In China, steel-made (galvanized steel) materials are usually adopted as the earthing materials; however, since the steel-made earthing material has short service life since it is easily corroded, it has been replaced by the new materials gradually. Since copper-made (copper or copper-clad steel) earthing material has excellent conductivity property and corrosion-resistance performance, its sectional area only is less than 1/2 of that of steel-made earthing material and service life is 3~6 times of that of steel-made earthing material, which makes it become the most important new material to replace the steel-made earthing material. However, since the surface copper of the copper-made earthing material has relatively high potential, if the material is directly connected or close to the underground pipeline (copper made), the underground pipeline will be easily corroded due to the potential difference; moreover, if cathodic protection is adopted, the protective potential will be raised. To solve such defect, our company’s technicians have developed a new type of material – hot-dip galvanized continuous casting copper-clad steel earth wire through experiments and studies. Not only the property of this product is superior to the copper-made earth material, but also the problem that copper-made earth material causes corrosion of underground pipeline due to potential difference can be solved.
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.
Model and specification
Sectional area (mm2)
Electric wire diameter (mm)