What is corrosion? Corrosion, or rust, is an electrochemical process involving an anode (a piece of metal that gives away electrons), an electrolyte (a liquid that helps electrons move), and a cathode (a piece of metal that accepts electrons). When water comes into contact with iron, the water reacts with carbon dioxide in the air and forms a weak carbonic acid, which is an excellent electrolyte. As the acid begins to dissolve the iron, some of the water begins to break up into oxygen and hydrogen. The oxygen steals electrons from the iron and begins to combine to form iron oxide (a.k.a. rust). However, there are a group of metals that do not follow this process, called Noble Metals.
What are noble metals? Noble metals are most often characterized by their lack of chemical reactivity. This means these metals will resist oxidation, or corrosion, in any environment compared to normal metals, which will readily oxidize and rust. The following are each of the metals on the periodic table classified as the ‘Noble’ metals:
- The Platinum Group:
- Some also include Copper
Noble metals also have some of the best electrical conductivity among metal elements. Their combined corrosion resistance and conductivity make them popular selections for common electrical components, such as electrodes, contacts, and wiring.
These elements are also classified as siderophiles, or “iron lovers,” because they will readily dissolve in molten iron or iron solutions. Therefore, these metals can accumulate in the Earth’s core. They are also the only metals that occur in relatively pure form in nature. Uses for these metals can be extensive, as seen below.
Copper, silver, gold, platinum, and palladium are commonly used to make coins and jewelry, either as pure metals or as metal plating to protect the base metal and add value. These metals, mostly silver, can also be found in medicine due to their antimicrobial characteristics. Since these metals are excellent conductors, they can also commonly be found in electrical wiring and other components. Platinum can be utilized as an excellent catalyst in some chemical reactions. Organic metallic compounds containing platinum are also used for cancer chemotherapy drugs and many other applications.
Ruthenium is often used to strengthen other metals or alloys, especially other noble metals. Ruthenium also finds use in electrical contacts and can act as a catalyst in chemical reactions.
Rhodium can be electroplated over other noble metals, particularly silver, gold, and platinum, to add shine and offer additional protection from the elements. Rhodium is also applied as a catalyst in the automotive and chemical industries. It’s an outstanding electrical contact and can be used in neutron detectors.
Iridium is suited for many of the same applications as ruthenium, due to the metal’s hardness. Commonly found in spark plugs, electrodes, and crucibles, it has tremendous value in making small machine parts and is an excellent catalyst.
But what does this mean for the paint and coatings market segment? Well, as we now know, noble metals are great catalysts and offer significant corrosion protection, since these metals are non-oxidizing. You may ask, why not just coat every piece of metal with gold plating? Well, obviously the cost of these materials is a major roadblock. Perhaps one day the cost of these materials will become accessible enough for industrial manufacturers to be able to use these metals as additives for their standout characteristics.