Influence of Ga and Bi on electrochemical performance of Al-Zn-Sn sacrificial anodes

The influence of Ga and Bi on the microstructure and electrochemical performance of Al-7Zn-0.1Sn （mass fraction,%） sacrificial anodes was investigated by means of optical microscopy （OM）,scanning electron microscopy/energy dispersive X-ray analysis （SEM/EDAX） and electrochemical measurements.It was found that the coarse dendrites structure transformed into the equiaxed grains as well as a small amount of dendrite grains after adding Ga and Bi into Al-Zn-Sn alloys.A high current efficiency of 97% and even corrosion morphology were obtained for Al-7Zn-0.1Sn-0.015Ga-0.1Bi alloy.The results indicate that the proper amount of Ga and Bi is effective on improving the microstructure and electrochemical performance of Al-Zn-Sn alloy.

Effect of Zn/Mg ratio on cathodic protection of carbon steel using Al-Zn-Mg sacrificial anodes

Al-Zn-Mg alloys with different Zn/Mg mass ratios were evaluated as sacrificial anodes for cathodic protection of carbon steel in 3.5 wt.%Na Cl solution.The anodes were fabricated from pure Al,Zn and Mg metals using casting technique.Optical microscopy,SEM-EDS,XRD and electrochemical techniques were used.The results indicated that with decreasing Zn/Mg mass ratio,the grain size ofα(Al)and the particle size of the precipitates decreased while the volume fraction of the precipitates increased.The anode with Zn/Mg mass ratio>4.0 exhibited the lowest corrosion rate,while the anode with Zn/Mg mass ratio<0.62 gave the highest corrosion rate and provided the highest cathodic protection efficiency for carbon steel(AISI 1018).Furthermore,the results showed that the anode with Zn/Mg mass ratio<0.62 exhibited a porous corrosion product compared to the other anodes.

Influence of Mg and Ti on the microstructure and electrochemical performance of aluminum alloy sacrificial anodes

The experiments focused on the influence of magnesium and titanium as additional alloying elements on the microstructure and electro-chemical behavior of Al-Zn-In sacrificial anodes. The electrochemical behavior of the aluminum sacrificial anode with 3 wt.% sodium chloride solution was studied by electrochemical impedance spectroscopy (EIS) tests. It was found that a microstructure with few precipitates and refined grains could be achieved by adding 1 wt.% Mg and 0.05 wt.% Ti to the Al-Zn-In alloy,resulting...

Effect of Oxide Inclusions on Electrochemical Properties of Aluminium Sacrificial Anodes

Oxide films are incorporated into melts by an entrainment process, and are expected to be present in most metals, but particularly cast Al alloys. The oxides are necessarily present as folded-over double films （bifilms） that are effectively cracks. Their effect on the electrochemical behaviour of cast Al-SZn-0.021n sacrificial anodes was studied in 3 wt pct sodium chloride solution using the NACE efficiency evaluation. Three methods were employed to entrain progressive amounts of oxide in the alloy, including the addition of Al-Zn-ln maching chips to the charge, increasing the pouring height, and agitating the melt. The introduction of oxide bifilms in the cast alloy resulted in the deterioration of the electrochemical properties of the sacrificial anodes, such as current capacity and anode efficiency, and introduced increasing variability in these properties. The results suggest that corrosion behaviour is strongly related to the presence of bifilms suspended in the liquid alloy because bifilms provide crack paths allowing the corrodant to penetrate deeply into the metal matrix, and simultaneously provide localized galvanic cells because of the precipitation of Fe rich intermetallic compounds on their outer surfaces.

Effects of strain-induced melt activation treatment on the microstructure and properties of Zn sacrificial anodes

The microstructural properties and electrochemical performance of zinc(Zn)sacrificial anodes during strain-induced melt activation(SIMA)were investigated in this study.The samples were subjected to a compressive ratio of 20%-50% at various temperatures(425-435℃)and durations(5-30 min).Short-term electrochemical tests(anode tests)based on DNV-RP-B401 and potentiodynamic polarization tests were performed in 3.5wt%NaCl solution to evaluate the electrochemical efficiency and corrosion behavior of the samples,respectively.The electrochemical test results for the optimum sample confirmed that the corrosion current density declined by 90% and the anode efficiency slightly decreased relative to that of the raw sample.Energy-dispersive X-ray spectroscopy,scanning electron microscopy,metallographic images,and microhardness profiles showed the accumulation of alloying elements on the boundary and the conversion of uniform corrosion into localized corrosion,hence the decrease of the Zn sacrificial anode’s efficiency after the SIMA process.

Performance of Sacrificial Anodes in Reinforced Concrete

The electrochemical performance of the anodes was measured in the reinforced concrete test block in artificial sea water. Their chemical composition,metallographic structure and surface morphology were analyzed. It was found that concrete mix proportion and the covering layer thickness had an impact on the performance of sacrificial anodes. The thermal-sprayed zinc alloy anodes had a more negative corrosion potential and larger galvanic current than metallurgy ones in the same conditions. They had similar chemical composition. But metallographic structure showed that the structure of thermal-sprayed zinc alloy anodes was a loose porous. This structure had the catalytic effect on the andes electrochemical reactions and made the anodes the electrochemical exchange current density increase and the corrosion potential move to negative direction.

Sacrificial Anode Stability and Polarization Potential Variation in a Ternary Al-xZn-xMg Alloy in a Seawater-Marine Environment

In this paper, the effects of zinc （Zn） and magnesium （Mg） addition on the performance of an aluminum-based sacrificial anode in seawater were investigated using a potential measurement method. Anodic efficiency, protection efficiency, and polarized potential were the parameters used. The percentages of Zn and Mg in the anodes were varied from 2% to 8% Zn and 1% to 4% Mg. The alloys produced were tested as sacrificial anodes for the protection of mild steel in seawater at room temperature. Current efficiency as high as 88.36% was obtained in alloys containing 6% Zn and 1% Mg. The polarization potentials obtained for the coupled （steel/Al-based alloys） are as given in the Pourbaix diagrams, with steel lying within the immunity region/cathodic region and the sacrificial anodes within the anodic region. The protection offered by the sacrificial anodes to the steel after the 7th and 8th week was measured and protection efficiency values as high as 99.66% and 99.47% were achieved for the A1-6%Zn-l%Mg cast anode. The microstructures of the cast anodes comprise of intermetallic structures of hexagonal Mg3Zn2 and body-centered cubic A12Mg3Zn3. These are probably responsible for the breakdown of the passive alumina film, thus enhancing the anode efficiency.

Effect of Sacrificial Anode Protection for Steel Pipe Piles at Dandong Port

The sacrificial anode protection system for the steel pipe piles of the 3rd berth of Dandong; wharf at Dandong port has operated for eight years. In this paper, the program design and the protection effect of the sacrificial anode protection system are presented. The results of various inspections show that the piles are protected very satisfactorily.

Environmental Impact Assessment of Sacrificial Anode Method in Taiwan Strait

Taiwan Strait is one of the potential wind farm in the world. Cooperate with the development of national policies, thousands of offshore wind turbines will be installed in Taiwan Strait. In order to enable offshore wind turbine foundation to be erected in the ocean for a long time, the offshore structure facilities are protected by sacrificial anode or impressed current of today. This study utilized the MIKE21 numerical model, combined with ocean parameters such as sea waves and tidal current to simulate the change of the diffusion concentration and diffusion range of the materials released by the aluminum sacrificial anode blocks by the Changhua offshore wind farm located on Taiwan Strait in winter and summer, thus to evaluate the impact on the marine environment.

EIS studies the effect of Zinc to Al-Zn alloy used for cathodic protection in 3% NaCl solution

Electrochemical impendence spectroscopy （EIS） is applied to investigate the dissolution behavior of Al-Zn alloys in 3% NaCl solution at different polarization potentials. A new reaction model is proposed, and the activation mechanism of zinc in Al-Zn alloys is achieved. There are three intermediates in the dissolution process： Znad^＋, Znad^2＋ and Alad^＋, ,of which only Zni can activate Al-Zn alloys. Most Znnd^＋ is produced by β-phase,and the alloys with 2. 3% - 3. 8% （wt） Zn dissolve rapidly. The Al-Zn alloys of heart-shaped EIS are active in 3% NaCl solution, thus EIS characteristic can be used to distinguish the activa-tion of Al-Zn alloys.

Efficient Fixation of Carbon Dioxide by Electrolysis——Facile Synthesis of Useful Carboxylic Acids

Electrochemical fixation of atmospheric pressure of carbon dioxide to organic compounds is a useful and attractive method for synthesizing of various carboxylic acids. Electrochemical fixation of carbon dioxide, electrochemical carboxylation, organic halides, organic triflates, alkenes, aromatic compounds, and carbonyl compounds can readily occur in the presence of an atmospheric pressure of carbon dioxide to form the corresponding carboxylic acids with high yields, when a sacrificial anode such as magnesium or aluminum is used in the electrolysis. The electrochemical carboxylation of vinyl bromides was successfully applied for the synthesis of the precursor of nonsteroidal anti-inflammatory agents such as ibuprofen and naproxen. On the other hand, supercritical carbon dioxide （scCO2） has significant potential as an environmentally benign solvent in organic synthesis and it could be used both as a solvent and as a reagent in these electrochemical carboxylations by using a small amount of cosolvent.

Effect of lanthanum addition on microstructure and corrosion behavior of Al-Sn-Bi anodes

Novel Al-Sn-Bi anodes with and without lanthanum （La） were prepared.To evaluate the corrosion properties of the anodes,constant current and dynamic loop tests were carried out to determine its efficiency and corrosion rate.Optical microscopy （OM）,transmission electron microscopy （TEM） and energy spectrum analysis techniques were used to examine and analyze microstructure and corrosion behavior of the specimens.The result showed that the Al-Sn-Bi anodes with La additions revealed higher current efficiency and anticorrosion in artificial environment.Segregation phase of anodes with La additions got more homogenous than that without La additions.Its grains were fined and the amount of segregation Fe-phase was reduced.

Optimization of Manganese and Magnesium Contents in As-cast Aluminum-Zinc-Indium Alloy as Sacrificial Anode

In this study, effects of manganese and magnesium content on the electrochemical properties of Al-Zn-ln sacrificial anode were studied in 0.5 mol/L NaCl solution （pH=5）. The aluminum base alloy with different amounts of Mn and Mg were melted at 750℃, then casted at molds at 25℃. Corrosion experiments were mounted to determine the optimal effect of Mn and Mg on the efficiencies of the aluminum alloy anodes. The corroded and unexposed sample surfaces were subjected to microstructure characterization by optical and scanning electron microscopy. AI-Zn-ln alloy doped with 0%, 0.01%, 0.05%.0.2% and 0.3% by weights of Mn and 0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0% by weights of Mg were prepared to determine the effect of Mn and Mg on anode efficiency in the environment. The different microstructures of the evolved AI- Zn-ln-Mg-Mn alloy were correlated with the anode efficiencies. The Al-5.0%Zn-2.0%Mg-0.15%Mn-0.02%ln gave the best anode efficiency （about 83%）. The microstructures of the corroded surface of the optimized alloy revealed decreased distribution of the pockets of localized attacks which are characteristics of pitting （or crevice） corrosion.

Influence of yttrium addition on properties of Mg-based sacrificial anode

To improve lower current efficiency of Mg-based sacrificial anode,a Mg-based sacrificial anode material with yttrium addition was investigated.Its electrochemical properties were evaluated by the galvanostatic method,and its microstructure and constitution were characterized by metallurgical microscope and X-ray diffraction.The results showed that,the addition of yttrium refined dentrite grains,maximized current efficiency,and minimized potential of magnesium sacrificial anode.When 0.1% yttrium was doped,the anode showed the highest current efficiency,62.5%,which improved its current efficiency by 14%.