was his eponymous laws of electrolysis, which showed the relationship between current and amount of metal corroded. It is ironic that the most useful mathematical formula in corrosion science was discovered by Faraday, as he had left school at age 12 and was always self-conscious about his lack of mathematical prowess. He made other contributions. After discussions with Cambridge polymath, William Whewell, he coined the nomenclature of electrochemistry with which we are familiar today (electrode, anode, cathode, ion, anion, cation, electrolysis, and electrolyte). In 1836, he carried out experiments on iron passivity, noting that iron placed in concentrated nitric acid (HNO3 ) did not corrode while rapid dissolution was observed in dilute HNO3 . He is also probably the first to suggest the combined use of protective coatings and CP for marine structures, a technique widely used today, when asked for advice on protecting piles for lighthouses:

"Though iron be a body very subject to the action of sea water, it does seem … that it may be used to advantage in marine constructions intended to be permanent, especially if the joint effects of preserving coats and voltaic protectors were applied."

The Royal Institution is a worthy place to conclude this series as it brings us back to the most corrosion-resistant metal—iridium—discussed in the first article. According to the Royal Society of Chemistry, Smithson Tennant, the discoverer of iridium in 1803, announced his finding … at the Royal Institution.