Fighting corrosion
scientists in South Korea have shown how sunlight could be used to prevent rusting of steel. And the method promises to be inexpensive and easy. Rusting of iron leads to losses worth billions of dollars. Preventing rust with either paint or galvanisation of iron is also an expensive proposition.
Rusting occurs when iron comes into contact with the oxygen and moisture present in the air to turn into iron oxide. Galvanisation involves coating the iron with zinc that reacts with the air (being more reactive) instead of iron and saves it from rusting. The oxidation of a metal involves loss of electrons from the metal. In the case of galvanised iron, the zinc gives up electrons to iron.
H Park, researcher at Pohang University of Science and Technology, South Korea, and his team have devised a simple way to pass on electrons to iron atoms, thereby preventing rusting. They used a solar cell to provide current from to the iron. The solar cell absorbs sunlight and gives up electrons that are usually used for lighting bulbs or other applications. Instead, these electrons could be made to travel to a steel plate by a wire. Then as long as the electrons are flowing from the solar cell to the plate, the iron in the plate will not rust. Though high efficiency solar cells are usually expensive (since they are made from ultra pure semiconducting materials), the one used by Park's group is very cheap. It is basically a glass plate, coated with a conducting material and dipped in titanium dioxide. Titanium dioxide (the chemical from which white paint is made) gives up electrons readily when exposed to ultraviolet rays in sunlight.
The scientists tested their kit by immersing a steel plate in a salt solution for a few days. As long as the solar cell kept on working, the steel did not corrode. The problem is of operating the cell at nights or when it is cloudy. In this case, a small battery will need to be added to the device so that the current keeps on flowing. This simple, inexpensive device could be used for preventing rust in underground pipes and other steel structures (Chemical Communications, Vol 2001, p281).