Most of us have experienced the frustration of leaving a bike, tool, or piece of jewelry outside where it is subject to humidity and rain. In time, the metal corrodes, and you’re left with a rusty version of your original item. This process is called corrosion.
(Pixabay / moshehar)
When corrosion attacks a personal item that you value, it can be a great inconvenience. But corrosion can be much more insidious when it plays out on a grand scale. It can cause buildings and bridges to collapse and oil pipelines to rupture. It can also lead to leaks in chemical plants and plumbing systems. When electrical contacts corrode, fires can occur.
The corrosion process is often thought of as the opposite of electroplating. Both start with a base metal. In corrosion, the base metal will lose electrons. With the electroplating process, however, the base metal will gain electrons.
Here’s a closer look at the two processes:
Electroplating. With electroplating, a negatively charged base metal is covered with another metal that is positively charged. Electroplating does not happen organically. It requires a power supply. It allows manufacturers to build products with affordable base metals, then coat them with high-quality metals. If they were to make a product that consisted only of the high-quality metals, they would end up spending a lot more money. Manufacturers use electroplating to:
- Minimize corrosion
- Improve aesthetics
- Support conductivity
- Eliminate friction
- Make an object harder
- Make an object less susceptible to wear and tear
Corrosion. Unlike with electroplating, corrosion does not require a power supply. The corrosion process is electrochemical in nature. It starts with the outer layers of metal. Electrons that once adhered to the substrate are wooed away by oxygen and other substances in the air and water. As the oxygen gains electrons, it develops an oxide and compromises the metal.
Some substrates are more resistant to corrosion than others. These are called inert or cathodic materials. The most inert materials include gold, graphite, platinum, silver, and titanium. Materials that are more susceptible to corrosion are called active or anodic. These include stainless steel, iron and steel, aluminum alloys, and cadmium. Bronze, copper, and nickel lie somewhere in the middle. Through the process of electroplating, anodic materials can be coated with cathodic materials, resulting in fewer problems with corrosion.