ICCP systems as an effective method for corrosion control has been widely approved by people.
Its principle is based on the theory of electrochemical. The material to be protected from corrosion by passing of an external cathode current, reduce the surface potential of the protected material. Thus reducing the corrosion rate of metal.ICCP systems has been widely applied in reinforced concrete, ships, Bridges, tanks, chemical equipment, pipeline etc. Auxiliary anodes is one of the core components of ICCP systems, It is meaningful for correct choice of auxiliary anodes.
Requirements of Ideal auxiliary anode for ICCP
Superior electrical conductivity, Operated at high current density, low polarizability.
When applied in environment, Anode should have good chemistry (static), electrochemical (dynamic) stability, low consumption, long expected life.Anode should have certain mechanics performance.
*It’s easy to process, transport, install and use.
*Low cost of maintenance.
*No environment pollution during operation.
Choice of auxiliary anode for ICCP
In order to choose good auxiliary anodes, We must know the problem of thermodynamics and dynamic of anode with electrochemical reactions under the special environment.
M—ne Mn+ —————–（1）
2Cl- —2e Cl2 ——————（2）
2H2O —4e O2 + 4H+ ———（3）
The reaction of Soluble anode: (1)
The reaction of Micro soluble anode: (1)+(2) or three
The reaction of Insoluble anode(DSA):(2) or(2)+(3)
Choice of auxiliary anode for ICCP
Current intensity: No matter how to apply the power on the anode, the current density of anode is varying within limits, The current density will influence the over potential of anode, then affect the anode product.
The concentration changes of conductive ionic at working media, It including reactant and resultant. For example, The reaction of anode is Chlorine evolution, It result of large amount of Chlorine ion in seawater, and the potential of Chlorine evolution is lower than Oxygen evolution, If it is small and close environment of seawater. The anode will be Chlorine evolution firstly then Chlorine and Oxygen evolution together.it result of the chlorine ionic can’t supply anymore.
Comparison of several electrode
|Item||Resistivity（ohm.m)||Current density（A/m2)||Consumption rate（kg/A.a)|
|Chlorine Evolution||Oxygen Evolution|
|Pt Anode||4.8×10-7||600||6×10-6||175~200 ×10-6|
|Conductive Plastic (flexible anode ）||0.015||1.268||0.1（Superficial consumption）|
It can be seen from the graph, The consumption of Oxygen Evolution for the same electrode is obviously higher than Chlorine Evolution. However the MMO Electrode has low consumption in both Chlorine evolution and Oxygen evolution, And MMO Anode with other advantages such as good conductivity, large flow. Therefore MMO Anode is the good choice of ICCP systems.
MMO Anode Electrochemical Performance
Two types of MMO Coating：
Chlorine evolution type Anode：
The major Components of coating: Ru、Ir、Pd、Ti etc. Suitable for use in sea water where Cl2 is the principal anode product.
|The Potential of Chlorine Evolution（SCE）2KA/m2||Polarizability（mv)
|The potential of Oxygen Evolution (mercurous sulfate）2KA/m2|
Oxygen Evolution type Anode：
The major Components of coating: Ir,Ta oxide. Suitable for use in oxygen evolution environment such as soil, fresh water etc.
|Oxygen Evolution（V， Ref.SCE） 2KA/m2||Polarizability （mv)
(V， mercurous sulfate ）2KA/m2
MMO & platinized anode technics
The mixed metal oxides are formed on the titanium substrate through a process of thermal decomposition, creating an oxide coating of the platinum group metals.
Pt Coating . The platinum coating is formed through a process of electroplating.
MMO Anode Current density
|Electrolyte||Maximum Design Current Density （A/m2)||Anode Life(Y)|
|Calcined petroleum coke||100||20|
MMO Anode for ICCP
meet ASTM standard B348 Grade 1 or Grade 2
Copper cored titanium wire according to customer’s requests.
meet ASTM standard B265 Grade 1 or Grade 2
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