Company Logo

• 목록

(1) Definition of the corrosion 

In order to change the chemical materials into the metal materials, the energy from outside is required. In other words, when the chemical materials which has the low-electric potential receive the external energy it will change into the metal materials which has high electric potential. But, in the natural circumstance, The lower electric potential is, the more stabilization is. Thus what the material itself change in quality or the properties of material change in process of returning the high electric potential material into the low electric potential chemical material is called the corrosion. In short, the corrosion can be defined as blow state. 

"The corrosion is that the material itself changes in quality or the properties of it change reacting on the circumstance."

(2) The condition of corrosion occurrence 

Most cases of corrosion are caused by the electrochemical reaction that is defined as the chemical reaction including electron movement. Thus the following four conditions must be satisfied so that the corrosion can be caused by the electrochemical reaction.

　　 ⓐ Anode

　　 ⓑ Cathode

　　 ⓒ Electronic or metallic path

　　 ⓓ Ionic path or electrolyte

The association composed of above four conditions is called the corrosion battery. This corrosion cell sends the electric current along the course, Cathode-Electronic Path-Anode-Ionic Path, and as the electric current, the corrosion is caused in Anode by the following Anode reaction and cathode reaction.

☞ Anode reaction

The anode reaction is also called a oxidation reaction, is reaction divided metal into a metal ion and a electron, and is like the following expression (1).

M ------ M+ + ne- -------------- (1)

(Metal) (Metal ion) (electron)

☞ Cathode reaction

The cathode reaction is also called a reduction reaction, is that electron moved through the current channel from the anode reacts with a plus ion in electrolyte, and is like the following reaction.

Reduction reaction of oxygen (acidity electrolyte)

O2 + 4H+ 4e- --------------- 2H2O (2)

Reduction reaction of oxygen (neutrality and alkalinity)

O2 + 2H20 + 4e- ----------- 4HO- (3)

Generative reaction of hydrogen gas

2H+ + 2e- ------------------ H2 (4)

Reduction reaction of metal ion

3Fe+ + e- ------------ 2Fe+ (5)

Reduction reaction of metal

Cu++ + 2e- ---------- Cu (6)

(3)The concrete and soil corrosion

　 ⓐ If the metal structure penetrating the reinforcement concrete structure like buildings is connected with the reinforcement in the concrete at the piecing part or support electronically, the natural difference of electric potential between them forms the corrosion cell and metal structure become the Anode to corrode.

Generally, in the concrete/soil corrosion, as the area of cathode (reinforcement) is much larger then that of Anode (metal structure), the serious corrosion is caused.

　 ⓑ In case that the metal structure goes through the different permeable soil and is contact with the soil of poor permeability partly, the corrosion battery by different permeability is formed and the part of poor permeability become the Anode.