Titanium anode is a common auxiliary electrode for impressed current cathodic protection. The service life of titanium anode is related to the protection life of the whole cathodic protection system. It is a long-term concern for researchers to correctly evaluate the service life of titanium anode. In this paper, several testing methods of strengthening life of titanium anode in common medium environment are given. At the same time, through the comparison of several commonly used auxiliary electrodes for impressed current cathodic protection, it is shown that titanium anode is the most promising auxiliary electrode in impressed current cathodic protection.
1. Preparation of titanium anode
Titanium anode is a kind of insoluble electrode with noble metal oxide coating on its surface. According to the medium environment, titanium anode for impressed current cathodic protection can be roughly divided into three categories: soil or fresh water medium environment, reinforced concrete environment, seawater medium environment. The coating system of titanium anode is different due to the different environmental media. In the soil or fresh water medium, because there is no chlorine ion or the content of chloride ion is relatively low, oxygen evolution reaction mainly occurs in the anode, and iridium oxide is the main coating system of titanium anode. In the reinforced concrete medium, the chloride ion content is generally not high, and the oxygen evolution reaction mainly occurs on the anode. The titanium anode coating system is also mainly iridium oxide. Iridium oxide has good electrocatalytic activity and excellent corrosion resistance in oxygen evolution environment. In seawater, the content of chloride ion is high, the main reaction is chlorine evolution, and the anode coating system is mainly ruthenium oxide.
The electrode preparation process is as follows: industrial pure titanium TA1 or TA2 is selected as the base material, which is dried after degreasing, sand blasting and pickling, iridium chloride or ruthenium trichloride and other metal salts are dissolved in n-butanol and isopropanol solvent according to a certain proportion, and then the brush is brushed on the treated titanium substrate, dried at 200 ℃, and then sintered in a resistance furnace at 400-500 ℃ Min, repeat the above process until the paint is finished.
2.Test method for strengthening life of titanium anode
Generally, the life of titanium anode for impressed current cathodic protection is more than 20 A, so it is very important to detect the life of anode. Because the actual service life of the anode is more than 20 A, and the anode has almost no mass loss, so the life of the anode can not be calculated by extrapolation method with the actual current density, and the life of the anode can only be measured by high current until the passing charge amount reaches the standard. The following describes the detection methods of titanium anode strengthening life in soil or fresh water medium environment, reinforced concrete environment, seawater medium environment.
(1) Test method for enhanced life of titanium anode in soil or fresh water environment
The enhanced life test method of titanium anode in soil or fresh water environment is as follows: 1 mol / L Na2SO4 solution is used as electrolyte, current density is 10 000 a / m2, and water bath temperature is kept at (30 ± 5) ℃. At 10 000 a / m2 current density, the relationship between the total charge density of anode surface and the total charge density of anode surface during the actual service life of anode is as follows: JATA ≥ jsts.
In the formula: JA is the current density of anode surface in enhanced life test, a / m2;
JS is the current density of anode surface in actual use, a / m2;
TA is the strengthening life, H;
TS is the actual service life, H.
(2) Detection method of reinforced concrete anode life in titanium environment
Accelerated anode life test can not be used in concrete, high current will lead to early damage of concrete, accelerated test must be completed in aqueous solution. According to NACE standard, the anode life test is carried out in 3% NaCl solution, 4% NaOH solution and simulated pore fluid. The composition ratio of simulated pore fluid is as follows: NaOH 26.3 g, KCl 10.74 g, Ca (OH) 2 2.15 g per liter solution. Before testing the simulated pore fluid environment, the sand conforming to ASTM C 788 should be injected first, and then the prepared simulated pore fluid should be injected. There is no need to add sand in the detection of NaCl and NaOH environment, and the chemicals used are of chemical pure reagent grade. Deionized water is used to supplement the evaporation loss of the solution in the detection process. The relationship between the total charge density passing through the anode surface and the total charge density passing through the anode surface during the actual service life of the anode under the experimental current density is shown in the above formula.
(3) Enhanced life test of titanium anode in seawater
The test conditions for enhanced life of seawater medium are as follows: 0.5 mol / L H2SO4 solution as electrolyte, electrolyte temperature as (40 ± 5) ℃ and current density as 20 Ka / m2. In seawater, the actual current density of titanium anode is 300-600 A / m2, and the service life of titanium anode is required to be about 10 A and 150 h respectively.
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