| Aluminum, zinc, magnesium and their alloys are commonly used in CP engineers. But, research work such as local dissolution of aluminum alloy sacrificial anodes, effects of external mediums on zinc reference electrodes in seawater, electrochemical performances of magnesium alloy sacrificial anodes in Qinghai-Tibetan plateau frozen soil have not been reported. Therefore, study on the above-mentioned problems is of importance. Centered on the above problems, electrochemical methods were used to study the followings: effects of Ga on Al-Zn-In performances, effects of medium on zinc reference electrodes in seawater, magnesium alloy performance in frozen soil. Modern physical methods including SCE and XRD were used to characterize some relevant problems in order to discuss the activation mechanism and dissolution mechanism.Results show:Ga dissolves in the alloy uniformly but In segregates in the boundary, which forms a In-rich secondary phase. With the increase of Ga contents, the work potential of Al-Zn-In anodes shifts to a more negative value, the current coefficient drops and more serious pit corrosion happens. Al-4%Zn-0.02%In-0.015%Ga alloy is a kind of new ideal high-effective anode in man-mad seawater because of its potential (-1039 mV), current efficiency (96.3%), uniform dissolution, excellent anodic polarization performance and resistance to pit corrosion. In3+destroys the passivation membrane and shifts the potential to a more negative value and activates Ga3+. This promotes ions including Ga3+, In3+and Zn2+to precipitate together and maintains the dissolution of Al-Zn-In alloy. The process is called "dissolution-reprecipitation".Both high purity zinc and Zn-Al-Cd alloy are liable to establish a stable potential in seawater, diluted seawater and tap water. The two electrodes could be used as reference electrodes in cathodic protection engineering. The performance of Zn-Al-Cd alloy reference electrodes is better than that of high purity zinc. When Cl- concentration is below 0.1496 mol/L in tap water and diluted seawater, zinc electrode potentials shows a linear relationship with the increase of Cl" concentration. When Cl- concentration is higher, zinc electrode potentials have no relationships with Cl- concentration. As seawater flow velocity goes up, zinc potentials shift to more positive values. Seawater pH has no obvious effect on zinc potentials.10μA/cm2 anodic current improves the potential stability of high purity zinc remarkably. In simulated frozen soil, open potential of high purity magnesium is the most negative one and that of MGAZ31B is the most positive one. The sequence of dissolution activation and reaction activation from high to low is MGAZ63B, MGAZ31B, MGMIC and pure magnesium. Electrochemical performance of MGAZ63B with higher current efficiency is the best, MGAZ63B is suitable to act as a sacrificial anode in Qinghai-Tibetan plateau frozen soil. Grooving corrosion or secondary phase corrosion presents on the surface. The main elements appearing on the surface include Mg, O and bulk elements, which mainly form Mg(OH)2.Potential distributions on the steel protected by magnesium were calculated by BEM and Matlab. The errors between calculated potential, and measured ones is less than 10 percents. This illustrate that numerical calculation is reliable and effective. Numerical calculation could serve for the further CP in frozen soil.
|
PDF Full Text Request