what are causes of corrosion?

Answer 1

There are many types of corrosion. However, when most people think of corrosion, they think of "rust," which is the main type of oxidation corrosion on iron/steel -- in this case Oxygen reacts (oxidizes) with Iron atoms in the iron/steel to form Iron Oxides (rust). This type of corrosion falls into a broader category where an oxidizing agent (such as Oxygen, Chlorine, etc) bonds with a metal to form metal salts, for this type of corrosion to occur, the water molecule usually needs to be present. This is what is known as an electrochemical reaction.

A second type of corrosion can occur when there is a lack of Oxygen (pitting corrosion). This is commonly seen when saltwater contacts a metallic material.

Other types of corrosion can occur at high temperatures. Also, there are special types of corrosion caused by certain bacteria!

There is also non-metallic corrosion, the most destructive involves concrete degradation (especially below the ground), even plastics and ceramics can corrode.

Answer 2

when a metal is located in an acidic or basic environment or electrolyte , anodic and catodic reactions occure that leads to entrance of metalic ions into environment and resuts in corrosion.