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| Application: | Aviation, Electronics, Industrial, Chemical |
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| Standard: | GB |
| Purity: | >98% |
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Magnesium anode rod
Magnesium anode is a commonly used sacrificial anode material in electrochemical cathodic protection engineering. It has characteristics such as a negative electrode potential (-2.37V standard electrode potential), high driving voltage (>0.6V), and an easily dissolvable surface protective film. In water media, magnesium undergoes intense self-corrosion, and the cathode undergoes hydrogen evolution reaction (2H++2e→H), making it suitable for metal protection in soil and freshwater environments with a resistivity of 20-50Ω·m. It is mainly divided into three types: pure magnesium, Mg-Mn alloy, and Mg-Al-Zn-Mn alloy. Their common characteristics include low density, large theoretical capacitance, and low polarization rate [3-4].
During melting, the content of iron and nickel impurities in magnesium anodes needs to be controlled. Its theoretical capacitance is large and the polarization rate is low. The driving voltage for cathodic protection is >0.6V, and the operating temperature can reach 100ºC. Besides traditional anti-corrosion fields, magnesium battery research has demonstrated energy density advantages (theoretical energy density 6.8 kWh/kg), and the theoretical discharge voltage of magnesium-air batteries reaches 3.1V, with the highest specific capacity of 1180 mAh/g. The global market size reached millions of US dollars in 2023, mainly applied in the fields of oil and gas. The non-crystalline Mg64Zn36 alloy developed by Xiamen University has a corrosion rate of only 0.05mm/y, with no hydrogen evolution during anode dissolution; the discharge performance has been improved by regulating the morphology of the Mg2Sn phase.
Mg-A1-Zn-Mn
Depending on the content of aluminum and zinc, the performance varies. Among them, the Mg-6Al-3Zn-Mn alloy, which has better performance and is widely used, has a uniformly dissolved surface and an electric current efficiency greater than 50%. Aluminum is the main alloy element in the anode and can form the strengthening phase Mg17A112 with magnesium, thereby increasing the strength of the alloy. However, when aluminum is added alone to industrial magnesium, a large amount of MgAl, Mg2A13, Mg4A13 and other intermetallic compounds will be formed. The presence of these intermetallic compounds will increase the self-corrosion rate of magnesium and accelerate the destruction of the solid solution. Zinc can reduce the corrosion rate of magnesium and reduce the negative differential effect of magnesium, thereby increasing the anode current efficiency. A small amount of manganese can counteract the adverse effects of impurities such as iron and nickel. When the addition of manganese is 0.3%, the allowable content of iron can reach 0.02%, but it will also reduce the current efficiency. Therefore, the content of impurities such as iron and the corresponding manganese content should be as low as possible. The simultaneous presence of aluminum, zinc and manganese can further reduce the requirements for the content of impurity elements in industrial magnesium. To obtain good electrochemical performance, the impurity content of the Mg-AI-Zn-Mn alloy should be strictly controlled. Under similar alloy composition conditions, the current efficiency of the alloy with less impurities is significantly higher than that of the alloy with more impurities.
Cathodic protection is a corrosion prevention method based on the principle of electrochemical corrosion. The American Corrosion Engineers Association defines cathodic protection as: by applying an external electromotive force to shift the corrosion potential of the electrode to a less oxidative potential, thereby reducing the corrosion rate. Sacrificial anode cathodic protection is to connect or weld a metal with a more negative potential, such as aluminum, zinc or magnesium, on the metal structure. The anode material is constantly consumed, and the released current supplies the protected metal structure and causes cathodic polarization, thereby achieving protection. Externally applied current cathodic protection is to supply cathodic current to the protected metal through an externally applied direct current power supply, causing it to become cathodically polarized. This method is mainly used to protect large or metal structures in high soil resistivity soil. The protection potential refers to the potential required to stop (or ignore) the corrosion of the metal during cathodic protection. In practice, the protection potential of steel is often taken as -0.85V (CSE), which means that when the metal is at a more negative potential than -0.85V (CSE), it is protected and corrosion can be ignored.
Chemical reaction equations
Anode reaction: Mg - 2e → Mg2+
Cathode reaction: H2O + O2 + 2e → 2OH-
The role of the magnesium sacrificial anode is to reduce the corrosion rate of the cathode (such as steel and other metals), achieving the purpose of protection.
The basic premise for the protection of the cathode by magnesium alloy is that the corrosion of the cathode (such as steel and other metals) in the absence of external interference is electrochemical corrosion (that is, the corrosion process generates an electric current), but not all electrochemical corrosion can be protected by sacrificial anodes. In the specific application process, the following conditions should be met:
(1) The corrosive medium must be conductive to establish a continuous circuit.
(2) The medium in which the protected metal material is located should be easy to undergo cathodic polarization, otherwise the power consumption is large and it is difficult to perform cathodic protection.
(3) For complex metal equipment or structures, consider the shielding effect of geometry to prevent the non-uniformity of the protective current.
(4) Electrical insulation (between the anode and the cathode)
(5) Electrical continuity (between the cathode systems)
(6) The use of magnesium alloy sacrificial anodes is prohibited for internal tank protection.
According to different uses, the shape and size of magnesium alloy sacrificial anodes are also different. The D and S type anodes are mainly used in soil environments, while the strip anodes are mainly used in high resistivity soil, fresh water and local situations with narrow space.
The role of elements
Mn: Manganese readily combines with harmful impurity elements, thereby eliminating the influence of Fe on the corrosion resistance of the alloy, and significantly reducing the corrosion rate. Manganese forms the Mn-Fe compound with iron. Due to the effect of gravity, the compound precipitates at the bottom of the crucible, while the remaining Fe that has not formed the compound is surrounded by manganese, thereby greatly reducing its impact on the corrosion resistance of the alloy and improving the current efficiency. The ratio of Fe:Mn should be less than 0.032 to reduce the harm of Fe to the anode.
Fe: The solubility of Fe in the anode is very low. During the crystallization process of the alloy liquid, Fe precipitates on the grain boundaries and forms an electrochemical couple with magnesium. Due to the large potential difference between Fe and Mg, current is easily generated, which aggravates the self-dissolution tendency of the anode and accelerates the corrosion rate of the alloy, reducing the current efficiency of the anode.
Ni: It forms the compound Mg2Ni with magnesium, which is distributed in a net-like or island-like form on the grain boundaries, thereby exacerbating the corrosion of the magnesium anode and reducing the current efficiency.
Cu: It forms Mg2Cu or MgCu2 with magnesium, which is distributed on the grain boundaries, increasing the self-corrosion of the magnesium anode and reducing the current efficiency of the anode.
Si: The solubility of Si in magnesium is very low. It forms Mg2Si with magnesium and is distributed on the grain boundaries and within the grains, and when it coexists with Fe, it increases the self-corrosion tendency of the magnesium alloy, reducing the current efficiency of the anode.
Al: In the high potential anode, aluminum is a harmful element. It can form a cathode phase with magnesium, accelerating the corrosion rate, and its presence also reduces the solubility of manganese in magnesium.
Main effects of elements in the low potential anode:
Al: Aluminum forms the phase Mg17Al12 with magnesium, which is distributed in a net-like or island-like form near the grain boundaries. Due to the good corrosion resistance of Mg17Al12, the overall corrosion resistance of the alloy is improved.
Zn: The addition of zinc can enhance the anti-sea water corrosion ability of the alloy, mainly because zinc reduces the harm of impurities such as Fe and Ni.
Mn: In the low potential anode, the main role of manganese is purification. Its principle is the same as that in the high potential case.
Magnesium anode is used in technical method of electrochemistry cathode protection. theory is from that connect with the protected metal body ,with the exhausting and dissolving of negative metal material or alloy ,protective curer body will be protected from corrosion . Mg anode can produce higher quality potential power, is ideal sacrificial anode materials.
Grade: AZ31/AZ31B/AZ91/AZ91D/AM60/AM80/ZK60/WE43
Production process: rolling / extrusion / casting / continuous casting and rolling
Specifications: magnesium alloy plate 0.4MM-100MM, can be cut according to requirements, rod: diameter 6MM-200MM, spot, complete specifications, 3-5 days can be shipped (the company is in Dongguan, Guangdong, convenient transportation)
Use; laptop phone case, automotive industry, drone, anode, water heater, etc.
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