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Oct 19, 2019
copper plated steel wire uk

Hot-dip tin-plated continuous casting copper-clad steel stranded grounding wire

Working principle
When most of the metal contact various kinds of solutions, it will be automatically corroded; the metal coverts to metal ions and enters into the solution and corresponding electrons will be left on the metal surface; the more ions enter into the solution, the more electrons will be left on the surface; ionization of metal will become more and more difficult because of the attraction between negative electrons and positive ions and finally equilibrium will be realized, as shown in the equation below:

In different solutions, different metal has different ionization tendencies or degrees. When ionic equilibrium is reached, it means that metal establishes an equilibrium (electrode) potential in the solution according to electrochemistry terminology. The metal becomes an electrode in the solution and electrode potential and free energy also can express the spontaneous tendency of corrosion: high potential indicates that the ionization is not easily realized, for example, precious metal such as gold, silver, copper, etc.

Relationship between potential and free energy can be explained via the following electrochemical equation:

In the above equation:
refers to free energy change of corrosion reaction;
refers to the electromotive force of corrosion cell;
n refers to the number of electrons in oxidation reaction, that is, valence number of metal ions;
F refers to faraday constant and F=96500C.
It can be seen from the above equation that the larger electromotive force is, the greater of reduction of free energy () will be, that is, the larger corrosion tendency will be. Electromotive force equals to the difference of two electrodes (negative and positive) in the battery. The anodic reaction of corrosion cell refers to the conversion of metal into ions and cathodic reaction refers to the ionization of oxygen in solution. Only if the anodic reaction and cathodic reaction both exist, ions attached to the metal surface will be effectively removed and corrosion will proceed. Therefore, the lower the potential of anode metal is, the larger and will be.

The standard electrode potentials of some important metal are listed in the table below. Since the potential of metal changes with the ionic concentration and temperature in the solution, the solution (at 25℃) whose unit activity is the metal ions contained in one liter is treated as the standard solution and potentials of different metal are measured as the standard potential for the convenience of comparison. The absolute value of potential is hard to be measured, so that the standard potential of hydrogen is set as zero and electric difference between other metal and hydrogen electrode is measured and treated as the standard potential of metal.

In the above table, the standard potentials of metal are arranged in ascending (small to large or negative to positive) order. It can be seen from the table that the standard potential of Fe is -0.036(Fe3+) and -0.440 (Fe2+) and metal within that range mainly includes Cd (-0.403), Co (-0.277), Ni (-0.250), Sn (-0.136) and Pb (-0.126). Through comprehensive consideration of material cost and environmental protection, tin is selected to cover the copper earth material; as a result, the corrosion problem of underground pipeline due to its potential difference with copper earth material will be basically removed.

copper plated steel wire uk