When iron combines with oxides dissolved in water, it will rust. This means that if there is no water vapor in the air, or no water at all, or no dissolved oxygen in the water, rust will not form. When a drop of rain falls on the shiny iron surface, it will remain clean for a short time. However, before long, iron and oxygen in the water began to combine to form iron oxide, which is rust. Water drops will turn red and rust will be suspended in water. When the water droplets evaporate, rust will remain on the surface, forming a reddish rust layer. Once rust is formed, it will spread even in dry air. This is because rough rust is easy to condense water vapor in the air, and water vapor absorbs water vapor and stores it, which is why it is much easier to prevent iron from rusting than to prevent rust from expanding.
Rust is a fragile and porous substance, which can not protect the inner iron from corrosion, so over time, steel products may rust into a pile of useless waste products. It is particularly serious that steel will soon rust in water vapor containing acid gas and chlorine gas, or when it comes into contact with electrolyte solution. According to statistics, tens of millions of tons of steel have become rust in every country in the world, and the losses caused by the destruction of steel products, such as production stoppage, product quality decline, environmental pollution, harm to human health and even serious accidents, are incalculable.