Cathodic Protection Potential Sign

You have a potential between the Cu and Zinc. The zinc is the sacrificial metal.

The objective is for the zinc to corrode preferentially to the tank bottom. The zinc will require replacement at intervals.

The technique is used to protect outboard motors immersed in sea water. The anode in this case is more often magnesium.

Dear all, My question is about the meaning of the negative and positive sign if Cu/CuSO4 reference electrode pure Zinc(Zn) reference electrode are used respectively. Please can you help out.(read main question above)

The meaning is that there is a potential between the Cu and Zinc which means that there is a current flowing, and it's taking zinc with it. If the zinc weren't there, a lesser potential would be set up between the Cu and some other metal (steel), which would then erode (through electrolysis) the metal. The zinc is protecting whatever is in the ground. That's why the zinc is referred to as the sacreficial metal. Most water heaters contain a magnesium rod to protect the steel tank, Most tanks are glass or ceramic lined, but cracks and or crevaces occur that are not necessarily protected, so the magnesium rod protects the steel by being the sacreficial metal. Embedding anodes for protection is usually done on small direct buried pipe lines. Large systems usually have electrical (inverter) systems which imposes a potential that offsets the originating potential.

Corrosion is caused by oxidation, steel pipe for example will rust. Electrolysis is the "eating" away of the metal and can be identified its shiney appearence. Example: if you observe a shiney hole in a pipe line, electrolysis has eaten through the pipe wall.

The Cu/CuSO4 being negative, creates a net '0' potential, protecting the tank bottom from electrolysis, or creates an electrical current designed to use some other metal as a sacreficial metal. The Zinc electrode is a sacreficial metal, used to protect ste Zinc coating, galvanizing, etc. on steel protects it from rusting and electrolysis if buried.

The Cu/CuSO4, being negative, is protecting the tank by creating a net '0' potential, thus preventing any electrolysis occurring. The Zinc electrode is used to provide an electrical path that will erode the Zinc rather than the metal it is protecting.

Guys, Thanks to all who answered. It seems that you did not understand the question. I meant Cu/CuSO4 and Zinc REFERENCE ELECTRODES(reference cells) Not Anodes. The cathode is Steel (Tank bottoms), anodes are Anodeflex. Please dont be confused. Very best regards,

You have to refer to a third reference electrode, eg standard hydrogen electrode (she).

In she scale:

CuCUSO4 electrode potential is about +0.3V.

Zinc metal electrode potential is about -0.8 V

Steel potential about -0.3V

So if you use CuCuSO4 electrode connected to + voltmeter pole, as a reference, the potential difference with steel will be (-0.3+(-0.3))=-0.6V.

If you use zinc metal reference electrode as above, potential difference will be (+0.8+(-0.3))=+0.5V.

Pietro Anelli

Can anyone provide me the images of installation of whole cathodic protection..1. Anode installation, 2.pipe and anode connection , 3.thermit welding , 4.iccp , 5.reference electrode , 6. Connection between reference electrode and pipe. Pls provide me images so i can imagine...Cathodic Protection..